U.S. patent application number 12/758368 was filed with the patent office on 2010-11-18 for systems using a levitating, rotating pumping or mixing element and related methods.
Invention is credited to Alexandre N. Terentiev.
Application Number | 20100290308 12/758368 |
Document ID | / |
Family ID | 31993912 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100290308 |
Kind Code |
A1 |
Terentiev; Alexandre N. |
November 18, 2010 |
SYSTEMS USING A LEVITATING, ROTATING PUMPING OR MIXING ELEMENT AND
RELATED METHODS
Abstract
A system for pumping or mixing a fluid using a rotating pumping
or mixing element and various other components for use in a pumping
or mixing system are disclosed.
Inventors: |
Terentiev; Alexandre N.;
(Lexington, KY) |
Correspondence
Address: |
KING & SCHICKLI, PLLC
247 NORTH BROADWAY
LEXINGTON
KY
40507
US
|
Family ID: |
31993912 |
Appl. No.: |
12/758368 |
Filed: |
April 12, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12250180 |
Oct 13, 2008 |
7695186 |
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12758368 |
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11496702 |
Jul 31, 2006 |
7434983 |
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12250180 |
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10398946 |
Apr 8, 2003 |
7086778 |
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PCT/US01/31459 |
Oct 9, 2001 |
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11496702 |
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10491512 |
Apr 1, 2004 |
7481572 |
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PCT/US02/31478 |
Oct 2, 2002 |
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12250180 |
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11298406 |
Dec 9, 2005 |
7762716 |
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10491512 |
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10491512 |
Apr 1, 2004 |
7481572 |
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11298406 |
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60239187 |
Oct 9, 2000 |
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60282927 |
Apr 10, 2001 |
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60318579 |
Sep 11, 2001 |
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60326833 |
Oct 3, 2001 |
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60634664 |
Dec 9, 2004 |
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Current U.S.
Class: |
366/143 ;
366/241; 366/273; 366/279; 366/331 |
Current CPC
Class: |
B01F 11/0082 20130101;
F16C 32/0438 20130101; B01F 15/00831 20130101; B01F 15/0085
20130101; B01F 11/0097 20130101; B01F 13/0863 20130101; B01F
13/0818 20130101; B01F 11/0085 20130101; B01F 13/0845 20130101;
B01F 7/16 20130101; B01F 7/00908 20130101; F16C 37/005 20130101;
B01F 13/0872 20130101; B01F 2215/0032 20130101; B01F 13/0827
20130101; B01F 7/02 20130101 |
Class at
Publication: |
366/143 ;
366/241; 366/279; 366/273; 366/331 |
International
Class: |
B01F 5/12 20060101
B01F005/12; B01F 13/08 20060101 B01F013/08; B01F 15/00 20060101
B01F015/00 |
Claims
1. A mixing apparatus comprising a flexible bag including an
interior compartment for receiving a fluid, said bag including a
cavity bounded by a wall projecting into the interior compartment,
a mixing element in the interior compartment of the bag adjacent to
the wall of the cavity, and a motive device adapted for insertion
into the cavity for moving the mixing element.
2. The apparatus according to claim 1, wherein the motive device
comprises a rotating shaft.
3. The apparatus according to claim 1, wherein the mixing element
forms a non-contact coupling with the motive device.
4. The apparatus according to claim 1, wherein the mixing element
comprises at least one magnet.
5. The apparatus according to claim 1, wherein the wall comprises a
flexible sleeve.
6. The apparatus according to claim 1, wherein the motive device is
adapted to be electrically coupled to a power source.
7. The apparatus according to claim 1, wherein the mixing element
comprises at least one blade.
8. The apparatus according to claim 1, further including a rigid
container for supporting the bag.
9. The apparatus according to claim 1, wherein a surface on the
wall in the interior compartment is adapted for engaging a matching
surface of the mixing element
10. A mixing apparatus, comprising: a container having a
transparent sidewall at least partially defining an interior
compartment for the mixing of media, said container including a
cavity bounded by a wall projecting into the interior compartment,
a mixing element in the container adjacent to the wall of the
cavity, and a motive device for moving the mixing element.
11. The apparatus of claim 10, wherein the wall projects into the
interior compartment from other than a floor of the container.
12. The apparatus of claim 10, wherein the wall projects into the
interior compartment from an upper portion of the container.
13. The apparatus of claim 10, wherein the container comprises a
flexible bag.
14. The apparatus of claim 10, wherein the mixing element comprises
an opening for receiving the wall forming the cavity.
15. The apparatus of claim 14, wherein the mixing element comprises
an inner surface adapted for engaging a surface of the wall.
16. A mixing apparatus comprising a container including an interior
compartment for receiving a fluid, a mixing element in the interior
compartment of the container and capable of spinning about an axis,
and a tubular shaft projecting into the interior compartment and
adapted for moving the mixing element, said tubular shaft including
a cavity having a rigid rod positioned therein.
17. The mixing apparatus of claim 16, wherein the container
comprises a flexible bag.
18. The apparatus of claim 16, wherein the tubular shaft comprises
a flexible sleeve.
19. The apparatus of claim 16, wherein the tubular shaft is adapted
to rotate relative to the flexible bag.
20. The apparatus of claim 16, further including a motor for
rotating the tubular shaft.
21. The apparatus of claim 16, wherein the tubular shaft is
associated with at least one bearing.
Description
[0001] This application is a continuation of Ser. No. 12/250,180,
which is: (1) a continuation of Ser. No. 11/496,702, filed Jul. 31,
2006, and now U.S. Pat. No. 7,434,983, which is a continuation of
Ser. No. 10/398,946, which is the national stage of PCT/US01/31459,
filed Oct. 9, 2001, now U.S. Pat. No. 7,086,778, which claims the
benefit of the following U.S. Provisional Patent Applications: (a)
Ser. No. 60/239,187. filed Oct. 9, 2000; (b) Ser. No. 60/282,927,
filed Apr. 10, 2001; and (c) Ser. No. 60/318,579, filed Sep. 11,
2001; and (2) a continuation-in-part of Ser. No. 10/491,512, which
is the national stage of PCT/US02/31478, filed Oct. 2, 2002, which
claims the benefit of U.S. Provisional Patent Application Ser. No.
60/326,833, filed Oct. 3, 2001. This application is a
continuation-in-part of Ser. No. 11/298,406, which is a
continuation-in-part of U.S. patent application Ser. No. 10/491,512
and claims the benefit of U.S. Provisional Patent Application Ser.
No. 60/634,664, filed Dec. 9, 2004. The entire disclosures of the
foregoing applications are all incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates generally to the mixing arts
and, more particularly, to a system, related components, and
related method for pumping or mixing fluids using a rotatable
magnetic element.
BACKGROUND OF THE INVENTION
[0003] Most pharmaceutical solutions and suspensions manufactured
on an industrial scale require highly controlled, thorough mixing
to achieve a satisfactory yield and ensure a uniform distribution
of ingredients in the final product. Agitator tanks are frequently
used to complete the mixing process, but a better degree of mixing
is normally achieved by using a mechanical stirrer or impeller
(e.g., a set of mixing blades attached to a metal rod). Typically,
the mechanical stirrer or impeller is simply lowered into the fluid
through an opening in the top of the vessel and rotated by an
external motor to create the desired mixing action.
[0004] One significant limitation or shortcoming of such an
arrangement is the danger of contamination or leakage during
mixing. The rod carrying the mixing blades or impeller is typically
introduced into the vessel through a dynamic seal or bearing. This
opening provides an opportunity for bacteria or other contaminants
to enter, which of course can lead to the degradation of the
product. A corresponding danger of environmental contamination
exists in applications involving hazardous or toxic fluids, or
suspensions of pathogenic organisms, since dynamic seals or
bearings are prone to leakage. Cleanup and sterilization are also
made difficult by the dynamic bearings or seals, since these
structures typically include folds and crevices that are difficult
to reach. Since these problems are faced by all manufacturers of
sterile solutions, pharmaceuticals, or the like, the U.S. Food and
Drug Administration (FDA) has consequently promulgated strict
processing requirements for such fluids, and especially those
slated for intravenous use.
[0005] Recently, there has also been an extraordinary increase in
the use of biosynthetic pathways in the production of
pharmaceutical materials, but problems plague those involved in
this rapidly advancing industry. The primary problem is that
suspensions of genetically altered bacterial cells frequently used
to produce protein pharmaceuticals (insulin is a well-known
example) require gentle mixing to circulate nutrients. If overly
vigorous mixing or contact between the impeller and the vessel wall
occurs, the resultant forces and shear stresses may damage or
destroy a significant fraction of the cells, as well as protein
molecules that are sensitive to shear stresses. This not only
reduces the beneficial yield of the process, but also creates
deleterious debris in the fluid suspension that requires further
processing to remove.
[0006] In an effort to overcome this problem, others have proposed
alternative mixing technologies. The most common proposal for
stirring fluids under sterile conditions is to use a rotating,
permanent magnet bar covered by an inert layer of TEFLON, glass, or
the like. The magnetic bar is placed on the bottom of the agitator
vessel and rotated by a driving magnet positioned external to the
vessel. Of course, the use of such an externally driven magnetic
bar avoids the need for a dynamic bearing, seal or other opening in
the vessel to transfer the rotational force from the driving magnet
to the stirring magnet. Therefore, a completely enclosed system is
provided. This of course prevents leakage and the potential for
contamination created by hazardous materials (e.g., cytotoxic
agents, solvents with low flash points, blood products, etc.),
eases clean up, and allows for the desirable sterile interior
environment to be maintained. However, several well-recognized
drawbacks are associated with this mixing technology, making it
unacceptable for use in many applications. For example, the driving
magnet produces not only torque on the stirring magnetic bar, but
also an attractive axial thrust force tending to drive the bar into
contact with the bottom wall of the vessel. This of course
generates substantial friction at the interface between the bar and
the bottom wall of the vessel. This uncontrolled friction generates
unwanted heat and may also introduce an undesirable shear stress in
the fluid. Consequently, fragile biological molecules, such as
proteins and living cells that are highly sensitive to temperature
and shear stress, are easily damaged during the mixing process, and
the resultant debris may contaminate the product. Moreover, the
magnetic bar stirrer may not generate the level of circulation
provided by an impeller, and thus cannot be scaled up to provide
effective mixing throughout the entire volume of large agitation
tanks of the type preferred in commercial production
operations.
[0007] In yet another effort to eliminate the need for dynamic
bearings or shaft seals, some have proposed mixing vessels having
external magnets that remotely couple the mixing impeller to a
motor located externally to the vessel. A typical magnetic coupler
comprises a drive magnet attached to the motor and a stirring
magnet carrying an impeller. Similar to the magnetic bar technology
described above, the driver and stirrer magnets are kept in close
proximity to ensure that the coupling between the two is strong
enough to provide sufficient torque. An example of one such
proposal is found in U.S. Pat. No. 5,470,152 to Rains.
[0008] As described above, the high torque generated can drive the
impeller into the walls of the vessel creating significant
friction. By strategically positioning roller bearings inside the
vessel, the effects of friction between the impeller and the vessel
wall can be substantially reduced. Of course, high stresses at the
interfaces between the ball bearings and the vessel wall or
impeller result in a grinding of the mixing proteins and living
cells, and loss of yield. Further, the bearings may be sensitive to
corrosive reactions with water-based solutions and other media and
will eventually deteriorate, resulting in frictional losses that
slow the impeller, reduce the mixing action, and eventually also
lead to undesirable contamination of the product. Mechanical
bearings also add to the cleanup problems.
[0009] In an effort to address and overcome the limitations
described above, still others have proposed levitated pumping or
mixing elements designed to reduce the deleterious effects of
friction resulting from magnetically coupled mixers. By using a
specially configured magnetic coupler to maintain only a repulsive
levitation force in the vertical direction, the large thrust force
between the stirring and driving magnets can be eliminated, along
with the resultant shear stress and frictional heating. An example
of one such arrangement is shown in U.S. Pat. No. 5,478,149 to
Quigg.
[0010] However, one limitation remaining from this approach is that
only magnet-magnet interactions provide the levitation. This leads
to intrinsically unstable systems that produce the desired
levitation in the vertical direction, but are unable to control
side-to-side movement. As a result, external contact bearings in
the form of bearing rings are necessary to laterally stabilize the
impeller. Although this "partial" levitation reduces the friction
between the impeller and the vessel walls, it does not totally
eliminate the drawbacks of the magnetically coupled, roller bearing
mixers previously mentioned.
[0011] In an attempt to eliminate the need for contact or other
types of mechanical roller bearings, complex feedback control has
been proposed to stabilize the impeller. Typical arrangements use
electromagnets positioned alongside the levitating magnet. However,
the high power level required to attain only sub-millimeter
separations between the levitating magnet and the stabilizing
magnets constitutes a major disadvantage of this approach.
Furthermore, this solution is quite complex, since the stabilizing
magnets must be actively monitored and precisely controlled by
complex computer-implemented software routines to achieve even a
moderate degree of stability. As a consequence of this complexity
and the associated maintenance expense, this ostensible solution
has not been accepted in the commercial arena, and it is doubtful
that it can be successfully scaled up for use in mixing industrial
or commercial scale process volumes.
[0012] Thus, a need is identified for a system having a magnetic
element for pumping or mixing fluids, and especially ultra-pure,
hazardous, or delicate fluid solutions or suspensions, including
those which may be processed in vessels capable of withstanding
high pressurization. The system would preferably employ a magnetic
element capable of pumping or mixing a fluid that levitates in a
stable fashion in the vessel to avoid contact with the bottom or
side walls thereof when in use. No mixing rod or other structure
penetrating the mixing vessel would be required, which of course
eliminates the need for dynamic bearings or seals and all
potentially deleterious effects associated therewith. Also, the use
of a levitating magnetic element would eliminate the need for
mechanical bearings or the deleterious magnet-wall interactions
that create undesirable shear stresses and unwanted friction in the
fluid. Since penetration is unnecessary, the vessel could be
completely sealed prior to mixing, and possibly even pressurized.
This would reduce the chance for external exposure in the case of
hazardous or biological fluids, such as blood or the like, or
contamination, in the case of biologically active or sensitive
products. The vessel and pumping or mixing element could also
possibly be made of disposable materials, such as inexpensive,
flexible plastic materials, and discarded after each use to
eliminate the need for cleaning or sterilization.
SUMMARY OF THE INVENTION
[0013] A mixing apparatus comprising a flexible bag including an
interior compartment for receiving a fluid, said bag including a
cavity bounded by a wall projecting into the interior compartment,
a mixing element in the interior compartment of the bag adjacent to
the wall of the cavity, and a motive device adapted for insertion
into the cavity for moving the mixing element.
[0014] In one embodiment, the motive device comprises a rotating
shaft. The mixing element may form a non-contact coupling with the
motive device. The mixing element may comprise at least one magnet.
The wall may comprise a flexible sleeve. The motive device may be
adapted to be electrically coupled to a power source. The mixing
element may comprise at least one blade. The apparatus may further
include a rigid container for supporting the bag. A surface on the
wall in the interior compartment may be adapted for engaging a
matching surface of the mixing element.
[0015] A mixing apparatus, comprises a container having a
transparent sidewall at least partially defining an interior
compartment for the mixing of media, said container including a
cavity bounded by a wall projecting into the interior compartment,
a mixing element in the container adjacent to the wall of the
cavity, and a motive device for moving the mixing element.
[0016] In one embodiment, the wall projects into the interior
compartment from other than a floor of the container. The wall may
project into the interior compartment from an upper portion of the
container. The container may comprise a flexible bag. The mixing
element may comprise an opening for receiving the wall forming the
cavity. The mixing element may further comprise an inner surface
adapted for engaging a surface of the wall.
[0017] A mixing apparatus comprising a container including an
interior compartment for receiving a fluid, a mixing element in the
interior compartment of the container and capable of spinning about
an axis, and a tubular shaft projecting into the interior
compartment and adapted for moving the mixing element, said tubular
shaft including a cavity having a rigid rod positioned therein.
[0018] In one embodiment, the container comprises a flexible bag.
The tubular shaft may comprise a flexible sleeve. The tubular shaft
may be adapted to rotate relative to the flexible bag. A motive
device may be provided for rotating the tubular shaft. The tubular
shaft may be associated with at least one bearing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings incorporated in and forming a part
of the specification illustrate several aspects of the present
invention and, together with the description. assist in explaining
the principles of the invention. In the drawings:
[0020] FIG. 1 is a partially cross-sectional, partially cutaway,
partially schematic view of one embodiment of the system of the
present invention wherein the levitating pumping or mixing element
is rotated by an external drive or driving magnet to mix a fluid in
a vessel and the cooling source is a separate cooling chamber
defined by the outer wall of a cryostat holding a cryogen;
[0021] FIG. 2 is an enlarged cross-sectional, partially cutaway,
partially schematic view of an embodiment wherein the rotating,
levitating pumping or mixing element is used to pump a fluid
through a vessel positioned adjacent to the housing for the
superconducting element and the cooling source is a closed cycle
refrigerator;
[0022] FIG. 3 is a partially cross-sectional, partially cutaway,
partially schematic view of the system of the first embodiment
wherein the superconducting element, vessel, pumping or mixing
element, and drive magnet are axially aligned, but moved off-center
relative to the vertical center axis of the vessel;
[0023] FIG. 4a is a bottom view of the drive magnet used in
situations where exceptional rotational stability of the pumping or
mixing element of the preferred embodiment is required;
[0024] FIG. 4b is a partially cross-sectional, partially cutaway
side view of the system showing the drive magnet of FIG. 4a
magnetically coupled to a similarly constructed second permanent
magnet forming a part of the pumping or mixing element;
[0025] FIG. 4c is one possible embodiment of the pumping or mixing
system including a pumping or mixing element having a chamber for
holding a substance that is lighter than the surrounding fluid,
such as air, that assists in levitating the pumping or mixing
element;
[0026] FIG. 5 is a partially cross-sectional, partially schematic
side view of a second possible embodiment of a pumping or mixing
system using a pumping or mixing element levitated by a thermally
isolated cold superconducting element wherein the motive force for
rotating the pumping or mixing element in the vessel is provided by
rotating the superconducting element itself;
[0027] FIG. 6a is a top schematic view of one possible arrangement
of the levitating pumping or mixing element that may be driven by a
rotating superconducting element;
[0028] FIG. 6b shows the pumping or mixing element of FIG. 6a
levitating above a rotating superconducting element formed of two
component parts;
[0029] FIG. 7 is a partially cutaway, partially cross-sectional
schematic side view of a vessel in the form of a centrifugal
pumping head, including a levitating, rotating pumping or mixing
element for pumping fluid from the inlet to the outlet of the
centrifugal pumping head;
[0030] FIG. 8a shows an alternate embodiment of a pumping or mixing
element especially adapted for levitation in a vessel or container
having a relatively narrow opening;
[0031] FIG. 8b shows another alternate embodiment of a pumping or
mixing element adapted especially for use in a vessel or container
having a relatively narrow opening;
[0032] FIG. 8c illustrates the pumping or mixing element of FIG. 8b
in a partially folded state for insertion in the narrow opening of
a vessel or container;
[0033] FIG. 9 is a partially cross-sectional, partially schematic
side view of a second embodiment of a pumping or mixing system
wherein separate levitating and driven magnets are carried on the
same, low-profile pumping or mixing element, with the levitation
being supplied by a thermally isolated superconducting element and
the rotary motion being supplied a motive device including driving
magnets coupled to a rotating shaft and positioned in an opening in
the evacuated or insulated chamber surrounding the superconducting
element;
[0034] FIG. 9a is a top or bottom view of one possible embodiment
of a pumping or mixing element for use in the system of FIG. 9;
[0035] FIG. 9b is a partially cross-sectional side view of the
pumping or mixing element of FIGS. 9 and 9a levitating above the
superconducting element, and illustrating the manner in which the
driven magnets are coupled to the corresponding driving magnets to
create the desired rotational motion;
[0036] FIG. 10 is a top view of a most preferred version of a
cryostat for use with the pumping and mixing system of the
embodiment of FIG. 9;
[0037] FIG. 11 is a partially cutaway, partially cross-sectional
side schematic view of a centrifugal pumping head for use with the
system of FIG. 9;
[0038] FIG. 12 is a cross-sectional side view of another possible
embodiment of a pumping or mixing system of the present
invention;
[0039] FIG. 12a is a cross-sectional view taken along line 12a-12a
of FIG. 12;
[0040] FIG. 12b is a cross-sectional view taken along line 12b-12b
of FIG. 12;
[0041] FIG. 12c is a cross-sectional view of the embodiment of FIG.
12, but wherein the motive device is in the form of a winding
around the vessel for receiving an electrical current that creates
an electrical field and causes the pumping or mixing element to
rotate;
[0042] FIG. 13 is an alternate embodiment of an inline levitating
pumping or mixing element, similar in some respects to the
embodiment of FIG. 9;
[0043] FIG. 14 is an enlarged partially cross-sectional, partially
cutaway side view showing the manner in which a sealed flexible bag
carrying a pumping or mixing element may be used for mixing a
fluid, and also showing one example of how a transmitter and
receiver may be used to ensure that the proper pumping or mixing
element is used with the system;
[0044] FIG. 14a is an enlarged, partially cross-sectional,
partially cutaway side view showing an attachment including a
coupler for coupling with the pumping or mixing element;
[0045] FIG. 14b is an enlarged, partially cross-sectional,
partially cutaway side view showing a mixing vessel having
centering and alignment structures;
[0046] FIG. 14c is an enlarged, partially cross-sectional,
partially cutaway side view showing an alternate orientation of the
vessel with centering and alignment structures;
[0047] FIG. 14d is an enlarged, partially cross-sectional,
partially cutaway side view showing the use of a second motive
device in the system of FIG. 14, such as a linear motion device,
for moving the superconducting element, and hence, the pumping or
mixing element to and fro inside of the vessel;
[0048] FIG. 14e is an enlarged, partially cross-sectional,
partially cutaway side view showing a mixing vessel having
centering and alignment structures;
[0049] FIG. 15 illustrates one charging magnet including a spacer
that may form part of a kit for use in charging the superconducting
element as it is cooled to the transition temperature, as well as a
heater for warning the superconducting element to above the
transition temperature for recharging;
[0050] FIG. 16 is as partially cross-sectional, mainly schematic
view of an embodiment of the system for use with a vessel having a
thin-walled cavity;
[0051] FIG. 16a is a partially cutaway, partially cross-sectional
top view of the cryostat of FIG. 16;
[0052] FIG. 17 is an enlarged, schematic view showing a
superconductor or superconducting element comprised of a plurality
of segments of a superconducting material having crystallographic
planes for levitating a concentric annular levitation magnet, and
showing in particular a desired orientation of the crystallographic
C-axis of each segment relative to the magnetization vector of the
levitation magnet;
[0053] FIG. 18 is a cross-sectional view taken along line 18-18 of
FIG. 17;
[0054] FIG. 19 is an embodiment wherein a plurality of
superconductors or superconducting elements are used to levitate a
pumping or mixing element in a fluid containing vessel, and again
showing in particular a desired orientation of the crystallographic
C-axis of each segment relative to the magnetization vector of the
levitation magnet;
[0055] FIG. 19a is a top view of the cryostat and a portion of the
motive device in the system of FIG. 19;
[0056] FIG. 20 illustrates an embodiment where the cryostat
includes a cryocooler which rotates along with the superconducting
element to both levitate and rotate the pumping or mixing element
in a vessel, which is shown as having a cavity formed therein;
[0057] FIG. 21 is a schematic view showing one possible orientation
of the magnets and superconductors in the embodiment of FIG.
20;
[0058] FIG. 22 illustrates a flexible bag or container having a
cavity formed therein, which in addition to receiving the head end
of the cryostat may also act as a centering post for a concentric
pumping or mixing element; and
[0059] FIG. 23 illustrates an embodiment where permanent magnets
are used to provide a levitation-assist function to prevent the
pumping or mixing element from contacting the adjacent vessel;
[0060] FIG. 24 is another embodiment where permanent magnets are
used to provide a levitation-assist function to prevent the pumping
or mixing element from contacting the adjacent vessel;
[0061] FIG. 25 is yet another embodiment where permanent magnets
are used to provide a levitation-assist function to prevent the
pumping or mixing element from contacting the adjacent vessel;
[0062] FIG. 26 is a partially cross-sectional view showing a vessel
including an engagement structure for engaging and supporting the
pumping or mixing element when in a non-levitating condition;
and
[0063] FIG. 27 is a partially cross-sectional view showing the
moving of the cryostat to in turn move the magnetically coupled
pumping or mixing element of FIG. 26 to a levitated position.
DETAILED DESCRIPTION OF THE INVENTION
[0064] Reference is now made to FIG. 1, which shows a first
possible embodiment of the mixing or pumping system 10 of the
present invention. In this embodiment, a cryostat 12 is used to
hold the cooling source for the superconducting element that
produces the desired levitation in a pumping or mixing element 14.
This element 14 is placed in a vessel 16 positioned external to the
cryostat 12. The vessel 16 may already contain a fluid F or may be
filled after the pumping or mixing element 14 is in place. It
should be appreciated at the outset that the term "fluid" is used
herein to denote any substance that is capable of flowing, as may
include fluid suspensions, gases, gaseous suspensions, or the like,
without limitation. The vessel 16 for holding the fluid is shown as
being cylindrical in shape and may have an open top. Alternatively,
it may be completely sealed from the ambient environment to avoid
the potential for fluid contamination or leakage during mixing, or
adapted to pump the fluid F from an inlet to an outlet in the
vessel 16 (see FIG. 2). In any case, the vessel 16 may be
fabricated of any material suitable for containing fluids,
including glass, plastic, metal, or the like. Of course, the use of
lightweight plastic or other high density polymers is particularly
desirable if the vessel 16 is going to be discarded after mixing or
pumping is complete, as set forth in more detail in the description
that follows.
[0065] As illustrated in FIG. 1, the vessel 16 rests atop the outer
wall 18 of the cryostat 12. Preferably, this outer wall 18 is
fabricated of non-magnetic stainless steel, but the use of other
materials is of course possible, as long as the ability of the
pumping or mixing element 14 to levitate and rotate remains
substantially unaffected. Positioned inside of and juxtaposed to
this wall 18 is a superconducting element 20. The superconducting
element 20 is supported by a rod 22 that serves as the thermal link
to a cooling source 24. The outer wall 18 of the cryostat 12 thus
defines a chamber 25 that is preferably evacuated to thermally
isolate the cold superconducting element 20 from the relatively
warm vessel 16, pumping or mixing element 14, and fluid F.
Positioning of the superconducting element 20 in this vacuum
chamber 25 may be possible by virtue of the thermal link provided
by the rod 22. The thermal isolation and separation provided by the
chamber 25 allows for the superconducting element 20 to be placed
in very close proximity to the outer wall 18 without affecting its
temperature, or the temperature of the vessel 16. This allows the
separation distance from the superconducting element 20 to the
inner surface of the wall 18 to be narrowed significantly, such
that in the preferred embodiment, the gap G between the two is
preferably under 10 millimeters, and can be as narrow as
approximately 0.01 millimeters. This substantial reduction in the
separation distance enhances the levitational stability, magnetic
stiffness, and loading capacity of the pumping or mixing element
14.
[0066] In this first illustrated embodiment, the cooling source 24
is a separate, substantially contained cooling chamber 26 holding a
cryogen C, such as liquid nitrogen. The chamber 26 is defined by an
outer wall 28 that is substantially thermally separated from the
outer wall 18 of the cryostat 12 to minimize heat transfer. An
inlet I is provided through this wall 28 for introducing the
cryogen into the cooling chamber 26. To permit any vapor P to
escape from the chamber 26 as the cryogen C warms, an exhaust
outlet O is also provided (see action arrows in FIG. 1 also
designating the inlet and outlet). In the illustrated embodiment,
the inlet I and outlet O lines may formed of a material having a
low thermal conductivity, such as an elongate, thin walled tube
formed of non-magnetic stainless steel, and are sealed or welded in
place to suspend the cooling chamber 26 in the cryostat 12. As
should be appreciated by one of ordinary skill in the art, the use
of a thin walled tube formed of a material having a low thermal
conductivity, such as stainless steel, results in a negligible
amount of thermal transfer from the inlet or outlet to the wall 18.
The sealing or welding method employed should allow for the chamber
25 to be maintained in an evacuated state, if desired. Despite this
illustration of one possible support arrangement, it should be
appreciated that the use of any other support arrangement that
minimizes thermal transfer between the cooling chamber 26 and the
cryostat wall or other housing 18 is also possible (see. e.g., my
'672 patent).
[0067] The rod 22 serving as the thermal link between the cooling
source 24 and the superconducting element 20 may be cylindrical and
may extend through the outer wall 28 of the cooling chamber 26. The
entire surface area of the superconducting element 20 should
contact the upper surface of the cylindrical rod 22 to ensure that
thermal transfer is maximized. The rod 22 may be formed of
materials having low thermal resistance/high thermal conductance,
such as brass, copper, or aluminum.
[0068] As should be appreciated from viewing FIG. 1, and as briefly
noted in the foregoing description, the combination of the outer
wall 18 and the inner cooling chamber 26 in this first embodiment
defines the chamber 25 around the superconducting element 20.
Preferably, this chamber 25 is evacuated to minimize heat transfer
from the cooling chamber walls 28 and the superconducting element
20 to the outer wall 18 of the cryostat 12. The evacuation pressure
is preferably at least 10.sup.-3 torr, and most preferably on the
order of 10.sup.-5 torr, but of course may vary depending upon the
requirements of a particular application. The important factor is
that thermal transfer from the cooling source 24, which in this
case is the cooling chamber 26 holding a cryogen C, and the
superconducting element 20 to the outer wall 18 is minimized to
avoid cooling the vessel 16 or fluid F held therein. Although a
vacuum chamber 25 is proposed as one preferred manner of minimizing
this thermal transfer, the use of other means to provide the
desired thermal isolation is possible, such as by placing
insulating materials or the like in the chamber 25.
[0069] As is known in the art, by cooling the superconducting
element 20 in the presence of a magnetic field, it becomes capable
of distributing the current induced by a permanent magnet such that
the magnet levitates a certain distance above the superconducting
element, depending primarily upon the intensity and the direction
of the magnetic field generated by the levitating magnet. Although
basically a repulsive force is created, the peculiar nature of the
pinning forces generated actually tie the levitating magnet to the
superconducting element as if the two were connected by an
invisible spring. As should be appreciated, this form of attachment
cannot be achieved in conventional levitation schemes for pumping
or mixing elements that employ two opposed permanent magnets that
merely repel each other, since no pinning forces act to tie the two
magnets together, while at the same time provide a balancing
repulsive force.
[0070] In the preferred embodiment of the present system 10, the
element 20 providing the superconductive effects is a "high
temperature" or "type II" superconductor. Most preferably, the
superconducting element 20 is formed of a relatively thin
cylindrical pellet of melt-textured Yttrium-Barium Copper Oxide
(YBCO) that, upon being cooled to a temperature of approximately
77-78 Kelvin using a cooling source 24, such as the illustrated
liquid nitrogen chamber 26, exhibits the desired levitational
properties in a permanent magnet. Of course, the use of other known
superconducting materials having higher or lower operating
temperatures is also possible, and my prior U.S. Pat. No. 5,567,672
is incorporated herein by reference for, among other things, the
other high-temperature superconducting materials referenced
therein.
[0071] The pumping or mixing element 14 in the preferred embodiment
includes a first permanent magnet 32 for positioning in the vessel
16 adjacent to the superconducting element 20 such that it
levitates in the fluid F. Although the polarity of this first
magnet 32 is not critical to creating the desired levitation, the
magnet 32 is preferably disk-shaped and polarized in the vertical
direction. This ensures that a symmetrical magnetic field is
created by the magnet 32 and stable levitation results above the
superconducting element 20, while at the same time free rotation
relative to the vertical axis is possible.
[0072] In a version of the pumping or mixing element 14
particularly adapted for use in relatively deep fluid vessels, a
support shaft 34 is connected to and extends vertically from the
first permanent magnet 32. Along the shaft 34, at least one, and
preferably two, impellers 36 are carried that serve to provide the
desired pumping, or in the case of FIG. 1, mixing action when the
pumping or mixing element 14 is rotated. Rotation of the levitating
pumping or mixing element 14 in the vessel 16 is achieved by a
magnetic coupling formed between a second permanent magnet 38
(shown in dashed line outline in FIG. 1, but see also FIG. 2) and a
drive magnet 40 positioned externally of the vessel 16. The drive
magnet 40 is rotated by a drive means, such as an electric motor 42
or the like, and the magnetic coupling formed with the second
permanent magnet 38 serves to transmit the driving torque to the
pumping or mixing element 14 to provide the desired pumping or
mixing action. The direction of rotation is indicated by the action
arrows shown in FIGS. 1 and 2 as being in the counterclockwise
direction, but it should be appreciated that this direction is
easily reversed by simply reversing the direction in which the
drive magnet 40 is rotated.
[0073] In operation, and in practicing one possible method of
pumping or mixing a fluid disclosed herein, the vessel 16
containing the fluid F and pumping or mixing element 14 are
together placed external to the wall 18 of the cryostat 12 adjacent
to the superconducting element 20, which is placed in the evacuated
or insulated chamber 25. When the first disk-shaped permanent
magnet 32 is brought into the proximity of the superconducting
element 20, the symmetrical magnetic field generated causes the
entire pumping or mixing element 14 to levitate in a stable fashion
above the bottom wall of the vessel 16. This levitation brings the
second permanent magnet 38 into engagement with the drive magnet 40
to form the desired magnetic coupling. In addition to transmitting
the driving torque, this magnetic coupling also serves to stabilize
rotation of the pumping or mixing element 14. The motor 42 or other
motive device is then activated to cause the drive magnet 40 to
rotate, which in turn induces a steady, stable rotation in the
pumping or mixing element 14. Rotating impellers 36 then serve to
mix or pump the fluid F in a gentle, yet thorough fashion.
[0074] Since the pumping or mixing element 14 fully levitates and
can be completely submerged in the fluid, the need for mixing or
stirring rods penetrating through the vessel 16 in any fashion is
eliminated. The concomitant need for dynamic shaft seals or support
bearings in the vessel walls is also eliminated. Deleterious
friction is also not a concern. A related advantage is that the
vessel 16 containing the fluid F and the pumping or mixing element
14 can be completely sealed from the outside environment before
mixing to provide further assurances against leakage or
contamination. Yet another related advantage discussed in detail
below is that the vessel 16 and pumping or mixing element 14 can be
formed of relatively inexpensive, disposable materials and simply
discarded once mixing is complete. As should be appreciated, this
advantageously eliminates the need for cleanup and sterilization of
the pumping or mixing element 14 and vessel 16. Thus, by completely
sealing a disposable vessel, such as a plastic container or
flexible bag containing the pumping or mixing element and fluid
prior to mixing, the entire assembly can simply be discarded once
the fluid contents are recovered. This reduces the risk of exposure
both during and after mixing in the case of hazardous fluids, and
also serves to protect the fluid from contamination prior to or
during the pumping or mixing operation.
[0075] An alternative version of this first possible embodiment of
the system 10 of the present invention particularly adapted for
pumping a fluid F is shown in FIG. 2. In this version, the vessel
16 includes at least one fluid inlet 44 and at least one outlet 46.
The pumping or mixing element 14 preferably carries rotating
impellers 36 that serve to provide the desired pumping action by
forcing fluid F from the inlet 44 to the outlet 46 (see action
arrows). By increasing or decreasing the rotational speed of the
motor 42 or other motive device, or adjusting the size, shape or
style of the pumping or mixing element 14, impeller blades 36, or
substituting a different design altogether, a precise level of
pumping action may be provided.
[0076] Another possible modification shown in FIG. 2 is to use a
closed cycle refrigerator 48 to provide the necessary cooling for
the superconducting element 20 instead of a cryostat with a liquid
cryogen as the cooling source. The refrigerator 48 can be
positioned externally to a housing 18 containing the
superconducting element 20, which may be the equivalent of the
cryostat outer wall 18 previously described. As with the first
embodiment, a chamber 25 is defined by the housing 18. This chamber
25 is preferably evacuated or filled with other insulating
materials to minimize thermal transfer from the superconducting
element 20 to the housing 18. However, since no cooling source 24
is contained within the housing 18, it is not actually a "cryostat"
as that term is commonly defined. Nevertheless, the desired dual
levels of thermal separation are still possible, and the
concomitant advantages provided, since: (1) the cooling source 24,
48 is positioned away from the housing 18 and, thus, the vessel 16,
pumping or mixing element 14, and fluid F; and (2) the housing 18
still separates and defines a chamber 25 that thermally isolates
the superconducting element 20 and the vessel 16. In yet another
alternate arrangement, the refrigerator 48 can be used as a primary
cooling source, with the cryogenic chamber (not shown) serving as a
secondary or "backup" cooling source in the event of a power outage
or mechanical failure.
[0077] In accordance with another of the many important aspects of
the present system 10, the absence of a mixing rod or other
mechanical stirrer extending through a wall of the vessel 16 also
allows for placement of the pumping or mixing element 14 at an
off-axis position, as shown in FIG. 3. Specifically, the
superconducting element 20, pumping or mixing element 14, and drive
magnet 40 are all axially aligned away from the vertical center
axis of the vessel 16. One particular advantage of using this
approach is that the pumping or mixing element 14 may be rotated at
a very low speed while the vessel 16 is also rotated about its
center axis. This advantageously ensures that gentle, yet thorough
mixing, is achieved, which is particularly advantageous for use
with fluids that are sensitive to shear stress. As should be
appreciated, this arrangement can be used both whether the vessel
16 is completely sealed, provided with an inlet 44 and an outlet 46
for pumping as shown in FIG. 2, or open to the ambient environment.
For purposes of illustration only, FIG. 3 shows the cryostat 12 of
the embodiment shown in FIG. 1 having an outer wall 18 and a
cooling chamber 26 defined by a wall 28. However, it should be
appreciated that use of the housing 18 and closed-cycle
refrigerator 48 of the second embodiment of FIG. 2 as part of the
"cryostat" is also possible with this arrangement.
[0078] Through experimentation, it has been discovered that when
the pumping or mixing element 14 of the type described for use in
this first possible embodiment is employed, providing the requisite
degree of stability to ensure that all contact with the side walls
of the container 16 is avoided may in some instances be a concern.
Thus, to ensure that the pumping or mixing element 14 rotates with
exceptional stability and such deleterious contact is completely
avoided, the second permanent magnet 38 and the drive magnet 40 are
each provided with at least two pairs, and preferably four pairs of
cooperating sub-magnets 50a, 50b. As shown in FIGS. 4a and 4b,
these magnets 50a, 50b have opposite polarities and thereby serve
to attract each other and prevent the levitating pumping or mixing
element 14 from moving from side-to-side to any substantial degree.
However, the attractive force is counterbalanced by the combined
spring-like attractive and repulsive levitational/pinning forces
created between the first permanent magnet 32 and the
superconducting element 20 when cooled. This avoids the potential
for contact with the upper wall of the vessel 16, if present.
Overall, the pumping or mixing element 14 is capable of
exceptionally stable rotation using this arrangement, which further
guards against the undesirable frictional heating or shear stress
created if the rotating pumping or mixing element 14, or more
particularly, the first and second permanent magnets 32, 38 or the
blades of the impellers 36 could move into close proximity with the
bottom or side walls of the vessel 16.
[0079] As should be appreciated, it is possible to rearrange the
components of the system 10 such that the levitation and driving
forces are provided from other areas of the vessel, rather than
from the top and bottom of the vessel. Thus, as shown in FIG. 4c,
the cryostat 12 or other housing for containing the superconducting
element 20 may be positioned adjacent to one side of the vessel 16,
while the drive magnet 40 is positioned adjacent to the opposite
side. In that case, the pumping or mixing element 14 may be turned
on its side and supported by a separate stable support structure,
such as a table T or the like. The vessel 14 is shown as being
sealed, but it should be appreciated that any of the vessels
disclosed herein may be employed instead, including even a straight
or L-shaped pipe.
[0080] To assist in levitating the pumping or mixing element 14 in
either the embodiment of FIG. 1 or 2 or the other embodiments
disclosed herein, at least one, and preferably a plurality of
chambers 60 are provided for containing a substance lighter than
the surrounding fluid F. The chambers 60 may be provided adjacent
to each magnet 32, 38 in the pumping or mixing element 14, as well
as around the shaft 34, if desired. In the preferred embodiment
where the fluid F is or has a specific gravity similar to that of
water, the substance contained in the chambers 60 may be air.
However, in more viscous fluids, such as those having a specific
gravity more like glycerin, it may be possible to use lighter
fluids, such as water, even lighter gases, or combinations thereof.
These chambers 60 thus serve to assist in levitating the pumping or
mixing element 14 by helping it "float" in the fluid F. However,
the "pinning" force created by the superconducting element 20, plus
the levitating and aligning force created between the second
permanent magnet 38 and the driving magnet 40, both also serve to
assist in keeping the pumping or mixing element 14 in the proper
position as it rotates. In the case of disk or pancake shaped
permanent first and second magnets 32, 38 and a cylindrical shaft
34, annular chambers 60 may be used. Instead of fluid or gas filled
chambers, the use of other buoyant materials is also possible to
provide the levitation-assist function.
[0081] As previously mentioned, one of the many advantages of the
system 10 of the present invention is that, since the pumping or
mixing element 14 levitates in the fluid F and no mixing or
stirring rods are required for rotation, the vessel 16 can be
completely sealed from the outside ambient environment. Thus, by
forming the pumping or mixing element 14 and vessel 16 of
relatively inexpensive or disposable materials, both can simply be
discarded after mixing is completed and the fluid F is recovered.
Of course, such disposable materials can also be used to form the
vessel 16 designed for pumping fluids (FIG. 2), or to form the
open-top container for mixing fluids to avoid the need for clean up
or sterilization once the operation is complete.
[0082] It should also be appreciated that the pumping or mixing
element 14 illustrated is an example of one preferred arrangement
only, and that other possible configurations are possible. For
instance, impeller blades are not required, since a smooth-walled,
disk-shaped pumping or mixing element alone creates some gentle
mixing action simply by rotating. If present, the blade or blades
could simply be placed circumferentially around the disk-shaped
first permanent magnet 32 to reduce the length of the shaft 34, or
eliminate it altogether, especially if the vessel 16 has a
relatively small vertical dimension. Instead of a bladed impeller
assembly 36, the use of other structural arrangements is also
possible, such as disk-shaped wheels having vanes or like
structures designed to create more or less efficient rotation, and
a concomitant increase in the desired mixing or pumping action when
rotated. Depending on the depth of the vessel 16, the length of the
shaft 34, if present, can also be increased or decreased as
necessary. All components forming the pumping or mixing element in
any embodiment described above may be coated with TEFLON or other
inert materials to reduce the chances of contamination or
corrosion, as well as to facilitate clean up, if required.
[0083] Of course, besides use in the mixing or pumping of small
batches of fluid solutions or suspensions used during
experimentation and research in the laboratory setting, all
components are also easily scaled up for use in industrial or
commercial pumping or mixing operation, such as those commonly used
in the manufacture of large batches pharmaceuticals or food
products. The stable, reliable levitation of the magnetic pumping
or mixing element can still be readily achieved in systems of much
greater capacity than the one shown for purposes of illustration in
the drawings, thus making the present arrangement particularly
well-suited for the commercial production of pharmaceuticals or any
other solutions or suspensions that require gentle, yet thorough
mixing during processing.
[0084] Experiments conducted to date have demonstrated the efficacy
of the system 10 described above. The set-up utilized in conducting
these experiments included a pumping or mixing element having
axially aligned upper and lower magnets and an impeller assembly
mounted on a vertically extending support shaft, as shown in FIG.
1. A cylindrical pellet of melt-textured YBa.sub.2Cu.sub.3O.sub.7+x
having a diameter of 30 millimeters and a thickness of 25
millimeters was used as the superconducting element and placed in a
cryostat having a configuration similar to the one shown in FIG. 1.
The cryostat included a cooling chamber filled with approximately 1
liter of liquid nitrogen. A Nd--Fe--B permanent magnet with a
surface field intensity of 0.4 Tesla was used as the lower, first
permanent magnet.
[0085] Using this set-up, the experiments demonstrated that the
desired exceptionally stable levitation of the pumping or mixing
element above the top surface of the cryostat in a vessel filled
with a relatively warm fluid was possible. A separation distance of
up to seven millimeters was achieved, and the levitation was stable
for up to five hours using just a liter of liquid nitrogen as the
cryogen. In the first experiment using this set up, water was
selected as a model low viscosity fluid. Rotational speeds of up to
600 rpm were achieved--this upper limit being defined by only the
limited capabilities of the motor used to rotate the drive magnet
in this experiment. No decoupling or instability in the pumping or
mixing element was observed at any speed. In the case of glycerin,
a model high viscosity fluid, a maximum rotational speed of 60 rpm
was achieved before some decoupling of the pumping or mixing
element was observed. To further demonstrate the mixing
capabilities using the proposed system, SEPHADEX powder (dry bead,
50-150 micron diameter) was placed on the bottom of a water-filled
vessel and the levitating pumping or mixing element rotated. A
uniform suspension was achieved after approximately five minutes of
mixing.
[0086] As should be appreciated, the system 10 described above and
shown in FIGS. 1-4 is based on the use of a stationary
superconducting element 20 and a pumping or mixing element 14 that,
in addition to a "levitation" magnet, includes one or more separate
driven magnets for coupling with a drive mechanism, such as one
positioned at the opposite end of the vessel or container relative
to the superconducting element. However, other embodiments of the
pumping or mixing system may include a levitating, rotating pumping
or mixing element with magnets that are simultaneously used not
only for levitation, but also for transmitting driving torque. In
one embodiment, this driving torque is simultaneously provided by
the pinning forces that couple the pumping or mixing element with a
rotating superconducting element. Thus, the superconducting element
causes the pumping or mixing element to both levitate and rotate,
even though there is no physical contact between the two
elements.
[0087] More specifically, and in accordance with this second
possible embodiment of the present invention illustrated in FIG. 5,
the pumping or mixing system 100 includes a cryostat 102, which may
be formed of two separate components: a first component 102a
including an outer wall 104 that surrounds a relatively thin,
disk-shaped superconducting element 106 to define a chamber 108,
and a second component 102b including the cooling source 110.
Preferably, the outer wall 104 is formed of thin, non-magnetic
material, such as non-magnetic stainless steel or the like, but the
use of other materials is possible, as long as they do not
interfere with the operation of the system 100 and have relatively
poor thermal conductivity. The chamber 108 surrounding the
superconducting element 106 may be evacuated or insulated as
described above to thermally isolate and separate it from the wall
104. However, in this embodiment, and as noted further below, it is
possible to eliminate the chamber 108 entirely in the case where a
non-temperature sensitive fluid is being pumped or mixed.
[0088] In the case where the chamber 108 is evacuated, a valve 112
may be provided in the outer wall 104 for coupling to a vacuum
source. An optional getter 114 (such as an activated carbon insert
or the like) may be positioned in the chamber 108 for absorbing any
residual gases and ensuring that the desired evacuation pressure is
maintained. As with the embodiments described above, the evacuation
pressure is preferably on the order of 10.sup.-3 torr or greater,
but may vary depending on the particular application.
[0089] The superconducting element 106 is supported in the chamber
108 independent of the outer wall 104 of the first portion 102a of
the cryostat 102. The support may be provided by a platform 116
that is enclosed by wall 104 and supported at one end of an
elongated thermal link 118, preferably formed of metal or another
material having a high degree of thermal conductivity (e.g., 50
Watts/Kelvin or higher). To supply the necessary cooling to the
superconducting element, the opposite end of the elongated thermal
link 118 is positioned in contact with the cooling source 110,
which as described above forms a part of the second component 102b
of the "cryostat" 102 (the term cryostat being used throughout to
denote a structure or combination of structures that are capable of
maintaining a superconducting element in a cold state, whether
forming a single unit or not). The cooling source 110 is
illustrated schematically as an open-top container 119, such as a
Dewar flask, containing a liquid cryogen C, such as nitrogen.
However, it is also possible to use a closed-cycle refrigerator or
any other device capable of supplying the cooling necessary to
levitate a magnet above a superconducting element after field
cooling is complete. In the case where the wall 104 of the first
portion 102a of the cryostat 102 makes contact with the cryogenic
fluid C, as illustrated, it should be appreciated that there is
only negligible thermal transfer to the portion of the wall 104
adjacent the vessel, since: (1) the wall 104 may be formed of a
thin material having low thermal conductivity; and (2) the portion
of the wall 104 adjacent to the vessel is surrounded by the
ambient, room-temperature environment.
[0090] To permit the superconducting element 106 to rotate, a
roller bearing assembly 120 comprising one or more annular roller
bearings 122 supports the first portion of the cryostat 102a,
including the wall 104 defining the chamber 108. As should be
appreciated from viewing FIG. 5, these roller bearings 122 permit
the first portion of the cryostat 102a housing the superconducting
element 102 to rotate about an axis, which is defined as the axis
of rotation. A bearing housing 124 or the like structure for
supporting the bearing(s) 122 is secured to an adjacent stable
support structure 126. In the illustrated embodiment, a motive
device includes an endless belt 128 that serves to transmit
rotational motion from the pulley 129 keyed or attached to the
shaft 130 of a motor 131 to the first portion of the cryostat 102a.
The motor 131 may be a variable speed, reversible electric motor,
but the use of other types of motors to create the rotary motion
necessary to cause the superconducting element 106, and more
particularly, the first portion of the cryostat 102a housing the
superconducting element 106, to rotate is possible.
[0091] The vessel 132 containing the fluid to be mixed (which as
described below can also be in the form of a centrifugal pumping
head for transmitting a fluid) is positioned adjacent to the
rotating superconducting element 106, preferably on a stable
support surface T fabricated of a material that does not interfere
with the magnetic field created by the pumping or mixing element
134. As previously noted, the vessel 132 can be a rigid vessel of
any shape (open top, sealed having an inlet or outlet, cylindrical
with a hollow center, such as a pipe, or even a flexible plastic
bag (by itself, with rigid inserts, or inserted into a rigid or
semi-rigid vessel)). The only requirement is that the vessel 132
employed is capable of at least temporarily holding the fluid F (or
gas) being mixed or pumped.
[0092] To create the desired mixing action in this embodiment, a
pumping or mixing element 134 is positioned in the vessel 132 and
simultaneously levitated and rotated by the superconducting element
106. More specifically, the first portion of the cryostat 102a
containing the superconducting element 106, thermal link 118, and
the evacuated chamber 108 is rotated as a result of the rotational
motion transmitted by the endless belt 128. This rotation causes
the pumping or mixing element 134 in the vessel 124 to rotate and
either pump or mix the fluid F held therein. In the case where the
chamber 104 is evacuated or insulated, the pumping or mixing
element 134 is rotated in a stable, reliable fashion while the
desired thermal separation between the cold superconducting element
106 supplying the levitation force, the vessel 124, and hence the
fluid F, is achieved. The pumping or mixing element 134 may include
a plurality of mixing blades B (see FIGS. 6a and 6b), vanes V (not
shown, but see FIG. 7), or like structures to create an impeller.
However, again referring back to FIG. 5, a low-profile, disk-shaped
pumping or mixing element 134 may also be used to provide the
desired mixing action, especially for particularly delicate fluids,
such as blood or other types of cell suspensions.
[0093] As perhaps best understood by viewing FIGS. 6a and 6b
together, the pumping or mixing element 134 may include at least
two magnets 135a, 135b, and possibly more than two (see FIG. 20).
These magnets 135a, 135b not only serve to generate the magnetic
field that causes the pumping or mixing element 134 to levitate
above the superconducting element 106, but also transmit rotational
motion to the pumping or mixing element. As should be appreciated
by one of ordinary skill in the art, the magnetic field generated
by the magnets 135a, 135b should be axially non-symmetrical
relative to the axis of rotation of the superconducting element 106
in order to create the magnetic coupling necessary to efficiently
transmit the rotary motion. In one embodiment, the magnets 135a,
135b are disk-shaped and polarized along a center vertical axis
(see FIG. 6b, showing permanent magnets 135a, 135b of alternating
polarities (N-North; S-South) levitating above a pair of
superconducting elements 106a, 106b, with the corresponding action
arrows denoting the direction and axis of polarity). These magnets
135a, 135b can be fabricated from a variety of known materials
exhibiting permanent magnetic properties, including, but not
limited to, Neodymium-Iron-Boron (NdFeB), Samarium Cobalt (SMCo),
the composition of aluminum, nickel, and cobalt (Alnico), ceramics,
or combinations thereof The magnets 135a, 135b may be
interconnected by a piece of an inert matrix material M, such as
plastic or inert, non-corrosive metals. Alternatively, the magnets
135a, 135b may each be embedded in separate pieces of a matrix
material M, or may be embedded in a single unitary piece of
material (not shown). Also, as previously mentioned, the pumping or
mixing element 134 may carry one or more optional blades B, vanes
or like structures to enhance the degree of pumping or mixing
action created.
[0094] In another possible embodiment, the second portion of the
cryostat 102b including the cooling source (either a liquid cryogen
container (open top, sealed with inlet/outlet ports, or a
refrigerator (preferably a "cryocooler," as described further
below)) may be rigidly attached to the first portion 102a and both
components may be simultaneously rotated together (see the dashed
lines at the top of the open cooling container 119 in FIG. 5, and
see also the embodiment described below and shown in FIGS. 20-21).
The rotational motion may be supplied by an endless belt/motor
combination, as described above, or alternatively may be provided
through a direct coupling between the second portion of the
cryostat 102b (comprising any type of cooling source) and an inline
shaft extending from or coupled to a motor or similar motive device
(not shown).
[0095] As briefly mentioned above, it is possible to use this
embodiment of the system 100 without evacuating, insulating, or
otherwise thermally separating the superconducting element 106 from
the ambient environment, such as for mixing or pumping cold
(cryogenic) or non-temperature sensitive fluids. In that case,
there is no specific need for a wall 104 or chamber 108 surrounding
the superconducting element 106, since thermally separating it from
the structure supporting the vessel 132 (e.g., a table, stand or
the like) is unnecessary. Even with this modification, reliable and
stable levitation of the pumping or mixing element 134 is still
achieved.
[0096] From the foregoing, it should be appreciated that the same
driving mechanism and cryostat shown in FIG. 5 can be used for
pumping a fluid instead of mixing it. One version of a vessel 132
in the form of a centrifugal pumping head 150 is shown in FIG. 7.
This pumping head 150 includes a pumping chamber 152 having an
inlet 154 and an outlet 156 (which of course, could be reversed,
such as in a non-centrifugal pumping head (see FIG. 2)). The
chamber 150 contains the levitating pumping or mixing element 158,
which as shown may include a plurality of vanes V, or may
alternatively carry a plurality of blades (not shown). At least two
permanent magnets 160a, 160b having different polarities are
embedded or otherwise included in the pumping or mixing element
158, which may be substantially comprised of an inert matrix
material M having any desired shape to facilitate the pumping or
mixing action. As described above, these magnets 160a, 160b provide
both levitation and torque transmission as a result of the adjacent
rotating superconducting element 106.
[0097] As should be appreciated, one advantage of providing the
driving force for the levitating pumping or mixing element 158 from
the same side of the vessel/pumping head 150 from which the
levitating force originates is that the fluid inlet 154 (or outlet
156, in the case where the two are reversed) may be placed at any
location along the opposite side of the vessel/pumping head 150,
including even the center, without interfering with the pumping or
mixing operation. Also, this same side of the vessel/pumping head
150 may be frusto-conical or otherwise project outwardly, as
illustrated, without interfering with the rotation or necessitating
a change in the design of the pumping or mixing element 134,
158.
[0098] As briefly noted above, in some instances the opening in a
vessel may be too small to permit an even moderately sized pumping
or mixing element 134 to be inserted into the fluid F. In such a
case, alternate versions of a pumping or mixing element 134 meeting
this particular need are shown in FIGS. 8a-8c. In the first
alternate version, the pumping or mixing element 134a is in the
form of a slender rod formed of an inert matrix material M carrying
one of the levitating/driven magnets 135a, 135b at or near each
end. As should be appreciated, this pumping or mixing element 134a
may be easily turned to an upstanding position and inserted in the
opening. Upon then coming into engagement with the rotating
superconducting element 106, the pumping or mixing element 134a
would simultaneously levitate and rotate to pump or mix a fluid
held in the vessel. To further facilitate insertion in the narrow
opening, the matrix material M may be an elastomeric material or
another material having the ability to freely flex or bend.
[0099] A second version of a pumping or mixing element 134b for use
with a vessel having a narrow opening is shown in FIG. 8b. The
pumping or mixing element 134b includes first and second thin rods
180 formed of a matrix material M. The rods 180 each carry the
levitating/driven magnets 135a, 135b at each end thereof, with at
least two magnets having the identical polarity being held on each
different rod. In one version, the rods 180 are pinned about their
centers (note connecting pin 182) and are thus capable of folding
in a scissor-like fashion. As should be appreciated from FIG. 8c,
this allows the pumping or mixing element 134b to be folded to a
low-profile position for passing through the opening of the vessel
132. The rods 180 of the pumping or mixing element 134b may then
separate upon coming into engagement with an appropriately field
cooled superconducting element 106 positioned adjacent to the
bottom of the vessel 132. Since magnets 135a or 135h having the
same polarity are positioned adjacent to each other, the
corresponding ends of the rods 180 repel each other as the pumping
or mixing element 132b rotates. This prevents the rods 180 from
assuming an aligned position once in the vessel 132. As should be
appreciated, instead of pinning two separate rods 180 together to
form the pumping or mixing element 134b, it is also possible to
integrally mold the rods 180 of a flexible material to form a
cross. This would permit the rods 180 of the pumping or mixing
element 134h to flex for passing through any narrow opening, but
then snap-back to the desired configuration for levitating above
the superconducting element 106.
[0100] In accordance with yet another aspect of the present
invention, a third version of a pumping or mixing system 200 is
disclosed. In this third embodiment, which is illustrated in FIGS.
9, 9a, 9b, and 10, the forces for driving and levitating the
pumping or mixing element 204 are supplied from the same side of a
fluid vessel 202 (which is shown as an open-top container, but as
described above, could be a sealed container, a pumping chamber or
head, a flexible bag, a pipe, or the like). In this system 200, the
pumping or mixing element 204 actually includes two magnetic
subsystems: a first one that serves to levitate the pumping or
mixing element 204, which includes a first magnet 206, preferably
in the form of a ring, and a second magnetic subsystem that
includes at least two alternating polarity driven magnets 208a,
208b, preferably positioned inside of the first, ring-shaped magnet
206, to transmit driving torque to the pumping or mixing element
(see FIGS. 9a and 9b).
[0101] FIG. 9 shows one embodiment of the overall system 200 in
which the ring-shaped permanent magnet 206 or array of magnets (not
shown) provides the levitation for the pumping or mixing element
204. Polarization of the ring magnet 206 is vertical (as shown by
the long vertical arrows in FIG. 9b). The driven magnets 208a, 208b
are shown as being disk-shaped and having opposite or alternating
polarities (see corresponding short action arrows in FIG. 9b
representing the opposite polarities) to form a magnetic coupling
and transmit the torque to the levitating pumping or mixing element
204. Levitation magnet 206 and driven magnets 208a, 208b are
preferably integrated in one rigid structure such as by embedding
or attaching all three to a lightweight, inert matrix material M,
such as plastic or the like.
[0102] To correspond to the ring-shaped levitation magnet, the
superconducting element 210 for use in this embodiment is annular,
as well. This element 210 can be fabricated of a single unitary
piece of a high-temperature superconducting material (YBCO or the
like), or may be comprised of a plurality of component parts or
segments. Upon being cooled to the transition temperature in the
presence of a magnetic field and aligning with the ring-shaped
permanent magnet 206 producing the same magnetic field, the
superconducting ring 210 thus provides the combined
repulsive/attractive, spring-like pinning force that levitates the
pumping or mixing element 204 in the vessel 202 in an exceptionally
stable and reliable fashion. In FIG. 9, the vessel is shown as
being supported on the outer surface of a special cryostat 220
designed for use with this system 200, a detailed explanation of
which is provided in the description that follows. However, it is
within the broadest aspects of the invention to simply support the
vessel 202 on any stable support structure, such as a table (not
shown), as long as it remains sufficiently close to the
superconducting element 210 to induce the desired levitation in the
pumping or mixing element 204 held therein.
[0103] As in the embodiments described above, a motive device is
used to impart rotary motion to the pumping or mixing element 204,
and is preferably positioned adjacent to and concentric with the
annular superconducting element 210. One example of a motive device
for use in the system 200 of this third embodiment includes driving
magnets 212a, 212b that correspond to the driven magnets 208a, 208b
on the pumping or mixing element 204 and have opposite polarities
to create a magnetic coupling (see FIG. 9b). The driving magnets
212a, 212b are preferably coupled to a shaft 214 also forming part
of the motive device. The driving magnets 212a, 212b may be
attached directly to the shaft 214, or as illustrated in FIG. 9,
may be embedded or attached to a matrix material (not numbered in
FIG. 9, but see FIG. 9b). By positioning the driving magnets 212a,
212b close to the pumping or mixing element 204, such as by
inserting them in the opening or bore 219 defined by the annular
superconducting element 210, and rotating the shaft 214 using a
motor 216 also forming a part of the motive device, synchronous
rotation of the levitating pumping or mixing element 204 is
induced. The pumping or mixing element 204 may include one or more
blades B that are rigidly attached to the ring or levitation magnet
206 (or any matrix material forming the periphery of the pumping or
mixing element 204). However, it remains within the broadest
aspects of the invention to simply use a smooth, low-profile
pumping or mixing element (see FIG. 5) to provide the desired
mixing action.
[0104] As shown in FIGS. 9 and 10 and briefly mentioned above, the
mixing or pumping system 200 including the pumping or mixing
element 204 comprised of the magnetic levitation ring 206 and
separate driven magnets 208a, 208b may use a special cryostat 220
to ensure that reliable and stable rotation/levitation is achieved.
As perhaps best shown in the cross-sectional side view of FIG. 9,
the cryostat 220 includes a cooling source 221 for indirectly
supplying the necessary cooling to the superconducting element 210,
which as described below is supported and contained in a separate
portion of the special cryostat 220. In the illustrated embodiment,
the cooling source 221 (not necessarily shown to scale in FIG. 9)
includes a container 222, such as a double-walled Dewar flask, in
which a first chamber 224 containing a liquid cryogen C (nitrogen)
is suspended. A second chamber 223 defined around the first chamber
224 is preferably evacuated or insulated to minimize thermal
transfer to the ambient environment, which is normally at room
temperature. A port 226 is also provided for filling the suspended
chamber 224 with the chosen liquid cryogen C, as well as for
possibly allowing any exhaust gases to escape. As with the first
and second embodiments described above, the cooling source 221 may
instead take the form of a closed-cycle refrigerator (not shown),
in which case the double wall container 222 may be entirely
eliminated from the system 200.
[0105] A thermal link 228 is provided between the cooling source
(in the illustrated embodiment, the container 222) and a platform
230 suspended in the cryostat 220 for supporting the
superconducting ring 210. The use of the platform 230 is desirable
to ensure that the temperature of the superconducting element 210
is kept below the transition temperature, which in the case of a
"high temperature" superconducting material (such as YBCO) is most
preferably in the range of between 87-93 Kelvin. However, the use
of the platform 230 is not critical to the invention or required as
part of the special cryostat 220, since the thermal link 228 could
extend directly to the superconducting element 210. The thermal
link 228 may be a solid rod of material, including copper, brass,
or any other material having a relatively high thermal
conductivity. Instead of a solid rod, it is also possible to
provide an open channel 232 in the thermal link 228, especially
when a liquid cryogen C capable of flowing freely, such as
nitrogen, is used as the cooling source 221. This channel 232
allows the cryogen C from the suspended container 224 to reach the
platform 230 directly. Of course, the direct contact with the
cryogen C may provide more efficient and effective cooling for the
superconducting element 210, but is not required.
[0106] The ring-shaped platform 230 that supports the
superconducting element(s) 210 and supplies the desired cooling via
thermal conduction may be made of copper, brass, aluminum, or
another material having good thermal conductivity. It may be in the
form of a solid ring, as illustrated, or may be in the form of a
hollow ring (such as a substantially circular or elliptical torus,
not shown). This would allow the liquid cryogen C to flow
completely around the ring to further increase the efficiency with
which the cooling is transferred to the superconducting element
210. In any case, where a platform 230 is used, care should be
taken to ensure that full contact is made with at least a majority
of the corresponding surface of the superconducting element 210,
since even cooling helps to ensure that the desired smooth, even,
and reliable levitation is achieved.
[0107] To reduce the thermal transfer to the vessel 202 in the case
where a temperature sensitive fluid is being pumped or mixed by the
system 200, a ring-shaped wall or enclosure 234 surrounding the
platform 230 and the annular superconducting element 210 defines a
first chamber 235. In addition, a hollow cylindrical wall or
enclosure 236 may also surround the thermal link 232 and define a
second chamber 237. Preferably, these first and second chambers
235, 237 are evacuated or insulated to minimize thermal transfer
between the ambient environment and the cold elements held therein.
In a preferred embodiment, each enclosure 234, 236 is fabricated
from non-magnetic stainless steel, but the use of other materials
is of course possible, as long as no interference is created with
the levitation of the pumping or mixing element 204. As with the
second embodiment described above, it is also possible to use the
system 200 of the third embodiment to pump or mix cryogenic or
non-temperature sensitive fluids, in which case there is no need to
evacuate or insulate the enclosures 234, 236, or to even use the
special cryostat 220 described herein.
[0108] As should be appreciated, it is possible to create the
chambers 235, 237 defined by the enclosures 234, 236 and the
chamber 223 such that all three are in fluid communication and thus
represent one integrated vacuum space (not shown). This facilitates
set-up, since all three chambers 223, 235, 237 may be evacuated in
a single operation, such as by using a vacuum source coupled to a
single valve (not shown) provided in one of the chambers. However,
separately evacuating each chamber 223, 235, 237 is of course
entirely possible. Also, instead of or in addition to evacuating
the chambers 223, 235, 237, some or all may be instead filled with
a suitable insulating material (not shown).
[0109] As should be appreciated, to rotate the pumping or mixing
element 204 in this embodiment, it is desirable to place the drive
magnets 212a, 212b in close proximity to the pumping or mixing
element, but preferably on the same side of the vessel 202 as the
superconducting element 210. Accordingly, the special cryostat 220,
and more specifically, the wall or enclosure 234 defines a
room-temperature cylindrical bore or opening 240 that allows for
the introduction of the end of the shaft 214 carrying the driving
magnets 212a, 212b, which are at room temperature. As a result of
this arrangement, the shaft 214, which is part of the motive
device, is concentric with the superconducting element 210. The
shaft 214 is also positioned such that the driving magnets 212a,
212b align with the driven magnets 208a, 208b on the pumping or
mixing element 204 when the levitating magnet 206 is aligned with
the superconducting element 210. Thus, despite being positioned
adjacent to and concentric with the superconducting element 210,
the shaft 214 and driving magnets 212a, 212b remain at room
temperature, as does the vessel 202, the fluid F, and the pumping
or mixing element 204.
[0110] An example of one possible embodiment of a centrifugal
pumping head 250 for use with the system 200 of FIG. 9 is shown in
FIG. 11. The head 250 includes a levitating pumping or mixing
element 252 that carries one or more optional blades or vanes V
(which are upstanding in the side view of FIG. 11), a fluid inlet
254 (which as should be appreciated can be in the center at one
side of the pumping head 250 in view of the fact that the
levitation and driving forces are both supplied from the same side
of the vessel 202), a fluid outlet 256, driven magnets 258a, 258b,
and a ring-shaped levitation magnet 260.
[0111] In yet another possible embodiment of the invention, as
shown in the cross-sectional view of FIG. 12, the system 300
includes a pumping or mixing element 302 adapted for inline use,
such as when the vessel is in the form of a hollow pipe 304. The
pumping or mixing element 302 includes first and second spaced
levitating magnets 305a, 305b, one of which is preferably
positioned at each end to ensure that stable levitation is
achieved. The magnets 305a, 305b preferably correspond in shape to
the vessel, which in the case of a pipe 304, means that they are
annular. The magnets 305a, 305b are carried on a shaft 306 forming
a part of the pumping or mixing element 302, which further includes
a driven magnet 308. The driven magnet 308 may be comprised of a
plurality of sub-magnets 308a . . . 308n having different
polarities and arranged in an annular configuration to correspond
to the shape of the pipe 304 serving as the vessel in this
embodiment (see FIG. 12b). All three magnets 305a, 305b, and 308
may be embedded or attached to an inert matrix material M, such as
plastic, that provides the connection with the shaft 306. The shaft
306 of the bearing 302 may also carry one or more blades B.
[0112] First and second "cryostats" 310a, 310b are also provided.
As perhaps best understood with reference to the cross-sectional
view of FIG. 12a, the first "cryostat" 310a includes a
superconductor for levitating the pumping or mixing element in the
form of an annular superconducting element 312a. This
superconducting element 312a is suspended in a chamber 314a defined
by the cryostat 310a, which may be evacuated or insulated to
prevent thermal transfer to the pipe 304 or the passing fluid F.
The cryostat 310a may include an inner wall adjacent to the outer
surface of the pipe 304 (not shown), but such a wall is not
necessary in view of the thermal separation afforded by the
evacuated or insulated space surrounding the superconducting
element 312a. The superconducting element 312a may be coupled to
annular support platform 316a, which in turn is thermally linked to
one or more separate cooling sources 318. The connection is only
shown schematically in FIG. 12, but as should be appreciated from
reviewing the foregoing disclosure, may include a rod that serves
to thermally link a container holding a liquid cryogen or a closed
cycle refrigerator to the superconducting element 312a. While not
shown in detail. "cryostat" 310b may be similar or identical to the
cryostat 310a just described.
[0113] With reference now to FIGS. 12b and 12c, two different
motive devices for rotating the pumping or mixing element 302 in
the pipe 304 are disclosed. The first motive device includes a
driving magnet assembly 320 that is rotatably supported on a
bearing 322, such as a mechanical ball or roller bearing, carried
on the outer surface of the pipe 304. The magnet assembly 320
includes a plurality of driving magnets 320a . . . 320n, also
having different or alternating polarities. As with the driven
magnets 308a . . . 308n, the driving magnets 320a . . . 320n are
embedded or attached to an inert, non-magnetic matrix material M,
such as plastic. An endless belt 324 also forming a part of the
motive device frictionally engages both the driving magnet assembly
320 and a pulley or wheel W earned on the spindle or shaft of a
motor (preferably a reversible, variable speed electric motor, as
described above).
[0114] As should now be appreciated, the pumping or mixing element
302 is caused to levitate in the pipe 304 as a result of the
interaction of the levitation magnets 305a, 305b with the adjacent
superconducting elements 310a, 310b, which may be thermally
separated from the outer surface of the pipe 304 (or the adjacent
inner wall of the cryostat 310a, 310b, if present). Upon then
rotating the magnetic drive assembly 320, the pumping or mixing
element 302 is caused to rotate in the pipe 304 serving as the
vessel to provide the desiring pumping or mixing action. Even if
the fluid F is flowing past the pumping or mixing element 302, it
remains held in place in the desired position in the pipe 304 as a
result of the pinning forces created by the superconducting
elements 310a, 310b acting on the levitation magnets 305a,
305b.
[0115] The second version of a motive device is shown in the
cross-sectional view of FIG. 12c, which is similar to the
cross-section taken in FIG. 12b. However, instead of a magnetic
driving assembly 320, endless belt 324, and motor, rotary motion is
imparted to the pumping or mixing element 302 by creating an
electrical field around the pipe 304. This may be done by placing a
winding 326 around the outer wall of the pipe 304 and supplying it
with an electrical current, such as from a power supply 328 or
other source of AC current. Since the pumping or mixing element 302
carries magnets 308a . . . 308n having different polarities, the
resulting electric field will thus cause it to rotate.
[0116] Yet another embodiment of an inline pumping or mixing system
400 is shown in FIG. 13. The cryostat 402 in this case is
essentially positioned directly in the path of fluid flow along the
pipe 403, thus creating an annular (or possibly upper and lower)
flow channels 404a, 404b. The cryostat 402 has an outer wall 406
that defines a chamber 408 for containing a superconducting element
410. The superconducting element 410 may be annular in shape, in
which case the chamber 408 is of a similar shape. The chamber 408
may also be evacuated or insulated to thermally separate the
superconducting element 410 from the outer wall 406. The
superconducting element 410 is thermally linked to a separate
cooling source 412, with both the thermal link and the cooling
source being shown schematically in FIG. 13. It should be
appreciated that this cryostat 402 is similar in many respects to
the one described above in discussing the third embodiment
illustrated in FIG. 9, which employs a similar, but somewhat
reoriented, arrangement.
[0117] The wall 406 creating annular chamber 408 for the
superconducting element 410 defines a room temperature bore or
opening 414 into which a portion of a motive device may be
inserted, such as the end of a shaft 416 carrying at least two
driving magnets. FIG. 13 illustrates the motive device with three
such driving magnets 418a, 418b, 418c, one of which is aligned with
the rotational axis of the shaft 416. The opposite end of the shaft
416 is coupled to a motor (not numbered), which rotates the shaft
and, hence, the driving magnets 418a, 418b, and 418c. The magnets
418a, 418b, 418c may be coupled directly to the shaft 416, or
embedded/attached to an inert matrix material M.
[0118] The pumping or mixing element 420 is positioned in the pipe
403 adjacent to the outer wall 406 of the cryostat 402. The pumping
or mixing element 420 includes a levitation magnet 422 that
corresponds in size and shape to the superconducting element 410,
as well as driven magnets 424a, 424b, 424c that correspond to the
driving magnets 418a, 418b, and 418c. The levitation magnet 422 and
driven magnets 424a-424c are attached to or embedded in a matrix
material M, which may also support one or more blades B that
provide the desired pumping or mixing action.
[0119] In operation, the motor rotates the shaft 416 to transmit
rotary motion to the driving magnets 418a, 418b and 418c. As a
result of the magnetic coupling formed between these magnets 418a-c
and the opposite polarity driven magnets 424a-c, the pumping or
mixing element 420 is caused to rotate in the fluid F. At the same
time, the pumping or mixing element 420 remains magnetically
suspended in the fluid F as the result of the pinning forces
created between the superconducting element 410 and the levitation
magnet 422. The operation is substantially the same as that
described above with regard to the third embodiment, and thus will
not be explained further here.
[0120] Various optional modifications may in some circumstances
enhance the set-up or performance of any of the systems described
herein, or instead adapt them for a particular use, purpose, or
application. As noted previously, the disposable vessel or
container for holding the fluid undergoing pumping or mixing may be
in the form of a flexible bag. An example of such a bag 500 is
shown in FIG. 14, along with the system 100 for levitating the
pumping or mixing element 502 of FIG. 5. The bag 500 may be sealed
with either fluid F or the pumping or mixing element 502 (which may
take the form of one of the several pumping or mixing elements
disclosed above or an equivalent thereof) inside prior to
distribution for use, or may be provided with a sealable (or
resealable) opening that allows for the fluid and pumping or mixing
element to be introduced and later retrieved.
[0121] Both the pumping or mixing element 502 and bag 500, whether
permanently sealed or resealable, may be fabricated of inexpensive,
disposable materials. Accordingly, both can simply be discarded
after the pumping or mixing operation is completed and the fluid F
is retrieved. It should also be appreciated that the vertical
dimension of the bag 500 is defined by the volume of fluid F held
therein. Thus, instead of placing the bag 500 containing the
pumping or mixing element 502 directly on the surface of the
cryostat, table T, or other support structure adjacent to the
superconducting element 106, it is possible to place the flexible
bag 500 in a separate rigid or semi-rigid container (see, e.g.,
FIG. 22). This helps to ensure that the fluid F provides the bag
500 with a sufficient vertical dimension to permit the pumping or
mixing element 502 to freely rotate in a non-contact fashion.
Alternatively, the bag 500 may include internal or external
reinforcements (not shown) to enhance its rigidity without
interfering with the rotation of the pumping or mixing element.
[0122] In cases where the pumping or mixing element 502 is
prepackaged in the bag 500, with or without fluid, it may
inadvertently couple to adjacent magnets or other metallic
structures. Breaking this coupling may render the bag susceptible
to puncturing, tearing, or other forms of damage. Accordingly, as
shown in FIGS. 14a and 14b, it may be desirable to hold the pumping
or mixing element 502 place prior to use with any of the systems
described herein, especially in cases where it is sealed inside the
vessel/bag 500 during manufacturing
[0123] As shown in FIG. 14a, one manner of holding the element 502
in place is to use an attachment 520, cover, or similar device
including a coupler 522 formed of a ferromagnetic material or the
like adjacent to the bag 500. This coupler 522 is thus attracted to
and forms a magnetic coupling with the pumping or mixing element
502 when the attachment 520 is in place. As a result of this
coupling, the pumping or mixing element 502 is prevented from
coupling with magnets in adjacent bags or other magnetic structures
(not shown). The attachment 520 should be fabricated of a
non-magnetic material, such as rubber. In the operative position,
the coupler 522 shields the magnetic field created by the pumping
or mixing element 502. When the assembly including the bag 500 and
the pumping or mixing element 502 is ready for use, the attachment
520 may simply be removed from the bag 500 to break the magnetic
coupling between the pumping or mixing element 502 and the coupler
522.
[0124] A second manner of keeping the pumping or mixing element 502
at a desired location to facilitate coupling with the particular
levitation/rotation devices used is to provide the bag 500 with a
"centering" structure, such as a post 528. As shown in the
embodiment illustrated in FIG. 14b, which includes the basic
levitation and rotation system of FIG. 5, this post 528 may take
the form of a rigid or semi-rigid piece of material projecting into
the interior of the bag 500. Preferably, the post 528 is formed of
the same material as the bag 500 or other container (plastic) and
has an outer diameter that is less than the inner diameter or a
bore or opening formed in the pumping or mixing element 502. As
should be appreciated, the pumping or mixing element 502 may be
held in place on the post 528 by gravity during shipping, prior to
use, and even between uses. As illustrated, the upper end of the
post 528 could also include a T-shaped or oversized head 529 (which
could have a spherical, pyramidal, conic, or cubic shape).
Alternatively, the head could have one or more transversely
extending, deformable cross-members, an L-shaped hook-like member,
or another type of projection for at least temporarily capturing
the pumping or mixing element 502 to prevent it from inadvertently
falling off when not in use. Of course, the positioning of the head
529 for capturing the pumping or mixing element 502 is preferably
selected such that it does not interfere with the free levitation
or rotation. As should be appreciated, the post 528 provides not
only centering function, but also holds the pumping or mixing
element 502 in place in case it accidentally decouples during the
pumping or mixing operation. This significantly eases the process
of returning the pumping or mixing element 502 to the proper
position for initiating or resuming levitation/rotation by the
corresponding system (which may be, for example, systems 10, 100,
200, 300, 800 etc.).
[0125] In FIG. 14b, this post 528 is adapted to receive the pumping
or mixing element 502, which has a corresponding opening (and thus,
may be annular or have any other desired shape or size). Since the
post 528 preferably includes an oversized head portion 529 that
keeps the pumping or mixing element 502 in place, including before
a fluid is introduced, the vessel 500 may be manufactured, sealed
(if desired), shipped, and stored prior to use with the pumping or
mixing element 502 already in place. The vessel 500 may also be
sterilized as necessary for a particular application, and in the
case of a flexible bag, may even be folded for compact storage. As
should be appreciated, the post 528 also serves the advantageous
function of keeping the pumping or mixing element 502 substantially
in place (or "centered") should it accidentally become decoupled
from the adjacent motive device, which as in this case is a
rotating annular superconducting element 106. However, the
centering post 528 could also be used in the embodiment of FIG. 9
as well by simply forming a center opening in the pumping or mixing
element 204.
[0126] In the illustrated embodiment, the post 528 is shown as
being formed by an elongated rod-like structure inserted through
one of the nipples 530 typically found in the flexible plastic bags
frequently used in the bioprocessing industry (pharmaceuticals,
food products, cell cultures, etc.). The oversized head portion 529
is preferably formed of a material that is sufficiently
flexible/deformable to easily pass through the opening in the
nipple 530. A conventional clamp 531, such as a cable or wire tie,
may be used to form a fluid-impervious seal between the nipple 530
and the portion of the post 528 passing therethrough, but other
known methods for forming a permanent or semi-permanent seal could
be used (e.g., ultrasonic welding in the case of plastic materials,
adhesives, etc.). Any other nipples 530 present (shown in phantom
in FIG. 14b) may be used for introducing the fluid prior to mixing,
retrieving a fluid during mixing or after mixing is complete, or
circulating the fluid in the case of a pumping operation.
Advantageously, the use of the rod/nipple combination allows for
easy retrofitting. Nevertheless, instead of using a separate rod,
the post 528 may be integrally formed with the material forming the
vessel 500, either during the manufacturing process or as part of a
retrofit operation. Also, as noted in my prior applications, the
oversized head portion 529 may be cross-shaped, disc-shaped,
L-shaped, Y-shaped, or may have any other desired shape, as long as
the corresponding function of capturing the pumping or mixing
element 502 is provided. The head portion 529 may be integrally
formed, or alternatively may be provided as a separate component
that is clamped or fastened to the post 528.
[0127] In yet another embodiment, the vessel 500 may also include a
structure that helps to ensure that proper alignment is achieved
between the centering post 528 and an adjacent structure, such as a
device for rotating and/or levitating the pumping or mixing element
502. In the embodiment of FIG. 14b, this alignment structure is
shown in the form of an alignment post 532 projecting outwardly
from the vessel 500 and co-extensive with the centering post 528.
The post 532 extends through an opening 536 formed in the lower
portion, such as the floor, of a semi-rigid support container 534
defining a compartment for receiving the vessel 500. The container
543 thus serves as a support structure (which may instead be the
table T, as shown in FIG. 14e).
[0128] The adjacent motive device, which as shown as including a
cryostat 102 containing a rotating superconducting element 106,
includes a locator bore 533. This bore 533 is concentric with the
superconducting element 106 and is sized and shaped for receiving
the alignment post 532 (which may have any desired cross-sectional
shape, including circular, elliptical, square, polygonal, etc.). As
a result of the centering and alignment posts 528, 532, assurance
is thus provided that the pumping or mixing element 502 is in the
desired position for forming a coupling with an adjacent motive
device, such as the cryostat 102 housing the rotating
superconducting element 106 (which may both rotate together, as
described above). This is particularly helpful for properly
aligning the pumping or mixing element 502 with the cryostat, such
as cryostat 102, in the case of opaque vessels or adjacent
containers, sealed or aseptic containers, large containers, or
where the fluid is not clear. Instead of forming the alignment post
532 from an elongated rod inserted into a nipple 530 or the like,
it should be appreciated that it may also be integrally formed with
the vessel 500 during manufacturing, or later during a
retrofit.
[0129] FIG. 14b also shows the centering post 528 projecting
upwardly from a bottom wall of the vessel 500, but as should be
appreciated, it could extend from any wall or other portion
thereof. For example, as illustrated in FIG. 14c, the rod serving
as both the centering post 528 and the alignment post 532 may be
positioned substantially perpendicular to a vertical plane.
Specifically, in the particular embodiment shown, the vessel 500 is
an empty flexible bag as shown above positioned in a rigid or
semi-rigid support container 534 having an opening 536 formed in
the lower portion thereof. Once the vessel 500 is inserted in the
container 534, but preferably prior to introducing a fluid, the
alignment post 532 is positioned in the opening 536 such that it
projects therefrom (along with any inlet or outlet hoses present).
The proximal end of the alignment post 532 is then inserted into a
corresponding receiver in the motive device, such as the locator
bore 533 formed in the cryostat 102 (which is easily reoriented, as
described herein). This ensures that the pumping or mixing element
502 is in the desired position to form the magnetic coupling with
the superconducting once field cooling is complete to achieve
levitation and/or rotation without the need for external
intervention. As noted above, the coupling may be formed either
before or after the introduction of the fluid into the vessel 500.
Also, while shown in conjunction with a particular embodiment of
the pumping or mixing system, it should be appreciated that the
alignment and centering posts 528, 532 may, either together or
separately, be used in conjunction with different types of pumping
or mixing elements or with any of the pumping or mixing systems
disclosed herein.
[0130] In many of the above-described embodiments, the pumping or
mixing action is essentially localized in nature. This may he
undesirable in some situations, such as where the vessel is
relatively large compared to the pumping or mixing element. To
solve this problem, the particular system used to supply the
pumping or mixing action may be provided with a motive device for
physically moving the superconducting element (which may also be
simultaneously rotated). This of course will cause the levitating
pumping or mixing element to follow a similar path.
[0131] With reference to the schematic view of FIG. 14d, and by way
of example only, the particular arrangement is shown in use on the
system 100 of FIG. 5, but with the bag 500 of FIG. 14. In addition
to a motive device 540 for rotating the first portion of the
cryostat 102a (which may comprise the bearing(s) 120, endless belt
128, motor 131, shaft, and pulley) and a cooling source 541, the
system 100 may include a second motive device 542. In one
embodiment, this second motive device 542 (shown schematically in
dashed line outline only in FIG. 14c) is capable of moving the
first portion of the cryostat 102a, and hence the superconducting
element 106, to and fro in a linear fashion (see action arrow L in
FIG. 14c). Thus, in addition to levitating and rotating the pumping
or mixing element 502, the side-to-side motion allows it to move
relative to the bag 500 or other vessel containing the fluid. This
advantageously permits non-localized pumping or mixing action to be
provided. The second motive device 542 may include a support
structure, such as a platform (not shown) for supporting all
necessary components, such as the first portion of the cryostat
102a (or the entire cryostat, such as in the embodiment of FIG. 9),
the first motive device 540 for rotating one of the superconducting
element 106 (or the pumping or mixing element 502 such as in the
embodiment of FIG. 9), and the cooling source 541 (which may form
part of the cryostat as shown in FIG. 9, or may be a separate
component altogether, as shown in FIG. 2). Instead of using a
linear motion device, it should also be appreciated that the second
motive device 542 may be capable of moving the superconducting
element 106 in a circular or elliptical path relative to the fixed
position of the bag 500 or other vessel, or in any other direction
that will enhance the overall mixing or pumping action provided by
the rotating pumping or mixing element 502. Also, the bag 502 or
vessel may be separately rotated or moved to further enhance the
operation (see the above-description of the embodiment of FIG.
3).
[0132] Ensuring that the pumping or mixing elements are both proper
for a particular system and are of the correct shape and size may
also be important. To do so, it is possible to provide a
transmitter in one of the pumping or mixing element or the vessel
for generating a signal that is received by a receiver in the
system (or vice versa), such as one positioned adjacent to the
superconducting element or elsewhere. An example of one possible
configuration is shown in FIG. 14, wherein the transmitter 550 is
provided on the pumping or mixing element 502 itself and the
receiver 560 is positioned in the cryostat 102 (but see FIG. 14a,
wherein the transmitter 550 or receiver 560 is provided in the bag
500 serving as the vessel). A controller for the system, such as a
computer (not shown) or other logic device, can then be used to
maintain the system for rotating the pumping or mixing element 502
in a non-operational, or "lock-out," condition until the receiver
and transmitter 550, 560 correspond to each other (that is, until
the transmitter 550 generates an appropriate signal that is
received by the receiver 560). The transmitter/receiver combination
employed may be of any type well known in the art, including
electromagnetic, ultrasound, optical, or any other wireless or
remote signal transmitting and receiving devices.
[0133] In accordance with another aspect of the invention, a kit is
also provided to assist in the set-up of any of the systems
previously described. Specifically, and as briefly noted in both
this and my prior applications, it is necessary during field
cooling to cool the superconducting element to below its transition
temperature in the presence of a magnetic field in order to induce
levitation in a permanent magnet producing the same magnetic field.
This cooling process causes the superconducting element to
"remember" the field, and thus induce the desired levitation in the
pumping or mixing element each time it or any other magnet having
either a substantially similar or identical magnetic field
distribution is placed over the superconducting element. While it
is possible to use the pumping or mixing element itself to produce
the magnetic field required during field cooling, oftentimes the
pumping or mixing element will be sealed in the vessel or
container. This makes it difficult, if not impossible, to ensure
that the magnets held therein are properly aligned and spaced from
the superconducting element during field cooling.
[0134] One way to overcome this potential problem is to use a
set-up kit. As illustrated in FIG. 15, the set-up kit may comprise
at least one charging magnet 600 having a size, shape, and magnetic
field distribution that is identical to the levitation magnet
contained in the particular pumping or mixing element slated for
use in one of the pumping or mixing systems previously described.
The charging magnet 600 is placed adjacent to the superconducting
element 602, such as on the upper surface of the cryostat 604,
table (not shown), or other structure. As illustrated, the charging
magnet 600 may further include a spacer 606. This spacer 606 allows
the charging magnet 600 to simulate the spacing of the pumping or
mixing element (not shown) above the superconducting element 602
during field cooling. This ensures that the desired levitation
height is achieved for the pumping or mixing element (not shown)
once the vessel is in position. The spacer 606 is formed of a
non-magnetic material to avoid interfering with the charging
process. By providing a variety of different sizes, shapes, and
configurations of charging magnets in the kit (e.g., annular
magnets), it is possible to easily perform field cooling for any
corresponding size or shape of levitation magnet in the
corresponding pumping or mixing element, and then simply place the
vessel containing the pumping or mixing element over the
superconducting element 602 to induce the desired stable, reliable
levitation. It is also possible to field cool the superconducting
element 602 while the cryostat 604 is in one orientation, and then
reorient it for forming the coupling with the pumping or mixing
element (see, e.g., FIG. 14c).
[0135] During field cooling, and regardless of whether the pumping
or mixing element or a separate charging magnet 600 is used to
produce the charging magnetic field, it is possible to
unintentionally or accidentally induce an undesired magnetic state
in the superconducting element 602, such as if the position of the
pumping or mixing element (not shown) or charging magnet 600 is not
correct. Since improper charging may prevent the pumping or mixing
element from levitating in a stable fashion, recharging the
superconducting element 602 may be required. To facilitate
recharging the superconducting element, it is provided with a
heater H, such as an electric heating coil (not shown). By
energizing this coil using a power supply P or other source of
electrical current (not shown), the superconducting element 602 may
be quickly brought up from the transition temperature for
recharging. As shown schematically, the power supply P is
preferably positioned externally to the cryostat 604. Once the
position of the pumping or mixing element or charging magnet 600 is
adjusted or corrected, the heater H may be turned off and the
superconducting element once again allowed to cool to the
transition temperature in the presence of the desired magnetic
field. Yet another embodiment of a system 700 is provided for use
with a particular type of vessel including a cavity, such as of the
type designed to withstand high internal pressures. Even with this
cavity, the system 700 permits a strong magnetic coupling to be
formed between an external magnet or superconductor and one or more
magnets forming part of an internal mixing element, such as a rotor
or impeller, inside the vessel to ensure that stable, reliable
levitation is achieved.
[0136] As shown in the schematic, partially cross-sectional side
elevational view of FIG. 16, the vessel 702 includes a cavity 704
formed in one sidewall thereof. As briefly explained above, the
shape of this cavity 704 is preferably cylindrical. In the
cylindrical case, this shape allows for the outer sidewall of the
cavity 704 to be fabricated having a first thickness t.sub.1 (about
2 millimeters in one possible embodiment, but possibly even less),
with the remainder of the vessel 702 being formed from the same or
a different material having a second, greater thickness t.sub.2
(e.g., more than 2 millimeters, and preferably about 7
millimeters). To form a unitary vessel, the cavity 704 may be
formed as a separate "hat-shaped" section, including an annular
flange that is welded (see weld 705 in FIG. 16) to a corresponding
flange (not numbered).
[0137] With this construction, the vessel 702 is able to withstand
relatively high internal pressures (up to about 7 bar, and possibly
greater), yet the relatively thin sidewall of the cavity 704 allows
for strong magnet-magnet/magnet-superconductor interactions to be
achieved. Of course, the potential reduction in thickness of the
sidewalls of the cavity 704 and the upper limit of the internal
pressure are directly influenced by the type of material used, with
the dimensions provided above corresponding to a vessel 702 formed
of conventional non-magnetic stainless steel. Although a
cylindrical cavity 704 is shown, it should be appreciated that
other equivalent geometric arrangements may also be used, including
those having regular or irregular polygonal cross-sections or the
like.
[0138] To adapt the superconducting levitation scheme described
immediately above to a vessel 702 having such a cavity 704, a
special "cryostat" 706 may be used, which is generally similar in
construction to the one shown in FIG. 9. In the illustrated
embodiment, the cryostat 706 includes an external wall 708 that
defines an enclosed space or chamber (not numbered). This space is
evacuated, such as by using a vacuum source (not numbered), and
together with the wall 708 creates a vacuum "jacket" 710 around a
superconductor or superconducting element 712 held therein. The
superconducting element 712 is preferably a "high temperature"
superconducting element formed of melt-textured
ReBa.sub.2Cu.sub.3O.sub.x, with Re representing a rare earth
element (e.g., Yttrium, of which YBCO is a common example), but the
use of other such materials either already known or discovered
after the filing is of course possible without departing from the
broadest aspects of the invention. Also, as is known in the art,
the superconducting element 712 may be formed from a single annular
or ring shaped piece of material, or as outlined further in the
description that follows, may be comprised of a plurality of
contiguous or non-contiguous segments or sections, each formed of a
piece of superconducting material interconnected or arranged in an
annular or substantially polygonal configuration.
[0139] In the illustrated embodiment, the superconducting element
712 is positioned in a "head" portion of the cryostat 706 sized
and/or otherwise adapted for extending or projecting into the
cavity 704 formed in the vessel 702. The cryostat 706 also includes
or houses a thermal link 714 for supplying the cooling that keeps
the element 712 in the desired superconducting state. As described
above, the thermal link 714 is preferably formed of a material
having a high degree of thermal conductivity/low thermal resistance
(metals, such as copper, brass, or the like). Although not
critical, the link 714 may include an engagement portion
corresponding generally in size and shape to the superconducting
element 712 to ensure that the desirable full contact and
engagement is established between the corresponding surfaces to
improve thermal transfer. As also described above, the thermal link
714 is connected to a cooling source, such as a Dewar flask filled
with a liquid cryogen, a closed cycle refrigerator, or the like
(see, e.g., FIG. 9). It should be appreciated by skilled artisans
that the particular cooling source or thermal link used is not
important or critical, as long as it is capable of maintaining the
element 712 in the desired superconducting state to induce
levitation in the mixing element 722.
[0140] As with the embodiment in FIG. 9, the outer wall 708 of the
cryostat 706 may be configured to create a bore or opening that
allows for a shaft 716 or the like to pass therethrough (see FIG.
16a). One end of the shaft 716 is coupled to a motive device, such
as a motor 718, while the other carries a plurality or array of
drive magnets 720. The drive magnet array 720 is preferably
positioned in close proximity to the inside surface of the sidewall
of the cavity 704, and is comprised of a plurality of magnets
having alternating polarities or polar orientations (with the N-S
poles preferably being arranged perpendicular to the vertical plane
and spaced sufficiently close to the wall of the cavity 704 to
create the strongest possible magnetic coupling, and hence, the
most efficient torque transfer).
[0141] Turning now to the mixing element 722, it is preferably in
the form of a rotor or impeller comprised of a hollow,
substantially cylindrical or tubular body sized so as to permit a
concentric orientation with the cylindrical cavity 704 inside the
vessel 702. The mixing element 722 may comprise a levitation magnet
724 generally corresponding in shape and proportional in size to
the superconducting element 712, and preferably having its poles
oriented in a direction parallel to a vertical plane. Spaced from
the levitation magnet 724, and preferably embedded in a matrix
material M, is an array of strategically positioned driven magnets
726. The driven magnets 726 correspond generally in size and shape
to the array of alternating polarity drive magnets 720 carried on
the shaft 716. The driven magnets 726 are also of alternating
polarity to create the desired magnetic coupling with the drive
magnets 720 for transmitting the drive torque from the motive
device, such as the motor, to the shaft 716, and ultimately to the
levitating mixing element 722. As shown in FIG. 16, the mixing
element 722 may also carry one or more blades 728, vanes, or the
like to further enhance the mixing action provided (or pumping
action, in the case of a pumping chamber having a cavity
bottom).
[0142] Hence, as depicted in FIG. 16, it is possible to easily
adapt the mixing system 700 for use with a vessel 702 having a
thin-walled cavity 704 that is nevertheless capable of withstanding
high pressures, such as those possibly created during cleaning or
sterilization. As an example of one possible application, the
vessel 702 may thus be pre-sealed with the magnetic mixing element
722 (e.g., rotor or impeller) inside, and then simply placed over
the cryostat 706, such as by positioning the vessel on an adjacent
stable support surface, such as a table, support platform, stand or
the like (see reference character T in FIG. 16). Assuming that
field cooling has previously been completed (such as by using a
"kit" for supporting a corresponding "set-up" magnet adjacent to
the superconducting element 712 during cooling, which in this case
could be an annular set-up magnet, as opposed to the disc-shaped
one in FIG. 15), the vessel 702 is simply positioned over the
cryostat 706, as shown in FIG. 16, such that the magnetic field of
the permanent levitation magnet 724 creates the desired flow of
current through the superconducting element 712 to achieve the
simultaneous attraction and repulsion that results in stable
levitation.
[0143] During experimentation using the system 700, it was
discovered that it may be advantageous in terms of levitational
stability to form the superconducting element 712 of a plurality of
segments of the melt-textured/melt-processed rare-earth
superconductor described above, with the particular orientation of
the crystallographic axis or planes of each segment being selected
to significantly enhance the magnetic stiffness of the coupling, as
well as the load capacity of the levitating mixing element 722.
Specifically, as shown in FIG. 17, which is a plan schematic view
of the levitation magnet 724 and a plurality of segments 712a . . .
712n formed of a superconducting material having crystallographic
planes (see below) and arranged in a non-contiguous polygonal
configuration, and FIG. 18, which is a cross-sectional view of the
same taken along line 18-18 of FIG. 17, the crystallographic
"C-axis" of each superconducting segment 712a . . . 712n is
oriented in a radial direction, or in the illustrated embodiment,
substantially perpendicular to the magnetization vector of the
levitation magnet 724, and preferably passes through the center
thereof. Accordingly, the A-B planes are oriented substantially
parallel to the polar magnetization axis of the levitation magnet
724. Superconducting materials having these crystallographic
planes/axes include those comprised of ReBa.sub.2Cu.sub.3O.sub.x,
formed by a melt-texturing or "melt-processing" as is known in the
art (see, e.g., U.S. Pat. No. 5,747,426 to Abboud, the disclosure
of which is incorporated herein by reference).
[0144] Using this arrangement, it was found that the levitation
force, magnetic stiffness, and concomitant load capacity of the
levitation magnet 724 is increased on the order of two to three
times without a corresponding change in any other parameter of the
system 700 described above. Of course, these increases serve to
enhance the rotational stability of the mixing element 722 when
such an arrangement is used in a pumping or mixing system, which in
turn improves the operational reliability. These increases also
advantageously reduce the tendency of the pumping or mixing element
722 to decouple at higher rotational speeds or in pumping or mixing
high viscosity fluids or the like.
[0145] It is also noted that the system 700 is generally described
above as a mixing system for use with vessels 702 or containers
capable of withstanding high pressures. However, it should also be
appreciated that the system 700 could also be used for the mixing
or pumping of fluids through a vessel 702 in the form of a
flexible, open-top container or any other type of container having
the cavity 704 or a similar configuration. Of course, the strategic
orientation of the elements of a segmented superconductor could
also be used to enhance the levitational and rotational stability
of a pumping or mixing element used in any of the systems described
herein as well.
[0146] Yet another embodiment of a pumping or mixing system 800 is
proposed in FIG. 19. Perhaps the best way to describe this
embodiment is to begin with a description of the vessel 810 and the
pumping or mixing element 812. The vessel 810, like vessel 702, is
preferably created having a cavity 814 that defines a concentric
annular protruding portion 815. Preferably, the wall defining each
side of cavity 814 and each side of the annular portion 815 is
fabricated of a relatively thin, non-magnetic material, such as
stainless steel. As noted above with regard to vessel 702, by
forming the remainder of the vessel 810 having relatively thick
sidewalls, it may withstand high pressures, such as those created
during sterilization using steam under pressure or the like.
However, in the case where the vessel 810 is not subjected to high
pressures or is used as a pumping chamber, the walls may be formed
of a substantially homogeneous material (disposable plastics,
glass, stainless steel, etc.) having substantially the same
relative thickness. A description of an embodiment wherein a
flexible plastic bag is provided with a cavity is described below
and shown in FIG. 22.
[0147] The pumping or mixing element 812 is capable of being
positioned in the vessel 810 and includes a levitation magnet 816.
In particular, the levitation magnet 816 is sized and shaped for
extending into the interior of the annular portion 815 of the
vessel 810. In the illustrated embodiment, the levitation magnet
816 is polarized in the vertical direction (the specific
orientation of the poles is not critical) to create a vertical
magnetization vector. However, the magnetization vector could also
be oriented in a horizontal or substantially horizontal plane
(although those skilled in the art will recognize that forming a
single ring shaped magnet having opposite poles oriented in a
horizontal plane is more difficult than forming one having a
vertical magnetization vector).
[0148] To levitate the pumping or mixing element in the vessel 810,
at least one, and preferably a plurality of superconducting
elements 818 are positioned in an annular cryostat 802. This
cryostat 802 is specially adapted for receiving the annular
protruding portion 815 of the vessel 810 (see FIG. 19a) and may
even support the vessel, as shown in FIG. 19. More specifically, in
the illustrated embodiment, the cryostat 802 includes an annular
channel 806 for receiving the corresponding annular portion 815 of
the vessel 810. The outer wall 808 of the cryostat 802 defines a
space or chamber that is preferably evacuated to create a vacuum
jacket, as described above. Alternatively, the chamber could be
filled with an insulating material to reduce the thermal transfer.
Regardless of the means used, the important point is that in the
case of pumping or mixing non-cryogenic, warm or temperature
sensitive fluids, no or only negligible thermal transfer from the
cold superconductor to the vessel and hence the fluid results.
[0149] Preferably, the superconducting elements 818 are comprised
of a plurality of segments, each of which is in thermal
communication with a cooling source (e.g., a Dewar flask or a
closed-cycle refrigerator) via a thermal link 820 positioned and
supported in the cryostat 802. The segments comprising each of the
one or more superconducting elements 818 are preferably formed of a
"high-temperature" superconducting material having crystallographic
A-B planes and a C-axis, which as noted above, is a characteristic
of melt-textured or melt-processed ReBa.sub.2Cu.sub.3O.sub.x, with
Re representing a rare earth element (e.g., Yttrium, of which YBCO
is a common example).
[0150] In the preferred embodiment, three superconducting elements
818a, 818b, 818c are provided on the thermal link 820, although it
should be appreciated from reviewing the description that follows
that using only a single superconducting element or two
superconducting elements to levitate the pumping or mixing element
812 is entirely possible (see FIG. 16). A first of the
superconducting elements 818a is positioned adjacent to a first
side of the annular channel 806 formed in the cryostat 802 adjacent
to a first side of the annular levitation magnet 816. The second
superconducting element 818b is also positioned adjacent to a
second side of the annular levitation magnet 816. The third
superconducting element 818c is positioned adjacent to a third side
of the annular levitation magnet 816. Each of the superconducting
elements 818a, 818b, 818e may be in thermal communication with the
same thermal link 820, as shown in FIG. 19 and positioned internal
to the corresponding cryostat 802, which by way of insulation or
vacuum jacket prevents any thermal transfer to the room temperature
vessel 810, the fluid F held therein, or the pumping or mixing
element 812.
[0151] In a most preferred version of this embodiment, the
crystallographic planes/axes of the segments forming the
superconducting elements 818a, 818b, 818c are oriented so as to
significantly improve the levitation force, the resulting loading
capacity, and the magnetic stiffness of the coupling formed with
the pumping or mixing element 812. Specifically, the first and
third superconducting elements 818a, 818c (or more particularly,
the segments comprising these elements) are oriented such that the
C-axes thereof are perpendicular to the magnetization vector of the
levitation magnet 816, while the second superconducting element
818b is oriented such that the C-axis of each segment thereof is
aligned with and parallel to the magnetization vector of the
levitation magnet 816. Another way to describe the arrangement is
that the A-B crystallographic planes of the first and third
superconducting elements 818a, 818c are parallel to the axis of
polarization of the levitation magnet 816, while the A-B
crystallographic planes of the second superconducting element 818b
are perpendicular to the polarization axis (note the substantially
parallel lines representing the A-B planes drawn on each
superconducting element 818a-c in FIG. 19). As used herein, the
terms "parallel" and "perpendicular" are intended to mean generally
or substantially parallel or perpendicular, it being recognized
that variations in the orientation of the various crystallographic
planes or axes relative to the magnetization vector are either
inherent or may be created by slight misalignments of adjacent
elements, or may be intentionally varied within a range to adjust
or fine tune the levitation force provided or rotational
stability.
[0152] The particular arrangement shown in FIG. 19 results in a
system 800 in which the pumping or mixing element 812 is levitated
in a most stable fashion. This stable levitation results primarily
from the interaction between the specially oriented segments
forming each superconducting element 818a-c and the annular
levitation magnet 816. As a result of this arrangement, the loading
capacity of the pumping or mixing element is increased, as it the
stiffness of the magnetic coupling. This combination allows for a
greater amount of torque to be supplied to the pumping or mixing
element 812 without accidental decoupling, which allows for higher
angular velocities to be achieved. It also allows for use of the
system 800 with fluids having higher viscosities.
[0153] The drive system for rotating the pumping or mixing element
may be substantially as described above. Specifically, a shaft 822
coupled at one end with a motive device, such as a motor 824, is
positioned in a room temperature bore or through an opening formed
in the cryostat 802. The end of the shaft 822 adjacent to the
vessel 810 carries a plurality of drive magnets 824 having
alternating polarities. Corresponding driven magnets 826 having
alternating polarities are provided on the pumping or mixing
element 812. As shown in FIG. 19, the pumping or mixing element may
also include impeller blades 828, vanes, or like structures to
further enhance the pumping or mixing action provided.
[0154] In accordance with yet another embodiment of the present
invention, a specific pumping or mixing system 900 using a rotating
superconducting element 901 is shown in FIG. 20. The
superconducting element 901 may be supported by a plate 902 in
thermal engagement with a cooling source forming a part of a
cryostat 903 and preferably rotating therewith. The superconducting
element 901 is surrounded by a wall 905 defining an evacuated
chamber 906, which may together be considered to form a vacuum
jacket comprising part of the cryostat 903 (although as described
above the chamber 906 could also be insulated or any other known or
yet-to-be discovered means for obviating thermal transfer between a
cold superconducting element could be used).
[0155] In the illustrated embodiment, the cooling source is a
portable refrigerator or "cryocooler" 904 that also forms part of
the cryostat 903. The cryocooler 904 is shown as having a "head"
end 905 that extends into the chamber 906 to directly engage and
support the plate 907 which in turn supports the superconducting
element 901, although the use of a separate thermal link (not
shown) is also possible, depending on the relative dimensions of
the system. As with the thermal link previously described, both the
plate 902 and the head end 907 of the cryocooler are typically
formed of a material having a high degree of thermal
conductivity/low thermal resistance (e.g., a metal) to ensure that
the desirable efficient thermal transfer is established. The plate
902 may also be supported from the wall 905 by one or more
connecting members 908, which are preferably thin, but relatively
strong, and formed of a material having a low degree of thermal
conductivity so as to create only negligible thermal transfer to
the wall 905.
[0156] The cryostat 903 is rotatably supported by at least one, and
preferably a pair of bearings or bearing assemblies 909a, 909b,
which are in turn supported by a stable support structure, such as
an adjacent vertical wall VW or another type of support frame
(which may or may not engage the adjacent structure, such as table
T, supporting the vessel). For example, one bearing may engage the
outer wall 905 of the cryostat 903, while the other engages the
outer wall of the cryocooler 904. The use of two bearing assemblies
909a, 909b of course ensures that the cryostat 903 rotates about a
vertical center axis in a most stable and reliable fashion and is
capable of resisting any skewing forces, and may also allow it to
be turned on its side (such as it would appear if FIG. 20 is
oriented in a landscape view, rather than a portrait view). As
shown in FIG. 20, the bearing assemblies 909a, 909b may include
mechanical roller or ball bearings, or other elements that may
provide low-friction, rotatable support the cryostat 903.
[0157] To transmit the desired rotational motion, an endless belt
910 may be placed in frictional engagement with a first pulley 911
coupled to or carried by the cryostat 903. The belt 910 also
engages a second pulley 912 supported by the shaft 914 of a motive
device 916, such as a variable speed electric motor. As should be
appreciated, the rotation of the shaft 914 thus causes the cryostat
903, and hence, the superconducting element 901 positioned therein
to rotate. As noted above, the cryostat 903 could also be mounted
"inline" on a shaft that is in turn connected or coupled directly
to a motive device, such as an electric motor.
[0158] One particularly preferred example of a commercially
available closed-cycle refrigerator or cryocooler 904 for use in
the present invention is a type of substantially self-contained,
compact, closed-cycle cryocooler employing the Stirling cycle to
produce the desired refrigeration, several models of which are
manufactured and distributed by Sunpower, Inc. of Athens, Ohio. As
shown schematically in FIG. 20, this cryocooler 904 includes a
lower portion 904a which serves to house an electric motor and an
upper portion 904b adjacent to the head 907 which houses a
reciprocating piston (not shown). In light of the commercial
availability of several suitable models, the workings of such a
cryocooler need not be understood to practice the present
invention. However, it is noted that Sunpower, Inc. holds a number
of U.S. patents on various types of cryocoolers, each of which is
incorporated herein by reference to the extent deemed necessary to
allow a skilled artisan to make or use this invention. Regardless
of the type of cooling source used, the important point is that it
is fully capable of generating the "high temperatures" (e.g.,
77K-90K) necessary to induce a superconducting state in, for
example, a YBCO superconducting element (which may be comprised of
a plurality of segments, as described below).
[0159] To supply the necessary power to the cryocooler 904 such
that it keeps the superconducting element 901 at the desired
temperature, yet allows it to rotate even at high speeds, a dynamic
electrical connection is provided. Specifically, contacts 918,
which are shown in the form of annular rings surrounding the outer
wall of the cryocooler 904, are provided for engaging corresponding
"stationary" flexible or pivoting contacts 920 in electrical
communication with a power source 922 (120/220V), which may be
remote. As should be appreciated, this configuration allows the
cryocooler 904 to freely rotate at both high and low speeds while
continuously receiving the power necessary to run the motor/drive
the piston and keep the head end 907 at the desired cold
temperature. Instead of this illustrated configuration, a
well-known type of dynamic electrical connection called a "slip
ring" may be used, such as those manufactured by Siemens, Litton,
and the Kaydon Corp. A slip ring is also sometimes referred to in
the art as a "rotary electrical interface," a "commutator," a
"swivel." or a "rotary joint."
[0160] The system described above can be substituted into the
system 100 shown in FIGS. 5-7 for rotating a pumping or mixing
element in the form of a flat, disc-shaped rotor or impeller 134
for pumping or mixing a fluid in a flat-bottomed rigid vessel or
bag. In that case, the plate 902 could be eliminated and a
disc-shaped superconducting element, such as element 106, used in
its place. However, in FIG. 20, the vessel 922 is illustrated
having a cavity 924, which may of course be similar in construction
to the cavity provided in a vessel capable of withstanding high
internal pressures, as described above and shown in FIG. 16.
Alternatively, the cavity 924 could be formed in a conventional
open-top vessel, in a flexible bag or container (see FIG. 22), or
in any other type of vessel used in applications where high
pressures are not a concern. In the case where the cavity 924 is
formed in a flexible bag or container, as shown in FIG. 22, is
should also be appreciated that the cavity 924 may serve a function
similar to that of centering post 528 shown in FIG. 14b (and could
even include a peripheral flange, projections, or like structures
at the upper end to ensure that the pumping or mixing element 926
remains fully held in place during shipping, storage, or between
uses, yet spaced far enough away to avoid creating any interference
with the desired levitation/rotation).
[0161] In any case, in the embodiment in FIG. 20, the pumping or
mixing element 926 is substantially cylindrical and includes only a
levitation magnet 928, since both the levitation force and the
driving torque are provided by the superconducting element 901.
This levitation magnet 928 may be comprised of a plurality of
segments of permanent magnets 928a . . . 928n having alternating
polarities and arranged in a substantially annular or polygonal
configuration (see the schematic illustration merely showing a
preferred orientation/arrangement in FIG. 21). As also shown
schematically in FIG. 21, the superconducting element 901 is
concentric with the levitation magnet 928 and is also comprised of
a plurality of segments 901a . . . 901n arranged in an annular or
polygonal configuration. Preferably, each segment 901a . . . 901n
is oriented having its crystallographic C-axis aligned in the
radial direction (i.e., oriented generally parallel to the
magnetization vector of a corresponding segment 928a . . . 928n of
the permanent magnet 928, and preferably passing substantially
through the center thereof). Accordingly, the A-B planes of the
segments 901a . . . 901n comprising the superconducting element 901
are oriented generally perpendicular to the radial direction, and
hence, the magnetization vector. As a result of this arrangement,
the rotating superconducting element 901 not only reliably induces
stable levitation in the pumping or mixing element 926 via
levitation magnet 928, but also forms a magnetic coupling which
causes the pumping or mixing element 926 to rotate. As shown in
FIG. 20, the pumping or mixing element 926 may also carry one or
more impeller blades, vanes, wings, or like structures 930 to
further enhance the pumping or mixing action.
[0162] FIG. 23 shows an embodiment of the pumping or mixing system
950 for use with a vessel (such as a tank K, but any vessel
disclosed herein would also work) having a cavity that is generally
similar to the embodiment shown in FIG. 20 with a few
modifications. The first is that the rotating cryostat 952 includes
two arrays of superconducting elements 954, 956, with each array
spaced in the vertical direction. The pumping or mixing element 958
includes corresponding arrays of alternating polarity magnets 960,
962 (see, e.g., FIG. 21), with each magnet in the array 960 having
a neighboring magnet with an alternating polarity. The rotation of
the cryostat 952 and, hence, the superconducting, element arrays
954, 956 thus induces both levitation and rotation in the pumping
or mixing element 958 (which is shown having a plurality of
upstanding blades B). As should be appreciated, the dual arrays
enhance the vertical stiffness of the coupling and improve torque
transfer.
[0163] The superconducting element arrays 954, 956 are supported on
a thermally conductive platform 963 by an upstanding cylindrical
wall 964. The platform 963 in turn is coupled to a rod 965 serving
as a thermal link to a cooling source, such as the SUNPOWER
cryocooler described above or a Dewar flask filled with a liquid
cryogen, which is in turn coupled to a motive device (shown in
block form only, but see FIG. 20 for an example of one possible
embodiment). As noted above, insulating or evacuating the chamber
966 in the cryostat 952 prevents the cold superconducting element
arrays 954, 956 from cooling the adjacent tank K to any significant
degree, which means that the system is well-adapted for pumping or
mixing non-cryogenic fluids, including room-temperature fluids.
[0164] The embodiment of FIG. 23 also differs from the one shown in
FIG. 20 in that the pumping or mixing element 958 carries a first
ring magnet 968 (or an equivalent array of magnets, such as
vertically polarized magnetic discs (not shown)). A corresponding
ring magnet 970 (or array of magnets) is carried by the rotating
cryostat 952 (preferably externally and at the top, as shown in
FIG. 23). The first ring magnet 968 and the second ring magnet 970
are oriented such that like poles are adjacent to each other. This
magnet-magnet interaction thus repels the pumping or mixing element
958 from the cryostat 952. However, the interaction between the
superconducting element arrays 954, 956 and the arrays of magnets
960, 962 together generally levitate and hold the pumping or mixing
element 958 in place. The net result is that the pumping or mixing
element 958 is levitated, but is able to resist any force tending
to move it into contact with the tank K, including the outer
surface of the adjacent cavity.
[0165] Another distinction in the illustrated embodiment is that
the pumping or mixing element 958 is generally cylindrical and
includes an opening 967. As a result of this construction, when the
pumping or mixing element 958 is rotated, fluid is drawn into the
gap between it and the adjacent cavity in the tank K (see action
arrows F). The fluid then passes through the opening 967, which
enhances the fluid agitation created by the rotation of the pumping
or mixing element 958, even at relatively low angular
velocities.
[0166] A related embodiment is shown in FIG. 24. In this
embodiment, the first ring magnet 968 (or array) is again provided
on or in the pumping or mixing element 958, but the second ring
magnet 970 (or array) is positioned external to the tank K. Again,
the rings 968, 970 have like polarities along the adjacent faces to
create a repelling force. In this case, this force helps to prevent
the pumping or mixing element 958 from "bottoming out" on the
adjacent surface of the tank K. Although not preferred for most
applications due to the clean-up and sterilization problems
possibly created, the second ring magnet 970 could be positioned
just inside the tank K as well. Instead of attaching the ring
magnet 970 to the tank K, it could also be supported by the
cryostat 952, such as a flange (note dashed lines in FIG. 24) or a
related structure that rotates therewith. Also, the possibility of
providing neighboring magnets in each array 960, 962 with like
polarities is shown (with the polarities of vertically adjacent
magnets in each array still alternating), which is somewhat less
preferred than the embodiment of FIG. 23 in which the polarities of
neighboring magnets in each array alternate.
[0167] These two approaches could also be combined into the same
system, as shown in FIG. 25. In particular, first and second ring
magnets 968a, 970a are provided in one portion of the pumping or
mixing element 958, and third and fourth ring magnets 968b, 970b
are provided in another. The repelling forces created thus provide
dual levels of protection against the rotating pumping or mixing
element 958 inadvertently contacting the vessel or tank K. Also,
either or both approaches could be used in the embodiments of FIG.
16 or 19 as well. Also note that the polarities of adjacent magnets
in the arrays 960, 962 are alike, although each vertically adjacent
pair has a different polarity that the next-adjacent pair. This is
somewhat less preferred than the arrangement of FIG. 23 in terms of
stiffness, but would work nevertheless.
[0168] By switching the polarities, it is also possible to provide
one or more sets of magnets like ring magnets 968, 970 that
attract, rather than repel each other. The attractive force thus
created may help to prevent the pumping or mixing element 958 from
moving in a vertical direction relative to the cavity as it rotates
(or in the horizontal direction, in the case where the cavity is
positioned with its centerline axis parallel to a horizontal
plane). The magnets would preferably be sufficiently weak in power
to avoid creating any instability in the levitation and/or rotation
induced by the superconducting element arrays 954, 956.
[0169] FIGS. 26 and 27 show a method and apparatus for centering
and setting up a pumping or mixing element 980 that is capable of
levitating in a vessel 981, such as in a hermetically sealed tank,
in a sterile vessel, such as a flexible bag, or even in an open-top
vessel where access to the corresponding surface adjacent to
levitating the pumping or mixing element is restricted. The vessel
981 includes a cavity 982, as described above. Inside the vessel
981, the cavity 982 may include along its outer surface an
engagement structure for contacting, engaging, or supporting the
pumping or mixing element 980 when in a non-levitating or resting
position. In the preferred embodiment, this engagement structure
comprises a frusto-conical surface 984 that is tapered relative to
the horizontal plane. The pumping or mixing element 980, which is
of course generally annular, includes a matching surface 986 along
at least a portion of an adjacent inner surface thereof.
Preferably, the matching surface 986 is formed in an inert portion
of the pumping or mixing element 980, such as the matrix material
(e.g., plastic, metal, composites, etc.) used to support the
levitation magnet or magnet array 988 (which is shown
schematically, but could be any appropriate one of the arrangements
described herein). The pumping or mixing element 980 is shown
slightly raised in the vertical direction to illustrate the shape
of the surfaces 984, 986. However, it should be appreciated that
these surfaces 984, 986 would normally be in contact with each
other as the result of gravity when the pumping or mixing element
980 is at rest (i.e., non-levitating), such that a radial centering
function is inherently provided.
[0170] A cryostat 989, which may be substantially identical to
those described above, is positioned in the cavity 982. In
particular, the cryostat 989 contains one or more superconducting
elements 990 (which may in turn be formed of segments) that are
mounted on a platform 983 that is in turn coupled via thermal link
991 to a cooling source, which in view of the various versions
described herein is merely shown in block form. The entire cryostat
989 is preferably coupled to a second motive device 994, also shown
in block form, that rotates it along with the superconducting
element(s) 990. It may also be coupled to a second motive device
for moving it relative to an inner surface of the cavity 982, such
as in the vertical direction as shown in FIG. 26. As described
above, in the case of non-cryogenic fluids, the cryostat 989, or at
least the portion housing the superconducting element(s) 990 and
any other cryogenic structures, is preferably evacuated or
insulated to prevent thermal transfer to the adjacent vessel
981.
[0171] To form a magnetic coupling between the superconducting
element(s) 990 and the levitation magnet 988 of the pumping or
mixing element 980, the cryostat 989 is moved to a position within
the cavity 982 where these two structures are substantially
aligned. In particular, the alignment is such that the
superconducting element(s) 990 face the adjacent levitation/driven
magnet(s) on the pumping or mixing element 980, which of course is
inside of the vessel 981. Once this alignment is achieved, the
superconducting element(s) 990 are cooled to below the transition
temperature (preferably less than 90K for a YBCO superconductor) in
accordance with a field cooling protocol. As a result, a magnetic
coupling is established with the levitation/driven magnet 988 and
the desired pinning forces are created that permit stable,
exceptionally reliable levitation of the pumping or mixing element
980 (and rotation, in the case where the superconducting clement
990 is rotated, such as by using the configuration shown in FIG.
21).
[0172] Once the magnetic coupling is formed, the cryostat 989 may
be moved further into the cavity 982, either manually or using a
third motive device 996, such as a linear actuator or the like. As
a result of the coupling formed between the superconducting
element(s) 990 and the levitation magnet 988, this causes the
matching surface 986 of the pumping or mixing element 980 to
separate from the frusto-conical engagement surface 984 (see FIG.
27 and note action arrow Z). Rotation of the cryostat 989 using the
second motive device 994 may then be effected as described above to
cause the levitating pumping or mixing element 980 to rotate and,
hence, pump or mix the fluid in the vessel 981.
[0173] To return the pumping or mixing element 980 to a resting
position such that contact is re-established between surfaces 984,
986, the superconducting element(s) 990 need only be returned to
above the transition temperature, at which point the magnetic
coupling is lost. To expedite this operation, and as described
above, a heater 998 may be used. Once the coupling is no longer
formed, it should be appreciated that the pumping or mixing element
980 gently comes to rest such that the surfaces 984, 986 are in
engagement and the desired centering function is provided as a
result of the matching tapers or slopes. Advantageously, this means
that the user of the system need not have access to the pumping or
mixing element 980 to ensure that it is properly centered for
purposes of field cooling prior to levitation, and actually avoids
the need for the use of a set-up kit, as described above (which in
this case could be hat-shaped with a set-up or charging magnet
corresponding in magnetic field and polarity to levitation magnet
being placed over the head end of the cryostat 989).
[0174] The use of this "moving cryostat"' arrangement with the
other embodiments of pumping or mixing systems disclosed herein is
also possible, and in particular, with the embodiment shown in
FIGS. 19, 20, 23-25 (which may require adjusting the relative
dimensions or adding an annular piece of inert material to the
pumping or mixing element to provide the matching surface 986).
Also, instead of forming the frusto-conical surface as part of the
cavity 982, it could actually be a separate, freestanding structure
positioned at the same location or adjacent to the outer surface of
the pumping or mixing element 980 (see the phantom depiction of
engagement structure 999 in FIG. 27), in which case the matching
surface 986 would be positioned accordingly (i.e., along the outer
surface of the pumping or mixing element 980). The entire
arrangement could also be inverted (not shown), with the engagement
surface 984 being provided on the upper end of the cavity 982 and
the matching surface 986 being on a corresponding surface of the
pumping or mixing element 980 (in which case, the cryostat 989
would be withdrawn from the cavity 982 once the desired magnetic
coupling is formed). If the vessel 981 is inverted, the cavity 982
would preferably be elongated to avoid interfering with the
adjacent wall of the vessel 981.
[0175] Each of the embodiments of pumping or mixing systems
disclosed herein 10, 100, 200, 300, 700, 800, or 900 could also be
used for mixing a fluid with a product, such as a bacterial
nutrient culture media, eukaryotic cell nutrient culture media,
buffer, reagent, or like intermediate product for forming one or
more end products. As a result of the levitating nature of the
pumping or mixing element, application of these systems to vessels
where the product and the pumping or mixing element are sealed in
the vessel before use, including in an aseptic environment, is of
course possible.
[0176] In summary, a number of systems 10, 100, 200, 300, 700, 800,
900 as well as variations on these systems and related methods, are
disclosed that use or facilitate the use of superconducting
technology to levitate a magnetic element that, when rotated,
serves to pump or mix a fluid. In one system 10, the magnetic
element 14 is placed in a fluid vessel 16 positioned external to a
cryostat 12 having an outer wall or other housing 18 for containing
a superconducting element 20. A separate cooling source 24 (either
a cryogenic chamber 26, FIGS. 1 and 3 or a refrigerator 48, FIG. 2)
thermally linked to the superconducting element 20 provides the
necessary cooling to create the desired superconductive effects and
induce levitation in the magnetic element 14. Since the pumping or
mixing element levitates in the fluid F, no penetration of the
vessel walls by mixing or stirring rods is necessary, which
eliminates the need for dynamic bearings or seals.
[0177] Additionally, the outer wall 18 of the cryostat 12 or other
housing defines a chamber 25 that thermally isolates and separates
the superconducting element 20 from the vessel 16 containing the
fluid F and pumping or mixing element 14. The thermal isolation may
be provided by evacuating the chamber 25, or filling it with an
insulating material. By virtue of this thermal isolation and
separation, the superconducting element 20 can be positioned in
close proximity to the outer wall or housing 18 adjacent to the
vessel 16 and pumping or mixing element 14, thereby achieving a
significant reduction in the separation distance or gap G between
the pumping or mixing element 14 and the superconducting element
20. This enhances the magnetic stiffness and loading capacity of
the magnetic levitating pumping or mixing element 14, thus making
it suitable for use with viscous fluids or relatively large volumes
of fluid.
[0178] The exceptionally stable levitation provided as a result of
the reduced separation distance also significantly reduces the
potential for contact between the rotating pumping or mixing
element and the bottom or sidewalls of the vessel. This makes this
arrangement particularly well-suited for use in fluids that are
sensitive to shear stress or the effects of frictional heating.
However, since the superconducting element 20 is substantially
thermally isolated and separated from the vessel 16, the magnetic
element 14, and hence the fluid F contained therein, may be
shielded from the cold temperatures generated by the cooling source
24 to produce the desired superconductive effects and the resultant
levitation. This allows for temperature sensitive fluids to be
mixed or pumped. By using means external to the vessel 16 to rotate
and/or stabilize the magnetic element 14 levitating in the fluid F,
such as one or more rotating driving magnets coupled to the
magnetic element 14, the desired pumping or mixing action is
provided.
[0179] Additional embodiments of systems 100 (900), 200 for pumping
or mixing a fluid wherein the necessary motive force is provided
from the same side of the vessel at which the superconducting
element is positioned are also disclosed, as are systems 300, 400
for rotating an inline pumping or mixing element positioned in a
vessel in the form of a pipe or the like in a similar fashion.
Alternative systems 700, 800, and 900 are also disclosed, which are
particularly well adapted for applications using special vessels
having cavities that assist in withstanding high internal
pressures. Particular orientations of the crystallographic planes
of the material used as the superconductor are also described to
enhance the levitation force and magnetic stiffness of the
coupling, which in turn increases the stability and load capacity
of the pumping or mixing element, as is the use of opposing pairs
of permanent magnets to provided a levitation-assist function. A
manner of centering and setting up a pumping or mixing element in a
hermetically sealed vessel is also disclosed.
[0180] The foregoing description of various embodiments of the
present invention have been presented for purposes of illustration
and description. The description is not intended to be exhaustive
or to limit the invention to the precise forms disclosed. Obvious
modifications or variations are possible in light of the above
teachings. For example, while the use of a thermally separated
superconducting element is disclosed, the subsequent development of
room temperature superconductors would obviate this need. Instead
of using a superconducting element as the motive device, another
option is to use a separate drive structure (e.g., an
electromagnetic coil) to form a coupling capable of transmitting
torque to the particular fluid-agitating element (which may be
"levitated" by a hydrodynamic bearing; see, e.g., U.S. Pat. No.
5,141,327 to Shiobara). The embodiments described provide the best
illustration of the principles of the invention and its practical
applications to thereby enable one of ordinary skill in the art to
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. All
such modifications and variations are within the scope of the
invention as determined by the appended claims when interpreted in
accordance with the breadth to which they are fairly, legally and
equitably entitled.
* * * * *