U.S. patent application number 11/740194 was filed with the patent office on 2007-08-23 for vortex-enhanced filtration devices.
Invention is credited to Jennifer K. McLaughlin, Don Schoendorfer.
Application Number | 20070193941 11/740194 |
Document ID | / |
Family ID | 32990796 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070193941 |
Kind Code |
A1 |
McLaughlin; Jennifer K. ; et
al. |
August 23, 2007 |
VORTEX-ENHANCED FILTRATION DEVICES
Abstract
Preferred aspects of the present invention relate to a device
for filtration comprising at least one rotor configured to create
Taylor vortices on at least one side of a filtration membrane,
thereby providing substantially enhanced mass or heat transfer
across the membrane.
Inventors: |
McLaughlin; Jennifer K.;
(Valley Center, CA) ; Schoendorfer; Don; (Santa
Ana, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
32990796 |
Appl. No.: |
11/740194 |
Filed: |
April 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10797510 |
Mar 10, 2004 |
7220354 |
|
|
11740194 |
Apr 25, 2007 |
|
|
|
60453620 |
Mar 10, 2003 |
|
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|
Current U.S.
Class: |
210/321.68 ;
210/321.87 |
Current CPC
Class: |
A61M 1/265 20140204;
B01D 2315/02 20130101; A61M 1/16 20130101; B01D 63/16 20130101;
B01D 61/243 20130101; A61M 2205/3365 20130101; B01D 63/065
20130101; A61M 2205/50 20130101; B01D 61/28 20130101 |
Class at
Publication: |
210/321.68 ;
210/321.87 |
International
Class: |
B01D 63/00 20060101
B01D063/00 |
Claims
1. A system for hemodialysis, comprising: an extraction tube for
drawing blood from a patient; a return tube for returning blood to
the patient; a hemodialysis device for extracting waste by-products
from blood, including: a housing having a housing wall; a first
rotor having a first wall comprising a dialysis membrane and
defining a first interior, wherein said first rotor is disposed
within said housing and is adapted to rotate therein, such that a
first gap exists between the dialysis membrane and the housing
wall; a first inlet port in the housing wall for conducing the
blood into the first gap and a first outlet port in the housing
wall for conducting dialyzed blood out of the first gap; a second
inlet port in the housing for conducting dialysis fluid into the
first interior and a second outlet port in the housing for
conducing dialysate out of the first interior; and a first
rotational drive means for rotating the first rotor within said
housing at a speed sufficient to create Taylor vorticity in the
first gap; a separator for extracting plasma water; and a junction
at which the plasma water is integrated with the blood.
2. The system of claim 1, wherein the junction connects to the
extraction tube.
3. The system of claim 1, wherein the junction connects to the
return tube.
4. The system of claim 1, wherein the separator comprises: a
separator housing having a separator housing wall; a first
separator rotor having a first separator wall comprising a
separation membrane and defining a first separator interior,
wherein said first separator rotor is disposed within said
separator housing and is adapted to rotate therein, such that a
first separator gap exists between the separation membrane and the
separator housing wall; a first separator inlet port in the
separator housing wall for conducing a first fluid into the first
separator gap and a first separator outlet port in the separator
housing wall for conducting the first fluid out of the first
separator gap; a second separator outlet port in the separator
housing for conducing the plasma water out of the first separator
interior; and a first separator rotational drive means for rotating
the first separator rotor within said separator housing at a speed
sufficient to create Taylor vorticity in the first separator
gap.
5. The system of claim 4, wherein the first fluid is dialysate.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
10/797,510 filed on Mar. 10, 2004, which claims priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Application No. 60/453,620,
filed on Mar. 10, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Preferred aspects of the present invention relate to a
device that creates Taylor vortices on at least one side of a
filter, thereby improving mass transfer and minimizing
concentration polarization. Preferred embodiments of the present
invention are particularly useful in dialysis of blood from
patients with kidney disease. In other embodiments, the present
invention can be used in areas of heat and mass transfer.
[0004] 2. Description of the Related Art
[0005] Traditionally, dialysis is the maintenance therapy used to
treat kidney disease. There are two common approaches. One is
peritoneal dialysis, where the process is done internally to the
patient, in the patient's pericardium. Peritoneal dialysis uses the
patient's abdominal lining as a blood filter. The abdominal cavity
is filled with dialysate, thereby creating a concentration gradient
between the bloodstream and the dialysate. Toxins diffuse from the
patient's blood stream into the dialysate, which must be exchanged
periodically with fresh dialysate.
[0006] The second approach is by filtration dialysis. This was
initially accomplished using flat sheet dialysis membranes,
requiring square meters of the membranes. Devices were large and
taxing on patients. In the 1960's, hollow fiber dialysis filtration
units became popular. This was an improvement, as a large filter
membrane area could be compressed into a small volume, and the
volume of blood needed to fill the unit was greatly reduced.
[0007] While hollow fiber technology provides a relatively safe and
cost effective means for dialysis, problems remain. Manufacturing
hollow fiber cartridges is challenging. The patient is still
exposed to a large surface area of material foreign to the human
system. Many of the chemicals needed in manufacture are toxic to
the patient. Cuprophane is the most common membrane material for
hollow fiber manufacture, but it has biocompatibility issues, and
relatively low permeability performance. There are superior
membrane materials available in flat sheet, but these materials are
challenging to form into hollow fibers.
[0008] One of the most limiting problems in any type of filtration
process, including dialysis, is filter clogging, scientifically
described as "concentration polarization." As a result of the
selective permeability properties of the membrane, the filtered
material that cannot pass through the membrane becomes concentrated
on the surface of the membrane. This phenomenon is clearly
illustrated in the case of a "dead-end" filter, such as a coffee
filter. During the course of the filtration process, the filtered
material (coffee grounds) building up on the filter creates flow
resistance to the filtrate, the fluid (coffee), which can pass
through the filter. Consequently, filtrate flux is reduced and
filtration performance diminishes.
[0009] Various solutions to the problem of concentration
polarization have been suggested. These include: increasing the
fluid velocity and/or pressure (see e.g., Merin et al., (1980) J
Food Proc. Pres. 4(3):183-198); creating turbulence in the feed
channels (Blatt et al., Membrane Science and Technology, Plenum
Press, New York, 1970, pp. 47-97); pulsing the feed flow over the
filter (Kennedy et aL, (1974) Chem. Eng. Sci. 29:1927-1931);
designing flow paths to create tangential flow and/or Dean vortices
(Chung et al, (1993) J Memb. Sci. 81:151-162); and using rotating
filtration to create Taylor vortices (see e.g., Lee and Lueptow
(2001) J Memb. Sci. 192:129-143 and U.S. Pat. Nos. 5,194,145,
4,675,106, 4,753,729, 4,816,151, 5,034,135, 4,740,331, 4,670,176,
and 5,738,792, all of which are incorporated herein in their
entirety by reference thereto). In U.S. Pat. No. 5,034,135, Fischel
discloses creating Taylor vorticity to facilitate blood
fractionation. Fischel also describes variations in the width of
the gap between a rotary spinner and a cylindrical housing, but
does not teach variation in this width about a circumferential
cross-section.
[0010] Taylor vortices may be induced in the gap between coaxially
arranged cylindrical members by rotating the inner member relative
to the outer member. Taylor-Couette filtration devices generate
strong vorticity as a result of centrifugal flow instability
("Taylor instability"), which serves to mix the filtered material
concentrated along the filter back into the fluid to be processed.
Typically, a cylindrical filter is rotated within a stationary
outer housing. It has been observed that membrane fouling due to
concentration polarization is very slow compared to dead-end or
tangential filtration. Indeed, filtration performance may be
improved by approximately one hundred fold.
[0011] The use of Taylor vortices in rotating filtration devices
has been applied to separation of plasma from whole blood (See
e.g., U.S. Pat. No. 5,034,135). For this application, the separator
had to be inexpensive and disposable for one-time patient use.
Further, these separators only had to operate for relatively short
periods of time (e.g., about 45 minutes). Moreover, the separator
was sized to accept the flow rate of blood that could reliably be
collected from a donor (e.g., about 100 ml/minute). This technology
provided a significant improvement to the blood processing
industry. The advantages and improved filtration performance seen
with rotating filtration systems (Taylor vortices) have not been
explored in other areas of commercial fluid separation--including
kidney dialysis.
[0012] The use of Taylor vortices does not alleviate all problems
with filtration however. Another common problem with the use of
such rotating filtration devices is concentration polarization on
the inner side of the filter membrane. While centrifugal flow
instability circulates the fluid between inner and outer members,
the rotating inner member does not prevent concentration
polarization near the walls of its interior. As a result, filter
performance could be further improved by solving this problem of
interior concentration polarization.
SUMMARY OF THE INVENTION
[0013] In a preferred embodiment, the present invention relates to
a device for hemodialysis. The device comprises a cylindrical
housing having a housing wall; a first cylindrical rotor having a
first wall comprising a dialysis membrane, wherein the first
cylindrical rotor is disposed coaxially within the housing and
adapted to rotate therein, such that a first coaxial gap exists
between the dialysis membrane and the housing wall. There is also
included a second cylindrical rotor having a second wall, wherein
the second cylindrical rotor is disposed coaxially within the first
cylindrical rotor and adapted to rotate therein, such that a second
coaxial gap exists between the first and second walls. The device
also includes a first inlet port in the housing wall for conducing
blood into the first coaxial gap and a first outlet port in the
housing wall for conducting dialyzed blood out of the first coaxial
gap. A second inlet port is included in the housing for conducting
dialysis fluid into the second coaxial gap and a second outlet port
is included for conducing dialysate out of the second coaxial gap.
The device also comprises first and second rotational drive means
for rotating the first and second cylindrical rotors respectively
within the cylindrical housing. Consequently, when the first and
second rotors are spun, Taylor vortices may be created in the first
and second coaxial gaps, thereby enhancing mass transfer across the
dialysis membrane and preventing concentration polarization on both
sides of the membrane.
[0014] In another preferred embodiment, a device is provided for
hemodialysis comprising an outer housing having a housing wall, and
a first rotor having a first wall comprising a dialysis membrane
defining a first interior. The first rotor is disposed within the
outer housing and is adapted to rotate therein, such that a first
gap exists between the dialysis membrane and the housing wall. The
device further comprises a first rotational drive means for
rotating the first rotor within the outer housing at a speed
sufficient to create Taylor vorticity in the first gap.
[0015] In another preferred embodiment, a system is provided for
hemodialysis. The system comprises an extraction tube for drawing
blood from a patient, and a return tube for returning blood to the
patient. The system further comprises a hemodialysis device for
extracting waste by-products from blood. The hemodialysis device
includes an outer housing having a housing wall and a first rotor
having a first wall comprising a dialysis membrane. The first rotor
also defines a first interior, and is disposed within said outer
housing and is adapted to rotate therein, such that a first gap
exists between the dialysis membrane and the housing wall. The
hemodialysis device further includes a first inlet port in the
housing wall for conducing the blood into the first gap, and a
first outlet port in the housing wall for conducting dialyzed blood
out of the first gap. The hemodialysis device further includes a
second inlet port in the outer housing for conducting dialysis
fluid into the first interior and a second outlet port for
conducing dialysate out of the first interior. The hemodialysis
device further includes a first rotational drive means for rotating
the first rotor within said outer housing at a speed sufficient to
create Taylor vorticity in the first gap. The system further
comprises a separator for extracting plasma water, and a junction
at which the plasma water is integrated with the blood.
[0016] In another preferred embodiment, the present invention
relates to a device to facilitate mass transfer. The device
comprises a housing having a housing wall; a first rotor having a
first wall comprising a filtration membrane, wherein the first
rotor is disposed within the housing and adapted to rotate therein,
such that a first gap exists between the filtration membrane and
the housing wall. There is also included a second rotor having a
second wall, wherein the second rotor is disposed within the first
rotor and adapted to rotate therein, such that a second gap exists
between the first and second walls. The device also includes a
first inlet port in the housing wall for conducing a first fluid
into the first gap and a first outlet port in the housing wall for
conducting filtered first fluid out of the first gap. The device
also comprises first and second rotational drive means for rotating
the first and second rotors respectively within the housing.
Consequently, when the first and second rotors are spun, Taylor
vortices may be created in the first and second gaps, thereby
enhancing mass transfer across the filtration membrane and
preventing concentration polarization on both sides of the
membrane.
[0017] In another preferred embodiment, the present invention
relates to a device to facilitate heat transfer. The device
comprises a housing having a housing wall; a first rotor having a
first wall comprising a filtration membrane, wherein the first
rotor is disposed within the housing and adapted to rotate therein,
such that a first gap exists between the filtration membrane and
the housing wall. There is also included a second rotor having a
second wall, wherein the second rotor is disposed within the first
rotor and adapted to rotate therein, such that a second gap exists
between the first and second walls. The device also includes a
first inlet port in the housing wall for conducing a first fluid
into the first gap and a first outlet port in the housing wall for
conducting filtered first fluid out of the first gap. The device
also comprises first and second rotational drive means for rotating
the first and second rotors respectively within the housing.
Consequently, when the first and second rotors are spun, Taylor
vortices may be created in the first and second gaps, thereby
enhancing mass transfer across the filtration membrane and
preventing concentration polarization on both sides of the
membrane.
[0018] In another preferred embodiment, the present invention
relates to a device to facilitate mass transfer from a first fluid.
The device comprises a housing having a housing wall, and a rotor
having a wall comprising a filtration membrane and defining an
interior, wherein said rotor is disposed within said housing and is
adapted to rotate therein. The device further comprises a gap
between the filtration membrane and the housing wall, wherein the
gap has a cross-section with a width varying about a circumference,
and a rotational drive means for rotating the rotor within said
housing at a speed sufficient to create Taylor vorticity in the
gap.
[0019] In one embodiment of a method incorporating the present
invention, hemodialysis is performed on a patient by providing a
hemodialysis device configured to create Taylor vorticity. Blood is
introduced from the patient into the hemodialysis device, and a
first rotor within the hemodialysis device is rotated to create
Taylor vorticity within the blood. Dialysis fluid is introduced
into the hemodialysis device, and dialyzed blood is collected from
the hemodialysis device for return to the patient.
[0020] In another embodiment of a method of performing hemodialysis
on a patient, a hemodialysis device is first provided. The device
comprises a housing having a housing wall; a first cylindrical
rotor having a first wall comprising a dialysis membrane, wherein
the first cylindrical rotor is disposed coaxially within the
housing and adapted to rotate therein, such that a first coaxial
gap exists between the dialysis membrane and the housing wall.
There is also included a second cylindrical rotor having a second
wall, wherein the second cylindrical rotor is disposed coaxially
within the first cylindrical rotor and adapted to rotate therein,
such that a second coaxial gap exists between the first and second
walls. The device also includes a first inlet port in the housing
wall for conducing blood into the first coaxial gap and a first
outlet port in the housing wall for conducting dialyzed blood out
of the first coaxial gap. A second inlet port is included in the
housing for conducting dialysis fluid into the second coaxial gap
and a second outlet port is included for conducing dialysate out of
the second coaxial gap. The device also comprises first and second
rotational drive means for rotating the first and second
cylindrical rotors respectively within the housing. Blood is
introduced from the patient into the first coaxial gap through the
first inlet port. Taylor vorticity is created within the blood by
rotating the first cylindrical rotor using the first rotational
drive means. Dialysis fluid is introduced into the second coaxial
gap through the second inlet port, and Taylor vorticity is created
within the dialysis fluid by rotating the second cylindrical rotor
using the second rotational drive means. Dialyzed blood is
collected from the hemodialysis device through the first outlet
port, and dialysis fluid is collected from the hemodialysis device
through the second outlet port.
[0021] In one embodiment of a method of performing mass transfer
from a first fluid, a filtration device is first provided. The
filtration device has a housing with a housing wall, and a first
cylindrical rotor with a first wall comprising a filtration
membrane. The first cylindrical rotor is also disposed coaxially
within said housing and adapted to rotate therein, such that a
first coaxial gap exists between the filtration membrane and the
housing wall. The filtration device also has a second cylindrical
rotor with a second wall, wherein said second cylindrical rotor is
disposed coaxially within said first cylindrical rotor and adapted
to rotate therein, such that a second coaxial gap exists between
the first and second walls. The filtration device further has a
first inlet port in the housing wall and a first outlet port in the
housing wall. The filtration device also has first and second
rotational drive means for rotating the first and second
cylindrical rotors within said housing. The first fluid is
introduced into the first coaxial gap through the first inlet port.
Taylor vorticity is created within the first fluid by rotating the
first cylindrical rotor using the first rotational drive means.
Taylor vorticity is also created by rotating the second cylindrical
rotor using the second rotational drive means. The filtered first
fluid is collected from the filtration device through the first
outlet port.
[0022] In one embodiment of a method of performing heat transfer
from a first fluid, a filtration device is first provided. The
filtration device has a housing with a housing wall, and a first
cylindrical rotor with a first wall comprising a membrane. The
first cylindrical rotor is also disposed coaxially within said
housing and adapted to rotate therein, such that a first coaxial
gap exists between the membrane and the housing wall. The
filtration device also has a second cylindrical rotor with a second
wall, wherein said second cylindrical rotor is disposed coaxially
within said first cylindrical rotor and adapted to rotate therein,
such that a second coaxial gap exists between the first and second
walls. The filtration device further has a first inlet port in the
housing wall and a first outlet port in the housing wall. The
filtration device also has first and second rotational drive means
for rotating the first and second cylindrical rotors within said
housing. The first fluid is introduced into the first coaxial gap
through the first inlet port. Taylor vorticity is created within
the first fluid by rotating the first cylindrical rotor using the
first rotational drive means. Taylor vorticity is also created by
rotating the second cylindrical rotor using the second rotational
drive means. The heat-exchanged first fluid is collected from the
filtration device through the first outlet port.
[0023] In another embodiment of a method of increasing mass
transfer across a semi-permeable barrier, vorticity is created on
both sides of the barrier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows a cross sectional view of one embodiment of a
vortex-enhanced dialysis device of the present invention.
[0025] FIG. 2 shows an overhead cross sectional view of one
embodiment of the device of FIG. 1;
[0026] FIG. 3 shows an overhead cross sectional view of a second
embodiment of a vortex-enhanced dialysis device;
[0027] FIG. 4 shows an overhead cross sectional view of a third
embodiment of a vortex-enhanced dialysis device;
[0028] FIG. 5 shows a cross sectional view of one embodiment of a
dual rotor vortex-enhanced device of the present invention;
[0029] FIG. 6 shows the cross-sectional view of FIG. 5, with the
flow-paths of the blood (outer gap) and dialysate (inner gap)
highlighted.
[0030] FIG. 7 shows mass transfer correlations in rotating RO.
Filled symbols indicate the experimental data. Error bars are
smaller than the symbol size except in cases where error bars are
shown. Bold lines indicate a least squares fit. (.box-solid.: NaCl,
6 atm; .tangle-solidup.: NaCl, 8 atm; : NaCl, 10 atm;
.diamond-solid.: Na.sub.2SO.sub.4, 10 atm)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] It is well known that Taylor vortices, otherwise referred to
herein as Taylor vorticity, can increase the mass transfer through
a filter by one or two orders of magnitude. This is useful where it
is desirable to remove a component of a fluid by size separation
from a feed fluid. For example, Taylor vorticity is useful in
removing plasma from blood. Here the separation mechanism is
accomplished by the pore size of the filter.
[0032] In other separation processes the components of the feed
fluid are removed by following a concentration gradient. An example
of this is in dialysis and, in particular, blood dialysis. Here,
urea and other low molecular weight waste by-products are removed
from blood by placing blood on one side of a membrane and a fluid
with low concentrations of urea and other waste by-products on the
other side of the membrane. The urea and other waste by-products
follow the concentration gradient and move through the membrane
from the blood to the dialysis fluid. Alternatively, a combination
of pore size and concentration gradient may be used in dialysis.
Plasma water moves more freely across a membrane as a result of its
small molecular size, and the waste by-products in the blood
diffuse across the membrane as a result of their size and the
resulting concentration gradient.
[0033] The performance of such blood dialysis devices may be
improved by using a system that generates Taylor vorticity to
diminish concentration polarization and increase mass transfer of
low molecular weight waste by-products through the filtration
membrane. In one embodiment of the invention, a blood dialysis
device that generates such Taylor vorticity may be provided.
[0034] As described above, concentration polarization can be a
problem on the dialysate side of the membrane as well as the blood
side. In preferred embodiments of the present invention, the
problems of concentration polarization on both sides of a
filtration membrane are solved by creating Taylor vortices on both
sides of the membrane. Creating Taylor vorticity on both sides of a
filtration membrane comprising a first rotor may be accomplished in
accordance with a preferred embodiment of the present invention by
providing a second rotating rotor inside the first rotor. This can
be used to improve transfer both from a first fluid into the
membrane and from the membrane into a gap between the first and
second rotors.
[0035] FIG. 1 shows a cross section of one possible embodiment of
this invention, in which a single rotor device creates Taylor
vorticity. In the illustrated embodiment, the filtration device 10
is used to perform hemodialysis, filtering undesirable waste
by-products from blood. In other embodiments, the device 10 may be
used, more generally, to transfer mass from one fluid to another.
In still other embodiments, the device 10 may be used to transfer
heat from one fluid to another. As would be well known to those of
skill in the art, the invention should not be limited to medical
applications.
[0036] In one embodiment, the filtration device 10 comprises a
cylindrical case 12 housing a cylindrical rotor 14. A gap 16 exists
between the case 12 and the rotor 14, and, in a preferred
embodiment, the rotor 14 is disposed coaxially within the
cylindrical case 12. In other embodiments, different geometries and
configurations may be chosen for the case and rotor, to accommodate
other fluids and other means of generating Taylor vorticity.
[0037] In the illustrated embodiment, the cylindrical,
circumferential walls of the rotor 14 are at least partially
composed of a filtration membrane 18, and partially define a rotor
interior 20. The rotor interior 20 is further defined by the top
and bottom walls of the rotor 14, which may or may not comprise
filtration membrane. As illustrated in FIG. 1, the filtration
membrane 18 is a dialysis membrane, porous for the small to
medium-sized molecules that might represent waste by-products
present in blood. In a typical application, the dialysis membrane
18 is porous up to a mass of approximately 10,000 Daltons. In other
embodiments, varying degrees of filtration and/or heat transfer may
be facilitated by the use of different filtration membranes. For
example, in a heat transfer application, the filtration membrane
may comprise an impermeable structure, which nevertheless is an
effective transferor of heat.
[0038] In the illustrated embodiment, the cylindrical case 12 has
three fluid access ports 22, 24, 26, two 22, 24 leading to the gap
16 between the case 12 and rotor 14, and one 26 leading from the
rotor interior 20. In other embodiments, different fluid access
configurations may be provided. For example, in one embodiment,
only one fluid access port leads to the gap between the case and
rotor, and two ports lead to the rotor interior.
[0039] In one embodiment, mounted in the axis A of the cylindrical
case 12 are two pivot pins 30, 32, one on either end. These pivot
pins 30, 32 define the axis of rotation A for the rotor 14, and
facilitate the free rotation of this rotor 14. As illustrated, the
bottom pivot pin 32 may be hollow, providing fluid transport
passage through the case 12 and rotor 14. Of course, in other
embodiments, the top pivot pin 30 may also be hollow to accommodate
another fluid access port. Other means of facilitating rotation may
be provided, including, e.g., ball-bearing assemblies and other
means well known to those of skill in the art.
[0040] In one embodiment of the invention, the rotor 14 can rotate
freely within the cylindrical case 12. In order to control this
rotation, a spinner magnet 34 may be mounted internally to the
rotor 14, and an external rotating magnetic field (not shown) may
be configured to interact with this spinner magnet 34. By
modulating the external magnetic field, the magnet 34 and, in turn,
the rotor 14 can be made to spin in different directions and at
varying speeds. In a preferred embodiment of the invention, the
rotor 14 can be spun at a speed sufficient to create Taylor
vorticity within a fluid in the gap 16 between the rotor 14 and
case 12. By creating Taylor vorticity in this gap 16, filtration
performance can be dramatically improved. Other means of spinning
the rotor 14 in order to create Taylor vorticity may be used in
keeping with this invention, as is known to those of skill in the
art. For example, in one embodiment, a motor may be attached to at
least one of the pivot pins, e.g. the top pivot pin 30, attached to
the rotor 14.
[0041] In one embodiment, the rotating magnetic fields that control
the rotor 14 can be produced by a series of magnetic coils that
surround the filtration device 10 at its top. These electrical coil
assemblies can be formed in half arch ("C" sections) that can be
closed around the device 10, although other configurations are
possible.
[0042] The illustrated size of the device 10 is considered adequate
for hemodialysis, although in other applications, larger or smaller
filtration devices may be utilized to suit the particular fluids
being processed.
[0043] In a hemodialysis application, the gap 16 between the rotor
14 and inside wall of the case 12 is selected to provide adequate
Taylor vorticity in the blood. This gap 16 depends on the diameter
and the RPM of the rotor 14, which parameters can be modified by
one of skill in the art. With a centrifugal speed in the range of
about 1000-5000 RPM and a rotor diameter of about 0.1 to 10 inches,
the width adequate to generate Taylor vortices may be in the range
of about 0.003 to about 0.3 inches. More preferably, a gap 16
having a width of about 0.03 inches should provide adequate
vorticity for a rotor 14 of about 1 inch in diameter spun at about
2,400 RPM.
[0044] FIGS. 2-4 illustrate some further structural features of
different embodiments of the hemodialysis device described above.
In particular, different geometries and configurations of the
housing and rotor are shown, which may be implemented to attain
various advantages. In FIG. 2, the embodiment described above is
shown. As can be more clearly seen in this Figure, the rotor 14 is
cylindrical and disposed coaxially within the cylindrical case 12.
Thus, the gap 16 is of constant width about the circumference of
the device 10. In this relatively simple embodiment, calibrating
the appropriate speed of the rotor 14 is more easily accomplished,
and the Taylor vortices are fairly constant in strength about the
entire filtration membrane 18.
[0045] In FIG. 3, another configuration of the case 12 and rotor 14
is shown. In this embodiment, the case 12 and rotor 14 have
individual cross-sections similar to those in FIG. 2, but are no
longer aligned coaxially. As shown in FIG. 3, the gap 16 therefore
varies in width about the circumference of the case 12. Since the
Taylor number, reflecting the strength of resulting vortices, is
directly proportional to the width of the gap, the sections of
rotor 14 farther from the wall of the case 12 experience greater
Taylor vorticity than those sections nearer to the wall. As the
rotor 14 passes these wider gap locations, residual concentration
polarization and any clogging of the filter membrane 18 will be
"blown" off by the stronger vortices, opening up blinded zones in
the membrane 18. As a result, once per revolution, the
longitudinally extending sections of the membrane 18 will be
"cleaned" by passing the widened portions of the gap 16, and the
efficiency of the device 10 may be improved. In addition, where the
width of the gap 16 decreases, the shear forces in the gap
increase, and this varying shear force may also tend to increase
mass transport across the membrane 18. Thus, once per revolution,
we can increase shear and decrease vorticity at any point on the
membrane 18 on rotor 14.
[0046] In FIG. 4, another configuration of the case 12 and rotor 14
is shown that will similarly create a non-constant width gap. In
this configuration, the case 12 and rotor 14 are configured
similarly to those in FIG. 2, but the case 12 further has a bulge
42 incorporated into its wall. The gap 16 therefore varies in width
about the circumference of the case 12, widening at the site of the
bulge 42, producing the advantages discussed above with reference
to FIG. 3. The abrupt shift between wide and narrow widths in this
embodiment may introduce further vortex characteristics that may
facilitate dialysis. In other embodiments, the case 12 and rotor 14
may have other cross-sectional geometries, resulting in a variable
width gap 16.
[0047] Returning to FIG. 1, one method of implementing the
hemodialysis device 10 may be discussed with reference to the
Figure. Arrows 36, 38 and 40 show the input and output of the flows
into and out of the device 10. In the illustrated embodiment, blood
from a patient flows through the gap 16 between the rotor 14 and
the case 12, while plasma water and waste by-products are filtered
into the rotor interior 20. Due to the concentration gradient
between the blood and the plasma water that initially crosses the
membrane 18, certain waste by-products will preferentially flow
through the dialysis membrane 18 into the plasma water, thereby
dialyzing the blood. The rotor 14 spins at a speed sufficient to
create Taylor vortices in the blood and prevents concentration
polarization in the blood near the dialysis membrane 18. In this
way, one embodiment of the present invention enables use of a
smaller, more biocompatible hemodialysis device 10.
[0048] In further detail, a blood inlet port 22 is located at the
top of the cylindrical case 12 and a blood outlet port 24 is
located at the bottom. This allows blood to flow from top to bottom
simply using gravitational energy, and pressure from the blood
influx. The device 10 is preferably designed such that in the time
it takes a certain quantity of blood to travel from the top of the
hemodialysis device 10 to the bottom, the desired amount of waste
by-product has been extracted. A plasma water and waste by-product
outlet port 26 is located at the bottom of the rotor 14. In a
preferred embodiment, this solution flows out of the device 10 for
further filtering as described in further detail below.
[0049] In another embodiment, a dialysis fluid may be used to
facilitate hemodialysis. Another fluid access port may be added to
the top of the device 10 to allow dialysis fluid to enter the
device. As is described in detail with reference to FIG. 6, waste
by-products diffuse into the dialysis fluid and are carried away
from the device by the dialysate flow. Other modifications may also
be made in keeping with the present invention.
[0050] FIG. 5 shows a cross section of another possible embodiment
of the present invention, in which a dual rotor device creates
Taylor vorticity. In the illustrated embodiment, the filtration
device 110 is used to perform hemodialysis, filtering undesirable
waste by-products from blood and into a dialysis fluid. In other
embodiments, the device 110 may be used, more generally, to
transfer mass from one fluid to another. In still other
embodiments, the device 110 may be used to transfer heat from one
fluid to another. As would be well known to those of skill in the
art, the invention should not be limited to medical
applications.
[0051] In one embodiment, the filtration device 110 comprises a
cylindrical case 112 housing a cylindrical outer rotor 114. A first
gap 116 exists between the case 112 and the outer rotor 114 through
which blood flows, and, in a preferred embodiment, the outer rotor
114 is disposed coaxially within the cylindrical case 112. In other
embodiments, different geometries and configurations may be chosen
for the case and rotor, as discussed above with reference to FIGS.
2-4.
[0052] In the illustrated embodiment, the cylindrical,
circumferential walls of the outer rotor 114 are at least partially
composed of a filtration membrane 118, and partially define an
outer rotor interior 120. The outer rotor interior 120 is further
defined by the top and bottom walls of the outer rotor 114, which
may or may not comprise filtration membrane. As illustrated in FIG.
5, the filtration membrane 118 is a dialysis membrane. In other
embodiments, varying degrees of filtration and/or heat transfer may
be facilitated by the use of different filtration membranes. For
example, in a heat transfer application, the filtration membrane
may comprise an impermeable structure, which nevertheless is an
effective transferor of heat.
[0053] In one embodiment, mounted in the axis A of the cylindrical
case 112 are two pivot pins 130, 132, one on either end. These
pivot pins 130, 132 define the axis of rotation A for the outer
rotor 114, and facilitate the free rotation of this rotor 114. As
illustrated, the pivot pins 130, 132 may also be hollow, providing
fluid transport passages through the case 112 and outer rotor 114.
In other embodiments, other means of facilitating rotation may be
provided, including, e.g., ball-bearing assemblies and other means
well known to those of skill in the art.
[0054] In one embodiment of the invention, the outer rotor 114 can
rotate freely within the cylindrical case 112. In order to control
this rotation, a spinner magnet 134 may be mounted internally to
the outer rotor 114, and an external rotating magnetic field (not
shown) may be configured to interact with this spinner magnet 134.
By modulating the external magnetic field, the magnet 134 and, in
turn, the outer rotor 114 can be made to spin in different
directions and at varying speeds. In a preferred embodiment of the
invention, the outer rotor 114 can be spun at a speed sufficient to
create Taylor vorticity within a fluid in the first gap 116 between
the outer rotor 114 and case 112. By creating Taylor vorticity in
this first gap 116, filtration performance can be dramatically
improved. Other means of spinning the outer rotor 114 in order to
create Taylor vorticity may be used in keeping with this invention,
as is known to those of skill in the art. For example, in one
embodiment, a motor may be attached to at least one of the pivot
pins, e.g. upper pivot pin 130, attached to the outer rotor
114.
[0055] Inside the outer rotor 114, an inner rotor 144, also
supported by the upper and lower pivot pins 130, 132, may be
mounted coaxially, with a second gap 146 created between the two
rotors 114, 144. Although the inner rotor 144 may partially
comprise another filtration membrane, in a preferred embodiment,
the inner rotor is relatively impermeable, simply defining the
second gap between the two rotors 114, 144. As described in further
detail above with respect to the outer rotor and case, the inner
rotor 144 may also have differing cross-sectional geometries, and
may be mis-aligned to accommodate other fluids and other means of
generating Taylor vorticity. In these alternative embodiments, the
inner rotor 144 may be supported by structures other than those
supporting the outer rotor 114, and may spin about a different
axis.
[0056] In a preferred embodiment, the inner rotor 144 rotates
freely within both the outer rotor 114 and cylindrical case 112. In
order to control this rotation, a second spinner magnet 148 may be
mounted internally to the inner rotor 144, and a second external
rotating magnetic field (not shown) may be configured to interact
with this second spinner magnet 148. In the illustrated embodiment,
the second spinner magnet 148 for the inner rotor 144 is located at
the top of the device 110, and the spinner magnet 134 for the outer
rotor 114 is located at the bottom of the device 110. Thus, two
separate and independent magnetic fields can control the rotation
of the two rotors 114, 144. As described in further detail above,
the second spinner magnet 148 mounted to the inner rotor 144 may be
controlled similarly to the one mounted to the outer rotor 114. In
a preferred embodiment, the inner rotor 144 can be spun at a speed
sufficient to create Taylor vorticity within a fluid in the second
gap 146 between the inner and outer rotors. In a further preferred
embodiment, the inner rotor 144 is spun in a direction opposite the
outer rotor 114 to create even more powerful Taylor vortices. By
creating Taylor vorticity in this second gap 146, filtration
performance can be further improved, as concentration polarization
is prevented on the side of the filtration membrane 118 facing the
inner rotor 144. Other means of spinning the inner rotor 144 in
order to create Taylor vorticity may be used, as is known to those
of skill in the art. For example, in one embodiment, a motor may be
attached to at least one of the pivot pins, e.g. lower pivot pin
132, attached to the inner rotor 144.
[0057] In one embodiment, the rotating magnetic fields that control
the two rotors can be produced by a series of magnetic coils that
surround the filtration device 110 at its top and bottom. Since
pre-connected tubing (not shown) enters and exits the device 110 on
axis A in the illustrated embodiment, these electrical coil
assemblies can be formed in half arch ("C" sections) that can be
closed around the device 110.
[0058] The illustrated size of the device 110 is considered
adequate for hemodialysis, although in other applications, larger
or smaller filtration devices may be utilized to suit the
particular fluids being processed.
[0059] In a hemodialysis application, the first gap 116 between the
outer rotor 114 and inside wall of the case 112 is selected to
provide adequate Taylor vorticity in the blood. This first gap 116
depends on the diameter and the RPM of the outer rotor 114, which
parameters can be modified by one of skill in the art. With a
centrifugal speed in the range of about 1000-5000 RPM and an outer
rotor diameter of about 0.1 to 10 inches, the width adequate to
generate Taylor vortices may be in the range of about 0.003 to
about 0.3 inches. More preferably, a first gap 116 having a width
of about 0.03 inches should provide adequate vorticity for an outer
rotor 114 of about 1 inch in diameter spun at about 2,400 RPM.
[0060] In the illustrated embodiment, the second gap 146 between
the inner and outer rotors is selected to provide adequate Taylor
vorticity in the dialysate. This second gap 146 depends on the
diameters and the RPM difference between the inner and outer
rotors. With a centrifugal speed in the range of about 1000-5000
RPM and an inner rotor diameter of about 0.1 to 10 inches, the
width adequate to generate Taylor vortices between the inner rotor
144 and outer rotor 114 may be in the range of about 0.003 to about
0.3 inches. Preferably, a second gap 146 having a width of about
0.03 inches should create adequate vorticity for an inner rotor
diameter of about 0.8 inches spun at about 3,600 RPM. This
preferred set of parameters would give a rotating speed of the
inner rotor 144 relative to the outer rotor 114 of about 1,200 RPM.
Alternatively, by spinning the inner rotor 144 in the opposite
direction of the outer rotor 114, powerful Taylor vorticity can be
created in the dialysate.
[0061] For the various potential applications, the dimensions and
speeds of the inner and outer rotors and casing may be dramatically
different. For example, in certain industrial applications, the
filtration device 110 may be designed on a much larger-scale in
order to accommodate larger flows and liquids of varying viscosity.
Optimizing the ranges of gap and rotor sizes, as well as
centrifugal speed and rotor direction can be done by one of skill
in the art based on the teaching herein.
[0062] In the illustrated embodiment, the cylindrical case has four
fluid access ports 122, 124, 126, 128. A first inlet port 122 is
located at the top of the cylindrical case 112, and a first outlet
port 124 is located at the bottom. In a hemodialysis application,
this allows blood to flow from top to bottom through the first gap
116 simply using gravitational energy, and pressure from the blood
influx. The device 110 is preferably designed such that in the time
it takes a certain quantity of blood to travel from the top of the
hemodialysis device 110 to the bottom, the desired amount of waste
by-product has been extracted. A second inlet port 126 is located
at the bottom of the outer rotor 114, and a second outlet port 128
is located at the top of the outer rotor 114. In the hemodialysis
application, the dialysis fluid flows through these ports from the
bottom of the device 110 to the top through the second gap 146
between the inner and outer rotors. In this preferred embodiment,
the fluid paths are designed to take advantage of counter-current
mass transfer, meaning that the paths of blood and dialysate are
opposite. Fresh dialysate is exposed through the dialysis membrane
118 with mostly dialyzed blood, where the concentration gradient is
the lowest. As is well known to those of skill in the art, however,
other numbers and configurations of fluid access ports may be used
in keeping with the present invention.
[0063] Since the first inlet and outlet ports 122, 124 are on the
outer diameter of the case 112, there is no need for high pressure
on that flow path. This being the case, in the illustrated
embodiment, blood will not be forced to the center of rotation of
the outer rotor 114, thus fluid seals are not necessary there to
prevent blood from entering the inner rotor 144. Fluid seals can be
added if higher fluid pressures are employed in hemodialysis or
other applications, or if fluids for filtering enter the inner
rotor 144 for any reason.
[0064] In a preferred embodiment, the second inlet port 126 for
dialysate is configured so that the dialysate passes through the
lower pivot pin 132 and is then directed into the second gap 146
between the inner and outer rotors, and not downward into the first
gap 116 between the outer rotor 114 and case 112. A fluid seal 150
at the top pivot pin 130 is included in the illustrated embodiment
to prevent migration of dialysate into the first gap 116 between
the outer rotor 114 and case 112. This seal 150 can be any
conventional polymer lip seal. As is well known to those of skill
in the art, other seals may be implemented. In an alternative
embodiment, another fluid seal is included at the bottom pivot pin
132.
[0065] In one method of practicing the present invention, blood is
exposed to the dialysis membrane 118 with Taylor vorticity
resulting in a minimal concentration polarization layer in the
first gap 116 between the outer rotor 114 and case 112, maximizing
the ability to remove low molecular weight waste by-products from
the patient's blood. In the process of passing through the
filtration device 110, dialysate is also exposed to Taylor
vorticity, resulting in a minimal concentration polarization layer
near the interior of the dialysis membrane 118, maximizing the
ability to mix the low molecular weight waste by-products into the
dialysate flow.
[0066] In connection with FIG. 6, an exemplary method of performing
hemodialysis will be described using the device described in FIG.
5. Within the device 110, the inner and outer rotors are spinning
in opposite directions at speeds sufficient to create Taylor
vortices in fluids between the outer rotor 114 and case 112, and
between the inner rotor 144 and outer rotor 114. Blood is collected
from the patient at a particular flow rate 136, and enters the
hemodialysis device 110 through the blood inlet port 122, located
at the top of the device 110. Dialysis fluid also enters the
hemodialysis device 140, but from the bottom, through a second,
dialysate inlet port 126. The two fluids are subjected to the
forces from the rotors, and Taylor vortices form within them. Thus,
concentration polarization is largely alleviated at the dialysis
membrane 118 of the outer rotor 114, and a more constant flow of
waste by-products travels through the membrane 118 into the
dialysate. The dialysate travels through the hemodialysis device
110, within the second gap 146 between the outer and inner rotors,
and exits the top through a dialysate outlet port 128, while the
dialyzed blood exits through the blood outlet port 124 at the
bottom of the device 110 and is returned to the patient.
[0067] One problem with both of the above described methods of
hemodialysis is that the illustrated dialysis membrane may be
porous to water as well as waste by-products. Thus, large volumes
of plasma water accompany waste by-products traveling through the
dialysis membrane, and the flow of dialyzed blood exiting through
the blood outlet port is dramatically reduced from the blood
entering the hemodialysis device. In one embodiment, a sterile
replacement fluid may be added to the dialyzed blood at a junction
prior to return to the patient. However, this embodiment risks
patient exposure to contaminated replacement fluid, and increases
the costs of hemodialysis by the cost of the replacement fluid.
[0068] In another, more preferred embodiment, the patient is used
as one source of replacement fluid. This may be accomplished by
directing the dialysate, or plasma water emerging from the
hemodialysis device through a second separator. The second
separator has a membrane of a smaller pore size, selected to allow
water and salts to pass through, preferably leaving the waste
by-products. The water and salts comprise a biocompatible
replacement fluid that can then be added to the dialyzed blood to
replace much of the volume lost in the original hemodialysis. In
one implementation, the second separator comprises a second
filtration device that functions similarly to the hemodialysis
device 10 or 110 described above. This second filtration device may
differ only in the porosity of the filtration membrane, as its
membrane is used to separate water and salts from the rest of the
fluid flowing from the device.
[0069] In one implementation used with a device configured
according to FIG. 5, blood is collected from the patient and flows
through a hemodialysis device 110. Dialysate also flows through the
hemodialysis device 110 and receives an influx of plasma water as
well as waste by-products through the hemodialysis membrane 118.
The dialysate flows out of the hemodialysis device 110 into a
second filtration device as described above, which acts as a second
separator to separate plasma water from the extracted waste
by-products. The plasma water extracted in this second filtration
device is then combined with the dialyzed blood at a junction and
returned to the patient. In some embodiments, not all of the plasma
water may be recovered in this system, and so additional
replacement fluid must be added to the dialyzed blood prior to
return to the patient. However, the volume of artificial
replacement fluid is reduced by use of the patient himself as a
donor.
[0070] It should be further understood that although the second
filtration device is described herein as filtering the dialysate
flowing from the hemodialysis device 110 and returning the plasma
water to the dialyzed blood, it may also filter plasma water out of
and back into the system at other locations. For example, in one
embodiment, plasma water is filtered out of the dialysate, and that
plasma water is then returned to the blood prior to dialysis. Other
embodiments using the patient as a donor of replacement fluid may
be implemented, as is well known to those of skill in the art.
[0071] With reference to FIG. 7, the benefit of Taylor vorticity
can be seen with regard to increasing mass transport across a
reverse osmosis (RO) membrane. This figure is derived from the
manuscript of Lee and Lueptow, attached hereto and incorporated in
its entirety. The results agree with the inventor's observations of
the benefit of Taylor vorticity in plasmapheresis. Plasma flux
(mass transfer) increased by 100 times over that observed in
conventional tangential flow. When applied to the vortex-enhanced
devices of the present invention, an increase in the rate of mass
transfer of approximately 100-fold should result in approximately a
100-fold reduction in the area of membrane required for effective
filtration. Moreover, this design will allow use of hemodialysis
membranes of many materials that are not compatible with the
conventional hollow fiber geometry (e.g., difficulty in fashioning
membrane materials into the hollow tubes).
[0072] Those skilled in the art will appreciate that numerous
changes and modifications may be made to the preferred embodiments
of the invention and that such changes and modifications may be
made without departing from the spirit of the invention disclosed
herein. It is therefore intended that the appended claims cover all
such equivalent variations as may fall within the true spirit and
scope of the invention.
* * * * *