U.S. patent application number 11/680943 was filed with the patent office on 2008-09-04 for system including a heat exchanger with different cryogenic fluids therein and method of using the same.
This patent application is currently assigned to PHILIPS MEDICAL SYSTEMS MR, INC.. Invention is credited to Robert A. Ackermann, Philippe Menteur, Chandra T. Reis.
Application Number | 20080209919 11/680943 |
Document ID | / |
Family ID | 39732139 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080209919 |
Kind Code |
A1 |
Ackermann; Robert A. ; et
al. |
September 4, 2008 |
SYSTEM INCLUDING A HEAT EXCHANGER WITH DIFFERENT CRYOGENIC FLUIDS
THEREIN AND METHOD OF USING THE SAME
Abstract
A system can include a heat transfer structure and a heat
exchanger. The heat transfer structure is to cool an object, and
the heat exchanger is to cool a portion of the heat transfer
structure. The system can be cooled significantly faster than a
conventional system that uses conductive cooling. The system has no
or less liquid cryogen that would be vaporized as compared to a
conventional system that immerses the object to be cooled within a
bath of liquid cryogen or has a substantial mass of liquid cryogen
within a cooling loop.
Inventors: |
Ackermann; Robert A.;
(Schenectady, NY) ; Menteur; Philippe; (Niskayuna,
NY) ; Reis; Chandra T.; (Altamont, NY) |
Correspondence
Address: |
LARSON NEWMAN ABEL POLANSKY & WHITE, LLP
5914 WEST COURTYARD DRIVE, SUITE 200
AUSTIN
TX
78730
US
|
Assignee: |
PHILIPS MEDICAL SYSTEMS MR,
INC.
Latham
NY
|
Family ID: |
39732139 |
Appl. No.: |
11/680943 |
Filed: |
March 1, 2007 |
Current U.S.
Class: |
62/51.1 ;
62/62 |
Current CPC
Class: |
F25B 25/005 20130101;
G01R 33/3815 20130101; F25B 9/14 20130101; F25D 19/006 20130101;
G01R 33/3804 20130101 |
Class at
Publication: |
62/51.1 ;
62/62 |
International
Class: |
F25B 19/00 20060101
F25B019/00 |
Claims
1. A system comprising: a coldhead; a first heat exchanger operable
to receive a first cryogenic fluid and coupled to the coldhead; a
vessel designed to be operated at a cryogenic temperature; and a
heat transfer structure including a closed loop and further
including a first portion disposed within the first heat exchanger
and a second portion disposed, wherein: the closed loop is operable
to contain a second cryogenic fluid that would be disposed therein;
and the first heat exchanger is designed such that the first
cryogenic fluid and the second cryogenic fluid would be spaced
apart from each other.
2. The system of claim 1, wherein: the system is designed such that
the first cryogenic fluid would have a different phase state as
compared to the second cryogenic fluid; the system is designed such
that the first cryogenic fluid would have a different composition
as compared to the second cryogenic fluid; or any combination
thereof.
3. The system of claim 1, wherein the first heat exchanger is
operable to receive the first fluid cryogen as a liquid cryogen
from the coldhead.
4. The system of claim 1, further comprising a wetsock coupled to
the coldhead, wherein the coldhead is disposed within the
wetsock.
5. The system of claim 1, further comprising a reservoir coupled to
the first heat exchanger, wherein the reservoir has a capacity
sufficient to receive spillover from the first cryogenic fluid
during a typical operating state.
6. The system of claim 1, further comprising a second heat
exchanger, wherein the second heat exchanger is coupled to the
coldhead and the first heat exchanger.
7. The system of claim 6, further comprising a thermal switch
including a first terminal and a second terminal, wherein: the
first terminal is coupled to the first heat exchanger; and the
second terminal is coupled to the second heat exchanger.
8. A superconducting system comprising: a vessel; a superconducting
element disposed within the vessel; a first heat exchanger disposed
within the vessel; and a heat transfer structure disposed within
the vessel and thermally coupled to the superconducting element and
the first heat exchanger.
9. The superconducting system of claim 8, wherein the first heat
exchanger is operable to cool a first fluid with a second fluid,
wherein the first fluid includes gaseous He, and the second fluid
includes gaseous He and liquid He.
10. The superconducting system of claim 8, wherein the first heat
exchanger lies at an elevation higher than a lowest point of the
heat transfer structure.
11. The superconducting system of claim 10, wherein the heat
transfer structure is configured to allow a fluid to flow within
the heat transfer structure by natural convection when the
superconducting system would be operating at steady state.
12. The superconducting system of claim 8, further comprising: a
coldhead operable to condense a first gaseous cryogen into a liquid
cryogen; and a wetsock coupled to the first heat exchanger, wherein
the first heat exchanger is operable to receive the liquid cryogen
when the coldhead would be operating.
13. The superconducting system of claim 12, further comprising: a
second heat exchanger; a thermal switch connected to the first heat
exchanger and the second heat exchanger; and a reservoir connected
to the first heat exchanger.
14. A method of using a system comprising: providing a first
cryogenic fluid; cooling a second cryogenic fluid with the first
cryogenic fluid, wherein the first cryogenic fluid and the second
cryogenic fluid remain spaced apart from each other; flowing the
second cryogenic fluid disposed within a heat transfer structure
that is coupled to a cooled object; and cooling the cooled object
to a cryogenic temperature using the second cryogenic fluid.
15. The method of claim 14, further comprising condensing a gaseous
cryogen within the first cryogenic fluid into a liquid cryogen.
16. The method of claim 15, wherein cooling the second cryogenic
fluid comprises contacting the heat transfer structure with the
liquid cryogen.
17. The method of claim 14, wherein cooling the cooled object is
performed while a superconducting element is disposed within the
vessel.
18. The method of claim 17, further comprising operating the
superconducting element, wherein: operating the superconductor
element is performed while a first pressure within the vessel is
less than atmospheric pressure; and flowing the second gaseous
cryogen is performed at a second pressure less than atmospheric
pressure.
19. The method of claim 18, wherein the first pressure is at least
three orders of magnitude lower than the second pressure.
20. The method of claim 18, further comprising closing a thermal
switch between a first heat exchanger and a second heat
exchanger.
21. The method of claim 20, further comprising opening the thermal
switch after flowing the second gaseous cryogen before the
superconducting element is in its typical operating state.
22. The method of claim 14, further comprising flowing the first
cryogenic fluid from a reservoir to a heat exchanger.
23. The method of claim 22, further comprising flowing a liquid
cryogen from the heat exchanger to the reservoir.
Description
BACKGROUND
[0001] 1. Field of the Disclosure
[0002] The disclosure relates to systems, and methods, and more
particularly to cooling systems including heat exchangers with
different cryogenic fluids therein and methods of using the
systems.
[0003] 2. Description of the Related Art
[0004] A conventional low-temperature superconducting system can be
cooled by immersion, convection, or conduction. Conventional
immersion cooling of a cryogenic system can include using a liquid
cryogen. FIG. 1 includes a schematic drawing of a conventional
magnetic resonance imaging ("MRI") system 100 that includes a
superconducting coil 190 that is contained within a vessel 140. The
vessel 140 has an outer wall 142, an inner wall 144, and a thermal
shield 182 disposed therebetween. An interior space 160 is disposed
within the inner wall 144. The vessel 120 can include another wall
172, a patient wall 174 with a space 176 in which a patient (not
illustrated) may be placed when using the MRI system 110 during
normal operation.
[0005] The MRI system 100 is cooled by condensing gaseous cryogen
into a liquid cryogen by the use of a cryocooler 120. More
particularly, gaseous cryogen, which lies above line 170, is
condensed, and the superconducting coil 190 is at least partially
immersed within a bath of liquid cryogen (below line 170), such as
He.
[0006] As can be seen in FIG. 1, a significant amount of the
interior space 160 within the interior wall 144 is filled with
liquid cryogen. Although coils can be provided to customers with
the cryogen installed, it is common for routine service and
expected failure modes to deplete some of that cryogen. Many areas
of the world do not have ready supply of replacement liquid cryogen
or an equivalent high purity gas. Therefore, a magnet system with
limited or no liquid cryogen is desirable.
[0007] A dual-phase, convective cooling loop is described in U.S.
Pat. No. 5,461,873. A superconducting coil is disposed within the
dual-phase cooling loop. The superconducting coil is cooled by
boiling the liquid cryogen within the dual-phase cooling loop.
Thus, the system has a substantial amount of liquid cryogen that is
thermally connected to the superconducting coil. The dual-phase,
convective cooling loop suffers from the same problem as the
immersion cooling. A quench can cause all liquid cryogen to become
vaporized and exhausted from the system. Again, the system will
need to be recharged with cryogen after a quench occurs.
[0008] For conduction cooling, only minimal amounts of liquid
cryogen are used. A cooling source, such as a cryocooler, has a
cold surface in contact with a surface of an object that is to be
cooled, such as a superconducting coil. As compared to convective
cooling, the conductive cooling is very slow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present disclosure may be better understood, and its
numerous features and advantages made apparent to those skilled in
the art by referencing the accompanying drawings.
[0010] FIG. 1 includes a schematic drawing of a magnetic resonance
imaging system. (Prior art).
[0011] FIG. 2 includes a schematic diagram of a superconducting
system in accordance with an embodiment described in more detail
below.
[0012] The use of the same reference symbols in different drawings
indicates similar or identical items. Skilled artisans will
appreciate that elements in the figures are illustrated for
simplicity and clarity and have not necessarily been drawn to
scale.
DETAILED DESCRIPTION
[0013] A system can include a heat transfer structure and a heat
exchanger. The heat transfer structure is to cool an object, and
the heat exchanger is to cool a portion of the heat transfer
structure. The system can be cooled significantly faster than a
conventional system that uses conductive cooling. The system has no
or less liquid cryogen that would be vaporized as compared to a
conventional system that immerses the object to be cooled within a
bath of liquid cryogen or has a substantial mass of liquid cryogen
within a cooling loop. Thus, the system is more likely to withstand
a fault or other undesired condition without having to recharge the
system with a cryogen.
[0014] A few terms are defined or clarified to aid in understanding
of the terms as used throughout this specification. As used herein,
the term "coupled" is intended to mean a connection, linking, or
association of two or more components, sub-systems, or any
combination thereof in such a way that a fluid or energy may be
transferred from one to another. Coupling may be direct or
indirect. For example, thermal coupling can include a direct
contact between a cold surface and an object to be cooled, or an
indirect thermal connection in which an object is cooled by a first
medium, which in turn is cooled by a second medium, wherein the
second medium does not contact the object (i.e., the object is
thermally coupled to the first medium). Coupling can include
thermal coupling, fluidal coupling, mechanical coupling, etc.
[0015] The term "typical operating state" is intended to mean a
state in which all superconducting elements along a superconducting
current path are in their superconducting states.
[0016] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive or
and not to an exclusive or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present).
[0017] Additionally, for clarity purposes and to give a general
sense of the scope of the embodiments described herein, the use of
the "a" or "an" are employed to describe one or more articles to
which "a" or "an" refers. Therefore, the description should be read
to include one or at least one whenever "a" or "an" is used, and
the singular also includes the plural unless it is clear that the
contrary is meant otherwise.
[0018] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. All
publications, patent applications, patents, and other references
mentioned herein are incorporated by reference in their entirety.
In case of conflict, the present specification, including
definitions, will control. In addition, the materials, methods, and
examples are illustrative only and not intended to be limiting.
[0019] To the extent not described herein, many details regarding
specific materials, processing acts, and components, assemblies,
and systems are conventional and may be found in textbooks and
other sources within the superconducting, cryogenic, and medical
device arts.
[0020] While much of the description herein is directed to an MRI
system, after reading this specification, skilled artisans will
appreciate that the concepts described herein may also be extended
to a different system. In another embodiment, the system may
include a superconducting element in a different application (e.g.,
a transmission or distribution cable, a transformer, a fault
current limiter, one or more other suitable electronic devices, or
any combination thereof). Thus, the systems and methods described
herein are not limited only for use with an MRI system.
[0021] Further, the concepts described herein are not limited to
superconducting systems. The concepts can be extended to other
systems that operate at temperatures no greater than about 110 K. A
cryogen that can be used for such systems can include an elemental
material (e.g., He, Ne, Ar, etc.) or a molecular material (H.sub.2,
N.sub.2, CH.sub.4, etc.).
[0022] FIG. 2 includes a schematic of a system 200 in accordance
with an embodiment. In one embodiment, the system 200 can be an MRI
system. In the illustrated embodiment, nearly all of the components
and sub-systems are disposed within a vessel 202. Parts of a
fill/vent line 274 and a coldhead 244 extend outside the vessel
202. In other embodiments (not illustrated), more, fewer, or
different components, sub-systems, or any combination thereof are
disposed within or outside the vessel 202.
[0023] The system 200 includes a superconducting element 212 within
the vessel 202 that is evacuated. In one embodiment, the vessel 202
is operated at a pressure less than 10.sup.-3 Torr, and in another
embodiment, less than 10.sup.-5 Torr, 10.sup.-8 Torr, or even
lower.
[0024] In the illustrated embodiment, the superconducting element
212 is an object to be cooled by the heat transfer structure 220.
The superconducting element 212 is thermally connected to a portion
214 of the heat transfer structure 220 using a conventional or
proprietary configuration. In one embodiment, the superconducting
element 212 can include a low-temperature superconductor. In a
particular embodiment, the superconducting element 212 can include
a superconducting coil, a superconducting transformer, a
superconducting switch, a superconductor (e.g., a wire, a terminal,
a solder connection, etc.), or any combination thereof. The
superconducting element 212 can operate using alternating current,
direct current, ramped or pulsed signals, or any combination
thereof. If cooled with a liquid cryogen, the superconducting
element 212 is at about the same temperature as the boiling point
of a liquid cryogen used within the heat transfer structure 220.
Thus, if He is used as the liquid cryogen, the superconducting
element 212 may be cooled to approximately 4 K, if H.sub.2 is used
as the liquid cryogen, the superconducting element 212 may be
cooled to approximately 20 K, and if Ne is used is used as the
liquid cryogen, the superconducting element 212 may be cooled to
approximately 27 K. If a gaseous cryogen is used, the
superconducting element 212 can be any temperature capable of being
achieved at the operating pressure of the gaseous cryogen within
heat transfer structure 220.
[0025] The heat transfer structure 220 includes the portion 214
that is coupled to another portion 234, via a portion 224. The
other portion 234 of the heat transfer structure 220 is disposed
within a heat exchanger 230. The heat transfer structure 220 can
include a single loop, a manifold system, or the like. A cryogenic
fluid flows within the heat transfer structure 220. The cryogenic
fluid can operate by a thermosiphon principle, natural convection,
or forced convection. The cryogenic fluid can be any cryogen
previously described herein. In one embodiment, the cryogenic fluid
within the heat transfer structure 220 is in a single phase state,
such as a gas.
[0026] The cryogenic fluid within the heat transfer structure 220
can be at a pressure such that sufficient cryogenic fluid is
present to provide effective cooling to the object being cooled
(e.g., the superconducting element 212) but not so high of a
pressure that a significant amount of liquid cryogen is present
within the heat transfer structure 220. Thus, in one embodiment,
the heat transfer structure 220 includes a principally single-phase
cooling loop. In one embodiment, the pressure is in a range of
approximately 0.5 to 100 atmospheres, and in a particular
embodiment, can be in a range of approximately 0.8 to 1.0
atmospheres. Therefore, the pressure of the cryogenic fluid within
the heat transfer structure 220 is at least three orders of
magnitude different from the pressure within the vessel 202. In
another embodiment, the pressure difference is at least is at least
six orders of magnitude different, is at least nine orders of
magnitude different, or even more.
[0027] In one embodiment, the cryogenic fluid enters the heat
exchanger 230 within portion 234 of heat transfer structure 220.
The cryogenic fluid is cooled and becomes denser. The denser
cryogenic fluid flows to and cools the superconducting element 212,
which in turn heat the cryogenic fluid and makes it lighter (i.e.,
less dense). In one embodiment, the cryogen disposed within the
heat transfer structure 220 remains in a single state, even though
its density changes. In another embodiment, a gaseous cryogen
disposed within the heat transfer structure 220 can condense to
form a liquid cryogen, and the liquid cryogen can be vaporized to
form the gaseous cryogen.
[0028] The lighter cryogenic fluid disposed within the heat
transfer structure 220 flows to heat exchanger 230 (within the
portion 234 of the heat transfer structure 220) and is cooled by a
different cryogenic fluid within the heat exchanger 230, which in
turn makes the cryogenic fluid denser. In this manner, natural
convention can be used to circulate the cryogenic fluid within the
heat transfer structure 220 when the system 200 is operating at
steady state. In an alternative embodiment (not illustrated),
forced convection can be used to circulate the cryogenic fluid
within the heat transfer structure 220. To simplify understanding
of the embodiments, the cryogenic fluid within the heat transfer
structure may also be referred to as the "circulating fluid," and
the different cryogenic fluid may also be referred to as the
"buffer fluid."
[0029] Within the heat exchanger 230, the circulating fluid within
the heat transfer structure 220 is spaced apart and does not
physically contact the buffer fluid within the heat exchanger 230.
The buffer fluid may be in a single phase state or more than one
phase state. For example, the buffer fluid can include a gaseous
cryogen 236 and a liquid cryogen 238. The buffer fluid may have the
same or different composition as compared to the circulating fluid.
In a particular embodiment, the buffer can include He that is in a
gaseous state and a liquid state within the heat exchanger 230. The
portion 234 of the heat transfer structure 220 disposed within the
heat exchanger 230 is immersed in liquid He. In one embodiment, the
portion 234 is partially immersed, and in another embodiment, the
portion 234 is substantially completely immersed.
[0030] A coldhead 244 is coupled to the heat exchanger 230 via a
wetsock 242. The coldhead 244 can have a single stage or more than
one stage. The coldhead can include a Sterling cycle,
Gifford-McMahon cycle, pulse tubes, or any other conventional or
proprietary design. The wetsock 242 can have a conventional or
proprietary design. In a particular embodiment, the wetsock 242 can
have a design and be used as described in U.S. patent application
Ser. No. 11/339,134, entitled "Method of Using a System Including
an Assembly Exposed to a Cryogenic Region" by Jones et al., filed
Jan. 25, 2006. In another embodiment (not illustrated), a plurality
coldheads and wetsocks similar to coldhead 244 and wetsock 242,
respectively, can be used.
[0031] When operating, the gaseous cryogen 236 can migrate from the
heat exchanger 230 to the wetsock 242 and contact the coldhead 244.
The gaseous cryogen 236 can be condensed by the coldhead 244 into
the liquid cryogen 238. In one embodiment, the amount of liquid
cryogen 238 within the heat exchanger 230 is no greater than 100
liters, and in another embodiment, is no greater than 10 liters, or
even smaller.
[0032] The design, size, and configuration of the heat exchanger
230 may depend on the amount of heat to be transferred, the space
available within the vessel 202, the compositions and phase(s) of
the buffer and circulating fluids, the material separating the
buffer and circulating fluids (i.e., the material of the wall of
the heat transfer structure 220), other suitable consideration, or
any combination thereof. After reading this specification, skilled
artisans will appreciate how to design, size, and configure the
heat exchanger 230 to meet their particular needs or desires.
[0033] The system 200 can further include another heat exchanger
250, which is optional. The heat exchanger 250 is thermally coupled
to the coldhead 244 and is thermally coupled to the heat exchanger
230, via a thermal switch 262. In one embodiment, the heat
exchanger 250 is permanently thermally coupled to the coldhead 244.
In another embodiment, the heat exchanger 250 is thermally
connected to a different cooling stage of coldhead 244 other than a
stage of the coldhead 244 to which the heat exchanger 230 is
coupled. Each of the heat exchanger 250 and the thermal switch 262
can include a conventional or proprietary design. In one
embodiment, a portion 232 of the thermal switch 262 is disposed
within the heat exchanger 230, and another portion 252 of the
thermal switch 262 is disposed within the heat exchanger 250.
[0034] The heat exchanger 250 can be used to accelerate the rate of
cooling down the heat exchanger 230 during start-up of the system
200. The design, size, and configuration of the heat exchanger 250
may depend on the amount of heat to be transferred, the space
available within the vessel 202, other suitable consideration, or
any combination thereof. After reading this specification, skilled
artisans will appreciate how to design, size, and configure the
heat exchanger 250 to meet their particular needs or desires.
[0035] The thermal switch 262 can be closed during cooldown from
warmer temperatures, and the thermal switch 262 can be opened
before reaching steady state. In one particular embodiment, the
thermal switch 262 can include terminals (e.g., heat transfer
surfaces) that are spaced apart from each other. The thermal switch
262 can be mechanical, gas-based, or other suitable design. For a
gas-based switch, when the thermal switch 262 is closed, a
significant amount of gas fills the space between the terminals and
allow a significant amount of thermal conduction between the
terminals. When the thermal switch 262 is open, the space between
the terminals is evacuated and substantially reduces the amount of
thermal conduction between the terminals (as compared to when the
thermal switch 262 is closed).
[0036] The system 200 further includes a reservoir 270 that is
coupled to the heat exchanger 230 via tubing 272. The reservoir 270
occupies some of the otherwise unused space within the vessel 202.
Alternatively, the vessel 202 can have the design modified to
accommodate the reservoir 270. In one embodiment, the reservoir has
a volume of at least 2 liters, and in another embodiment, at least
20 liters, at least 50 liters, at least 101 liters or even larger.
The system 200 also includes a fill/vent line 274 that can be used
to initially charge the reservoir 270 with a cryogen. In an
alternative embodiment, the reservoir 270 can be used in
conjunction with or replaced by a set of reservoirs. In another
alternative embodiment, the fill/vent line 274 can be replaced by a
separate fill line and a separate vent line. In still another
alternative embodiment, more than one fill/vent line, fill line,
vent line, or any combination thereof can be used.
[0037] After the system 200 is manufactured, it can be charged with
a cryogen (for the buffer fluid) by flowing the cryogen through the
fill/vent line 274 to the reservoir 270. In one embodiment, the
pressure within the reservoir 270 can be at least 0.5 atm, and in
other embodiment, the pressure can be at least 1.5 atm, or even
greater. At the same or different time, the same or different
cryogen (for the circulating fluid) can be used to charge the heat
transfer structure 220. The cryogen(s) may be added to the system
200 at the place where the system 200 is manufactured, at the final
installation (e.g., in a laboratory, a hospital examination room,
etc.), near the final installation (e.g., at the loading dock of
the facility having the laboratory, hospital examination room,
etc.), or at nearly any location after the manufacturing and before
final installation locations (e.g., at a helium or liquefied gas
storage facility).
[0038] Although not illustrated, other components, sub-systems, or
any combination thereof can be present in the system 200. For
example, a computer, a controller, or any combination thereof can
be used to control the system 200 when it is operating. The system
200 can include valves, pumps, sensors, switches, regulators, or
any combination thereof, which are not illustrated, to allow for
the proper operation of the system 220. In addition, tubing or
other connections can be made. For example, more than one piece of
tubing may couple the reservoir 270 to the heat exchanger 230. One
piece of tubing may be connected between the reservoir 270 and the
heat exchanger 230 to allow gaseous cryogen to flow from the
reservoir 270 to the heat exchanger 230, and another piece of
tubing (not illustrated) may be connected at a point near the
bottom of the heat exchanger 230 and to a point at a lower
elevation in the reservoir 270 to allow liquid cryogen to flow from
the heat exchanger 230 to the reservoir 270. In a particular
embodiment, the liquid levels of the liquid cryogen 238 within the
heat exchanger 230 and within the reservoir 270 are at
substantially the same elevation.
[0039] Alternative embodiments can be used. For example, the
reservoir 270 may be external to the vessel 202 and may be
connected or disconnected as needed or desired. The heat transfer
structure 220 can include more than one cooling loop. In a
particular embodiment, the heat transfer structure 220 can include
separate loops that can include the same cryogenic fluid or
different cryogenic fluids as compared to each other.
[0040] The heat exchanger 250 can be replaced by a plurality of
heat exchangers, the thermal switch 262 can be replaced by a
plurality of thermal switches, the coldhead 244 can be replaced by
a plurality of coldheads, or any combination thereof. Many
different configurations of coldhead-heat exchanger-thermal switch
combinations are possible. A plurality of coldheads may be
thermally connected to a single heat exchanger or a plurality of
heat exchangers. Alternatively, the coldhead 244 may be thermally
connected to a plurality of heat exchangers. In one embodiment, the
thermal coupling may be accomplished by a permanent thermal
connection or a thermal switch. The heat exchanger(s) and thermal
switch(es) may correspond to a one-to-one, one-to-many,
many-to-one, or many-to-many configuration, or a combination of
different configurations.
[0041] In still other embodiment, the concepts can be extended to
other cryogenic systems, such as high-temperature superconductors.
If high-temperature superconductors are present, the selection of
potential cryogens that can be used can increase. For example,
N.sub.2 can be used. Further, the concepts described herein are not
limited to only electronic applications. The system can be used
where an object, a chamber, etc. is to be taken to a cryogenic
temperature (e.g., testing physical properties when a material is
at a cryogenic temperature).
[0042] The operation of the system 200 can include three or more
portions. The operation as described below is directed to a system
that includes a superconductor, such as superconducting element
212. Before starting the system, substantially no current is
flowing within or through the superconducting element 212. The heat
transfer structure 220 has the circulating fluid disposed within.
The reservoir 270, the heat exchanger 230, or both have the buffer
fluid disposed therein. No liquid cryogen may be present or may
only be within the reservoir 270, the heat exchanger 230, or both
before starting the system.
[0043] During a first portion, initial cooling will begin, and the
vessel 202 will be evacuated, if evacuation has not yet occurred.
The vessel 202 can be evacuated to a very low pressure during a
single stage or more than one stage. If the vessel 202 included air
before starting, the vessel 202 can be evacuated by the roughing
pump and backfilled with the substantially dry inert gas for a
plurality of times to remove substantially all moisture within the
vessel 202 before activating the diffusion or cryogenic pump. The
vessel 202 can be finally taken to a pressure as previously
described.
[0044] With respect to the initial cooling, the coldhead 244 is
activated. If the heat exchanger 250 and thermal switch 262 are
present, the thermal switch 262 can be closed to accelerate cooling
of the system 200. Within the wetsock 242, gaseous cryogen 236 is
condensed by the coldhead 244 to form the liquid cryogen 238 that
can collect within the heat exchanger 230. Some of the liquid
cryogen 238 may flow into the reservoir 270. As the temperature
within the heat exchanger 230 decreases, the circulating fluid
disposed within the portion 234 of the heat transfer structure 220
becomes denser, and the denser circulating fluid flows to the
portion 214 that is thermally connected or coupled to the object to
be cooled, which is the superconducting element 212. Heat is
transferred from object being cooled (e.g., superconducting element
212) to the circulating fluid disposed within the heat transfer
structure 220. The recirculation fluid becomes less dense and flows
from the portion 214 to the portion 234 within the heat transfer
structure. If natural convection is used, the circulating fluid
will continue to flow until a temperature difference between the
portions 214 and 234 no longer is maintained. If forced convection
is used for the heat transfer structure 220, a pump or other
equipment can be activated, so that the circulating fluid
circulates within the heat transfer structure 220.
[0045] During a second portion, after the initial cooling, if
present, the thermal switch 262 is opened, so that heat exchangers
230 and 250 are no longer thermally connected to each other. During
the second portion, the heat exchanger 250 may not accelerate and
could inhibit further cooling within the heat exchanger 230. The
thermal switch 262 can be opened after the heat exchanger 230
reaches a predetermined temperature, or after a predetermined time,
using another suitable criterion, or any combination thereof. When
temperature is used, the thermal switch may be opened when the
temperature within the heat exchanger 250 is operating at a
temperature less than 90 K, less than 50 K, or less than 20 K. If
the system 200 does not include the thermal switch 262 or if the
thermal switch 262 was not closed during the first portion, the
second portion can be omitted.
[0046] During a third portion, the system 200 is further cooled so
that the object to be cooled (e.g., superconductor element 212) is
at or near a steady state temperature. The steady state temperature
depends on the selection of the cryogens used. In one embodiment,
the steady state temperature is about the boiling point of the
liquid cryogen 238 disposed within the heat exchanger 230. At
steady state, the circulating fluid can be in a single phase state,
and the buffer fluid can be in at least two phase states (liquid
and gas).
[0047] After the superconducting element 212 is at or near the
steady state temperature, the superconducting element 212 can be
activated. In one embodiment, the superconducting element 212
includes a superconducting coil, and the superconducting coil can
be taken to its typical operating state (e.g., at field). After the
superconducting coil is at its typical operating state, a patient
or other specimen can be placed into an analyzing region and be
analyzed.
[0048] The system 200 does not need to be recharged with a
significantly large volume of cryogen after a quench or other
undesired condition. Thus, the cost and difficulty related to
recharging a system with a cryogen, particularly a cryogen (e.g.,
He, H.sub.2, Ne) used for a low-temperature superconductor, can be
obviated altogether or at least delayed for a relatively long
period of time (e.g., years, after multiple quenches or other
undesired conditions would have occurred, etc.). Alternatively, if
lost cryogen would be replaced, additional gaseous cryogen can be
added near room temperature and cooled by the system to the
operating temperature, state, and pressure.
[0049] After the quench or other undesired condition no longer
exists, the system 200 can be taken to its steady state temperature
as previously described, and then the superconducting element 212
can be activated.
[0050] In addition to the ability to withstand faults or other
undesired conditions without having to recharge the system 200 with
a cryogen, the system 200 and its use has other advantages. The
initial cryogenic charging of the system 200 can take place at
nearly any time. The ability to charge the system 200 with a
cryogen at any state or temperature earlier in the process and not
having to recharge the system 200, particularly following a fault
or other undesired condition, at the final installation location
can obviate the need to have a costly or difficult apparatus or
method for getting a cryogen to the system 200 after it is
installed.
[0051] The ability to use a liquid cryogen allows the system 200 to
be cooled significantly faster as compared to conventional
conductive cooling. The system 200 can use natural or forced
convention to aid in cooling. When the optional heat exchanger 250
and thermal switch 262 are used, the cooling can be even
faster.
[0052] The coldhead 244 can include a bellows and seal (not
illustrated) coupled to the wetsock 242 or other portion of the
vessel 202. The bellows and seal can allow the coldhead 244 to be
moved to allow for easier servicing without compromising the vacuum
space in chamber 202.
[0053] The cryogen for the buffer fluid, circulating fluid, or both
can be added during operation, if needed or desired. The cryogen
can flow through the fill/vent line 274 at a relatively low
temperature or even near room temperature (e.g., 20-25 C) to the
reservoir 270. When operating, the newly added cryogen may be able
to have its temperature lowered to the operating state (e.g.,
boiling point of the cryogen) relatively quicker. Thus, the system
200 allows for more flexibility if additional cryogen is to be
added. Regarding the heat transfer structure 220, the cryogen can
be added to the return line (line where cryogen flows from the
superconducting element 212 to the heat exchanger 230) or to the
heat exchanger 230, such that the cryogen will be at or near the
boiling point of the material used for the buffer fluid before the
newly added cryogen reaches portion 214 of the heat transfer
structure 220.
[0054] Many different aspects and embodiments are possible. Some of
those aspects and embodiments are described below. After reading
this specification, skilled artisans will appreciate that those
aspects and embodiments are only illustrative and do not limit the
scope of the present invention.
[0055] In a first aspect, a system can include a coldhead, a first
heat exchanger operable to receive a first cryogenic fluid and
coupled to the coldhead, a chamber designed to be operated at a
cryogenic temperature. The system can also include a heat transfer
structure including a closed loop and further includes a first
portion disposed within the first heat exchanger and a second
portion disposed within the chamber. The closed loop can be
operable to contain a second cryogenic fluid that would be disposed
therein, and the first heat exchanger can be designed such that the
first cryogenic fluid and the second cryogenic fluid would be
spaced apart from each other.
[0056] In one embodiment of the first aspect, the system is
designed such that the first cryogenic fluid would have a different
phase state as compared to the second cryogenic fluid, the system
is designed such that the first cryogenic fluid would have a
different composition as compared to the second cryogenic fluid, or
any combination thereof. In another embodiment, the first heat
exchanger is operable to receive the first fluid cryogen as a
liquid cryogen from the coldhead. In still another embodiment, the
system further includes a wetsock coupled to the coldhead, wherein
the coldhead is disposed within the wetsock. In yet another
embodiment, the system further includes a reservoir coupled to the
first heat exchanger, wherein the reservoir has a capacity
sufficient to receive spillover from the first cryogenic fluid
during a typical operating state.
[0057] In a further embodiment of the first aspect, the system
further includes a second heat exchanger, wherein the second heat
exchanger is coupled to the coldhead and the first heat exchanger.
In a particular embodiment, the system further includes a thermal
switch including a first terminal and a second terminal, wherein
the first terminal is coupled to the first heat exchanger, and the
second terminal is coupled to the second heat exchanger.
[0058] In a second aspect, a superconducting system can include a
chamber, a superconducting element disposed within the chamber, a
first heat exchanger disposed within the chamber, and a heat
transfer structure disposed within the chamber and thermally
coupled to the superconducting element and the first heat
exchanger.
[0059] In one embodiment of the second aspect, the first heat
exchanger is operable to cool a first fluid with a second fluid,
wherein the first fluid includes gaseous He, and the second fluid
includes gaseous He and liquid He. In another embodiment, the first
heat exchanger lies at an elevation higher than a lowest point of
the heat transfer structure. In a particular embodiment, the heat
transfer structure is configured to allow a fluid to flow within
the heat transfer structure by natural convection when the
superconducting system would be operating at steady state.
[0060] In a further embodiment of the second aspect, the
superconducting system further includes a coldhead operable to
condense a first gaseous cryogen into a liquid cryogen, and a
wetsock coupled to the first heat exchanger, wherein the first heat
exchanger is operable to receive the liquid cryogen when the
coldhead would be operating. In a particular embodiment, the
superconducting system further includes a second heat exchanger, a
thermal switch connected to the first heat exchanger and the second
heat exchanger, and a reservoir connected to the first heat
exchanger.
[0061] In a third aspect, a method of using a system can include
providing a first cryogenic fluid, cooling a second cryogenic fluid
with the first cryogenic fluid, wherein the first cryogenic fluid
and the second cryogenic fluid remain spaced apart from each other,
flowing the second cryogenic fluid disposed within a heat transfer
structure that is coupled to a cooled object, and cooling the
cooled object to a cryogenic temperature using the second cryogenic
fluid.
[0062] In one embodiment of the third aspect, the method further
includes condensing a gaseous cryogen within the first cryogenic
fluid into a liquid cryogen. In a particular embodiment, cooling
the second cryogenic fluid includes contacting the heat transfer
structure with the liquid cryogen. In another embodiment, cooling
the cooled object is performed while a superconducting element is
disposed within the chamber.
[0063] In a further embodiment of the third aspect, the method
further includes operating the superconducting element, wherein
operating the superconductor element is performed while a first
pressure within the chamber is less than atmospheric pressure, and
flowing the second gaseous cryogen is performed at a second
pressure less than atmospheric pressure. In a particular
embodiment, the first pressure is at least three orders of
magnitude lower than the second pressure. In another particular
embodiment, the method further includes closing a thermal switch
between a first heat exchanger and a second heat exchanger. In a
more particular embodiment, the method further includes opening the
thermal switch after flowing the second gaseous cryogen before the
superconducting element is in its typical operating state.
[0064] In another embodiment of the third aspect, the method
further includes flowing the first cryogenic fluid from a reservoir
to a heat exchanger. In yet another embodiment, the method further
includes flowing a liquid cryogen from the heat exchanger to the
reservoir.
[0065] Note that not all of the activities described above in the
general description or the examples are required, that a portion of
a specific activity may not be required, and that one or more
further activities may be performed in addition to those described.
Still further, the order in which activities are listed is not
necessarily the order in which they are performed.
[0066] The illustrations of the embodiments described herein are
intended to provide a general understanding of the structure of the
various embodiments. The illustrations are not intended to serve as
a complete description of all of the elements and features of
apparatus and systems that utilize the structures or methods
described herein. Many other embodiments may be apparent to those
of skill in the art upon reviewing the disclosure. Other
embodiments may be utilized and derived from the disclosure, such
that a structural substitution, logical substitution, or another
change may be made without departing from the scope of the
disclosure. Additionally, the illustrations are merely
representational and may not be drawn to scale. Certain proportions
within the illustrations may be exaggerated, while other
proportions may be minimized. Accordingly, the disclosure and the
figures are to be regarded as illustrative rather than
restrictive.
[0067] One or more embodiments of the disclosure may be referred to
herein, individually or collectively, by the term "invention"
merely for convenience and without intending to voluntarily limit
the scope of this application to any particular invention or
inventive concept. Moreover, although specific embodiments have
been illustrated and described herein, it should be appreciated
that any subsequent arrangement designed to achieve the same or
similar purpose may be substituted for the specific embodiments
shown. This disclosure is intended to cover any and all subsequent
adaptations or variations of various embodiments. Combinations of
the above embodiments, and other embodiments not specifically
described herein, will be apparent to those of skill in the art
upon reviewing the description.
[0068] The Abstract of the Disclosure is provided to comply with 37
C.F.R. .sctn.1.72(b) and is submitted with the understanding that
it will not be used to interpret or limit the scope or meaning of
the claims. In addition, in the foregoing Detailed Description,
various features may be grouped together or described in a single
embodiment for the purpose of streamlining the disclosure. This
disclosure is not to be interpreted as reflecting an intention that
the claimed subject matter requires more features than are
expressly recited in each claim. Rather, as the following claims
reflect, inventive subject matter may be directed to less than all
of the features of any of the disclosed embodiments. Thus, the
following claims are incorporated into the Detailed Description,
with each claim standing on its own as defining separately claimed
subject matter.
[0069] Benefits, other advantages, and solutions to problems have
been described above with regard to specific embodiments. However,
the benefits, advantages, solutions to problems, and any feature(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature of any or all the claims.
[0070] It is to be appreciated that certain features are, for
clarity, described herein in the context of separate embodiments,
may also be provided in combination in a single embodiment.
Conversely, various features that are, for brevity, described in
the context of a single embodiment, may also be provided separately
or in any subcombination. Further, reference to values stated in
ranges includes each and every value within that range.
[0071] The above-disclosed subject matter is to be considered
illustrative, and not restrictive, and the appended claims are
intended to cover any and all such modifications, enhancements, and
other embodiments that fall within the scope of the present
invention. Thus, to the maximum extent allowed by law, the scope of
the present invention is to be determined by the broadest
permissible interpretation of the following claims and their
equivalents, and shall not be restricted or limited by the
foregoing detailed description.
* * * * *