Title:
SYSTEM INCLUDING A HEAT EXCHANGER WITH DIFFERENT CRYOGENIC FLUIDS THEREIN AND METHOD OF USING THE SAME
Kind Code:
A1


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, US)
Menteur, Philippe (Niskayuna, NY, US)
Reis, Chandra T. (Altamont, NY, US)
Application Number:
11/680943
Publication Date:
09/04/2008
Filing Date:
03/01/2007
Assignee:
PHILIPS MEDICAL SYSTEMS MR, INC. (Latham, NY, US)
Primary Class:
Other Classes:
62/62
International Classes:
F25B19/00
View Patent Images:
Related US Applications:



Primary Examiner:
BALDRIDGE, LUKAS M
Attorney, Agent or Firm:
LARSON NEWMAN, LLP (AUSTIN, TX, US)
Claims:
What is claimed is:

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

1. Field of the Disclosure

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.

2. Description of the Related Art

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.

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.

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.

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.

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

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.

FIG. 1 includes a schematic drawing of a magnetic resonance imaging system. (Prior art).

FIG. 2 includes a schematic diagram of a superconducting system in accordance with an embodiment described in more detail below.

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

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.

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.

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.

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).

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.

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.

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.

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.

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 (H2, N2, CH4, etc.).

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.

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 10−3 Torr, and in another embodiment, less than 10−5 Torr, 10−8 Torr, or even lower.

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 H2 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.

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.

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.

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.

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.”

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.

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.

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.

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.

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.

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.

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).

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.

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).

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.

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.

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.

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, N2 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).

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.

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.

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.

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.

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).

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.

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, H2, 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §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.

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.

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.

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.