Closed-Cycle Cryogenic Refrigeration System

Abstract

A multi-stage closed-cycle cryogenic refrigeration system is disclosed. The system includes an adsorption refrigerator having a multi-chambered pump unit that can be flexibly configured in the context of the cryogenic refrigeration system resulting in a more efficient design that has a smaller overall size than prior systems and other advantages.

Claims

1. A multi-stage cryogenic refrigeration system, comprising: an outer housing; a first cooling stage comprising a cryostat within said outer housing; and a second cooling stage comprising a sorption refrigerator, said sorption refrigerator comprising: an evaporator; a condenser; a sorption pump assembly comprising (a) a plurality of sorption pump chambers in fluid communication with one another, each said sorption pump chamber having an open end and a closed end defined by at least one wall of a housing, said housing surrounding an interior volume of said sorption pump chamber, said interior volume comprising an adsorbing material, and (b) a shared structural cap directly contacting said open end of each said sorption pump chamber to enclose each said sorption pump chamber, wherein said shared structural cap defines a network of fluid channels that directly interconnects a first and a second of said plurality of sorption pump chambers to one another and that indirectly interconnects a third sorption pump chamber to said first and said second sorption pump chambers, said network of fluid passages extending to said open end of each said sorption pump chamber; and an insulated fluid conduit that extends from said evaporator to one of said fluid channels defined in said shared structural cap, said fluid conduit passing through said condenser.

2. The system of claim 1, wherein at least some of said plurality of sorption pump chambers are connected in fluid communication with one another in a series configuration so that a discharge of a first sorption pump chamber is directed to an inlet of a second sorption pump chamber in said pump assembly, with a terminal one of said sorption pump chambers discharging to said condenser of said sorption refrigerator stage.

4. The system of claim 1, said shared structural cap comprising a machined copper cap defining said fluid channels and having a plurality of mechanical coupling points to mechanically secure said shared structural cap to said open end of each said sorption pump chamber.

5. The system of claim 4, wherein shared structural cap comprises at least two sections that are mechanically secured to one another.

6. The system of claim 1, said plurality of sorption pump chambers being configured radially with respect to an axis that extends through said insulated fluid conduit.

7. The system of claim 1, wherein said shared structural cap, said evaporator, said condenser, and said cryostat are aligned along axis that extends through said insulated fluid conduit.

8. The system of claim 1, said sorption pump assembly and said shared structural cap being mechanically configured to substantially surround and accept a cold head of said cryostat centrally disposed within said housing of said system.

9. The system of claim 8, said cold head of said cryostat being axially disposed within said sorption refrigerator's sorption pump assembly.

10. The system of claim 1, wherein said shared structural cap operates as said condenser.

11. The system of claim 1, wherein said shared structural cap is thermally conductive.

12. The system of claim 11, wherein said shared structural cap is formed of a metal.

13. The system of claim 12, wherein said shared structural cap comprises copper, stainless steel, aluminum, or a combination of two or more of the foregoing.

14. The system of claim 1, further comprising thermal heating elements coupled to or mounted on the shared structural cap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] For a fuller understanding of the nature and advantages of the present concepts, reference is made to the following detailed description of preferred embodiments and in connection with the accompanying drawings, in which:

[0031] FIG. 1 illustrates an adsorption refrigerator according to the prior art;

[0032] FIG. 2 illustrates a multi-stage cryogenic refrigeration system according to the prior art;

[0033] FIGS. 3A, 3B, 3C, 4, 5, and 6 illustrate exemplary cryogenic refrigeration systems according to embodiments hereof, including a multi-chamber sorption pump assembly.

DETAILED DESCRIPTION

[0034] As mentioned above, present adsorption refrigeration systems lack structural, design and packaging features that would be beneficial in many applications. Furthermore, their designs are bulky, expensive to manufacture and cause the system to cool slower than desired. The present embodiments, which are provided by way of illustration of preferred embodiments and concepts address many problems of the prior art systems.

[0035] FIG. 3A illustrates a sorption fridge system 30. The system has a sorption pump assembly section 300 comprising a plurality of sorption pump chambers 310. The sorption pump chambers 310 have respective housing walls 312 and contain a sorbent material 314, for example charcoal. The housing walls 312 define and enclose an internal volume of each sorptive pump chamber 310 that includes a sorbtive material 314. The housing walls 312 further define an open end 316 and a closed end 318 of each sorption pump chamber 310. As illustrated, the open end 316 and the closed end 318 are on opposing sides of sorption pump chamber 310. The sorption pump chambers 310 can be formed of a thermally conductive material, such as a metal (e.g., copper, stainless steel, aluminum, a combination of two or more of the foregoing) or other thermally-conductive material.

[0036] The pump chambers 310 are closed off at one end by a solid structural cap 302 shared among the plurality of chambers 310. The shared solid structural cap 302 can be in direct physical contact with the housing walls 312 that define the open end 316 of each sorption pump chamber 310. Thus, the shared solid structural cap 302, together with the housing walls 312, define and enclose the internal volume of each sorption pump chamber 310.

[0037] The shared structural cap 302 is typically machined from a single piece or block of solid metal, or from two or more pieces or blocks of solid metal. A network of fluid communication channels 304 with fluid couplings 306 leading to two or more of the pump chambers 310 are defined in the shared structural cap 302. Using two or more pieces or blocks of solid metal can be useful to machine the fluid communication channels 304 and fluid couplings 306 in the shared structural cap 302. The two or more pieces or blocks of solid metal can then fused (e.g., by welding or other methods) or adhered back together to form the shared structural cap 304, for example while maintaining a fluid seal for the fluid communication channels 304 and fluid couplings 306 defined therein. In some embodiments, the shared structural cap 302 comprises copper, stainless steel, aluminum, or a combination of two or more of the foregoing. In one or more embodiments, the shared structural cap is thermally conductive.

[0038] In some embodiments, the network of fluid communication channels 304 defines distinct fluid pathways between two or more of the sorption pump chambers 310. For example, a first fluid pathway can fluidly connect a first sorption pump chamber 310 with a second sorption pump chamber 310. The first fluid pathway can retain the fluid contained therein such that it does not (or cannot) reach a third sorption pump chamber 310 that is outside of the first fluid pathway. An example of such a configuration is illustrated in FIG. 3B, which illustrates three separate fluid communication channels 304A-C connected in series with one another. The first fluid communication channel 304A connects the first and second sorption pump chambers 310A, 310B. The first fluid communication channel 304A does not allow fluid to pass directly into sorption pump chambers 310C or 310D, or into tube 320. The second fluid communication channel 304B connects the second and third sorption pump chambers 310B, 310C. The second fluid communication channel 304A does not allow fluid to pass directly into sorption pump chambers 310A or 310D, or into tube 320. The third fluid communication channel 304C connects the third sorption pump chamber 310C with tube 320 and sorption pump chamber 310D. Thus, in order for fluid located in the first sorption pump chamber 310A to flow into tube 320, the fluid must pass though sorption pump chambers 310B and 310C and fluid communication channels 304A-C. Likewise, in order for fluid located in the second sorption pump chamber 310B to flow into tube 320, the fluid must pass though sorption pump chambers 310C and fluid communication channels 304B,C. It is noted that other connections and networks may be provided in shared structural cap 302. For example, one or more of the fluid communication channel 304A may be interconnected, for example, with additional fluid communication channels that pass into or out the cross-sectional plane illustrated in FIG. 3B (and/or FIG. 3A and/or 3C).

[0039] In one embodiment, the separate sorption pump chambers 310 of the sorption pump assembly 300 are generally cylindrical in shape, having a solid casing or housing 312 surrounding the interior volume thereof. The housing of the sorption pump chamber 310, with the portion of shared structural cap 302 covering its remaining end therefore substantially enclose and define the volume of the interior of the sorption pump chamber 310. An opening 311 allows fluid to pass into and out of the chamber 310 and into and out of the sorbtive material 314 as necessary during the cycle of the system 30.

[0040] The fluid communication channel 304 is coupled to a tube 320 of low thermal conductivity (e.g., thin-walled stainless steel), which allows the fluid to pass through the cooled condenser 330 and into the evaporator 340. Evaporator 340 and condenser 330 have designs similar to those described earlier. Condensed liquid fluid (e.g., liquid He) can be found in the condenser 340 volume. The system 30 may be thermally coupled to a cold head 350 or other stages of the cooling system.

[0041] In some embodiments, the sorption pump chambers 310 can extend radially from an axis 375 that passes through tube 320. In some embodiments, axis 375 is an axis of symmetry with respect to the number and/or location of sorption pump chambers 310. For example, there can be an equal number of sorption pump chambers 310 disposed on either side of axis 375. Similarly, the location of each sorption pump chamber 310 on one side of axis 375 can be the same as the location of each sorption pump chamber 310 on another side (e.g., an opposing side) of axis 375. The location of each sorption pump chamber 310 can be disposed along an axis or radius that is orthogonal to axis 375. For example, if axis 375 is in the z direction in a Cartesian coordinate system, the location of each sorption pump chamber 310 can in the x-y plane, such as along the x direction or along the y direction.

[0042] Thermal (e.g., electrical) heating elements 308 may be coupled to and/or mounted on the pump portion 300 of the system 30. In operation, the pump assembly 300 acts as a heat pump bringing He-4 to about 40K, which causes it to expel the helium. If condenser 330 is at 4.2K or below, helium gas starts condensing into liquid helium in evaporator 340. Once sufficient liquid helium has condensed, the heat pump is secured or switched off and pump 300 is cooled by closing a thermal switch between itself and cold head 350. The pump 300 will then begin absorbing helium. The unit 30 can achieve temperatures at the base 342 of evaporator 340 around or below a degree Kelvin in some embodiments, and in an embodiment, a temperature around 0.6K, depending on load and other conditions. An orifice and film killer 344 may be employed to prevent leakage of superfluid liquid helium from evaporator 340.

[0043] In an embodiment, the fluid used in the cooling cycle of cryogenic sorption refrigeration system 30 comprises helium gas (e.g., He-4). In an aspect, the system 30 is a closed cycle system that is sealed from the outside so as to not lose or contaminate the fluid. In another aspect, the system 30 can be coupled to other units or stages of a cryocooler apparatus.

[0044] As can be seen, the foregoing device can be manufactured in a simple way that is also flexible in its design. The modular multi-chamber pump assembly 300 allows for inclusion of other components within the overall structure of the refrigerator design to optimize their performance and reduce the size of the system.

[0045] Additionally, those skilled in the art will appreciate that the present design, having smaller individual pump chambers 310 can be made using thinner wall material 312. The compact design and thinner wall thicknesses mean that the system can be cooled more quickly than traditional designs employing a single large sorption pump with the necessary thicker and more massive housing walls. It is noted that the evaporator 330, condenser 340, and shared structural cap 302 can be disposed along or adjacent to axis 375 (e.g., as illustrated in FIGS. 3, 4, and 6), which can provide a more compact design of cryogenic sorption refrigeration system 30. In addition or in the alternative, axis 375 can be an axis of symmetry with respect to the evaporator 330, condenser 340, and shared structural cap 302.

[0046] FIG. 3C illustrates a sorption fridge system 30. Sorption fridge system 30 is the same or similar to sorption fridge system 30 with the exception that the heating elements 308 are coupled to and/or mounted on the shared structural cap 302 of system 30. The heating elements 308 are in thermal communication with the fluid communication channels 304 through the thermally-conductive shared structural cap 302. The heating elements 308 can also be in thermal communication with the sorption pump chambers 310, through the thermally-conductive shared structural cap 302 and/or through thermal radiation emitted from the heating elements 308. In some embodiments, the heating elements 308 can be disposed along or proximal to at least a portion of a wall (e.g., as illustrated in FIG. 3C) of at least one of the sorption pump chambers 310. Likewise, the heating elements 308 can disposed along or proximal to at least a portion of a surface of the shared structural cap 302 (e.g., as illustrated in FIG. 3C). In other embodiments, the heating elements 308 are disposed along or proximal to at least a portion of a surface of the shared structural cap 302 but they are not disposed along or proximal to at least a portion of a wall of at least one of the sorption pump chambers 310.

[0047] FIG. 4 illustrates a croyogenic cooling system 40. The system includes a vacuum chamber 416 capable of holding a vacuum therein. In an example, the vacuum chamber, which also acts as an outer housing for the system 40, has a diameter of about 6 inches. The vacuum chamber housing 416 is enclosed with a mounting flange 414. Atop the flange 414 is mounted a cold head motor assembly 415, to which are coupled a power connector and a pair of helium flex lines connected to a helium compressor (not shown).

[0048] A first stage cooler 412, for example a 25K to 40K cooler, is coupled by tube 411 to a second stage cooler 410, which is sub 4K in an example.

[0049] The system 40 includes an adsorption refrigeration apparatus like that described above with respect to the previous figure. This portion of the system includes a multi-chamber sorption pump assembly comprising a plurality of sorption pump chambers 400, 401 and 402. The sorption pump chambers 400-402 are enclosed at one end by a common shared support cap 403, which includes fluid passageways 404 permitting fluid flow from one chamber to another. The common shared support cap 403 can be the same or substantially the same as shared structural cap 302, described above. Likewise, sorption pump chambers 400-402 can be the same or substantially the same as sorption pump chambers 310, described above

[0050] Additionally, the system includes a condenser 406 thermally coupled to the second stage cooler 410. It also has an evaporator 407 containing liquid helium fluid 408 on an evaporator base 409. A tube 405 of low thermal conductivity (e.g., an insulated tube) extends along an axis 475 from a first passageway 404 defined in common shared support cap 403 through condenser 406 to evaporator 407. The evaporator 407, condenser 406, common shared support cap 403, and first stage cooler 412 are disposed along or proximal to axis 475.

[0051] An experiment or specimen is usually mounted to or coupled to the evaporator base 409 and reaches the lowest cryogenic temperatures in the system.

[0052] FIG. 5 illustrates another embodiment of a cryogenic cooling system 50. The system is similar to the one previously described, having multiple closed-cycle cooling stages and associated connections 510 through 513 in a vacuum housing 516 and a motor assembly 515 coupled to a flange 514. A thermal coupling 509 thermally couples a cold head (e.g., second stage cryocooler having a temperature, e.g., 4K) to condenser 505.

[0053] A sorption pump assembly including a plurality of sorption pump chambers 500, 501, 502 are arranged around the thermal coupling shaft 509. The arrangement can place the pump chambers 501-502 so that they axially surround other components of the system. For example, the pump chambers 500-502 can be disposed about thermal coupling shaft 509, or surrounding other components, e.g., connector tube 504 that extends, along axis 575, down to condenser 505 and evaporator 506. The end result is an efficient and rapid cooling of a sample proximal to the base 508 of evaporator 506 containing fluid 507. The cooling can achieve temperatures below 1K in an embodiment. The evaporator 506, condenser 505, and cold head are disposed along or proximal to axis 575.

[0054] FIG. 6 illustrates yet another embodiment of a cryogenic cooling system 60. The system again is surrounded by a vacuum housing 620 supporting a flange 618 and motor 619, leading down through one or more cooling stages 617 through 614. A second stage 614 may be directly or substantially directly to a shared manifold 608 containing fluid passageways 609 allowing fluid communication between at least two sorption pump chambers 600-603 in a multi-chamber sorption pump assembly. Thermally insulating connector tubes 604-607 connect the individual sorption pump chambers 600-603 to respective fluid coupling connections or ports in shared manifold 608. The shared manifold 608 acts as a condenser and is therefore in thermal communication with cooling stage 614 and the fluid passageways 609 are in fluid communication with evaporator 611. Again, the fluid 612 cycles in the refrigeration system to achieve a cold cryogenic temperature below 1K in some embodiments. The shared manifold 608 can be a solid material with fluid passageways 609 defined therein. For example, shared manifold 608 can be the same or substantially the same as common shared support cap 403 and/or shared structural cap 302.

[0055] Those of skill in the art will appreciate the flexibility of this design, its compactness compared to prior art single pump systems and the advantages of the thin-walled and rapidly cooled components in the present system.

[0056] The present invention should not be considered limited to the particular embodiments described above. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable, will be readily apparent to those skilled in the art to which the present invention is directed upon review of the present disclosure.