HEAT EXCHANGER ASSEMBLY

Abstract

A heat exchanger assembly for transferring heat across a wall of a housing is disclosed. The assembly comprises an outer heat exchanger having an outer ring disposed outside the housing and having an interior surface in contact with an exterior surface of the wall; an inner support disposed inside the housing and having an exterior surface; and a plurality of inner heat fins connecting the exterior surface of the inner support to an interior surface of the wall of the housing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 schematically shows a Stirling cryocooler in an embodiment of the invention;

FIG. 2 shows a cross-sectional view of the heat exchanger assembly of the Stirling cryocooler shown in FIG. 1;

FIG. 3 shows a portion of an outer heat fins in another embodiment of the invention;

FIG. 4 shows a portion of an outer heat fins in an alternative embodiment of the invention;

FIG. 5 is a perspective view of an internal heat exchanger in an alternative embodiment of the invention;

FIG. 6 is a cross-sectional view of the internal heat exchanger shown in FIG. 5;

FIG. 7( a) is a schematic cross-sectional view of a portion of the Stirling cryocooler in an embodiment of the invention, showing the outer ring and inner heat fins sandwiching a portion of the house wall; and

FIG. 7( b) is a schematic cross-sectional view of a portion of the Stirling cryocooler in an embodiment of the invention, showing a portion of the outer ring and a portion of the inner heat fins sandwiching a portion of the house wall

FIG. 8 shows a schematic cross-sectional view of a further alternative embodiment of the invention.

FIG. 9 shows a schematic cross-sectional view of another alternative embodiment of the invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the appended claims. In particular, while the embodiments illustrated herein are described in the context of Stirling cycle machines such as Stirling cryocoolers, other embodiments not limited to Stirling cycle machines are possible.

Referring to FIG. 1, in an embodiment of the invention, a heat exchanger assembly is employed in a Stirling cycle machine, which is configured as a cryocooler 100 includes sealed columnar housing 120, with sections of various diameters disposed along a longitudinal axis 150. The gas space inside the housing 120 is generally divided into a working space 124 and a bounce space 126 by seals. The housing 120 includes at one end a cold finger 110, which houses a displacer assembly 114. The cold finger 110 also includes a cold heat exchanger, or heat acceptor unit, 112, which serves to transfer heat from the exterior of the housing 120 to a working gas confined in the working space 124. The cryocooler housing 120 also encloses in its interior volume a linear motor 170 and a piston 180 driven by the motor for compressing and expanding a portion of the working gas in a compression region 160. The cryocooler 100 further includes a vacuum flange 130, which is also used for positioning the heat acceptor unit 112 in a vacuum chamber. In addition, a warm heat exchanger assembly 200 is positioned to be in thermal contact with the compression region 160 for dissipating heat from the working gas to the exterior of the housing 120.

The general structures and operation of Stirling cycle machines, including those of Stirling cryocoolers, are well known in the art. For example, a Stirling cryocooler with a housing section having different diameters drawn from a single piece of stainless steel is disclosed in the U.S. patent application Ser. No. 10/729,719, filed Dec. 5, 2003, and issued on Nov. 21, 2006, as U.S. Pat. No. 7,137,259. The aforementioned U.S. Pat. No. 7,137,259 is incorporated herein by reference.

Referring to FIG. 2, the warm heat exchanger assembly 200 in this illustrative embodiment includes outer heat fins 220 outside the housing wall 122 of the housing 120, an outer ring 210, which is seated against an exterior surface of the housing wall 122 and supports the outer heat fins 220. The assembly further includes inner heat fins 230 inside the housing wall 122 of the housing 120. The assembly 200 further includes an inner support member 240, which is disposed inside, and in contact with, the inner heat fins 230. At least a portion of the outer ring 210 and at least a portion of the inner heat fins 230 sandwich at least a portion of the housing wall. That is, at least a portion of the outer ring 210 and at least a portion of the inner heat fins 230 occupy the same axial position range (I, in the examples shown in FIGS. 7(a) and 7(b)) along the longitudinal axis 150.

In the illustrative embodiment of the invention, the inner support member 240 is integral with the inner heat fins 230. That is, both the inner support member 240 and the inner heat fins 230 are fabricated out of a single starting piece. For example, the fins can be formed on the inner support member 240 by removing material from the starting piece by machining, water cutting, laser cutting, chemical etching and other suitable techniques. The integral structure of the inner heat fins 230 and the inner support member 240 can also be formed by mold casting, powder metallurgy and any other suitable techniques for making metal parts. Alternatively, inner heat fins can be fabricated separately from the inner support member 240 and attached to the inner support member 240 by any suitable technique, including welding, brazing and soldering.

The inner heat fins 230 can be affixed to the housing wall 122 by a variety of suitable methods, including press-fitting, shrink fitting and bonding with a conductive adhesive. In this illustrative embodiment, the inner heat fins 230 are affixed to the housing wall 122 by shrink-fitting. The requisite rigidity to withstand the shrink-fitting process is supplied by the combined structure of the inner heat fins 230 and the inner support member 240. The inner support member 240 and inner heat fins 230 in this case are made of aluminum, which has a higher thermal expansion coefficient than the housing wall 122, which is made of a stainless steel. Other suitable material combinations can also be used. For example, copper, its alloys or other materials that have higher thermal conductivities can be used. In cases, such as for copper, where the thermal expansion coefficient of the inner fins is similar to that of the housing wall such that shrink-fitting may be unsuitable, other methods such as press-fitting and bonding can be used to affix the inner heat fins 230 to the housing wall 122. In attaching the inner heat fins 230 to the housing wall 122 by shrink-fitting, the assembly of the heat fins 230 and inner support 240 are placed in a medium, for example liquid nitrogen, having a lower temperature than the housing wall 122 before positioned inside the housing wall 122. Upon being warmed up, the assembly of the heat fins 230 and inner support 240 become shrink-fitted to the housing wall 122. Alternatively, the housing wall 122 can be heated before being slid over the inner heat fins 230 and then allowed to cool. Shrink fitting allows the inner heat fins 230 to be attached to the housing wall 122 without the need for other joining techniques such as welding, brazing and soldering, which tend to introduce non-uniform deformation into the components being joined.

For certain applications, such as in a Stirling cycle machine having a displacer, an interior surface 250 can be formed in the inner support 240, as shown in FIG. 2, to accommodate a sliding member (erg., the displacer) moving through the aperture defined by the interior surface 250. Moreover, the interior surface 250 in an illustrative embodiment is ground or honed to be concentric with the housing 120 and/or other components, such as the compressor bore, of the Stirling cycle machine and sufficiently smooth to act as a seal and/or a bearing surface for the sliding member. For example, in an embodiment for a Stirling cryocooler, the interior surface 250 is sized to accommodate a displacer and has the requisite tolerance and smoothness to form a displacer seal and for realizing a displacer gas bearing, which has gas ports for discharging pressurized gas in between the displacer surface and the interior surface 250 of the inner support 240.

Referring again to FIG. 2, the outer ring 210 is disposed between, and in contact with, the housing wall 122 and the outer heat fins 220. In this illustrative embodiment of the invention, the outer ring 210 is a cylindrical annular ring circumferentially surrounding the housing wall 122. The outer ring 210 in this illustrative embodiment is made of a material having a higher thermal conductivity, than the thermal conductivity of material for the housing wall 122. For example, the housing wall is typically made of a stainless steel. In such a case, copper, aluminum or their respective alloys or other materials that have higher thermal conductivities can be used for the outer ring.

As noted above, low heat flow resistance in circumferential directions is important for the proper functioning of a heat exchanger, and the prior art addresses this issue by using both an external and internal rings. In this respect, the illustrative embodiments of the invention employ a single outer ring 210 to achieve the same functionality as two rings used in the prior art, thereby reducing the components needed and simplifying the manufacturing process.

The outer ring 210 can be affixed to the housing wall 122 by a variety of methods. For example, an adhesive with good thermal conduction properties, such as a thermo-conductive adhesive, which has metal particles embedded in the resin, can be used to bond the outer ring 210 to the housing wall 122. The outer ring 210 can also be press-fitted, shrink-fitted, or otherwise connected, to the housing wall 122 in a similar way as discussed above for shrink-fitting the inner heat fins inside the housing. For example, an aluminum outer ring 210 can be heated prior to being slipped over a portion of a stainless steel housing 120 and then cooled to shrink-fit on the housing 120. In another embodiment of the invention, a sealant is applied between the outer ring 210 and the housing wall 122 prior to shrink-fitting to seal any gap between the outer ring 210 and the housing wall 122. This is useful in applications where the outer ring is connected to, or used as part of, a flange for a gas-tight chamber (e.g., a vacuum flange in a Stirling cryocooler). A variety of sealants well known in the art can be used to suit particular applications.

In addition to conducting heat away from housing wall 122, the outer ring 210 also serves to enhance the structural integrity of the housing wall 122, which is typically very thin, as mentioned above. In Stirling cooler applications, the interior of housing 120 is typically pressurized. It is therefore particularly desirable and typically more effective to reinforce the housing wall 122 from outside in Stirling cooler applications.

The outer heat fins 220 can be affixed to the outer ring 210 by a variety of methods, including welding, brazing and bonding with an adhesive. Instead of affixing the outer heat fins 220 to the outer ring 210, the outer heat fins 220 can be made from the same starting piece of material as the outer ring 210 in similar ways as described above for the inner heat fins 230.

As alternatives to the structures described above, the heat fins 220, 230 can be constructed from one or more pleated sheets of thin metal, such as copper. They can be shaped in a variety of ways as need to suit the particular design. For example, with further reference to FIG. 3, the outer heat fins 220 comprise fins 322 constructed from one or more pleated sheets of thin copper, but can be constructed from other thermal conductors and in other forms suitable for the specific application. For example, as show in FIG. 4, the heat fins 422 of the outer heat fins 420 can be constructed from individual sheets of copper.

In a further illustrative embodiment of the invention, as shown in FIGS. 5 and 6, an internal heat exchanger 500 includes inner heat fins 530 and inner support member 540 similar to the internal heat exchangers in the illustrative embodiments discussed above. In addition, an annular ring portion 590 is connected to the inner heat fins 530 and inner support member 540. The annular ring portion 590 in this embodiment is radially coextensive with the heat fins 530 on the outside and defines a chamber 592 on the inside and in fluid communication with the channels 532 between the inner heat fins 530. The annular ring portion 590 and the housing wall 122 form a seal between the working space and bounce space when the internal heat exchanger 500 is installed in the housing 120, with the longitudinal axis 550 of the heat exchanger 500 aligned with the longitudinal axis 150 of the housing 120.

In this example, the heat exchanger 500, the annular ring portion 590, the inner heat fins 530 and the inner support member 540 are an integral piece, made by cutting channels 532 (i.e., spaces between the inner heat fins 530) in a cylindrical stock partially through the length of the stock. Non-integral configuration of the annular ring portion 590, the inner heat fins 530 and the inner support member 540 can also be used.

As in certain other embodiments described above, the internal heat exchanger 500 can be affixed to the housing 120 by press-fitting, shrink-fitting, or other bonding methods, with both the inner fins 530 and the annular ring portion 590 in contact with the housing wall 122. In the example where the annular ring portion 590, the inner heat fins 530 and the inner support member 540 are an integral piece, the entire heat exchanger 500 can be affixed to the housing 120 as a whole. In cases where non-integral configurations of the annular ring portion 590, the inner heat fins 530 and the inner support member 540 are used, the annular ring portion 590 and the inner heat fins 530 can be affixed to the housing 120 by press-fitting, shrink-fitting, or other bonding methods. The inner support member 540 can further be press-fitted, shrink-fitted or otherwise bonded to the interior of the inner heat fins 530. Further, as with the outer ring 210, a sealant can be applied between the annular ring portion 590 and the housing wall 122 to eliminate any gap between them to further ensure a gas-tight seal.

In another embodiment of the invention, the inner support member 540 is omitted, with the inner heat fins 530 entirely supported by the annular ring portion 590.

A further alternative embodiment of the invention is schematically shown in FIG. 8. In this embodiment, the heat exchanger assembly 800 includes is similar to that (200) shown in FIG. 2 but without the external heat fins. The exchanger assembly 800 in this illustrative embodiment includes an outer ring 810, which is seated against an exterior surface of the housing wall 122. The assembly 800 further includes inner heat fins 830 inside the housing wall 122. The assembly 800 further includes an inner support member 840, which is disposed inside, and in contact with, the inner heat fins 830.

Optionally, the embodiment shown in FIG. 8 can further include additional heat transfer structures, or provisions for attaching additional heat-transfer structures, for transferring heat to or from the outer ring 810. Symbolically indicated at label 850 in FIG. 8, these structures and provisions can include tubings mounted on the surface of the outer ring 810, or channels formed within the outer ring 810, for carrying heat transfer fluids, such as water. The structures and provisions can also include heat sinks such as a volume of material with a large thermal mass. Further examples include recesses, protuberances or other structures on the outer ring 810 for affixing heat-transfer structures.

In another illustrative embodiment of the invention, schematically shown in FIG. 9, a heat exchanger assembly 900 includes inner heat fins 930 inside the housing wall 122, and an inner support member 940, which is disposed inside, and in contact with, the inner heat fins 930. Unlike certain other illustrative embodiments, the heat exchanger assembly 900 in this case is without an ring-shaped outer heat exchanger portion. Instead, the heat exchanger assembly 900 includes other outer heat transfer structures, or provisions for attaching outer heat-transfer structures, for transferring heat to or from the housing wall 122. Symbolically indicated at label 950 in FIG. 9, these structures and provisions can include tubings mounted on the outer surface of the housing wall 122. The structures and provisions can also include heat sinks such as a volume of material with a large thermal mass. The volume material can further include channels 952 for carrying a heat transfer fluid, such as water, other fluids or gasses. Further examples include recesses, protuberances or other structures on the housing wall 122 for affixing heat-transfer structures.

Thus, the illustrative embodiments of the invention offer several advantages over prior art devices and methods. Among the advantages are the ease of manufacturing of inner heat fins that project outwardly from the inner support, the compatibility with shrink-fitting process for contacting the inner heat fins with the housing, and the compatibility with precision alignment of an interior surface of the inner support for forming gas bearing or seal, or both, with a sliding member movably disposed through the interior surface.

All patents and publication referred to above are incorporated herein by reference. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

1. A heat exchanger assembly for transferring heat across a wall of a housing, the assembly comprising: an outer heat exchanger comprising an outer ring disposed outside the housing and having an interior surface in contact with an exterior surface of the wall;an inner support disposed inside the housing and having an exterior surface; anda plurality of inner heat fins connecting the exterior surface of the inner support to an interior surface of the wall of the housing, at least a portion of the outer ring and at least a portion of the inner heat fins sandwiching at least a portion of the housing wall.

2. The heat exchanger assembly as set forth in claim 1, wherein the inner heat fins are integral with the inner support.

3. The heat exchanger assembly as set forth in claim 2, wherein the outer ring is shrink-fitted on the housing and the inner support and inner heat fins are shrink-fitted in the housing.

4. The heat exchanger assembly as set forth in claim 3, wherein the outer ring, inner support and inner heat fins are made of a material having a higher thermal expansion coefficient than the wall.

5. The heat exchanger assembly of claim 4, wherein the outer ring, inner support and inner heat fins are made of aluminum.

6. The heat exchanger assembly as set forth in claim 1, wherein the outer heat exchanger further comprises a plurality of outer heat fins outwardly projecting from the outer ring.

7. The heat exchanger assembly as set forth in claim 6, wherein the outer heat fins are welded, soldered or bonded by a thermo-conductive adhesive to the outer ring.

8. The heat exchanger assembly as set forth in claim 1, wherein the inner support further comprises an interior surface.

9. The heat exchanger assembly as set forth in claim 8, wherein the interior surface of the inner support is adapted to form a gas bearing or a seal portion, or both, with a sliding member movably disposed through interior surface of the inner support.

10. The heat exchanger assembly as set forth in claim 8, further comprising a solid annular ring portion connected to the inner support or the inner fins and having an outer surface configured to be in contact with the interior surface of the wall of the housing when the annular ring portion is installed in the housing.

11. The heat exchanger assembly as set forth in claim 10, wherein the annular ring portion is integral with the inner support or the inner heat fins, or both.

12. The heat exchanger assembly as set forth in claim 11, further comprising a sealant on the outer surface of the annular ring portion.

13. A component of a Stirling cycle machine, comprising: a housing comprising a wall defining an interior volume and adapted to seal within the interior volume a working gas, the interior volume comprising a compression region where the working gas is subject to intermittent compression and expansion;an outer heat exchanger comprising an outer ring disposed outside the housing and having an interior surface in contact with an exterior surface of the wall;a plurality of outer heat fins connected to the outer ring;an inner support disposed inside the housing and having an exterior surface; anda plurality of inner heat fins connecting the exterior surface of the inner support to an interior surface of the wall of the housing, at least a portion of the outer ring and at least a portion of the inner heat fins sandwiching at least a portion of the housing wall.

14. The component as set forth in claim 13, wherein the inner heat fins are integral with the inner support.

15. The component as set forth in claim 14, wherein the outer ring is shrink-fitted on the housing and the inner support and inner heat fins are shrink-fitted in the housing.

16. The component as set forth in claim 15, wherein the outer ring, inner support or inner heat fins are made of a material having a higher thermal expansion coefficient than the wall.

17. The component as set forth in claim 15, further comprising a sealant between the outer ring and the housing.

18. The component of claim 16, wherein the outer ring, inner support or inner heat fins are made of aluminum, and wherein the housing wall is made of stainless steel at least in portions in contact with the outer ring and plurality of inner heat fins.

19. The component as set forth in claim 13, wherein the inner support comprises an interior surface.

20. The component as set forth in claim 19, wherein the interior surface of the inner support is adapted to form a gas bearing or a seal portion, or both, with a sliding member movably disposed through interior surface of the inner support.

21. A heat exchanger assembly for transferring heat across a wall of a housing, the assembly comprising: an outer ring disposed outside the housing and having an interior surface in contact with an exterior surface of the wall;a plurality of outer heat fins outwardly projecting from the outer ring; anda plurality of inner heat fins extending inwardly from the interior surface of the wall, at least a portion of the outer ring and at least a portion of the inner heat fins sandwiching at least a portion of the housing wall.

22. The heat exchanger assembly as set forth in claim 21, wherein the inner heat fins are brazed, soldered or bonded with a thermo-conductive adhesive to the interior surface of the wall.

23. The heat exchanger assembly as set forth in claim 21, wherein the inner heat fins are shrink-fitted to the housing.

24. The heat exchanger assembly as set forth in claim 21, wherein the outer heat fins are shrink-fitted to the outer ring.

25. The heat exchanger assembly as set forth in claim 21, further comprising a solid annular ring portion connected to the inner fins and having an outer surface configured to be in contact with the interior surface of the wall of the housing when the annular ring portion is installed in the housing.

26. The heat exchanger assembly as set forth in claim 25, wherein the annular ring portion is integral with the inner heat fins.

27. A method for making a heat exchanger assembly for transferring heat across a wall of a housing, the method comprising: positioning an outer heat exchanger comprising an outer ring outside the housing such that an interior surface of the outer ring is in contact with an exterior surface of the wall;positioning a plurality of outer heat fins on the outer ring;positioning an inner support inside the housing; andconnecting an interior surface of the wall and an exterior surface of the inner support using a plurality of inner heat fins such that at least a portion of the inner heat fins and at least a portion of the outer ring sandwich at least a portion of the housing wall.

28. The method as set forth in claim 27, further comprising constructing the inner support and the plurality of inner heat fins from the same piece of material.

29. The method as set forth in claim 28, wherein constructing comprises forming an integral body comprising the inner support and inner heat fins by removing material from the piece.

30. The method as set forth in claim 29, wherein removing comprises machining.

31. The method as set forth in claim 27, further comprising forming an aperture through the inner support.

32. The method as set forth in claim 27, wherein positioning the outer ring comprises shrink-fitting the outer ring on the housing; and connecting the interior surface of the wall and the exterior surface of the inner support using the inner heat fins comprises shrink-fitting the inner heat fins and the inner support inside and against the housing wall.

33. The method as set forth in claim 32, wherein shrink-fitting the outer ring on the housing comprises subjecting the outer ring to a higher temperature than the housing, and subjecting the inner heat fins and inner support to a lower temperature than the housing.

34. The method of claim 32, further comprising shrink-fitting a plurality of outer heat fins to the outer ring.

35. The method of claim 32, further comprising applying a sealant between the outer ring and the housing wall.

36. The heat exchanger assembly of claim 1, wherein the outer heat exchanger further comprises a heat-transfer structure in thermal contact with the outer ring and adapted to transfer heat from or to the outer ring.

37. The heat exchanger assembly of claim 36, wherein the heat-transfer structure comprises a tubing or channel adapted to carry a heat-transfer fluid.

38. The heat exchanger assembly of claim 1, wherein the outer ring comprises a mounting structure adapted to affix a heat-transfer structure to the outer ring.

39. A heat exchanger assembly for transferring heat across a wall of a housing, the assembly comprising: an inner support disposed inside the housing and having an exterior surface; anda plurality of inner heat fins connecting the exterior surface of the inner support to an interior surface of the wall of the housing.

40. The heat exchanger assembly of claim 39, further comprising an outer heat transfer structure in thermal contact with an exterior surface of the housing wall, at least a portion of the outer heat-transfer structure and at least a portion of the inner heat fins sandwiching at least a portion of the housing wall.

41. The heat exchanger assembly of claim 40, wherein the heat-transfer structure comprises a tubing or channel adapted to carry a heat-transfer fluid.

42. The heat exchanger assembly of claim 39, further comprises a mounting structure adapted to affix a heat-transfer structure to the housing wall.