Diffuser for cryogenic heat exchanger

Abstract

A diffuser for a heat exchanger of a cryocooler formed as a disc having a center and a peripheral edge. A plurality of slots are formed in the disc and extend radially inwardly from the peripheral edge of the disc to a point proximate to the center of the disc. The slots include a first set having a first length, a second set having a second length that is different than the first length, and a third set having a third length that is different than the first length and the second length. The slots may be arranged with each of the sets alternating about the center of the disc. The disc may be cooled and inserted into a heat exchanger in the flow path between the pulse tube and regenerator to provide a consistent height heat exchanger diffuser having consistent performance

Description

TITLEDIFFUSER FOR CRYOGENIC HEAT EXCHANGERBACKGROUND1. FIELD

[0001] The present disclosure relates to cryocoolers and, more specifically, to a high efficiency diffuser for use in a heat exchanger of a cryocooler.2. DESCRIPTION OF THE RELATED ART

[0002] Conventional cryocoolers employ one or more heat exchanger diffusers positioned in the heat exchanger of the cryocooler to assist with heat exchange between the cooling fluid and the outside environment. Existing heat exchanger diffusers employ a random matrix formed from a series of perforated plates and screens that form a stack in the cryocooler. Because of the variable thicknesses of the screens and plates, existing diffusers for heat exchangers do not have a consistent height and are difficult to manufacture. The inconsistency in height also contributes to variances in the performance of cryocooler and can only be resolved by manually disassembling the cryocooler and repacking the components of the heat exchanger. Accordingly, there is a need in the art for a diffuser that has a consistent height and resulting performance.BRIEF SUMMARY

[0003] The present invention is a diffuser for the heat exchanger of a cryocooler that is formed as a machined disc having a center and a peripheral edge along with a plurality of slots formed in the disc that extend radially inwardly from the peripheral edge. The slots include a first set having a first length, a second set having a second length that is different than the first length, and a third set having a third length that is different than the first length and the second length. The slots may be arranged with each of the sets alternating about the center of the disc. The disc may be cooled and inserted into a heat exchanger in the flow path between the pulse tube and regenerator to provide a consistent height heat exchanger diffuser having consistent performance.

[0004] In one embodiment, the present invention is a diffuser for a heat exchanger that is formed from a disc having a center and a peripheral edge and a plurality of openings extending through the disc from a first side of the disc to a second side of the disc, wherein the plurality of openings extend radially inwardly from the peripheral edge of the disc to a point proximate to the center of the disc. The plurality of openings may result in at least ten percent of the disc being open to a flow of fluid through the disc. The plurality of openings may be a plurality of slots that extend continuously from the peripheral edge of the disc to thepoint proximate to the center of the disc. The plurality of slots may include a first plurality of slots that extend a first distance toward to the center of the disc, a second plurality of slots that extend a second distance toward to the center of the disc that is different than the first distance, and a third plurality of slots that extend a third distance toward to the center of the disc that is different than both the first and second distances. Each of the plurality of slots may have a fixed width. The fixed width of each of the plurality of slots may be about 0.010 inches (0.254 mm). The disc may have a thickness between 1 / 8 of an inch and 3 inches. The disc may be formed from aluminum. The diffuser may be positioned in a heat exchanger of the cryocooler.

[0005] In another embodiment, the present invention is a method of facilitating the transfer of heat into and out of a fluid stream. In one step, the method involves providing a cryocooler having a heat exchanger and a fluid pathway extending therethrough. In another step, the method involves installing a disc having a center and a peripheral edge as well as a plurality of slots formed therethrough and extending from the center to the peripheral edge in the heat exchanger of the cryocooler. In a further step, the method involves allowing a gas to flow through the plurality of slots of the disc. The cryocooler may be a pulse tube cryocooler or a Gifford-McMahon cryocooler. The plurality of slots may result in at least ten percent of the disc being open to the flow of the gas through the disc. The method may further include the step of cooling the disc prior to installing the disc in the heat exchanger of the cryocooler. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0006] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0007] FIG. 1 is a longitudinal cross-section of a pulse tube cryocooler showing the location of a heat exchanger diffuser according to the present invention.

[0008] FIG. 2 is a top view of a heat exchanger diffuser according to the present invention.

[0009] FIG. 3 is a cross-section of a heat exchanger diffuser taken along line A-A of FIG. 2 according to the present invention.DETAILED DESCRIPTION

[0010] Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in FIG. 1 a diffuser 10 for a cryocooler 12 that facilitates the transfer of heat into and out of a fluid stream of a cryocooler 12. Diffuser 10 is positioned in the heat exchanger16 and the pulse tube 18 of cryocooler 12. Cryocooler 12 may either a pulse tube or Gifford- McMahon style device.

[0011] Referring to FIG. 2, diffuser 10 is formed as a disc 20 that includes a plurality of slots 22 that are open to the surrounding environment. Slots 22 extend radially inwardly from the perimeter 24 of disc 20 and terminate proximately to a center 26 of disc 20 that remains solid. As seen in FIG. 2, the plurality of slots 22 may include a first plurality of slots 30 that extend a first distance toward center 26, a second plurality of slots 32 that extend a second distance toward center 26 that is different than the first distance, and a third plurality of slots 34 that extend a third distance toward center 26 that is different than both the first and second distances. Slots 30, slots 32, and 34, may be formed as a repeating pattern radially about center 26 as seen in FIG. 2. Slots 22 provide openings extending from one side of disc 20 to the opposing side of disc 20 that are fixed in size and location and thus will allow gas to flow in a uniform and repeatable fashion from one side of disc 20 to the other side of disc 20. As a result, when disc 20 is positioned in cryocooler 12 as seen in FIG. 1, cooling fluid passing in the pathway between regenerator 16 and pulse tube 18 will pass through slots 22 for heat transfer and be diffused.

[0012] As seen in FIG. 2, disc 20 has a predetermined outer diameter 0 and each slot 22 has a fixed width W. Referring to FIG. 3, disc 20 has a first side 40 and an opposing second side 42 providing a predetermined thickness T. An example, an exemplary disc 20 having a diameter 0 of 1.689 inches (42.9 mm) and a thickness T of 0.330 inches (8.32 mm) may have slots 22 formed therein where each slot 22 has a length that is less than the radius of disc 20 and a width W of 0.010 inches (0.254 mm). Thickness T of disc 20 can be adapted for any particular cryocooler 12, and thus for conventionally available devices can be as small as 1 / 8 of an inch and as large as 3 inches.

[0013] In an exemplary embodiment, twenty percent (20%) of the surface area of disc 20 is open for the flow of fluid from first side 40 to second side 42. Thus, eighty percent (80%) of disc 20 is solid. The percentage of open surface area formed by slots 22 may increase or decrease by up to ten percent (10%) as desired so that seventy percent (70%) to ninety percent (90%) of disc 20 remains solid. It should be recognized by those of skill in the art that slots 22 may vary in width and length as described herein to provide the desired amount of flow and diffusion. As an alternative, each slot 22 may be formed as a row of multiple circular or elongate openings or apertures extending through disc 20 as long as the resulting percentage area that is open for the flow of fluid is provided in disc 20 as described above.

[0014] Disc 20 is preferably manufactured from copper with slots 22 machined into disc 20. It should be recognized that other materials and methods of manufacture may be used to form heat exchanger and diffuser 10, including aluminum and any other material that provides for thermal conductivity at cryogenic temperatures, i.e., below minus 150 °F (-101 °C). Precision machining of disc 20 also provides a consistent height that avoids variability in the performance of heat exchanger and diffuser 10 once installed in cryocooler 12.

[0015] Diffuser 10 may be installed into cryocooler by cooling disc 20, such as by using liquid nitrogen, and then installing diffuser 10 into its desired location in heat exchanger 14 of cryocooler 12. Disc 20 will lock into place in heat exchanger 14 as disc 20 warms and expands. The narrow gaps are very consistent, allowing any gas to flow in a uniform fashion, therefore, being very repeatable.

Claims

CLAIMSWhat is claimed is:

1. A diffuser for a heat exchanger, comprising: a disc having a center and a peripheral edge; and a plurality of openings extending through the disc from a first side of the disc to a second side of the disc, wherein the plurality of openings extend radially inwardly from the peripheral edge of the disc to a point proximate to the center of the disc.

2. The diffuser of claim 1, wherein the plurality of openings result in at least ten percent of the disc being open to a flow of fluid through the disc.

3. The diffuser of claim 2, wherein the plurality of openings are a plurality of slots that extend continuously from the peripheral edge of the disc to the point proximate to the center of the disc.

4. The diffuser of claim 3, wherein the plurality of slots include a first plurality of slots that extend a first distance toward to the center of the disc, a second plurality of slots that extend a second distance toward to the center of the disc that is different than the first distance, and a third plurality of slots that extend a third distance toward to the center of the disc that is different than both the first and second distances.

5. The diffuser of claim 4, wherein each of the plurality of slots has a fixed width.

6. The diffuser of claim 5, wherein the fixed width of each of the plurality of slots is about 0.010 inches (0.254 mm).

7. The diffuser of claim 6, wherein the disc has a thickness between 1 / 8 of an inch and 3 inches.

8. The diffuser of claim 7, wherein the disc is formed from aluminum.

9. A cryocooler having a diffuser according to claim 1 positioned in a heat exchanger of the cryocooler.

10. The cryocooler of claim 9, wherein the cryocooler is selected from group consisting of a pulse tube cryocooler and a Gifford-McMahon cryocooler.

11. A method of facilitating the transfer of heat into and out of a fluid stream, comprising the steps of: providing a cryocooler having a heat exchanger and a fluid pathway extending therethrough; andinstalling a disc having a center and a peripheral edge as well as a plurality of slots formed therethrough and extending from the center to the peripheral edge in the heat exchanger of the cryocooler; and allowing a gas to flow through the plurality of slots of the disc.

12. The method of claim 11, wherein the cryocooler is selected from group consisting of a pulse tube cryocooler and a Gifford-McMahon cryocooler.

13. The method of claim 12, wherein the plurality of slots result in at least ten percent of the disc being open to the flow of the gas through the disc.

14. The method of claim 13, further comprising the step of cooling the disc prior to installing the disc in the heat exchanger of the cryocooler.

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