Heat exchanger assembly

Abstract

An improved heat exchanger assembly and method. First and second plates made of a predetermined thermally conductive material are configured when mated to form a hermetically sealed vapor chamber. A wick made of the same predetermined thermally conductive material resides in the vapor chamber forming a gas chamber.

Claims

1. A heat exchanger assembly, comprising: first and second plates made of a thermally conductive material configured when mated to form a hermetically sealed vapor chamber; a wick made of the thermally conductive material in the vapor chamber forming a gas chamber, wherein the wick includes fins each extending continuously from the hermetically sealed vapor chamber toward one of two opposing edges of the first and second plates; and for each of at least one of the fins, multiple layers of carbon nanotubes adjacent to a surface of the fin that is normal to a plane of the plates, each layer of carbon nanotubes oriented obliquely with respect to a direction in which the fin extends from the hermetically sealed vapor chamber, wherein the multiple layers of carbon nanotubes are oriented in different directions, and wherein, within each layer of carbon nanotubes, the carbon nanotubes in that layer of carbon nanotubes are similarly oriented.

2. The heat exchanger assembly of claim 1, wherein the carbon nanotubes increase wicking action by the wick.

3. The heat exchanger assembly of claim 1, wherein at least some of the carbon nanotubes are positioned between adjacent pairs of fins.

4. The heat exchanger assembly of claim 1, wherein the fins have heights and sizes that facilitate liquid transport via fin wicking.

5. The heat exchanger assembly of claim 1, wherein the wick is configured to maximize fluid transfer via capillary action.

6. The heat exchanger assembly of claim 1, wherein the thermally conductive material of the first and second plates is aluminum.

7. The heat exchanger assembly of claim 1, wherein the thermally conductive material of the wick is aluminum.

8. The heat exchanger assembly of claim 1, wherein the wick is made of a metal foam.

9. A heat exchanger assembly, comprising: first and second plates formed of a thermally conductive material, each plate containing a cavity, the cavities forming a hermetically sealed vapor chamber when the first and second plates are stacked on top of each other with the cavities facing each other; an aluminum foam wick lining each of the cavities, the aluminum foam wick having a grooved surface defining fins separated by grooves, each of the grooves extending continuously from the hermetically sealed vapor chamber toward one of two opposing edges of the stacked first and second plates, the aluminum foam wick filling peripheral regions of each cavity while leaving a central region of each cavity unfilled, wherein the aluminum foam wick is configured to provide a wicking action of a liquid cooling medium, wherein, for each of at least one of the fins, multiple layers of carbon nanotubes are adjacent to a surface of the fin that is normal to a plane of the plates, each layer of carbon nanotubes oriented obliquely with respect to a direction in which the fin extends from the hermetically sealed vapor chamber, wherein the multiple layers of carbon nanotubes are oriented in different directions, and wherein, within each layer of carbon nanotubes, the carbon nanotubes in that layer of carbon nanotubes are similarly oriented; and a port extending from an outside of the first and second plates into the vapor chamber, wherein the aluminum foam wick is galvanically matched to the thermally conductive material.

10. The heat exchanger assembly of claim 9, wherein a cell size for the aluminum foam wick is selected to facilitate capillary action.

11. The heat exchanger assembly of claim 9, wherein the aluminum foam wick completely surrounds the vapor chamber.

12. The heat exchanger assembly of claim 9, further comprising: a plug made of the thermally conductive material and placed in the port.

13. The heat exchanger assembly of claim 9, wherein the thermally conductive material includes one of aluminum and carbon composites.

14. The heat exchanger assembly of claim 9, wherein at least a portion of a surface of the aluminum foam wick in each cavity is co-planar with a surface of a respective face of the cavity.

15. The heat exchanger assembly of claim 9, wherein the aluminum foam wick is formed to give the central region of each cavity a size and shape filled by the liquid cooling medium.

16. The heat exchanger assembly of claim 9, further comprising: a peripheral stir weld hermetically sealing the first and second plates.

17. A heat exchanger assembly, comprising: first and second plates made of a thermally conductive material, each plate containing a cavity, the cavities forming a hermetically sealed vapor chamber when the first and second plates are stacked on top of each other with the cavities facing each other; a wick that lines at least one of the cavities, the wick having (i) a flat side in contact with the first or second plate and (ii) a fin side facing the vapor chamber, the fin side comprising fins each extending continuously from one of the cavities toward one of two opposing edges of the first or second plate so as to form an area of a liquid-to-gas boundary; and a wick liner comprising, for each of at least one of the fins, multiple layers of carbon nanotubes adjacent to a surface of the fin that is normal to a plane of the plates, each layer of carbon nanotubes oriented obliquely with respect to a direction in which the fin extends, wherein the multiple layers of carbon nanotubes are oriented in different directions, and wherein, within each layer of carbon nanotubes, the carbon nanotubes in that layer of carbon nanotubes are similarly oriented.

18. The heat exchanger assembly of claim 17, wherein the fins have heights and sizes that facilitate liquid transport via fin wicking.

19. The heat exchanger assembly of claim 17, wherein the wick is configured to maximize fluid transfer via capillary action.

20. The heat exchanger assembly of claim 17, wherein at least some of the carbon nanotubes are positioned between adjacent pairs of fins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

(2) FIG. 1 is a schematic three-dimensional front view of a prior art cold plate used in connection with radar transmit and receive modules;

(3) FIG. 2 is a highly schematic top view showing one portion of the cold plate shown in FIG. 1;

(4) FIG. 3 is a highly schematic front view of a prior art heat pipe used in connection with the cold plate shown in FIGS. 1-2;

(5) FIG. 4 is a schematic top view showing four heat pipes installed in a cold plate;

(6) FIG. 5A-5B are schematic three-dimensional top views showing an example of first and second plates used to form the structure of an improved heat exchanger assembly in accordance with the subject disclosure;

(7) FIG. 6 is a schematic three-dimensional top view showing a particular configuration of cold plate with the wick material installed therein in accordance with one example of the subject disclosure;

(8) FIG. 7 is a schematic three-dimensional top view showing a completed heat exchanger assembly in accordance with an example of the subject disclosure;

(9) FIG. 8 is a schematic cross-sectional front view of the complete assembly shown in FIG. 7;

(10) FIG. 9 is a sectional view of a vapor chamber with a finned wick in accordance with the subject disclosure;

(11) FIG. 10 is a more detailed view of the wick fins;

(12) FIG. 11 is a view of the finned wick sectioned across the vapor chamber;

(13) FIG. 12 is another more detailed view of the finned wick;

(14) FIG. 13 is a view showing carbon nanotubes added to the fins of the wick;

(15) FIG. 14 is a view showing the fins including the carbon nanotubes of FIG. 13; and

(16) FIG. 15 is a view of a sectioned vapor chamber including the fins of FIG. 14.

DETAILED DESCRIPTION

(17) Aside from the preferred embodiment or embodiments disclosed below, this disclosure is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

(18) There is shown in FIG. 1 an example of a prior art cold plate 10 for radar transmit and receive modules 12a-12d. Cold plate 10 typically includes two halves one of which is schematically shown in FIG. 2. Cold plate half 10a, typically made of aluminum, is machined to form channels as shown at 14a-14b then nickel under plated with gold over plated. The other cold plate half is machined and plated in a similar fashion to form mirror image channels. Copper heat pipes such as heat pipe 16, FIG. 3 are then laid in the channels as shown in FIG. 4. The other cold plate half is then mated onto cold plate half 10a using solder paste spread over the machined faces of the cold plate halves.

(19) As explained in the background section above, one problem with copper used as the cold plate material is that it is heavy which is a concern in ship and airborne applications. When aluminum is used instead for the cold plate material, the copper heat pipes 16a-16d, FIG. 4 therein resulted in a galvanic mismatch which can then lead to corrosion and reliability problems. The use of different materials in a heat exchanger can also increase the thermal resistance of the assembly. Moreover, the process of making a cold plate such as the one shown in FIG. 1 can be labor intensive and costly. Other problems associated with the prior art discussed more fully in the background section above.

(20) FIGS. 5A-5B show first and second plates 40a and 40b in accordance with an example of the subject disclosure made of a predetermined thermally conductive material (such as aluminum) configured, when mated to form a hermetically sealed vapor chamber. In this particular example, the vapor chamber is formed via machining cavity 42a in one face of plate 40a and machining cavity 42b in one face of plate 40b. FIG. 6 shows the addition of aluminum foam wick material 44a lining the vapor chamber and forming gas chamber 46. One source of aluminum foam is available from ERG Materials and Aerospace Corp. (Oakland, Calif.) under the brand name Duocel. Typically, the aluminum foam lines all the walls defining the vapor chamber. The wick material may be formed in place in the chamber.

(21) FIG. 7 shows two such plates hermetically sealed via peripheral friction stir weld 50. Stir welding is an autogenous process meaning no additional materials are required which could galvanically corrode. Stir welding also reliably seals plates 40a and 40b with low distortion while retaining the original mechanical properties of the cold plate material which solder and other joining methods cannot provide. Soldering, bonding, and other techniques can be used to join the plates. If composite materials are used, thermal bonding techniques may be used. Metal foam wick material 44, FIG. 8 in vapor chamber 42 forming chamber 46 is beneficial because it is made of the same material as plates 40a and 40b and the cell and tendon size can be optimized for the best capillary action for any particular application and chamber configuration. The foam aluminum wick can be sized, shaped, or layered to maximize fluid transfer via capillary action. The chamber size can be optimized and can be designed to maximize gas transfer to the condenser section of the heat exchanger. But, wick material 44 could also be braided aluminum and brazing could also be used to hermetically seal plates 40a and 40b. The wick material is typically the same as the material forming the chamber but, at the least, the two materials should be galvanically matched.

(22) FIG. 7 also shows a port into vapor chamber 42, FIG. 8 plugged via aluminum cylinder 52, FIG. 7 inertial welded into the port. Again, if aluminum is used for plates 40a and 40b, aluminum is preferably used for both the wick material (aluminum foam) and the plug sealing the port. Other choices for all three components are copper and carbon based materials. Conductive composite materials may be used. Wick material 42, FIG. 8 which lines the walls 60a-60e of the vapor chamber and which defines gas chamber 46 can be placed in the vapor chamber, brazed to the walls of the vapor chamber, foamed in place on the walls of the vapor chamber, or bonded to the walls of the vapor chamber. Metal wick material 44 can be compressed or molded or cast into any desired shape, it can be layered, or machined. The wick may be configured to form fins. A sintered wick or a nanotube wick may be used. Also, although the heat exchanger assembly shown in FIGS. 7-8 includes plates 40a and 40b, any structure forming a hermetically sealed vapor chamber including a wick made of the same material or a galvanically matched material as the structure is within the scope of the subject disclosure. Gun drilling, casting, machining, EDM, and other processes may be used to form the chamber. And, plates 40a and 40b can be of any desired size, shape, configuration, and thickness.

(23) Manufacturing a heat exchanger in accordance with the example given above includes machining or otherwise forming cavities 42a and 42b, FIGS. 5A-5B in a face of plates 40a and 40b; installing the metallic wick material in each chamber as shown in FIG. 6; hermetically sealing plates 40a and 40b as shown in FIG. 7 but leaving a port as discussed above; adding a coolant such as water, ammonia, alcohol, or the like to the wick material via the port; heating the assembly until all of the air exits gas chamber 46, FIG. 8; and plugging the orifice as shown at 52 in FIG. 7 (typically by inertia welding).

(24) FIG. 11 shows an embodiment with plate 40a with finned wick 42 therein, also shown in FIGS. 10-12.

(25) In one example, the fin thickness was 0.010 and the fin spacing was 0.010. The result is a custom machined vapor chamber. Varying fin heights and sizes can be used to facilitate and optimize liquid transport via fin wicking. FIGS. 13-15 show another embodiment where a custom machined vapor chamber includes oriented carbon nanotubes 80, FIG. 13, attached to the fins 82, FIGS. 14-15 to improve the wicking action of the liquid cooling medium.

(26) The result in any embodiment is an improved heat exchanger assembly. Because all of the materials used are the same or gavanically compatible, galvanic corrosion is not typically a problem resulting in improved reliability. Because all of the materials used are the same, there is also typically a lower thermal resistance. The heat exchanger assembly of the subject disclosure can be manufactured easily and at a lower cost. If aluminum is used as discussed above for plates 40a and 40b, for wick 42, and for plug 52 (FIG. 7), the heat exchanger assembly is considerably lighter than a prior art copper based cold plate. A heat exchanger in accordance with the subject disclosure typically has higher cooling capacity and is more efficient. The use of the metal foam material as a wick also has the benefit of increasing the wicking volume and the gas handling volume above and beyond a typical heat pipe capacity. Thermal conductivity is improved because the thermal path only includes one aluminum plate, the foam aluminum wick, and the vapor chamber versus the alternative design with heat pipes wherein the thermal path included a copper plate, an under plate, and over plate, solder, a void or flux, the copper heat pipe, and the sinter material within the copper heat pipe. The use of a three dimensional scalable, flexible form factor integrated vapor chamber, joined by friction stir welding, achieves a synergistic structure that optimizes mechanical strength and thermal properties.

(27) Although specific features of the disclosure are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the disclosure. The words including, comprising, having, and with as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. As noted, structures other than plates may be used to form the vapor chamber.

(28) In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for any claim element amended.

(29) Other embodiments will occur to those skilled in the art and are within the following claims.