Mixed Carbon Foam/Metallic Heat Exchanger
A heat exchanger includes a thermally-conductive fluid barrier having first and second surfaces, at least one first type of foam element placed in thermally-conductive contact with the first surface of the thermally-conductive fluid barrier and having a first coefficient of thermal expansion and at least one second type of foam element placed in thermally-conductive contact with the second surface of the thermally-conductive fluid barrier and having a second coefficient of thermal expansion. The first coefficient of thermal expansion of the first type of foam element and the second coefficient of thermal expansion of the second type of foam element are substantially different.
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The disclosure relates to ram air heat exchangers for aircraft. More particularly, the disclosure relates to a mixed carbon foam/metallic heat exchanger having thermally conductive carbon foam layers which alternate with metal foam layers to allow for the fabrication of heat exchanger cores using materials having vastly different coefficients of thermal expansion (CTE).
BACKGROUNDIn the manufacture of ram air heat exchangers using thermally conductive carbon foam as a thermal management material, metallic and carbon elements may be used in fabrication of the heat exchanger core. The metallic and carbon elements used in fabrication of the heat exchanger core may have different coefficients of thermal expansion (CTE). Therefore, during fabrication, high-temperature vacuum brazing processes may generate thermal stresses within the heat exchanger core during the heat-up and cool-down phases of the brazing process.
Therefore, fabrication processes that address thermal stresses caused by mismatched coefficients of thermal expansion (CTE) in a mixed carbon foam/metallic heat exchanger may be desirable.
SUMMARYThe disclosure is generally directed to a heat exchanger. An illustrative embodiment of the heat exchanger includes a thermally-conductive fluid barrier having first and second surfaces, at least one first type of foam element placed in thermally-conductive contact with the first surface of the thermally-conductive fluid barrier and having a first coefficient of thermal expansion and at least one second type of foam element placed in thermally-conductive contact with the second surface of the thermally-conductive fluid barrier and having a second coefficient of thermal expansion. The first coefficient of thermal expansion of the first type of foam element and the second coefficient of thermal expansion of the second type of foam element are substantially different.
The disclosure is further generally directed to a mixed carbon foam/metallic foam heat exchanger method. An illustrative embodiment of the method includes providing a reticulated metal foam layer, providing a thermally conductive carbon foam layer in thermally-conductive contact with the reticulated metal foam layer, distributing a first fluid through the reticulated metal foam layer and distributing a second fluid through the carbon foam layer.
Referring initially to
At least one ductile thermal management material layer 10 may be provided in the heat exchanger frame 2. As shown in
As shown in
As shown in
In some applications of the heat exchanger 1, CTE induced thermal stresses may be a function of length scale. Therefore, as shown in
During fabrication of the heat exchanger 1, a vacuum brazing process may be used as is known to those skilled in the art. Accordingly, the ductile thermal management material layers 10 and the thermally conductive carbon foam layers 14, separated by thermally-conductive fluid barriers 18, may be stacked and brazed together during fabrication. It will be appreciated by those skilled in the art that during the vacuum brazing process, the high thermal stresses resulting from thermal expansion and contraction induced in the heat exchanger frame 2 of the heat exchanger 1 may be absorbed by the ductile thermal management material layers 10. The thermal management material layers 10 may not transfer the thermal stresses from the heat exchanger frame 2 to the thermally conductive carbon foam layers 14. This may prevent the application of excessive thermally induced stress on the carbon foam layers 14.
In application of the heat exchanger 1, a first slot (not shown) may be placed in fluid communication with the ductile thermal management material layers 10 and a second slot (not shown) may be placed in fluid communication with the thermally conductive carbon foam layers 14. A first fluid (not shown) may be distributed from the first slot through the thermal management material layers 10, and a second fluid (not shown) may be distributed from the second slot through the carbon foam layers 14. Accordingly, heat may be transferred by convection and conduction from the hotter to the cooler of the first fluid and the second fluid through the thermally-conductive fluid barrier 18 (
Referring next to
Referring next to
Each of the processes of method 78 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
As shown in
The apparatus embodied herein may be employed during any one or more of the stages of the production and service method 78. For example, components or subassemblies corresponding to production process 84 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 94 is in service. Also, one or more apparatus embodiments may be utilized during the production stages 84 and 86, for example, by substantially expediting assembly of or reducing the cost of an aircraft 94. Similarly, one or more apparatus embodiments may be utilized while the aircraft 94 is in service, for example and without limitation, to maintenance and service 92.
Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.
Claims
1. A heat exchanger, comprising:
- a thermally-conductive fluid barrier having first and second surfaces;
- at least one first type of foam element placed in thermally-conductive contact with said first surface of said thermally-conductive fluid barrier and having a first coefficient of thermal expansion;
- at least one second type of foam element placed in thermally-conductive contact with said second surface of said thermally-conductive fluid barrier and having a second coefficient of thermal expansion; and
- wherein said first coefficient of thermal expansion of said first type of foam element and said second coefficient of thermal expansion of said second type of foam element are substantially different.
2. The heat exchanger of claim 1 wherein said first type of foam element comprises a reticulated metal foam layer.
3. The heat exchanger of claim 2 wherein said reticulated metal foam layer comprises reticulated aluminum foam.
4. The heat exchanger of claim 1 wherein said second type of foam element comprises a thermally conductive carbon foam layer.
5. The heat exchanger of claim 4 wherein said thermally conductive carbon foam layer is segmented in multiple sections.
6. The heat exchanger of claim 1 further comprising a plurality of stress relief blind slots provided in said first type of foam element.
7. The heat exchanger of claim 6 wherein said stress relief blind slots are placed in staggered relationship with respect to each other.
8. The heat exchanger of claim 6 further comprising a plurality of stress relief blind slots provided in said second type of foam element.
9. A heat exchanger, comprising:
- a heat exchanger frame having a first end plate, a second end plate placed in opposed relationship with respect to said first end plate and at least one side bar member placed at each end of said first end plate and said second end plate;
- a thermally-conductive fluid barrier having first and second surfaces provided in said heat exchanger frame;
- at least one first type of foam element placed in thermally-conductive contact with said first surface of said thermally-conductive fluid barrier and having a first coefficient of thermal expansion;
- at least one second type of foam element placed in thermally-conductive contact with said second surface of said thermally-conductive fluid barrier and having a second coefficient of thermal expansion; and
- wherein said first coefficient of thermal expansion of said first type of foam element and said second coefficient of thermal expansion of said second type of foam element are substantially different.
10. The heat exchanger of claim 9 wherein said first type of foam element comprises a reticulated metal foam layer.
11. The heat exchanger of claim 10 wherein said reticulated metal foam layer comprises reticulated aluminum foam.
12. The heat exchanger of claim 9 wherein said second type of foam element comprises a thermally conductive carbon foam layer.
13. The heat exchanger of claim 12 wherein said thermally conductive carbon foam layer is segmented in multiple sections.
14. The heat exchanger of claim 9 further comprising a plurality of stress relief blind slots provided in said first type of foam element.
15. The heat exchanger of claim 14 wherein said stress relief blind slots are placed in staggered relationship with respect to each other.
16. The heat exchanger of claim 14 further comprising a plurality of stress relief blind slots provided in said second type of foam element.
17. A mixed carbon foam/metallic foam heat exchanger method, comprising:
- providing a reticulated metal foam layer;
- providing a thermally conductive carbon foam layer in thermally-conductive contact with said reticulated metal foam layer;
- distributing a first fluid through said reticulated metal foam layer; and
- distributing a second fluid through said thermally conductive carbon foam layer.
18. The method of claim 17 wherein said reticulated metal foam layer comprises a reticulated aluminum foam layer.
19. The method of claim 17 further comprising a plurality of stress relief blind slots in said reticulated metal foam layer.
20. The method of claim 17 further comprising a plurality of stress relief blind spots in said thermally conductive carbon foam layer.
Type: Application
Filed: May 20, 2008
Publication Date: Nov 26, 2009
Applicant:
Inventors: Michael F. Stoia (Rancho Santa Margarita, CA), David E. Blanding (Hawthorne, CA), Samuel Kim (Snohomish, WA), Jarrett Reed Datcher (Saint Louis, MO)
Application Number: 12/124,092