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Porous materials for thermal management under extreme conditions

Porous materials for thermal management under extreme conditions
Porous materials for thermal management under extreme conditions
A brief analysis is presented of how heat transfer takes place in porous materials of various types. The emphasis is on materials able to withstand extremes of temperature, gas pressure, irradiation, etc., i.e. metals and ceramics, rather than polymers. A primary aim is commonly to maximize either the thermal resistance (i.e. provide insulation) or the rate of thermal equilibration between the material and a fluid passing through it (i.e. to facilitate heat exchange). The main structural characteristics concern porosity (void content), anisotropy, pore connectivity and scale. The effect of scale is complex, since the permeability decreases as the structure is refined, but the interfacial area for fluid–solid heat exchange is, thereby, raised. The durability of the pore structure may also be an issue, with a possible disadvantage of finer scale structures being poor microstructural stability under service conditions. Finally, good mechanical properties may be required, since the development of thermal gradients, high fluid fluxes, etc. can generate substantial levels of stress. There are, thus, some complex interplays between service conditions, pore architecture/scale, fluid permeation characteristics, convective heat flow, thermal conduction and radiative heat transfer. Such interplays are illustrated with reference to three examples: (i) a thermal barrier coating in a gas turbine engine; (ii) a Space Shuttle tile; and (iii) a Stirling engine heat exchanger. Highly porous, permeable materials are often made by bonding fibres together into a network structure and much of the analysis presented here is oriented towards such materials.
1364-503X
125-146
Clyne, T.W.
00678bf7-17de-46e8-9b35-bf1ca73bce9b
Golosnoy, I.O.
40603f91-7488-49ea-830f-24dd930573d1
Tan, J.C.
64748a9f-f771-44c3-ac63-fd554193c592
Markaki, A.E.
26beec1d-29e3-45cb-81a6-5c6595491c30
Clyne, T.W.
00678bf7-17de-46e8-9b35-bf1ca73bce9b
Golosnoy, I.O.
40603f91-7488-49ea-830f-24dd930573d1
Tan, J.C.
64748a9f-f771-44c3-ac63-fd554193c592
Markaki, A.E.
26beec1d-29e3-45cb-81a6-5c6595491c30

Clyne, T.W., Golosnoy, I.O., Tan, J.C. and Markaki, A.E. (2006) Porous materials for thermal management under extreme conditions. Philosophical Transactions of The Royal Society A, 364 (1838), 125-146. (doi:10.1098/rsta.2005.1682).

Record type: Article

Abstract

A brief analysis is presented of how heat transfer takes place in porous materials of various types. The emphasis is on materials able to withstand extremes of temperature, gas pressure, irradiation, etc., i.e. metals and ceramics, rather than polymers. A primary aim is commonly to maximize either the thermal resistance (i.e. provide insulation) or the rate of thermal equilibration between the material and a fluid passing through it (i.e. to facilitate heat exchange). The main structural characteristics concern porosity (void content), anisotropy, pore connectivity and scale. The effect of scale is complex, since the permeability decreases as the structure is refined, but the interfacial area for fluid–solid heat exchange is, thereby, raised. The durability of the pore structure may also be an issue, with a possible disadvantage of finer scale structures being poor microstructural stability under service conditions. Finally, good mechanical properties may be required, since the development of thermal gradients, high fluid fluxes, etc. can generate substantial levels of stress. There are, thus, some complex interplays between service conditions, pore architecture/scale, fluid permeation characteristics, convective heat flow, thermal conduction and radiative heat transfer. Such interplays are illustrated with reference to three examples: (i) a thermal barrier coating in a gas turbine engine; (ii) a Space Shuttle tile; and (iii) a Stirling engine heat exchanger. Highly porous, permeable materials are often made by bonding fibres together into a network structure and much of the analysis presented here is oriented towards such materials.

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Published date: January 2006

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Local EPrints ID: 48588
URI: https://eprints.soton.ac.uk/id/eprint/48588
ISSN: 1364-503X
PURE UUID: 6f4311c3-6c5e-47bb-b470-3e3656b9ea9c

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Date deposited: 01 Oct 2007
Last modified: 13 Mar 2019 20:56

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