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Research Papers: Porous Media

Heat Transfer in Porous Graphite Foams

[+] Author and Article Information
Brian E. Thompson

Dean of Engineering and Professor
A'Sharqiyah University,
P.O. Box 42,
Ibra 400, Oman
e-mail: bthompson@asu.edu.om

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received July 9, 2013; final manuscript received October 27, 2013; published online December 19, 2013. Assoc. Editor: Andrey Kuznetsov.

J. Heat Transfer 136(3), 032602 (Dec 19, 2013) (7 pages) Paper No: HT-13-1342; doi: 10.1115/1.4025905 History: Received July 09, 2013; Revised October 27, 2013

Measured values of heat transfer and pressure loss are presented for a variety of porous graphite foams in subsonic turbulent airflow. These foams were developed over the last decade to find combinations of high conductivity, porosity, strength, and low density suitable for application to rapid cooling of electronics and to corrosionless heat-exchangers. Measured maxima in the thermal performance that is the ratio of heat transfer to pressure loss, were correlated the pore structure obtained from scanning electron microscopy, to show a linear dependence of thermal performance on the average diameter of interpore windows representative of the cross-sectional area through which cooling air flows. For the same heat transfer, measured pressure losses were reduced by over two orders of magnitude by increasing pore and window diameters. However, the best thermal performance of porous graphite foams that were strong enough for industrial application, had measured pressure losses that were more than an order of magnitude greater than losses in conventional finned heat exchangers.

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Figures

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Fig. 1

Exhaust-to-water heat exchanger made with porous graphite foam

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Fig. 2

Slotted element made with porous graphite foam bonded to copper tubes

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Fig. 3

Porous graphite foam elements in a gas-to-gas heat exchanger

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Fig. 4

Conductive and porous graphite foam

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Fig. 5

Schematic diagram of the experimental apparatus

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Fig. 6

Schematic diagram of the flow configuration

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Fig. 7

Structures of porous graphite foam. (a) Specimen 2A, (b) Specimen 3A, (c) Specimen 3B, (d) Specimen 3C, (e) Specimen 4A, (f) Specimen 4B, and (g) Specimen 4C.

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Fig. 8

Average Nusselt number versus Reynolds number based on bulk flow velocity. Symbols correspond to the three best specimens (A, B, C) from four generations (1, 2, 3, and 4) of trial-and-error development of thermal foams.

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Fig. 9

Pressure loss in height of water column (@ 20 °C) per unit length of foam in the streamwise direction versus Reynolds number based on bulk velocity. Symbols correspond to those shown on Fig. 8.

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Fig. 10

Average Nusselt number versus pressure loss in height of water column (@ 20 °C) per unit length of foam in the streamwise direction. Symbols correspond to those shown on Fig. 8.

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Fig. 11

Average convective heat transfer versus pressure losses in the streamwise direction. Symbols correspond to those shown on Fig. 8.

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Fig. 12

Average convective heat transfer versus pressure losses in the streamwise direction for the specimens shown on Fig. 7. Symbols correspond to those shown on Fig. 8.

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Fig. 13

Maximum measured thermal performance for specimens compared to the average diameter of interpore windows and pore diameter

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