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TECHNICAL PAPERS: Porous Media

Forced Convection Heat Transfer and Hydraulic Losses in Graphitic Foam

[+] Author and Article Information
A. G. Straatman, L. Betchen

Department of Mechanical and Materials Engineering, The University of Western Ontario, London, ON, N6A 5B9, Canada

N. C. Gallego

Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831

Q. Yu, B. E. Thompson

 Thermalcentric Inc., 24 Ravenglass Cres., London, ON, Canada, N6J 3J5

Porosity is defined in units of percent as the void fraction of the porous material.

J. Heat Transfer 129(9), 1237-1245 (Dec 01, 2006) (9 pages) doi:10.1115/1.2739621 History: Received April 24, 2006; Revised December 01, 2006

Experiments and computations are presented to quantify the convective heat transfer and the hydraulic loss that is obtained by forcing water through blocks of graphitic foam (GF) heated from one side. Experiments have been conducted in a small-scale water tunnel instrumented to measure the pressure drop and the temperature rise of water passing through the foam and the base temperature and heat flux into the foam block. The experimental data were then used to calibrate a thermal non-equilibrium finite-volume model to facilitate comparisons between GF and aluminum foam. Comparisons of the pressure drop indicate that both normal and compressed aluminum foams are significantly more permeable than GF. Results of the heat transfer indicate that the maximum possible heat dissipation from a given surface is reached using very thin layers of aluminum foam due to the inability of the foam to entrain heat into its internal structure. In contrast, graphitic foam is able to entrain heat deep into the foam structure due to its high extended surface efficiency and thus much more heat can be transferred from a given surface area. The higher extended surface efficiency is mainly due to the combination of moderate porosity and higher solid-phase conductivity.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scanning electron microscope images of the graphitic foam specimens tested

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Figure 2

Schematic of experimental setup showing the position and orientation of the graphitic foam, the fluid inlet and outlet, and the heat input

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Figure 3

Plot showing the pressure drop as a function of the filter velocity for the GF specimens considered. The symbols are measured data and the curves are generated from Eq. 1 using the values of permeability and form drag summarized in Table 2.

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Figure 4

Plot showing the Nusselt number as a function of Reynolds number based on De and Aeff for the four GF specimens tested experimentally

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Figure 5

Schematic of computational domain for porous plug computations

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Figure 6

A comparison of the computed and measured results for Nusselt number as a function of Reynolds number for calibration of the computational model

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Figure 7

Plot of the pressure drop as a function of the filter velocity for POCO™ foam and for Al T6201 foam

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Figure 8

Plot of the heat transfer as a function of filter velocity for POCO™ foam and for Al T6201 foam

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Figure 9

Local thermal non-equilibrium distributions on the x-z center plane for (a)U=0.0015m∕s, and (b)U=0.1500m∕s. The local thermal non-equilibrium is defined as: (Ts−Tf)∕(Tb−To)×100.

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Figure 10

Plot of the pressure drop as a function of filter velocity for POCO™ foam compared to three different compressed aluminum foams as reported in Boomsma (7)

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Figure 11

Plot of the Nusselt number (as defined in Boomsma (7)) as a function of filter velocity for POCO™ foam compared to three different compressed aluminum foams as reported in Boomsma (7)

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