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RESEARCH PAPERS: Porous Media

# Experimental Investigation of the Heat Transfer Characteristics of Aluminum-Foam Heat Sinks With Restricted Flow Outlet

[+] Author and Article Information
W. H. Shih, F. C. Chou

Department of Mechanical Engineering,  National Chung Cheng University, Chia-Yi 621, Taiwan, Republic of China

W. H. Hsieh1

Department of Mechanical Engineering,  National Chung Cheng University, Chia-Yi 621, Taiwan, Republic of Chinaimewhh@ccunix.ccu.edu.tw

1

Corresponding author.

J. Heat Transfer 129(11), 1554-1563 (Feb 10, 2007) (10 pages) doi:10.1115/1.2759972 History: Received April 26, 2006; Revised February 10, 2007

## Abstract

This study investigates the heat transfer characteristics of aluminum-foam heat sinks with restricted flow outlets under impinging-jet flow conditions. An annular flow-restricting mask is used to control the height of the flow outlet of the aluminum foam sink, forcing the cooling air to reach the heat-generation surface. The enhanced heat transfer characteristics of aluminum-foam heat sinks using these flow-restricting masks are measured experimentally in this work. The effects of porosity, pore density and length of sample, air velocity, and flow outlet height on the heat transfer characteristics of aluminum-foam heat sinks are investigated. Results show that the effect of the flow outlet height is stronger than that of the pore density, porosity, or height of the aluminum heat sinks studied in this work. A general correlation between the Nusselt number and the Reynolds number based on the equivalent spherical diameter of the aluminum foam is obtained for 32 samples of aluminum-foam heat sinks with different sample heights $(20–40mm)$, pore densities $(5–40ppi(pore∕inch))$, porosities (0.87–0.96), and flow outlet heights $(5–40mm)$. It should be noted that, based on the measured velocity profile, the increase of the Nusselt number of the aluminum-foam heat sink with the decrease in the flow outlet height is caused by the reduced convective resistance at the solid-gas interface through the increased velocity near the heat-generation surface. The reduction in flow outlet height increases the local thermal nonequilibrium condition near the heat-generation surface.

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## Figures

Figure 1

(a) Schematic diagram of an aluminum-foam heat sink with a flow-restricting mask and (b) a photo of an aluminum-foam heat sink used in the study (ppi=10 and porosity=0.92)

Figure 2

Experimental apparatus for the measurements of heat transfer characteristics of aluminum-foam heat sinks

Figure 3

Measured outlet velocity profiles from three repeated tests at three different angles (inset: top view of the heat sink showing the three different angles at which the velocity profiles are measured)

Figure 4

Apparatus for measuring heat loss

Figure 5

Measured and normalized Nusselt numbers as functions of the Reynolds number for heat sinks with different height of flow outlet

Figure 6

Measured gas velocity as a function of the normalized flow outlet height for three samples with different flow outlet heights

Figure 7

Effect of porosity and flow outlet height on the Nusselt number under different Reynolds numbers

Figure 8

Effect of pore density and flow outlet height on the Nusselt number under different Reynolds numbers

Figure 9

Effect of length of aluminum foam and flow outlet height on the Nusselt number under different Reynolds numbers

Figure 10

Comparison between the measured and calculated Nusselt numbers

Figure 11

Effect of the Reynolds number on the distributions of dimensionless solid-phase temperature of samples 3-4-4 and 3-4-2

Figure 12

Effect of the Reynolds number on the distributions of dimensionless gas-phase temperature of samples 3-4-4 and 3-4-2

Figure 13

Effect of the Reynolds number on the distributions of dimensionless temperature difference of samples 3-4-4 and 3-4-2

Figure 14

Comparison of the results from this work and previous studies

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