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Research Papers

Modeling Forced Convection in Finned Metal Foam Heat Sinks

[+] Author and Article Information
Christopher T. DeGroot

Department of Mechanical and Materials Engineering, University of Western Ontario, London, ON, N6A 5B9, Canadacdegroo@uwo.ca

Anthony G. Straatman1

Department of Mechanical and Materials Engineering, University of Western Ontario, London, ON, N6A 5B9, Canadaastraatman@eng.uwo.ca

Lee J. Betchen

Department of Mechanical and Materials Engineering, University of Western Ontario, London, ON, N6A 5B9, Canadaljbetche@uwo.ca

1

Corresponding author.

J. Electron. Packag 131(2), 021001 (Mar 27, 2009) (10 pages) doi:10.1115/1.3103934 History: Received November 21, 2007; Revised January 07, 2009; Published March 27, 2009

A numerical study has been undertaken to explore the details of forced convection heat transfer in finned aluminum foam heat sinks. Calculations are made using a finite-volume computational fluid dynamics (CFD) code that solves for the flow and heat transfer in conjugate fluid/porous/solid domains. The results indicate that using unfinned blocks of porous aluminum results in low convective heat transfer due to the relatively low effective thermal conductivity of the porous aluminum. The addition of aluminum fins to the heat sink significantly enhances the heat transfer with only a moderate pressure drop penalty. The convective enhancement is maximized when thermal boundary layers between adjacent fins merge together and become nearly developed for much of the length of the heat sink. It is found that the heat transfer enhancement is due to increased heat entrainment into the aluminum foam by conduction. A model for the equivalent conductivity of the finned/foam heat sinks is developed using extended surface theory. This model is used to explain the heat transfer enhancement as an increase in equivalent conductivity of the device. The model is also shown to predict the heat transfer for various heat sink geometries based on a single CFD calculation to find the equivalent conductivity of the device. This model will find utility in characterizing heat sinks and in allowing for quick assessments of the effect of varying heat sink properties.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A magnified view of a typical aluminum foam sample (4)

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Figure 2

Schematic of the domain under consideration

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Figure 3

Plot showing the grid used for computations for a four-finned heat sink

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Figure 4

Plot showing experimental and numerical results for the total heat transfer as a function of air velocity for several aluminum foam finned heat sinks

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Figure 5

Plot showing the pressure drop from experiments, as well as CFD calculations as a function of air velocity for several aluminum foam finned heat sinks

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Figure 6

Contour plots of the dimensionless air temperature, θF=(T−T∞)/(Tb−T∞), in aluminum foam heat sinks having (a) zero fins, (b) one fin, (c) two fins, (d) four fins, (e) six fins, and (f) eight fins. Plots are for a yz-plane located at the outlet and a fluid velocity of 1.0 m/s.

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Figure 7

Contour plots of the dimensionless air temperature, θF=(T−T∞)/(Tb−T∞), in aluminum foam heat sinks having (a) zero fins, (b) one fin, (c) two fins, (d) four fins, (e) six fins, and (f) eight fins. Plots are for a fluid velocity of 1.0 m/s, and cross sections are extracted from the xy-plane 5 mm above the base.

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Figure 8

Comparison of the heat transfer enhancement obtained by adding aluminum foam to finned and unfinned channels

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Figure 9

Comparison of the pressure drop penalty that results from adding aluminum foam to finned and unfinned channels

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Figure 10

Heat transfer results for increasing numbers of fins with no foam in comparison to the heat transfer results for an eight-finned aluminum foam heat sink (shown with dotted lines) at various bulk velocities

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Figure 11

Plot of the equivalent conductivities at each flow rate based on the arithmetic mean temperature and the standard definition of m

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Figure 12

Plot of the equivalent conductivities using the proposed definition at each flow rate and the effective conductivity of the foam input into the CFD code

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Figure 13

Plot of the equivalent conductivity of the heat sinks versus the number of solid fins

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Figure 14

Plot of heat transfer versus height of the heat sink based on the present model in comparison to CFD results

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