HEAT TRANSFER IN A CHANNEL WITH INTERMITTENT HEATED ALUMINUM-FOAM HEAT SINKS

2017 ◽  
Vol 48 (3) ◽  
pp. 211-220
Author(s):  
Ayla Dogan ◽  
Bahadir Oney
Keyword(s):  
Heat Transfer ◽  
Aluminum Foam ◽  
Heat Sinks

Height Effect on Heat-Transfer Characteristics of Aluminum-Foam Heat Sinks

2005 ◽  
Vol 128 (6) ◽  
pp. 530-537 ◽  
Author(s):  
W. H. Shih ◽  
W. C. Chiu ◽  
W. H. Hsieh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Temperature Difference ◽  
Thermal Equilibrium ◽  
Aluminum Foam ◽  
Heated Surface ◽  
Heat Sinks ◽  
Local Thermal Equilibrium ◽  
Cooling Air

This study investigates and demonstrates the two conflicting effects of the height on the cooling performance of aluminum-foam heat sinks, under the impinging-jet flow condition. In addition, the nonlocal thermal equilibrium phenomena are also investigated. When the H∕D (the height to diameter ratio) of the aluminum-foam heat sinks is reduced from 0.92 to 0.15, the Nusselt number of aluminum-foam heat sinks is found to first increase and then decrease. The increase in the Nusselt number is caused by the increased percentage of the cooling air reaching the top surface of the waste-heat generation block, resulting from the reduced flow resistance. The decrease in the Nusselt number is mainly caused by the reduction in the heat-transfer area between the cooling air and the solid phase of the aluminum-foam heat sink. As the porosity and pore density decrease, the Nusselt number increases and the convective heat transfer is enhanced. The correlation between the Nusselt and Reynolds numbers for each of the 15 samples studied in this work is reported. For samples with a H∕D>0.31, the temperature difference between the solid and gas phases of aluminum-foam heat sinks decreases with the increase of the distance from the heated surface. The non-local thermal equilibrium regime is observed to exist at low Reynolds number and small dimensionless height. On the other hand, for samples with a H∕D⩽0.31, the temperature difference first increases and then decreases with the increase of the distance from the heated surface; the maximum temperature difference is located at z∕H≒0.25 and is independent of the Reynolds number.

A Novel Semi-empirical Model for Evaluating Thermal Performance of Porous Metallic Foam Heat Sinks

2004 ◽  
Vol 127 (3) ◽  
pp. 223-234 ◽  
Author(s):  
Tzer-Ming Jeng ◽  
Li-Kang Liu ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Empirical Model ◽  
Aluminum Foam ◽  
Heat Sinks ◽  
Metallic Foam ◽  
Porous Aluminum ◽  
Transfer Behavior ◽  
Medium Porosity ◽  
Semi Empirical

A novel semi-empirical model with an improved single blow method for exploring the heat transfer performance of porous aluminum-foam heat sinks in a channel has been successfully developed. The influencing parameters such as the steady-state air preheating temperature ratio, Reynolds number and medium porosity on local and average heat transfer behavior of porous aluminum-foam heat sinks in a channel are explored. The heat transfer enhancement of using a porous heat sink in a channel to a hollow channel is, (Nu¯b)ss∕(Nu¯b)ε=1, much greater than unity and generally decrease with increasing Re. Furthermore, two new correlations of (Nu¯b)ss and (Nu¯i)ss in terms of ϴ,Re,Da,γ and ε are proposed. As compared with the results evaluated by the transient liquid crystal method, the channel wall temperatures predicted by the present semi-empirical model have a more satisfactory agreement with the experimental data, especially for the cases with smaller porosities. The limitations with relevant error maps of using the transient liquid crystal method in porous aluminum foam channels are finally postulated.

Modeling Forced Convection in Finned Metal Foam Heat Sinks

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Christopher T. DeGroot ◽  
Anthony G. Straatman ◽  
Lee J. Betchen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Heat Sink ◽  
Aluminum Foam ◽  
Heat Sinks ◽  
Moderate Pressure ◽  
Transfer Enhancement ◽  
Equivalent Conductivity ◽  
Porous Aluminum

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.

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

2007 ◽  
Vol 129 (11) ◽  
pp. 1554-1563 ◽  
Author(s):  
W. H. Shih ◽  
F. C. Chou ◽  
W. H. Hsieh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Generation ◽  
Aluminum Foam ◽  
Heat Sinks ◽  
Pore Density ◽  
Heat Transfer Characteristics ◽  
Measured Velocity ◽  
Transfer Characteristics ◽  
Convective Resistance

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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