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.

Thermal Performance Measurement for Confined Heat Sinks by Using a Modified Transient Liquid Crystal Technique

2003 ◽  
Author(s):  
S. T. Kuo ◽  
M. P. Wang ◽  
M. C. Wu ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Heat Sink ◽  
Heat Sinks ◽  
Experimental Investigations ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Preheating Temperature ◽  
Parametric Studies

A series of experimental investigations with a new modified transient liquid crystal method on the studies related to the fluid flow and heat transfer characteristics in a channel installed with a heat sink have been successfully performed. The parametric studies on the local and average effective heat transfer characteristics for confined heat sinks have been explored. The influencing parameters and conditions include air preheating temperature at channel inlet, flow velocity and heat sink types. Besides, a concept of the amount of enhanced heat transfer (AEHT) is introduced and defined as the ratio of j/f. The j/f ratio is almost independent of Reynolds number for a specific confined heat sink. The j/f ratios are 0.0603 and 0.0124 for fully-confined and unconfined heat sinks, respectively.

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 Semi-Empirical Heat Transfer Model for Forced Convection in Pin-Fin Heat Sinks Subjected to Nonuniform Heating

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
S. S. Feng ◽  
T. Kim ◽  
T. J. Lu
Keyword(s):  
Heat Transfer ◽  
Substrate Temperature ◽  
Analytical Model ◽  
Heat Sinks ◽  
Nonuniform Heating ◽  
Transfer Model ◽  
Substrate Thickness ◽  
Fluid Temperature ◽  
Pin Fin ◽  
Semi Empirical

This paper presents a cost effective semi-empirical analytical model for convective heat transfer in pin-fin heat sinks subjected to nonuniform heating set by a circular hot gas impinging jet. Based on empirical correlations taken from the open literature, temperature variations in the heat sink are obtained from the finite volume solution of the semi-empirical model. Based on a purpose-built experimental setup, measurements of a substrate temperature are performed using an infrared camera. These, along with the convective fluid temperature measured at the exit of the pin-fin array, are compared against analytical model predictions, with overall good agreement achieved. Subsequently, the influences of the convection Reynolds number, substrate thickness, and thermal conductivity of material on the distribution of substrate temperature are quantified by the validated model. It is demonstrated that the present model is capable of predicting local thermal behaviors such as the footprints of the pin fins. In addition, with the spreading resistance captured accurately, the model can be used for the design optimization of pin-fin/substrate systems subjected to nonuniform heating.

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