Experiments have been carried out to investigate the heat transfer characteristics from aluminum-foam heat sink placed on a heat source in a channel. Thermal performance of aluminum-foam heat sinks is evaluated in terms of the Nusselt number and thermal resistance of heat sinks. The pore density of aluminum-foam heat sinks and the Reynolds number are varied in the range of the parameters: 10, 20, 40 pores per inch (PPI) and 710 2900, respectively. It is found that thermal resistance is substantially reduced by employing an aluminum-foam heat sink with low pore density due to relatively intense airflow through the heat sink. The aluminum-foam heat sink may provide 28% or higher thermal performance than a conventional parallel-plate heat sink of the same size. Further, the aluminum-foam heat sinks can dramatically reduce the overall mass of electronics-cooling devices owing to high porosity.

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This paper provides an update on work at Penn State University on advanced thermal interface material (TIM) and attachment technology. The TIM concept consists of a “Low Melting Temperature Alloy” (LMTA) bonded to a thin copper substrate. The present work includes analytical modeling to separate the interface resistance (Rint) into “material” and “contact” resistance. Modeling indicates that contact resistance accounts for 1/3 of the interface resistance (Rint). Additional alloys have been identified that have thermal conductivity approximately three-times those identified in the previous 2002 publication. Thermal degradation of the LMTA TIM was also observed in the present work after extended thermal cycling above the melting point of the alloy. Possible mechanisms for this degradation are oxidation and contamination of the alloy layer rather than the inter-metallic diffusion. Use of the high thermal conductivity alloys, and soldered contact surfaces will provide very low Rint as well as minimizing the thermal degradation. It appears that Rint as small as, or less than, 0.005 cm2-K/W may be possible. Description of the modified Penn State TIM tester is provided, which will allow measurement of Rint = 0.01 cm2-K/W with less than 30% error.

Prediction of pressure drop for duct flow through heat sinks involves calculation of inlet and exit losses. These predictions are typically done using Kc and Ke for “parallel plate channels” from the Kays and London book, Compact Heat Exchangers. However, these equations assume fully developed flow at the exit and thus include the effect of full velocity profile development. Electronic heat sinks operate in the “developing flow” region. So, use of the published Kc and Ke from the Kays and London book will result in over-estimate of the actual Kc and Ke values. The authors have performed analysis that allows accurate calculation of Kc and Ke values with parallel plate channels for operation in the “developing flow” region. The results are presented in graphical form as a function of contraction ratio and x+ (= x/DhRe). These results will allow accurate estimate of Kc and Ke values for developing flow. Entrance and exit losses can account for as much as 30% of the total pressure drop in electronic heat sinks having short flow lengths. However, the error associated with evaluation of Kc and Ke based on fully developed flow for parallel plates is small.