Lotus-type porous copper is a porous medium made of copper that contains many straight pores. To effectively employ lotus-type porous copper as a heat sink, it is necessary to clarify the pore effect on the thermal conductivity of lotus copper. This article describes an experimental and analytical investigation on the effective thermal conductivities of lotus copper parallel and perpendicular to the pores. The lotus copper displayed anisotropy of the effective thermal conductivity. The effective thermal conductivity keff⊥ perpendicular to the pores was lower than that of the parallel ones keff∥ and was 40% that of lotus copper material ks with porosity ε of 0.4. Experimental data for keff∥ showed good agreement with analytical results derived from the assumption that heat flow through the cross-sectional area parallel to the pore axis is proportional to (1−ε). Experimental data for keff⊥ showed good agreement with the analytical results derived from the assumption of orthorhombic symmetry and with the numerical results under a uniform staggered array with a nonuniform pore diameter.
Lotus-type porous copper is a form of copper that includes many straight pores, which are produced by the precipitation of supersaturated gas dissolved in the molten metal during solidification. The lotus-type porous copper is attractive as a heat sink because a higher heat transfer capacity is obtained as the pore diameter decreases. We investigate a fin model for predicting the heat transfer capacity of the lotus-type porous copper. Its heat transfer capacity is verified to be predictable via the straight fin model, in which heat conduction in the porous metal and the heat transfer to the fluid in the pores are taken into consideration by comparison with a numerical analysis. We both experimentally and analytically determine the heat transfer capacities of three types of heat sink: with conventional groove fins, with groove fins that have a smaller fin gap (micro-channels) and with lotus-type porous copper fins. The conventional groove fins have a fin gap of 3 mm and a fin thickness of 1 mm, the micro-channels have a fin gap of 0.5 mm and a fin thickness of 0.5 mm, and the lotus-type porous copper fins have pores with a diameter of 0.3 mm and a porosity of 0.39. The lotustype porous copper fins were found to have a heat transfer capacity 4 times greater than the conventional groove fins and 1.3 times greater than the micro-channel heat sink under the same pumping power.
Lotus-type porous metal with many straight pores is attractive as a heat sink because larger heat transfer capacity is obtained due to the small diameter of the pores. The heat transfer capacity of the lotus-type porous copper heat sink was calculated using the model with the pores of uniform diameters. However, actual lotus-type porous metals have a distribution of pore diameter. In the present work, we investigated the lotus-type porous copper fin model (non-uniform pore model) by considering size distribution of measured on the actual measurement of the pore diameters on a cross-section of the lotus-type porous copper fin. Prediction of the heat transfer characteristics for the lotus-type porous copper heat sink shows a good agreement with the experimental data. In addition, the predicted heat transfer coefficient of non-uniform pore model also shows a good agreement with the uniform pore models. Thus, it is clarified that the heat transfer characteristic of the lotus-type porous copper heat sink can be predicted by the uniform pore model.
Lotus-type porous copper with many straight pores is produced by precipitation of supersaturated gas when the melt dissolving gas is solidified. Lotus-type porous copper is attractive as a heat sink because a higher heat transfer capacity is obtained as the pore diameter decreases. The main features of lotus-type porous metals are as follows; (1) the pores are straight, (2) the pore size and porosity are controllable, and (3) porous metals with pores whose diameter is as small as ten microns can be produced. We developed a lotus-type porous copper heat sink for cooling of power devices. Firstly we investigated the effective thermal conductivity of the lotus copper, considering the pore effect on heat flow. Secondly, we investigated a straight fin model for predicting the heat transfer capacity of lotus copper. Finally, we examined experimentally and analytically determined the heat transfer capacities of three types of heat sink with conventional groove fins, with groove fins having a smaller fin gap (micro-channels) and with lotus-type porous copper fins. The lotus-type porous copper heat sink were found to have a heat transfer capacity 4 times greater than the conventional groove heat sink and 1.3 times greater than the micro-channel heat sink at the same pumping power.
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