Heat and fluid flow in MEMS-based pin fin heat sinks.

摘要

Rapid progress in compact micro heat exchanger technology has stimulated the design of microchannel type micro heat exchangers in various engineering applications. Heat transfer in microchannels has received significant amount of attention and many studies have been conducted to unveil their heat transfer performance. However, enhancing the surface of microchannels to mitigate boiling heat transfer and improving their thermal-hydraulic performance have not extensively applied in micro scale yet. This might be due to the limitation imposed by micromachining surfaces in micro scale and the still existing ambiguity and lack of theory in micro scale heat transfer in plain microchannels. The research work has been directed towards proposing micro pin fin heat sinks as an alternative of plain microchannels and conducting experiments on micro pin fin devices. An experimental setup has been constructed to enable experimental investigation on boiling and single-phase flow in micro pin fin devices. A pioneering investigation on micro pin fin devices has been conducted to present them as an alternative type of second generation micro heat sinks and obtain their thermal-hydraulic and boiling heat transfer performance.; In single-phase flow studies, it has been found that existing conventional scale correlations were not able to predict the friction factors and Nusselt number accurately particularly for low Re due to the endwall effects and the effect of the delay in separation and provided fair agreement at high Reynolds numbers. The performance of the micro pin fin device is dependent on the performance evaluation criterion used, as well as on the hydrodynamic conditions. For fixed flow rate, un-streamlined densely packed pin fins promoting flow separation should be favored. For a fixed pressure drop and pumping power, utilizing streamlined pin fin heat sinks is favored at moderate pressure drops and flow rates, while for very high pressure drops and flow rates pin fins promoting flow separation should be favored.; In boiling studies, it has been found that existing large scale correlations provided large scatter and inability to predict the heat transfer coefficients. More research should be conducted to develop better prediction tools.