Flow Resistance And Heat Transfer Characteristics Of Staggered Micro Pin Fin Heat Sinks

Developments in microelectronic technology have led to significant increases in power densities in advanced equipment. Many techniques for improving cooling technology for such equipment with high heat fluxes have been proposed, as traditional cooling by air is insufficient. Recent improvements in microfabrication technology have enabled the realization of a microscale cooling method: forced convection across micro pin fin heat sinks. The heat sinks consist of arrays of micro pin fins which are arranged inside a rectangular microchannel. The pin fins can enhance heat transfer by increasing surface area and disturbance. A literature survey reveals the absence of any microscale studies pertinent to this cross flow configuration. Therefore, this paper reports an experimental investigation on flow resistance and heat transfer characteristics associated with the forced flow of de-ionized water through circular and diamond shaped micro pin fin arrays.An experimental investigation on flow resistance characteristics of the pin fin heat sinks has been first performed. It has found that the array with more and smaller pins can create greater flow resistance under the same pin density. The difference of flow resistances between circular pin fins arrays and diamond pin fins arrays increases as the increasing volume flow rate which demonstrates the importance of the pin shape. The existing conventional scale correlations do not accurately predict the friction factor for micro pin fin arrays due to endwall effects which bring higher flow resistance. There is a change in the relationship of f to Re around Re=100. It is necessary to investigate the characteristics at Re=80-130.Heat transfer characteristics associated with the forced flow of de-ionized water over diamond shaped micro pin-fin bundles have been experimentally investigated. It is shown that the heat sink can still keep the operating temperature at a relatively low level when the heat flux is more than 106W/m2. The dependence of the Nusselt number on the Reynolds number is considerably notable. The total thermal resistance decreases with the increasing pumping power. Compared with the convection thermal resistance, thermal resistance due to the increase in liquid temperature has more significant effect on the performance of the micro heat sink.A comparison of experimental results of heat transfer characteristics for the three devices has been conducted. In comparison with the circular pin fin heat sinks, the Nusselt numbers of the diamond pin fin heat sink are strongly dependent on the Reynolds numbers. For a fixed flow rate, the heat transfer performance of the diamond pin fin array is better than that of the circular pin fin arrays. For a fixed pumping power, the circular pin fin array with less and large pins is favored which has good cooling capacity. The diamond pin fins which has non-streamline body do not consume extra pumping power and have better thermal-hydraulic performance.As seen from the experimental results, the forced convection over micro pin fin heat sinks is a very effective heat transfer mode. Pioneering investigation on micro pin fin devices is needed to present them as an alternative type to compact micro heat exchanger.