Study On Cooling Capacity Of Micro-/mini-channel And Micro-jet Impingement Heat Sinks Using Liquid Metals

Heat disspation is an important factor limiting the development of MEMS.Water is most used in existing cooling technologies.Liquid metals have better thermophysical properties comparing with water,thus,cooling systems using liquid metals as coolant may obtain better cooling capacity.In this dissertation,a study was carried out on the cooling capacity of micro-/mini-channel and micro-jet impingement heat sinks using liquid metals.Because the liquid metal flow in the channel is often thermally fully developed while hydrodynamically developing due to its extremely low Prandtl number,the thermal resistance model for liquid metals is practicable only when the hydraulic diameter is small.Thus,the thermal resistances model for micro-/mini-channel heat sinks using liquid metals is developed,which represents satisfactory accuracy.The critical values and feasible regions of the micro-channel heat sinks are obtained.Comparing with water,liquid gallium(Ga)can only achieve a better cooling capacity when the parameter is larger or less than its critical value or the parameter combination lies within the feasible regions using in the same micro-channel heat sink.It is indicated that the liquid metals are more suitable for mini-channel heat sink due to the analysis of component proportion of the thermal resistance of the heat sink.An optimal design program is developed based on genetic algorithm.The minimum thermal resistances of water-and Ga-based heat sinks are compared.In the laminar regime,the Ga-based heat sink has a smaller minimum thermal resistance unless the heat sink is long enough or the channel is high enough.Without the laminar constraint,the minimum thermal resistance of Ga-based heat sink is always smaller.The thermal resistance models of JISC,JIBC and HBC heat sinks using water and liquid metals as coolants are established.Comparing with the experiment data,it is known that both thermal resistance models and numerical method have high precision when water is used,but only the numerical method can be applicated when liquid metal is used.The thermal resistance model is appropriately revised using the numerical results to make it has enough accuracy for liquid metals.Comparing the cooling capacity of liquid Ga or water in the same micro-jet heat sink,the influences of coolants and structure parameters on the micro-jet heat sinks are obtained.The thermal resistances of the same micro-jet impingement heat sinks using Ga are always smaller than the counterparts using water.Due to the asymmetry of the outlet,the orders of thermal resistances of the three systems using the two coolants are different.There exists an optimal space of adjacent nozzles to obtain a minimum thermal resistance of the heat sinks;the thermal resistances of the heat sinks increase with an increasing nozzle diameter;comparing with liquid Ga,the side gap affects the thermal resistance of HBC heat sink more obviously when water is used as coolant.The thermophysical properties of Ga In_y are predicted by using the artificial neural network.The optimal mass fraction of indium used in the micro-channel or JIBC heat sinks is obtained.The thermal resistances of the same heat sink,the corresponding optimal heat sinks or the same JIBC heat sink using gallium,optimal Ga In_yor Galinstan are compared,indicating that the heat sinks using optimal Ga In_y have the smallest thermal resistance.In summary,thermal resistance models that are applicable to micro-/mini-channel and micro-jet impingement heat sinks using liquid metals are established in this dissertation,which enriches the convection heat transfer theory of liquid metals.Besides,the comparative results of the cooling capacity of these two heat sinks using liquid metals or water can provide practical guidance for their coolant choice and optimization design.