Influence Of Structural Parameters On The Boiling Heat Transfer Characteristics Of Porous Microchannels

Nowadays,almost all electronic systems are developing toward small sizes,but the operating power of the system is getting larger and larger,and the local heat flux is constantly increasing.To deal with such kind of high heat flux devices,micro channel cooling is one of the most potential technology.Both of experimental systems,using deionized water and R134 a as working fluid respectively,are designed and built.The influence of two copper powder shapes is investigated.The structural parameters(pore size distribution,porosity,surface wettability)were characterized by Scanning electron microscopy,Archimedes method,Mercury intrusion method and Fixed droplet method.Experiment results show that for the microchannel with a single particle size,spherical copper powder samples show the best heat transfer performance at low heat flux,but their boiling onset point(ONB)is relatively late.At high heat flux,the critical heat flux density(CHF)of the dendritic copper powder samples is the largest.It is about 1.2 times that of the other microchannels,and its maximum heat transfer coefficient is also greater than that of spherical copper powder ones.When the inlet flow rate and the sintering bottom thickness are increased,the gap between the two copper powders can be reduced,but for the dendritic copper powder,it still exhibits better heat transfer performance in the high heat flux area.As for porous microchannels with mixed particles,the heat transfer performance of porous microchannels sintered with spherical,dendritic copper powders was compared and analyzed.The experiment results showed that dendritic copper powder samples were relatively superior.The heat transfer coefficient is highest.It is due that dendritic copper powder samples have more connected holes,which improves the liquid supply at high heat flux.Dendritic copper powder samples could suppress boiling instability effectively compared to the samples with spherical copper powder.For R134 a system,the experiment found that the heat transfer coefficient of the porous microchannel increases with heat flux,at first and then decreases.The higher flow rate could strengthen the heat transfer performance.The samples with mixed particle sizes can provide a large quantity of nuclear sites required for boiling and presents better heat transfer performance.Relative to single-particle-size micro-channels,mixed micro-channels can suppress pressure drop pulsation significantly.Porous microchannels with R134 a as the working medium have great potential for development in the field of micro-refrigeration.