Effect Of Micro-nano Composite Structure On Boiling Heat Transfer Performance Of Sintered Microchannels

With the rapid development of microelectronics heat dissipation,it is increasingly urgent to optimize hardware thermal management.Micro-channel flow boiling technology has become one of the most popular thermal management technologies due to its compact structure,high efficiency of heat transfer and low pump power.Among many micro-channel flow boiling enhanced heat transfer technologies,micro-nano surface is a promising choice,which needs further study because it may have better heat transfer performance.In this thesis,the sintered microchannel is taken as the research object,and the influence of mass flow rate and whether there is a channel on the boiling heat transfer performance of the microchannel is studied.Based on the sintered microstructure,the surface is modified by chemical etching method,and the surface with two size structures is prepared.The structural parameters of the sample are characterized,and the following three aspects of work are carried out:First of all,for four sintered microchannels with different particle sizes,particle size effect has a significant influence on the boiling heat transfer characteristics of sintered microchannels.When the bottom layer thickness is the same,there is an optimal particle size to achieve the best heat transfer performance(HTC and CHF).The PM-120 and PM-150samples have a maximum HTC of 120k W/m~2·K and a peak CHF of over 160W/cm~2 at a mass flow rate of 142kg/m~2·s.Increasing the mass flow rate can effectively enhance the heat transfer performance of the microchannel,restrain the irregularity of pressure pulsation,and make the whole boiling heat transfer more stable.Based on the pressure pulsation curve and the visualization synchronization theory,it is found that in the CHF mechanism,small particle size samples are mainly film boiling,which often occurs explosion boiling,leading to strong disorder of the pressure pulsation curve.For large-particle size samples,it is more because the latter part of the sample is completely dried up due to insufficient replenishment of liquid.When the heat flow is higher,the pressure pulsation periodicity of large-particle size samples is destroyed,which is related to the excellent capillary suction capacity of large-particle size samples.Then,the boiling heat transfer of the groovelless sintering channel was studied.The CHF value of the groovelless sintering channel is much lower than that of the ordinary micro-channel.The heat transfer performance of the groovelless samples with medium particle size is better,and the CHF value can reach about 72W/cm~2.The average pressure drop of the samples without grooves increases with the increase of heat flux.With the increase of heat flux,the pressure pulsation amplitude of the sample without grooves increases continuously,and the pressure pulsation is mainly characterized by high frequency and small period.It was found by visual acquisition that the sample was swayed into liquid near CHF,and film boiling appeared in the middle and downstream of the channel.The nano modification method of sintered microchannel surface by chemical method was explored.The results show that the surface nano modification has limited effect on the boiling heat transfer performance of 30 micron spherical sintered copper powder.For the 120micron spherical sintered copper powder microchannel,the boiling heat transfer performance is improved obviously under the mass flux of 284kg/m~2·s,and the CHF can be effectively improved.Nano modification has little effect on the average pressure drop of sintered microchannels,but can make the pressure pulsation more orderly.The visualization results show that for 120 micron samples,the nano-modification can significantly reduce the explosion and boiling,and the micro-nano pore structure on the wall of the micro-nano structure provides a great capillary force,which can ensure the timely replenishment of liquid in the dry area under high heat flux.Based on previous studies,this thesis further explored the influence of particle size effect and flow effect on sintering micro-channel boiling heat transfer,and studied the performance gain effect of surface nano modification.It lays a foundation for further exploration in this direction in the future.