微通道中纳米流体流动沸腾换热性能研究

Flow Boiling Heat Transfer Performance of Nanofluids in a Microchannel

为研究微通道中纳米流体流动沸腾的换热性能,设计了一种水力直径为143μm的矩形硅基微通道,搭建了研究微通道中纳米流体流动沸腾换热的高速测量和光学可视化实验平台。研究了质量分数为0.2%的Al2O3纳米流体及纯水在微通道中的流动沸腾换热性能。通过比较在两种换热工质中系统压降和壁温,并结合流型的同步变化分析了纳米流体的流动沸腾换热性能。结果表明:纳米粒子的加入会使微通道中流动沸腾时流型发生变化,以小气泡和泡状流为主。通道沸腾换热得到加强,壁温和系统压降波动幅度减小,出现沸腾不稳定性时的热流密度升高,系统的OFO(onset of flow oscillation)点明显后移,系统稳定沸腾区域增大。采用纳米流体做工质不仅对于微通道中流动沸腾不稳定性具有抑制作用,而且能够改善微通道中流动沸腾时的流动和换热性能。

In order to investigate the flow boiling heat transfer performance of nanofluids in microchannel,a single rectangular silicon microchannel with the hydraulic diameter of 143μm was designed,and the simultaneous measurement and visualization experimental systems were set up.The nanofluid with Al2O3 nanoparticles（mass fraction = 0.2%） and pure water were used respectively as the working fluids in the microchannel;the wall temperature and system pressure drop variations of the microchannel during the flow boiling of the two working fluids were compared.According to the results of comparison and combining with the observed simultaneous change in flow pattern,the flow boiling performances of nanofluids were studied.The results show that the flow boiling pattern in the microchannel changes when the nanoparticles were added in the fluid,which causes that the small bubbles and bubbly flow appear in the microchannel during flow boiling,and the boiling heat transfer in the microchannel is strengthened,the fluctuations of wall temperature and system pressure drop decrease.During the boiling instable period,the heat flux significantly increases,and the appearance of the OFO（onset of flow oscillation） point of the system is obviously delayed,so that the stable boiling region of the system becomes larger.In short,using nanofluids as the working fluid can curb the flow boiling instability and improve the heat transfer and flow boiling performance in the microchannel.