粗糙度对微通道内两相流摩擦压降的影响

Effect of surface roughness on two-phase fractional pressure drop through microchannels

以去离子水和质量分数为0.3%的水基Al_2O_3纳米流体为工质,对水力直径为1 241μm的矩形微通道内流动沸腾过程进行研究。为了探究微通道壁面粗糙度对两相流摩擦压降的影响情况,运用化学抛光处理手段来改变壁面粗糙度。研究结果表明:实验工况相同时,两相流摩擦压降随着微通道壁面粗糙度的增大而增大;纳米流体为工质时两相流摩擦压降高于去离子水为工质时两相流摩擦压降,高热流密度下更为差异明显;将实验值分别与3种分相模型的预测值对比来验证现有压降模型的准确性,结果偏差较大,而且壁面越粗糙预测效果越差。现有的压降计算模型需要进一步完善以增强其普适性。

Flow boiling in rectangular microchannels with a hydraulic diameter of 1 241 μm was investigated, the working fluids were deionized water and water based A1203 nanofluid （mass fraction of 0.3%）. In order to find the impact of surface roughness on the two-phase fractional pressure drop, chemical polishing process was used to change the surface roughness. The results indicate that the two-phase frictional pressure drop increases as the surface roughness increases under the same experimental conditions. The two-phase frictional pressure drop is higher when nanofluid is working fluid, and the difference is more obvious under the condition of high heat flux. To test the applicability of existing correlations for two-phase pressure drop in microchannels, the experimental data were compared with predicted value of three different separated flow correlations, respectively. Errors are quite big, and the accuracy of prediction would decrease when the surface roughness increases. The existing correlations need to be verified for better adaptability.