工质对微通道沸腾液膜瞬态变化的影响

The Effects of Working Fluids on Transient Change of Liquid Film During Boiling in the Microchannel

本文采用去离子水和无水乙醇两种工质,利用微通道流动沸腾同步测量实验系统,研究了液膜厚度的瞬态变化规律,实验发现流动沸腾形成的初始液膜厚度在毛细数Ca很宽的范围内都遵循Taylor流动原理;液膜形成后,在蒸发和蒸汽流动携带的耦合作用下,厚度迅速减薄直至蒸干;由于水的汽液黏度比小,速度梯度小,剪切作用带来的液膜厚度减少量小,且水的汽化潜热大,吸收相同热量时蒸发量小,导致水的液膜厚度变化斜率较小,通过理论分析提出了沸腾液膜厚度变化的计算模型,计算结果与实验结果的误差小于20%。

In this paper,two working fluids,deionized water and anhydrous ethanol,were used to study the transient change of liquid film thickness during boiling by microchannel flow boiling synchronous measurement experimental system.It was found that the initial liquid film thickness formed during flow boiling similar with Taylor flow in a wide range of capillary number Ca.The liquid film thickness decreases rapidly until it is evaporated under the coupling effect of evaporation and steam flow after the liquid film is formed.Due to the small ratio of the viscosity of vapor water and liquid water,velocity gradient is small,the shearing action of liquid film thickness reduction is small.The evaporation rate of water is small when the same heat is absorbed since the latent heat of water is large,which results in the small change in the liquid film thickness of the water.the liquid film thickness change calculation model is put forward through the theoretical analysis of boiling,and the error of the prediction of this model is less than 20%.