Abstract:

Annular flow in microchannels is widely used in the fields of chip heat dissipation and fine chemical synthesis due to its efficient thermal mass transfer. The on-line measurement of the thin liquid film thickness and flow pattern of annular flow was realized by using the Micro-LIF method with an accuracy of ±2 μm. The results show that as the gas phase shear force increases, the liquid film thickness decreases, and the wave shape changes from low-frequency and high-amplitude waves to high-frequency and low-amplitude waves. When dichloromethane liquid flow rate is 3 ml/min and the gas content is 0.7, the fluctuation frequency can reach up to 260 Hz. Under the same gas content, the liquid film morphology is determined by the viscosity and surface tension of liquids, the liquid film thickness increases with the fluid viscosity, and the frequency of liquid film fluctuation decreases with the liquid film surface tension. The prediction model of thin liquid film thickness for different fluids was constructed through the force analysis of thin liquid film, and the maximum deviation of the predicted value from the experimental value was ±15%. This study clarifies the effects of different fluids and gas velocities on the fluctuations and scales of the liquid film in the microchannel, and provides theoretical guidance for the enhanced heat and mass transfer of the thin liquid film.

Key words: microfluidics, two-phase flow, thin liquid film fluctuations, Micro-LIF method, gas content

摘要：

微通道中环状流广泛应用于精细化学品合成等领域，而环状流中薄液膜的流动形态及厚度对反应过程的热质传递影响显著，因此实验利用激光诱导荧光法对薄液膜厚度进行精准在线测量。结果表明，随气相剪切力增大，液膜厚度降低，波动形态由低频高振幅波转变为高频低振幅波。二氯甲烷液相流量为3 ml/min、含气率为0.7时波动频率最高可达260 Hz。在相同含气率下，液膜形态由流体黏度和表面张力决定，液膜厚度随流体黏度增大而增大，液膜波动频率随表面张力增大而减小。通过薄液膜在微通道内受力分析，构建了不同流体的薄液膜厚度的预测模型，预测值与实验值偏差±15%。本研究明晰了微通道内不同物性液体及气速对液膜波动及厚度的影响，为薄液膜强化热质传递提供理论指导。

关键词: 微流体学, 两相流, 薄液膜波动, 激光诱导荧光法, 含气率