Abstract:

The flow and heat transfer characteristics of the liquid-liquid two-phase flow in circular microchannels are experimentally studied. Deionized water was selected as the dispersed phase and high viscosity silicone oil as the continuous phase. The flow pattern and droplet length/shape characteristics were obtained by processing the visualized images taken by a high-speed camera. On this basis, the heat transfer characteristics of the slug flow on the microchannels were investigated. The results show that the average Nusselt number increases with the increase of Reynolds number, and the larger the oil-to-water rate ratio, the more significant the increase in heat transfer coefficient. The Nusselt number decreases with the increase of water content within the range of 0.17—0.83. Although the two-phase average heat capacity increases with the increasing of water content, this increase is offset by the weaker circulating strength in the long liquid droplet under the low Re. Three different types of junctions were selected to generate different lengths of the droplet with controlled mixture velocity and water content. The shorter droplet/slug is more conducive to heat transfer, and the optimization of the droplet length can increase the overall heat transfer coefficient by nearly 26%.

Key words: mini-channel, microfluidics, liquid-liquid two-phase flow, slug flow, heat transfer

摘要：

实验研究了圆形微小通道内液-液两相流的流动和换热特性。选用去离子水为分散相，高黏度二甲基硅油为连续相。通过处理高速摄像所拍摄的可视化图像，总结了液-液两相流流型和液滴的长度/形状特征。并在此基础上考察了低Reynolds数下液-液弹状流对微小通道的换热作用。结果表明，平均Nusselt数随着Reynolds数的增加而增加，且油水比越大传热系数增加幅度越明显。Nu随着含水率的增加而降低。虽然含水率增加会使两相平均热容量提高，但在低Reynolds数下，这种提高被其长液滴内较弱的循环强度所抵消。选用三种不同形式接头在相同混合速度和含水率的情况下生成不同长度的液滴，发现短液滴更有利于换热。相同工况下，液滴长度的优化可以使整体传热系数提高近26%。

关键词: 微小通道, 微流体学, 液-液两相流, 弹状流, 传热