Abstract:

A high-speed camera was utilized to observe the formation of the droplet in viscoelastic fluid in flow-focusing microchannel. The microchannel with a square section of 600 μm×600 μm was used in the experiment. Silicone oil and polyethylene oxide (PEO) solution (0.1%,0.3%,0.6%) with 0.3% surfactant sodium dodecyl sulfate (SDS) were used as dispersed and continuous phases, respectively. Three flow patterns were observed: slug flow, dripping flow and jetting flow. The transition lines for different flow patterns were obtained. The dynamics of breakup for slug droplets was studied. The effects of two-phase flow rates, capillary number and elasticity number of the continuous phase on the size of slug droplet were investigated experimentally. The results indicated that the size of slug droplet decreased with increasing flow rate, capillary number and elasticity number of the continuous phase, but it increased with increasing flow rate of the dispersed phase. The impact of the elasticity of the continuous phase on slug droplet size was relatively small. The correlations for predicting the size of slug droplet were proposed by taking the ratio of two-phase flow rates, and the capillary number and Reynolds number of the continuous phase into account. The prediction result agreed well with the experimental data.

Key words: microchannels, two-phase flow, hydrodynamics, droplet, viscoelasticity, size prediction

摘要：

利用高速摄像仪对十字聚焦微通道内液滴在黏弹性流体中的生成过程进行了实验研究。微通道截面为600μm×600 μm 的正方形结构,采用硅油作为分散相,含0.3%表面活性剂十二烷基硫酸钠(SDS)的聚环氧乙烷(PEO)水溶液(质量分数分别为0.1%,0.3%,0.6%)为连续相。实验观察到了弹状流、滴状流和喷射流3 种流型。对弹状流型下液滴生成过程的颈部动力学进行了研究,考察了两相流率、连续相毛细数及弹性数对液滴尺寸的影响。结果表明:弹状液滴尺寸随连续相流率、毛细数及弹性数的增加而减小,随分散相流率的增加而增加,连续相弹性对液滴尺寸的影响相对较小。以油水两相流率比和连续相的毛细数及Reynolds 数为变量建立了弹状液滴尺寸的预测关联式,预测值与实验值吻合良好。

关键词: 微通道, 两相流, 流体动力学, 液滴, 黏弹性, 尺寸预测