Abstract:

With high-speed camera, formation of ferrofluid droplets in mineral oil was studied in a Y-shaped microchannel with cross section of 400 μm×400 μm. In the system of water-based ferrofluid (EMG 807) as dispersed phase and mineral oil with 4%(mass) surfactant sorbitan lauric acid ester (Span-20) as continuous phase, three types of flow regimes were observed, i.e., slug, dripping and jetting flows. Study of two-phase flow rates, capillary number of continuous phase and magnetic flux density on droplet size and formation process showed that both two-phase flow rates and magnetic field could regulate droplet size. At constant flow rate of the dispersed phase, droplet size decreased with increasing ratio of two-phase flow rates. The droplet size decreased with the increase of capillary number of continuous phase and magnetic flux density, but increased along with the increase of flow rate of the dispersed phase. A correlation of droplet size was proposed on parameters of two-phase flow rates, capillary number of continuous phase, and magnetic Bond number, which offered accurate prediction with experimental data.

Key words: microchannels, microfluidics, two-phase flow, ferrofluid droplet, magnetic field

摘要：

利用高速摄像仪研究了截面为400 μm×400 μm Y聚焦型微通道内磁流体液滴在矿物油中的生成过程。以水基磁流体EMG 807为分散相，含4%表面活性剂Span-20的矿物油为连续相。实验观察到了3种流型：弹状流、滴状流和喷射流。分别考察了两相流量、连续相毛细数及磁感应强度对液滴尺寸及生成过程的影响。结果表明：可通过改变两相流量及磁场调控液滴尺寸。当分散相流量不变时，液滴尺寸随着两相流量比的增加而减小。液滴尺寸随着连续相毛细数及磁感应强度的增加而减小，随着分散相流量的增加而增加。以两相流量比、连续相毛细数和磁Bond数为参数提出了一个液滴尺寸的关联式，预测值与实验值吻合良好。

关键词: 微通道, 微流体学, 两相流, 磁流体液滴, 磁场