T型微通道反应器内气液两相流动机制及影响因素

基于液滴或气泡的多相微流控是近年来微流控技术中快速发展的重要分支之一.本文利用高速显微摄影技术和数字图像处理技术对T型微通道反应器内气液两相流动机制及影响因素进行实验研究.实验采用添加表面活性剂的海藻酸钠水溶液作为液相,空气作为气相.研究T型微通道反应器内气液两相流型的转变过程,并根据微通道内气泡的生成频率和生成气泡的长径比对气泡流进行分类.研究发现当前的进料方式下,可以观测到气泡流和分层流2种流型,且依据气泡生成频率和微通道内气泡的长径比可将气泡流划分为分散气泡流、短弹状气泡流和长弹状气泡流3种类型,并基于受力分析确定3种气泡流的形成机制分别为剪切机制、剪切-挤压机制和挤压机制.考察不同液相黏度和表面张力系数对不同类型气泡流范围的影响规律.结果表明:液相黏度相较于表面张力系数而言,对气泡流生成范围影响更大.给出不同类型气泡流流型转变条件的无量纲关系式,实现微通道生成微气泡过程的可控操作. 

GAS-LIQUID TWO-PHASE FLOW REGIMES AND IMPACT FACTORS IN T-JUNCTION MICROREACTOR

Multiphase microfluidics based on droplets or bubbles is one of the important branches in the microfluidic technology with rapid development in recent years. In this study, an experimental study of gas-liquid two-phase flow regimes and impact factors was conducted in a T-junction microchannel based on high-speed microscope photography and digital image processing technology. Surfactant-added sodium alginate aqueous solutions were selected as the liquid phase, and air was the gas phase. The transition process of the gas-liquid two-phase flow in the T-junction microchannel was studied, and then the bubble flow was classified according to the frequency of bubble generation and the aspect ratio of the generated gas slug in the microchannel. Under the current feeding mode, bubble flow and stratified flow were observed, and the bubble flow could be divided into dispersed bubble flow, short-slug bubble flow and long-slug bubble flow according to the frequency of bubble generation and the aspect ratio of the generated gas slug. Based on the force analysis, the formation mechanisms of the three types of bubble flow were observed as shearing, shearing-to-squeezing and squeezing. The effects of liquid viscosity and surface tension coefficient on the operating range of different types of bubble flows were investigated. It is indicated that liquid viscosity has a greater influence on the operating ranges of bubble flow than that of the surface tension coefficient. The dimensionless correlations of the bubble flow regime transition boundaries were proposed to achieve the controllable operation of the microbubble generation process.