Abstract:

Slug flow separation, a traditional process in biochemical and pharmaceutical industries, is a valid method to control two-phase flow patterns and enhance heat transfer. The fundamental to study evolution mechanism of two-phase flow patterns is to understand development rules of local parameters by numeric simulation of drainage on micro-channel walls and modulation process of slug flow. The VOF model coupling with dynamic grid adaption was chosen to precisely track gas liquid interface, to simulate movement of the interface at split, and to acquire hydrostatic and dynamic pressure evolution along axial direction and at wall. Results indicated that piston-like movement of bubbles at split was critical to slug flow separation in micro channels. Because of the presence of Laplacian pressure drop at the interface, pressure drop of slug flow was discontinuous with a periodic wavy variation following the interface piston-like movement. The overall pressure drop of slug flow was influenced by local pressure drop at liquid bridge region. Significant pressure drop near bubble head while minimal pressure drop near bubble tail where liquid flow rate was reduced. Such pressure drop characteristics of slug flow is distinguished from other two phase flows.

Key words: slug flow, liquid separation, local pressure, CFD, simulation

摘要：

弹状流分流不仅能调控两相流流型从而强化传热，同时也是生物化工、制药行业的传统过程。针对壁面微通道分流液相、调控两相流型的过程进行数值模拟，获得局部参数变化规律，是获得两相流流型演变机理的基础。采用VOF模型耦合动态自适应网格精准追踪气液界面，模拟气液界面在分液口的界面运动；获得轴向及壁面静压、动压的演变规律。通过模拟可知微通道分流弹状流的关键是气弹在分液口的类活塞运动；同时由于界面拉普拉斯压力差的存在，弹状流压降具有不连续性；且此不连续压力随气弹在分液口的类活塞运动具有周期波动性。而弹状流液桥部分的局部压降是影响总压降的关键；近气弹头部的液相区压降显著，近气弹尾部的液相区域由于液速降低其压降明显衰弱；此为弹状流有别于其他两相流流型的压降特点。

关键词: 弹状流, 分液, 局部压力, CFD, 模拟