壁面润湿性对微通道内Taylor流动特性的影响

Surface wettability effect on Taylor flow characteristics in microchannels

壁面润湿性不仅影响着Taylor气泡的形状,同时对通道内流体流动、相变换热等有着关键的作用。采用VOF模型对T型微通道内气液两相Taylor流动进行三维数值模拟,重点研究了接触角改变对Taylor气泡流体动力学特性的影响。模拟结果与他人实验数据对比基本吻合,验证了模型的有效性。结果表明:随着接触角增大,气泡周围液含量逐渐降低,相界面也由外凸形变为内凹形。壁面越接近润湿(或疏水)状态,气液接触面的曲率就越大;当120°≤θ≤150°时Taylor气泡稳定性变差。当θ≥150°时“拖曳流态”出现,分析指出在大接触角下气体更易贴附壁面导致接触区内流场发生变化,形成的涡流减弱了水对气相的水平剪切作用,进而引起流型转变。接触角对通道内压力有着重要影响,通道中心轴向压力曲线以θ=90°为过渡,润湿状态下呈凸函数递减且pG>pL,疏水状态下气液进口处的压力分配改变,曲线趋势相反。

Wall wettability affects the shape of the Taylor bubble and plays a key role in fluid flow and phase change heat transfer in the microchannel.In this paper,the VOF model was used to simulate the gas-liquid two-phase Taylor flow in T-type microchannels,and the influence of contact angle change on the hydrodynamic characteristics of Taylor bubbles was analyzed emphatically.The simulation results were basically consistent with the experimental data of others,which verified the validity of the model.The result showed that with the increase of the contact angle,the liquid content around the bubble decreased gradually,and the phase interface also changed from convex to concave.The closer of wall to the wet or hydrophobic state,the larger curvature of gas-liquid interface will be.When 120°≤θ≤150°,the stability of Taylor bubble was poor.When θ≥150°,"drag flow pattern" appeared,it was pointed out that the gas was easier to attach to the wall at large contact angle,and the vortex in the contact area weakened the horizontal shear effect of water on the gas phase,leading to the flow pattern transformation.The contact angle had an important effect on the pressure in the channel.The axial pressure curve in the center of the channel took θ=90° as the transition,it was a convex function in wet state and PG>PL,in the hydrophobic state that the pressure distribution at the gas-liquid inlet was changed,and the curve trend was opposite.