Effect of microscopic interfacial structure on gas-liquid two phase flow and application for flow control.

气液界面处的质量、动量和能量输运现象是气液两相流动的重要基础，随界面条件的变化而急剧变化。例如，已知表面活性剂的加入对气泡流的整体流动结构（包括液体中的气泡数）有较大的影响，可以防止气泡的结合，降低气泡的上升速度。本研究的目的是明确表面活性剂存在液的体积浓度与界面结构的关系，定量分析杂质对两相流宏观流动动力学的影响。用超纯水和已知浓度的表面活性剂溶液在静止液体中进行了气泡上升实验，并利用Navier-Stokes方程和Marangoni效应对气泡上升进行了模拟，探讨了基本界面现象的机理。在实验中，通过在静止水中产生100多个半径为50mm ~ 1mm的小单泡来研究气泡的上升行为。证实了超纯水中上升气泡的雷诺数与阻力系数的关系与纯液体的理论推导一致。此外，观察到在纯水中加入少量的3-戊醇可以显著降低上升速度。在数值模拟中，采用Henry型和Langmuir型吸收模型，采用沿气泡界面的正交曲线坐标系，分析了表面活性剂对不可变形球形气泡上升阻力的影响。数值模拟结果表明，即使表面活性剂用量很小，马兰戈尼效应也能显著增加上升气泡的阻力，并且对于相同直径和相同终端速度的气泡，马兰戈尼效应随着雷诺数的增加而变得重要。此外，模拟显示分离涡与气泡后面的次级涡在表面活性剂溶液中上升有关，在纯水中从未观察到。少

Transport phenomena of mass, momentum and energy at gas liquid interface is most important basis for gas-liquid two phase flow and various drastically with interface condition. For example, it is known that additon of surfactant gives large influence on whole flow structure of bubbly flow which includes numbers of bubbles in liquid by preventing coalition and reducing rising velocity of bubbles. The purpose of this research is to clarify relation between bulk concentration of surfactant existing liquid and interfacial structure, and quantitative analysis of influence of impurity on macroscopic flow dynamics of two phase flow. Experiment of rising bubble in stationaly liquid by using ultra pure water and surfactant solution of known concentration, and simulation of rising bubble by using Navier-Stokes equation coupled with Marangoni effect were conducted to investigate mechanism of basic interfacial phenomena.In the experiment, behavior of the rising bubble was investigated by generatin … More g small single bubble of 50mum to 1mm in radius in stationary water. Relation between Reynolds number and drag coefficient for rising bubble in the ultra pure water was confirmed to be same as one derived from theory for pure liquid. Moreover, it was observed that addition of small amount of 3-pentanol into pure water reduces rising velocity significantly.In the numerical simulation, effect of surfactant on drag of rising bubble was analyzed for undeformable spherical bubble by adopting absorption model of Henry type or Langmuir type and by using orthogonal curvilinear coordinate system along bubble interface. As a result of numerical simulation, it was demonstrated that drag of the rising bubble can remarkably increase by Marangoni effect for even small amount of surfactant, and that the Marangoni effect becomes important with Reynolds number for bubbles having same diameter and same terminal velocity. Further, the simulation shows separating vortices associated with secondary vortices behind the bubble rising in surfactant solution, never observed in pure water. Less