MARANGONI EFFECT ON BOILING OF MIXTURES

1.基于弯月面模型的汽泡生长分析建立了一种数值模拟方案，分析了核态沸腾中汽泡的生长过程以及微层蒸发对汽泡生长的影响。气泡生长所需的热量被假定为通过对流通过泡帽和通过传导通过弯月面提供。采用基于四边形单元的二维任意拉格朗日-欧拉有限元法求解瞬态Navier-Stokes方程和能量方程。结果表明，该方案提供了一个有用的手段来研究气泡的生长过程中没有假设的气泡形状，它可以定量描述周围的流动和温度场的增长气泡。微层蒸发在汽泡生长过程中起主导作用，因此微层蒸发在沸腾传热过程中起重要作用.蒸发弯月面内的流动与传热在与相变有关的传热过程中，薄膜蒸发是非常重要的。为了说明这一点，用马赫-曾德尔激光干涉仪测量了在倾斜加热的部分浸没在液体中的铜板上形成的弯月形膜的稳态温度分布。以水、乙醇、乙二醇及其混合物为实验流体，研究了Marangoni对流对蒸发弯月面内传热的影响。通过数值模拟分析了内弯月面区和相邻蒸发薄膜区的流动和传热特性。发现无论是正混合气还是负混合气，弯月面内的流动方向都是相反的。因此，Marangoni对流预计将发挥重要作用的弯月形膜蒸发的混合物。

1. Bubble Growth Analysis Based on Meniscus ModelA numerical simulation scheme was developed to analyze the bubble growth in nucleate boiling and the effect of microlayer evaporation on bubble growth. Heat for the bubble growth was assumed as supplied through the bubble cap by convection and the meniscus by conduction. Transient Navier-Stokes and energy equations were solved using a two-dimensional arbitrary Lagrangian-Eulerian finite element method based on quadrilateral elements. It was revealed that the scheme offers a useful mean to investigate the growth process of bubble with no assumption on the bubble shape and it enables a quantitative description of flow and temperature fields around growing bubbles. It was concluded that the microlayer evaporation dominates bubble growth so that it may be substantial in boiling heat transfer.2. Flow and Heat Transfer in Evaporating MeniscusEvaporation from thin film is very important in heat transfer processes associated with phase change. To make it clear, a steady-state temperature distribution of a meniscus film formed on an inclined and heated cooper plate partially submerged into liquid was measured using a Mach-Zehnder laser interferometer. Water, ethanol, ethylene glycol and their mixtures were used as test fluids to investigate the effect of Marangoni convection on heat transfer in the evaporating meniscus. A numerical analysis was also performed to elucidate heat and flow characteristics in the intrinsic meniscus region and the adjacent evaporating thin film region. It was found the flow direction in the meniscus is reversed, whether mixture is positive or negative. Thus Marangoni convection is expected to play an important role in the evaporation of meniscus film for mixtures.