MARANGONI EFFECT ON BOILING OF MIXTURES

1. 基于半月板模型的气泡生长分析为了分析有核沸腾过程中气泡的生长以及微层蒸发对气泡生长的影响，提出了一种数值模拟方案。假设气泡生长的热量通过对流和半月板通过传导通过气泡帽提供。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，该方案为研究气泡的生长过程提供了一种有用的手段，无需对气泡形状进行假设，并且可以定量描述气泡生长周围的流动和温度场。结果表明，微层蒸发对气泡生长起主导作用，因此在沸腾传热中可能起重要作用。蒸发过程中的流动与传热在相变传热过程中，薄膜的蒸发是非常重要的。为了说明这一点，用马赫-曾德激光干涉仪测量了在倾斜加热的部分浸入液体的铜板上形成的半月板膜的稳态温度分布。以水、乙醇、乙二醇及其混合物为试验流体，研究了马兰戈尼对流对蒸发半月板传热的影响。数值分析了本征半月板区域和邻近蒸发薄膜区域的热流特性。结果发现，无论是正混合还是负混合，半月板内的流动方向都是相反的。因此，马兰戈尼对流有望在混合物半月板膜的蒸发中发挥重要作用。

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.