【摘要】 采用高速摄像技术可视化观察5μl小液滴在铜、铝和不锈钢表面上的蒸发与核化过程,板温50~112℃。实验测量了液滴高度、湿润半径和接触角随时间的动态演化。板温低于100℃时蒸发处于自由界面蒸发模态,过程可分为两阶段,第一阶段液滴高度和接触角连续降低,湿润半径仅比初始值略有降低;第二阶段后退角恒定,湿润半径迅速降低至零。板温高于100℃时处于核态沸腾模态,液滴内部核化及气泡动力学过程强烈依赖壁面过热度。自由界面蒸发模态和核态沸腾模态,壁面平均热流与壁温均呈线性关系,斜率的不同反映两种模态换热机制的差别。更多还原

【Abstract】 Using high-speed video imaging system,the evaporation and nucleation of 5ml water droplet on copper,aluminum and stainless steel plates with temperature from 50℃ up to 112℃ were observed.The time-dependent height,wetting radius and contact angle of the droplet were measured.In film evaporation regime,the evaporation process could be divided into two stages.In the fist stage,the height and contact angle of the droplet continuously decrease,but the wetting radius of the droplet hardly alters.In the second stage,the contact angle remains constant as the preceding one,and the wetting radius rapidly approaches zero.In nucleate boiling regime,the nucleation and dynamics of the bubbles inside the droplet are strongly dependent on the surface superheat.It was found that the linear relationship between the mean heat flux of the surfaces and the temperature of the heated surfaces holds true for both regimes,and their different slopes indicate their different heat transfer mechanism.更多还原