壁面静止水滴冻结过程形状变化

低温表面上的液滴冻结时会形成具有尖顶的形状。针对这一现象开展了理论与实验研究,建立了新的动态曲形相界面模型用来模拟水滴冻结过程中的形状变化。模型考虑重力和成核再辉效应的影响,将冻结过程中的冰水相界面近似为球冠形曲面,并在三相点处引入动态生长角和直角关系。对壁面上20μL静止水滴进行了冻结实验,记录水滴三相点高度的演化过程,以此拟合得到了其随时间变化的关联式,基于该关联式求解理论模型,得到了水滴最终冻结形状。模拟结果与实验结果在水滴初始轮廓、成核再辉轮廓和最终冻结轮廓以及冻结时间上均吻合良好。曲面模型的计算结果表明,固液相界面上不同位置处的冻结速率不同;随着相界面向上推移,冻结速率逐渐减小。

Shape Variation of Sessile Water Droplet during Freezing

When a water droplet is deposited on a cold surface,it may freeze into a singular shape,which is studied theoretically and experimentally.A new dynamic curved interface model is developed to simulate the shape evolution of water droplet during freezing.The model considers the effects of supercooling and gravity,and assumes the freezing front as a spherical surface,it adopts the dynamic growth angle and perpendicular relationship at the triple-phase point.Experiments are conducted on20 μL water droplets on a cold surface and the evolution of triple-phase point height is recorded to get a fitting correlation which relates such a height with time.Based on the correlation,the model is solved to obtain the water droplet shape evolution during freezing.The initial profile,recalescence profile,final freezing profile of the droplet as well as the total freezing time calculated by the model all agree well with the experimental results.The calculation results show that the freezing rates at different places of the freezing front interface are different,and the freezing rate decreases with increasing interface height.