FLUID DYNAMIC, HEAT TRANSFER AND COMBUSTION OF LIQUID FUEL DROPLET COLLIDING WITH HEATED SUBSTRATEA

液滴在热固体表面上的撞击在许多工业领域都引起了人们的兴趣。了解液滴的流体动力学对这些工业过程的进一步发展具有重要意义。已知液滴的冲击动力学取决于壁面温度。然而，这个原因一直没有得到澄清。本研究试图通过动态接触角来解释撞击液滴的动力学随表面温度的变化。对蒸发半月板进行了宏观建模，以估计液滴撞击过程中的动态接触角。该模型与流体力学和传热仿真程序相结合。在实验中，正庚烷和水滴撞击从室温加热到莱顿弗罗斯特温度以上的不锈钢板表面。测量了扩散直径、液滴高度和视接触角随时间的变化。将数值计算结果与实验结果进行了比较，讨论了该模型的性能。本研究的工作总结如下：1。对于正庚烷液滴，壁面温度的升高会导致片状直径的减小和达到最大片状直径所需的时间的减小。它也引起更大的延伸液滴在反冲过程中。另一方面，对于水滴来说，壁面温度对扩散液滴的尺寸没有影响（尽管核沸腾取决于壁面温度）。在后坐过程中观察了壁温的影响。采用有限元法对所建立的模型进行了数值求解。该模型较好地预测了不同壁面温度下液滴尺寸的实验时间变化。比较了估算半月板蒸发速率的平衡模型和非平衡模型。结果表明，前一种模型能较好地预测液滴的变形过程。发现两液滴变形过程的壁温依赖关系的差异可以从液滴/基体界面温度的差异中推导出来。少

The impingement of liquid droplets on hot solid surfaces is of interest in a number of industrial areas. It is of great importance to understand fluid dynamics of liquid droplets for further development of these industrial processes. The droplet impact dynamics is known to depend on the wall temperature. However, this reason has not been clarified.This study attempts to explain the change in impact droplet dynamics with surface temperature through dynamic contact angle. Evaporating meniscus are macroscopically modeled to estimation dynamic contact angles during droplet impingement. The model was incorporated with the simulation code for the fluid dynamics and heat transfer. In the experiments, n-heptane and water droplets impacted a stainless-steel plate surface heated from room temperature to above the Leidenfrost temperature. Time variation of the spreading diameter, droplet height and apparent contact angle are measured. The numerical results are compared with the experimental resul … More ts, to discuss capability of the present mode. The efforts of this study are summarized bellow :1. For n-heptane droplets, an increase in the wall temperature leads to decreases in the slat diameter and the time required to reach a maximum splat diameter. It also causes greater elongation of the droplet during the recoiling process. For water droplets, on the other hand, there is no effect of the wall temperature on the dimensions of the spreading droplet (though nucleate boiling depends on the wall temperature). The effect of the wall temperature is observed during the recoiling process.2. The developed models are numerically solved using a finite element method. The model almost predicts the experimental time variation of the droplet dimensions for each wall temperature.3. Equilibrium and nonequilibrium models for estimating the evaporation rate from meniscus are compared. As a result, the former model gives a better prediction as for the deformation process of the droplets.4. The difference between the wall-temperature dependence of the deformation process of the two droplet is found to deduce from the difference between the temperatures at the droplet/substrate interface. Less