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中是令人感兴趣的。了解液滴的流体动力学特性对这些工业过程的进一步发展具有重要意义。已知液滴冲击动力学取决于壁温。本研究试图通过动态接触角来解释液滴撞击动力学随表面温度的变化。蒸发弯月面的宏观建模，以估计动态接触角在液滴撞击。将该模型与流体动力学和传热学的模拟代码相结合。在实验中，正庚烷和水滴冲击从室温加热到莱顿弗罗斯特温度以上的不锈钢板表面。测量了铺展直径、液滴高度和表观接触角随时间的变化。数值计算结果与实验结果进行了比较， 关于我们 ts，讨论了该模式的性能。本研究的主要工作概括如下：1.对于正庚烷液滴，壁面温度的增加导致板条直径的减小和达到最大飞溅直径所需的时间。它还导致在反冲过程中液滴的更大伸长。另一方面，对于水滴，壁面温度对扩散液滴的尺寸没有影响（尽管核态沸腾取决于壁面温度）。在卷取过程中，观察了壁面温度的影响.所开发的模型进行了数值求解，使用有限元法。该模型几乎预测了液滴尺寸随壁温的变化规律.比较了平衡模型和非平衡模型对弯月面蒸发速率的估算。结果表明，前者能较好地预测液滴的变形过程.两个液滴的变形过程的壁温依赖性之间的差异被发现推断从液滴/基板界面处的温度之间的差异。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