Numerical study of high-overload effect on liquid film of spray cooling

A two-dimensional numerical model was developed to study a heat and mass transfer process of liquid film formed by a row of droplets under high-overload conditions. The model was solved using the Volume of Fluid (VOF) method. Simulation cases were carried out with different droplets velocities and overload accelerations. The liquid film flow as well as no-phase-change heat transfer were studied during droplets hitting the flat surface. The simulation results obtained under high-overload and normal gravity conditions are compared to reveal the impact of acceleration on the heat and mass transfer performance. The analyses indicate that the average temperature of heated surface, T_sur, decreases with the increase of the droplet velocity under the normal gravity. While under horizontal high-overload conditions, T_sur decreases first and then increases with the increase of the droplet velocity. T_sur under horizontal high-overload is lower than the one under the normal gravity. When the droplet velocity is relatively high, the vertical overload acceleration has little influence on T_sur. However, when the droplet velocity is relatively low under vertical high-overload, weightless or overweight condition makes T_sur increase or decrease, respectively. The reason to cause this temperature change is that the shape of liquid film occurs different distortion phenomena in the high-overload conditions. High-overload inertia force plays an important role in the shape distortion of liquid film. The liquid film will be easy to pile up or break especially when the droplet velocity is relative low. This can cause adverse effect on the heat transfer process, such as local overheating. It will bring some harm on the cooling performance.