NUMERICAL SIMULATION OF NUCLEATE SPRAY COOLING: EFFECT OF DROPLET IMPACT ON BUBBLE GROWTH AND HEAT TRANSFER IN A THIN LIQUID FILM

摘要

A mathematical model is developed to investigate the details of two-phase flow and heat transfer when a liquid droplet impacts a thin liquid film with vapor bubble growing during the nucleate spray, including the dynamics of bubble growth, the movement of the interface between two fluids and the surface heat transfer characteristics. The model takes into account the effects of phase change between vapor and liquid, gravity, surface tension and viscosity. The influences of droplet falling velocity, droplet diameter and initial position, the multi-droplets impact on the flow and heat transfer are discussed in the present study. By comparing the computational results with available literature, it is found that the movement of the vapor-liquid interface and the fact that some new bubbles occur inside the film at the beginning of the bubble growth are in agreement with the results of the literature. The satisfactory coincidence proves that the model is reliable when modeling two-phase flow. The paper also provides an important method to further improve the effect of surface heat transfer during nucleate spray cooling.