Three-dimensional direct numerical simulation for film-boiling contact of moving particle and liquid droplet

Abstract

The hydrodynamics and heat transfer phenomena during the collision process of a liquid droplet and a hot particle, both in motion, are illustrated by direct numerical simulation in this study. The three-dimensional level-set method is used to portray the surface deformation of the droplet. The immersed boundary method is employed by means of the particle level-set function so that the particle-fluid boundary conditions are satisfied. The governing equations for the droplet and the surrounding gas phase are solved using the finite-volume method. To account for the multiscale effect due to lubrication resistance induced by the vapor layer between the droplet and solid surface or solid particle formed by the film-boiling evaporation, a vapor flow model is developed, which quantifies the pressure and velocity distributions along the vapor layer. The temperature fields in all phases and the local evaporation rate on the droplet surface are illustrated using a full-field heat transfer model. The convergence of the simulation model is analyzed and verified by using different grid sizes in the computation. The normal and oblique collisions between the droplet and the particle are simulated. It is found that the particle sizes have a significant effect on the collision dynamics in a normal collision. When the droplet size is larger than the particle size, the contact time is shorter than the droplet vibration period and is controlled by the dynamics of the particle. In an oblique collision, the increasing obliquity causes a decrease in contact area and contact time, and hence, a reduction in the heat loss of the particle during the collision process.