3D numerical study on droplet-solid collisions in the Leidenfrost regime

The hydrodynamics and heat transfer phenomena of a liquid droplet in motion and during the impact process with a hot flat surface as well as with a particle are illustrated. Such phenomena are of direct relevance to many engineering problems such as fluid catalytic cracking (FCC), polyethylene synthesis, and electronic materials coating. In the Leidenfrost regime, the vapor generated from the evaporation of the droplet forms a thin vapor layer, which prevents the direct contact of the droplet with the solid. The vapor layer also hinders the heat transfer from the solid to the droplet. In this study, a 3-dimensional numerical model is developed to simulate the process of collision between an evaporative droplet and a high-temperature solid object.; The simulation model of this study is built upon advanced DNS (direct numerical simulation) techniques for multiphase flow problems, coupled with a finite-volume algorithm in the fixed Eulerian grid. The 3D level-set method is employed to portray the droplet surface variation during its deformation. The immersed boundary method is applied to impose the solid-fluid boundary condition at the particle surface. To account for the multi-scale 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 to calculate 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 collision process between an evaporative droplet and a high-temperature particle is investigated through numerical simulation and the experiment. In the simulation, the particle-fluid boundary condition is imposed on the particle surface through the immersed boundary method involving a particle level-set function. The simulation results are compared with experimental data, and the convergence of the simulation model is analyzed and verified by using different grid sizes in the computation. The effects of the particle size and the collision velocity are examined numerically. Simulation model is further applied to study the oblique collision between the droplet and the particle. The effects of the obliquity on the outcome of the collision are analyzed. (Abstract shortened by UMI.)...