Numerical Study of the Collision Dynamics and Heat Transfer of Water Droplets Impinging on a Hot Solid

The present study is concerned with the collision of two droplets with a hot solid substrate whose temperature is maintained below the boiling temperature of the liquid. Computer simulations were performed to investigate the heat transfer from the hot solid to the coaxially incoming droplets. The conservation equations of mass, momentum and energy for unsteady incompressible viscous fluids in an axisymmetric coordinate system were approximated and solved with a finite difference method, taking account of viscosity, surface tension, gravity, and the heat transfer between the solid and the liquid. The effects of the impact conditions of the droplets, such as their impact velocity, their pre-impact diameters, and the vertical distance between two consecutive droplets on the heat transfer rate are examined. To validate the simulation results, experiments were performed in which the time evolution of the droplet shape was observed by photography. The numerical results are in reasonable agreement with the experimental data. We discuss the implications of these results for the theoretical understanding of the physics of heat transfer.