Numerical investigation on droplet wetting effect with the MPS method

The wetting effect of droplets is widely encountered in various industrial processes, such as mist cooling, dropwise condensation and electro wetting. Since these complicated processes are mostly free surface flow with large deformation, the moving particle semi-implicit (MPS) method is used for simulation in this study. The MPS method is a kind of Lagrangian meshless method and has advantages in simulating incompressible flows with large deformation. In order to simulate the surface tensions and interface tensions of different substances, the interparticle potential method was used in this paper. However, under the conventional surface tension model, the stable and well-formed droplets are hard to simulate due to the particle clustering and the shape distortion. In this paper, the parameters of interparticle potential model were studied and optimized to resolve these problems. Additionally, with the improved surface tension model, the oscillation and deformation process of a square droplet was simulated, and the result of which agreed well with the theoretical results. A circular relative error was defined to assess the final stable, well-formed droplet. Besides, the shrinkage and wetting effect, due to the surface tension, between multi-substances (gasliquid, solid-liquid or liquid-liquid) were examined and analyzed. The calculated wetting angle and wetting area were extracted and agreed with the analytical ones. The wetting relationships under different interface tensions agreed with the lowest energy principle. The droplets with different substances would wet each other in a certain order due to the differences between their interface tensions. The self-assembly processing in Micro-Electro-Mechanical Systems (MEMS) was simulated and the component finally moved to directly above the adhesive area.