We investigate collision characteristics of micro-sized particles (diameter less than 100 microns) via numerical simulations and experiments. Discrete element method (DEM) simulations, based on improved hard-sphere model, are performed to explore effect of initial velocity, surface energy, size, mass concentration, and wind speed on cohesive collisions and non-cohesive collisions between micro-sized particles. Aggregation and settlement process are considered as well. It is found that simulated cohesive collision rate agrees with experimental results of self-settlement of micro-sized particles.

A PML model based on fixed surface roughness is used in simulation of surface roughness effect on flow in mini-channels. Compared with 3-D simulation, results of pressure drop agree well. With PML model and 3-D model we simulate different flow rates and roughness, it shows that surface roughness results in speed linear flow substrate. Pressure drop and relative roughness follow a secondary power relation as Re number is fixed. Pressure drop increased linearly with Re number as roughness elements is equal.