Abstract: This paper presents the results of a numerical investigation of micro-sized particle removal by droplet impact.Computational fluid dynamics simulation is used to calculate the flow distribution of droplet impact on a flat surface.The hydrodynamic forces exerted on the particle are then computed.Key factors controlling particle removal are discussed.Both hydrophilic and hydrophobic surfaces are considered.The flow distributions,especially the front edge expanding upon impact at microscale,strongly depend on surface wettability.The associated hydrodynamic forces on the particles vary accordingly.In addition,the impact on a dry surface can produce higher removal efficiency than that on a wet surface.Under the same impact conditions,the drag force exerted on a particle residing on a dry surface can be three orders of magnitudes larger than on a wet surface.Improving droplet impact velocity is more effective than improving droplet size.

Key words: droplet impact, particle removal, drag force, lift force, wettability