Tailored surface roughnesses for enhanced deposition of fine liquid droplets from a flowing gas

Separating fine liquid droplets from a gas stream is an important operation in many industrial applications. In this paper, the effect of surface roughness on the deposition of droplets was investigated in a series of wind tunnel experiments. The roughness was modelled by 2-D rectangular ridges oriented at 45 degrees to the flow direction. The rate of droplet deposition onto the surface was measured by a conductivity method. It was found that the deposition of droplets onto the roughened surface was enhanced by the roughness and the enhancement increased with ridge size-based Reynolds number. The maximum enhancement of droplet deposition on roughened surfaces over that of the smooth surfaces was observed to be around 150%. Data obtained for droplets with different sizes also indicated that the deposition rate of fine droplets was more dependent on the Reynolds than that of the large droplets. For relatively larger droplets, the enhancement of deposition is mainly caused by momentum-dominated impact. However, for fine droplets this is mainly due to the enhancement of local turbulence.