Analysis of fluid flow and particle transport in evaporating droplets exposed to infrared heating

Abstract

Analysis of fluid flow and particle transport inside evaporating droplets exposed to external radiation was carried out by experiments and numerical simulations. In this study, we have shown that by altering the free surface temperature we can modify the fluid flow profile inside the droplet and hence the deposition pattern of solute particles on the substrate. The fluid velocity and particle concentration profiles inside the evaporating droplet were measured by Particle Image Velocimetry (PIV) technique. Experiments were carried out on a small sessile water droplet containing dispersed polystyrene particles. To avoid problem of image correction encountered in PIV measurements with 3D droplets, our experiments were performed on an equivalent disc shaped 2D drop sandwiched between two non-wetting surfaces, while the base of the droplet was pinned to a wetting surface. The top surface of the droplet was heated by Infrared (IR) light. The temperature of droplet surface was measured by thermocouples. The velocity field, particle concentration profile and particle deposition patterns were studied during evaporation process. We have also performed numerical simulations by solving continuity, momentum and energy transport equations. The computed velocity profiles resulting from buoyancy and Marangoni convection are in qualitative agreement with the experiments.