The importance of gravity in droplet evaporation: A comparison of pendant and sessile drop evaporation with particles

As a droplet with particles evaporates, the particles deposit on the substrate surface. In this work, we show the extent of gravitational effects on the particle deposition profile and propose a new model for particle tracing in an evaporating droplet which accounts for gravitational effects. Experimentally, we compare pendant and sessile water droplets with 1 and 3 μm polystyrene particles. Numerically, the finite element method was used to create a transport model of the evaporating droplet system and particle deposition. The numerical and experimental results have excellent agreement and show that a pendant water droplet with 1 and 3 μm polystyrene spheres has significant separation of the two particle sizes. Finally, a phase diagaram was created to map different deposition profiles for various gravitational Péclet numbers (Pe_G) and ratios of Péclet number to Damköhler number (Pe/Da). © 2015 American Institute of Chemical Engineers AIChE J, 62: 947–955, 2016