Transient flow patterns in an evaporating sessile drop: A numerical study on the effect of volatility and contact angle

Abstract In this paper, we numerically investigated the evolution of flow pattern inside an evaporating sessile drop using a transient numerical model based on the Arbitrary Lagrangian–Eulerian (ALE) frame that fully couples fluid flow and heat and mass transfer. Effects of both liquid volatility and initial contact angle on the transient flow pattern were explored. The results show that stronger volatile drops have more vortices whereas multi-vortices circulation lasts for shorter time. With the increasing of contact angle, the maximum number of vortices at first increases gently and then rapidly, while the duration of the multi-vortices circulation at first decreases rapidly and then increases a little bit. Marangoni flow is found to dominate the formation of vortices in most of the simulated cases, whereas natural convection plays a role in drops of large contact angles. These conclusions agree with the judgement criteria based on Marangoni number and Grashof number. Besides the classical symmetrical vortices, encompassing vortices are observed during the transient development of internal flow. These encompassing vortices normally form either through the merging of a big vortex with its adjacent small one or through the splitting of a big vortex into two smaller ones.