Modeling of the evaporation process of a pair of sessile droplets using a point source model (PSM)

Abstract

Many natural and practical applications, from macro- to microscale, entail the evaporation of an array of droplets on a substrate surface. A simplified point source model (PSM) was developed to simulate the evaporation of a pair of sessile droplets on a substrate surface, surrounded by still air. The model is for a purely diffusive isothermal quasi-steady-state evaporation process. The model determines the initial evaporation rate as a function of the separation distance between two droplets. A threshold separation distance between two droplets, beyond which the evaporation rate of the droplets is very similar to the evaporation of a single isolated droplet, is determined. The effect of the evaporation mode (Constant Contact Angle (CCA) mode and Constant Contact Radius (CCR) mode) was considered. Two expressions to determine the evaporation time under CCA and CCR evaporation mode are presented. The model is a simple and computationally inexpensive tool. An experimental setup was designed and built to investigate the validity of the proposed model. The effect of droplet volume, ambient relative humidity, surface wettability, and liquid volatility are tested experimentally. The predictions from the model were in excellent agreement with the experimental results regarding the droplet volume, ambient relative humidity, and surface wettability.