Numerical model for sessile drop evaporation on heated substrate under microgravity

Abstract

• One-sided numerical model is developed for sessile drop evaporation on heated substrate under microgravity. • Flow motion is analyzed by 3D resolved computations of evaporating sessile drop. • Transition from primary to secondary instability occurs at critical aspect ratio. • First time fine effects of secondary instabilities on evaporation rate are captured. Although sessile drops have simple geometries, the physics involved in their evaporation process is complex owing to their numerous intricate interactions and their fluid nature. An accurate quantitative model of the evaporation process will enable increased understanding and control over the process. In this study, a numerical model is developed for sessile drop evaporation on a heated substrate under microgravity based on the results of rocket and parabolic experiments to understand the ’internal dynamics of a sessile drop. The model is quantitatively validated through experiments. Subsequently, a correlation between substrate temperature and evaporation rate is suggested for an ethanol sessile drop. The flow motion is analyzed by conducting three-dimensional resolved computations of an evaporating sessile drop. This provides insights into the Marangoni effect in the dynamics of the evaporation process and the occurrence of secondary instabilities. For the first time, the fine effects of secondary instabilities on the evaporation rate are captured. Our numerical model is valid in the absence of convection in the vapor phase, producing an interface of an evaporating drop in a fully saturated vapor, which typically exists under microgravity conditions.