The dynamics of sessile drop during evaporation on a heated substrate under microgravity*

We have explored the dynamics of a sessile drop on a heated substrate under microgravity. Microgravity helps us to quantify and distinguish the influence of natural convection on the evaporation rate. By leverage of the microgravity condition, a numerical model have been developed to better understand the drop dynamics that take place during the evaporation process. Quantitative validation of our model has been performed by comparing it to experimental results. We suggest a correlation for the evaporation rate of an Ethanol sessile drop that accounts for relevant physical parameters of the problem. Simultaneously, we provide an analysis of the flow motion with 3D resolved computations for the whole lifetime of evaporating sessile drop. Thanks to this analysis, we provide an insight into the Marangoni effect in the dynamics of the evaporation process and the occurrence of secondary Marangoni instability. We capture the fine influences of the secondary instabilities appearance on the evaporation rate. Concurrently, we define the instability threshold for the transition from primary to secondary Marangoni instability via thermal Marangoni number and geometrical aspect ratio.