Influence of heating temperature and relative humidity in the evaporation of pinned droplets

The complete understanding of evaporating systems still motivates important scientific activity for both fundamental and industrial applications. We propose here to investigate numerically the properties of water evaporating droplets on a heating substrate. Droplets are assumed to be pinned and axi-symmetric for the duration of the evaporation process. The description of the evaporative dynamics is based on stationary hydrodynamic equations for the droplet whereas surrounding air properties are essentially determined by Laplace equation for the temperatures. Construction of the model is presented and the justification of stationary approximations discussed. The role of the temperature of the heating substrate and droplet radius are investigated. Influence of relative humidity is also discussed and indicates a strong influence only for low substrate temperatures. An empirical rule for droplet evaporation time as a function of the basic parameters of the system is finally proposed. Our main objective here is to propose guidelines for small sessile and pinned droplet experiments to help the understanding of the influence of three major parameters: temperature of the heating substrate, droplet size and far field humidity.