Modeling of the evaporation process of a pair of sessile droplets on a heated substrate

Sessile droplet evaporation is a complex process that involves both mass and heat transfer at the liquid/vapor interface. This process has many practical applications, including cooling microprocessors, and improving heat exchanger efficiency. This work builds upon a previously developed point source model for purely diffusive evaporation, expanding it to account for the effect of heated substrates on the evaporation behavior of a pair of sessile water droplets. Experimental investigations were carried out at various substrate temperatures and droplet separation distances to assess the validity of the diffusive model under these conditions. Results show that as the substrate temperature increases, convection becomes a more prominent factor alongside diffusion, enhancing the evaporation rate. When the temperature difference between the substrate and the ambient is small, diffusion dominates, but as this difference grows, natural convection plays a significant role. It is found that for Ra · L/d < 400, the evaporation rate is governed mainly by diffusion. Likewise, for Ra · L/d > 2400, the contribution of convection and diffusion stabilizes. An empirical correlation was developed to predict evaporation rates, accounting for both diffusion and convection. The proposed correlation shows excellent agreement with experimental data across different conditions, making it a valuable tool for predicting droplet evaporation rates on heated surfaces and its applications in thermal management systems.