Experimental and Analytical Investigation of an Array of Sessile Droplets Behaviour on Heated and Unheated Substrates

Abstract

Summary (194 words): This thesis investigates the evaporation and interaction dynamics of sessile droplets, crucial for applications in thermal management, microfluidics, and surface wetting. A novel and computationally efficient Point Source Model (PSM) was developed to predict droplet evaporation on isothermal and heated surfaces. By simplifying complex mass transfer processes, the PSM provides accurate results with minimal computational cost. Initially, the PSM modeled quasi-steady, purely diffusive evaporation of two droplets, capturing the effects of separation distance and evaporation modes—Constant Contact Angle (CCA) and Constant Contact Radius (CCR)—with deviations under 9% compared to experiments. A critical separation ratio (L/d ≥ 10) marked the onset of independent behavior. To address heated substrates, the model incorporated natural convection via a new empirical correlation. For Ra·L/d < 400, diffusion dominates, while for Ra·L/d > 2400, convection stabilizes. Further experiments explored vapor-mediated interactions between water and propylene glycol-water droplets at 24–135°C. Significant increases in droplet velocity and fragmentation were observed, especially at 20% PG, driven by surface tension gradients. Finally, the PSM was extended to a three-droplet array, revealing enhanced vapor shielding and a new isolation threshold (L/d > 20), emphasizing the impact of droplet geometry on evaporation behavior.