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.