Effect of volatility differences in binary mixture droplet components on evaporation dynamics

The evaporation of binary mixture droplets (BMDs) is a natural phenomenon, and this study presents a theoretical model for the evaporation of BMDs. Ethanol–water (EW) and ethylene glycol–water (EGW) BMDs are selected to investigate the impact of component volatility differences on evaporation dynamics. The dynamic evaporation processes of two BMDs on a heated substrate are simulated, and differences in internal flow structures are examined. A modified formula for the evaporation rate of BMDs is proposed, and the effects of substrate heating temperature and initial solute concentration on the evaporation dynamics are explored. The results indicate that during evaporation, EW-BMDs develop a complex and chaotic multi-vortex structure, while EGW-BMDs exhibit a pattern with only two coexisting vortices. The evaporation of EW-BMDs transitions into a water-dominated stage after an initial rapid decline in the droplet volume, while the evaporation rate of EGW-BMDs remains almost constant once they enter an ethylene glycol-dominated stage. Increasing the substrate heating temperature and initial solute concentration delays the onset time of the multi-vortex structure in EW-BMDs but accelerates its appearance in EGW-BMDs. Increasing the substrate heating temperature shortens the evaporation time of two BMDs and accelerates the evaporation rate. Increasing the initial solute concentration reduces the evaporation time of EW-BMDs but extends the evaporation time of EGW-BMDs, while also reducing the time required for the ethylene glycol mass fraction to reach 1.