Transport mechanisms during water droplet evaporation on heated substrates of different wettability

•A generalized numerical model is developed for evaporation of water droplets on heated hydrophilic, hydrophobic, and superhydrophobic substrates.•The present model matches experiments to within 8.7%, while diffusion-based analytical solutions deviate up to 52.5%.•Evaporative cooling and buoyant convection are recognized as the key mechanisms in addition to vapor diffusion.•Evaporative cooling significantly suppresses the evaporation rate and alters the evaporation flux along the interface.•Buoyant convection improves vapor transport in the surrounding gas, and thus significantly enhances the evaporation rate. The evaporation of water droplets placed on heated hydrophilic, hydrophobic, and superhydrophobic substrates is numerically investigated. Simplified analytical models for droplet evaporation only include vapor diffusion transport in the surrounding gas domain and assume an isothermal droplet interface at the substrate temperature. The comprehensive model developed in this study accounts for all of the pertinent transport mechanisms. The interface is cooled via absorption of latent heat during evaporation, and the saturated vapor concentration is coupled to local temperature at the droplet interface. Conjugate heat and mass transfer are solved throughout the system using temperature-dependent physical properties. Buoyancy-driven convective flows (induced by both species concentration and temperature gradients) in the droplet and gas domains are also simulated. The evaporation rates predicted as a function of the substrate wettability (contact angle from 10° to 160°) and substrate temperature (40 °C to 65.4 °C) are validated against experiments from the literature. The modeling approach yields quantitative insights into the influence of these transport mechanisms on the evaporation characteristics. As substrate temperature is increased, the buoyancy-induced convection significantly increases the evaporation rate by up to ~60% on the hottest substrate compared to the diffusion-based model, by enhancing vapor transport in the gas domain. Simultaneously, the liquid-gas interface is increasingly cooled by evaporation, leading to a large temperature drop across the droplet height, ~18 °C for a 3 μL droplet evaporating on the superhydrophobic substrate at 60 °C. This significantly alters the distribution of the vapor fraction and evaporation flux along the interface and suppresses the evaporation rate (by ~53%). When both factors are considered together, the