Evaporation and boiling of water-alcohol droplets: Dynamic characteristics of wetting and heat transfer

The evaporation and boiling of water-alcohol droplets have vast potential for applications in spray cooling, fuel combustion, and thermal management of electronic devices, while the dynamic characteristics of droplets around and above the boiling point remain open for investigations. This study utilizes water-ethanol and water-1propanol droplets to experimentally observe the evaporation and boiling process in this temperature range and explore the effect of concentration and substrate temperature on the droplet wetting and heat transfer. The model of competition between surface tension and surface pinning force is proposed to analyze the droplet wetting dynamics, and the maximum surface pinning force can be calculated via this model. Two stages of droplet volume variation are witnessed, and the prediction model of evaporation rate in Stage I for water-alcohol droplets is established to achieve deviations of less than +/- 10% from experimental values in most working conditions. Furthermore, the deviation phase maps of the model reveal the importance of selective evaporation and convective heat transfer in different boiling regimes. Heat flux at the solid-liquid interface of water-alcohol droplets is calculated, and the heat flux variation in different working conditions during evaporation and boiling is investigated, demonstrating the advantages of choosing azeotropes for related industrial applications.

Automated summary

This study investigates the evaporation and boiling process of water-alcohol droplets and explores the effects of concentration and substrate temperature on droplet wetting and heat transfer. A predictive model is established and proven accurate in predicting evaporation rates of water-alcohol droplets, revealing the importance of selective evaporation and convective heat transfer in different boiling regimes.