Coarsening-induced disappearing droplets contribute to condensation

Abstract

Condensation heat transfer is widely used in water and energy systems. Despite being extensively studied, since 1973, the models for dropwise condensation have strongly relied on the droplet size distribution. In this study, we report that the classical models underestimate the heat transfer performance of dropwise condensation on a hydrophilic liquid-infused surface, on which the meniscus-mediated coarsening droplets lead to a previously unachieved droplet coverage ratio down to 30%. We found that the time-averaged classical models have overlooked the coarsening-induced disappearing droplets. Moreover, these models cannot be used to determine the instantaneous heat transfer coefficient on the shedding-induced water-free surface under steam condensation. Thus, a dynamic model is developed for dropwise condensation by considering the disappearing droplets induced by both coarsening and shedding, which shows good agreement with the experimental validation. Such a dynamic model provides a theoretical foundation to design surfaces for condensation, giving rise to an advanced design guideline for water and energy systems.