DSMC Modeling of Dropwise Condensation With Variable Wettability

Abstract

Recent heat transfer studies on nanostructured surfaces have shown that enhanced dropwise condensation heat transfer can be attained through clusters with reduced droplet sizes. A Direct Monte Carlo Simulation (DSMC) approach is used here to investigate the limitations of dropwise condensation as droplet sizes are reduced. The model is idealized by assuming uniform droplet distribution with an effective diameter. To minimize computational time, the model further uses symmetry to focus the analysis on a quarter segment of a single droplet condensing on a cold wall. The effects of surface wettability are explored by accounting for variations in droplet conduction with contact angle, while changes of interfacial resistance with droplet curvature are also incorporated into the model. To investigate the effect of reduced droplet sizes, the simulations were run for droplets with radii between 1μm down to 5nm. The simulations were run for standard atmospheric conditions at different levels of subcooling and accommodation. In all instances, the same behavior is observed as non-continuum effects become significant at reduced diameters, causing heat transfer coefficients to reach a maximum. The predictions of the DSMC model are compared to previous work attempting to capture similar effects. The significance of the observations for current and future research in dropwise condensation is discussed in detail.