Predicting the growth of many droplets during vapor-diffusion-driven dropwise condensation experiments using the point sink superposition method

Abstract

Water vapor present in humid air will condense in the form of many small droplets on a cooled substrate. After nucleation, the diffusion of vapor from the environment to the droplets dominates their growth by condensation, and therefore, all droplets must compete for the vapor available in the surroundings. Models that assume droplets grow in isolation or as an equivalent film poorly capture their interaction during vapor-diffusion-driven condensation and do not correspond with experimental condensation rates. By treating the droplets as point sinks, the interaction between all droplets in a system can be captured by superposing the vapor distributions of each droplet. This paper presents direct comparisons of condensation rates measured in experiments and predicted with a point sink superposition method. The results indicate that it is critical to consider a large number of interacting droplets to accurately predict the condensation behavior. Even though the intensity of the interaction between droplets decreases sharply with their separation distance, droplets located relatively far away from a given droplet must be considered to accurately predict its condensation rate, due to the large aggregate effect of all such far away droplets. By considering an appropriate number of interacting droplets in a system, the point sink superposition method is able to predict experimental condensation rates to within 5%. Diffusion-based models that neglect the interactions of droplets located far away, or approximate droplet growth as an equivalent film, are shown to overpredict condensation rates. exp experiment film film-like growth model iso isolated from all neighboring droplets l liquid PSSM point sink superposition method s at the surface of the drop sub at the substrate sys in the system of droplets  far field

Spatial Control of Condensation: The Past, the Present, and the Future

“…This has been done using the point sink superposition method (Figure 4c). [92,93] Based on the present literature, I believe that particularly three recurring themes are currently limiting the full utilization of spatial control. These are 1) their issues with robustness, 2) their fixed behavior, and 3) only spatial control of water is considered.…”

“…c) Point-sink superposition method using Voronoi polygons to determine growth rates of the individual droplets. Reproduced with permission [93]. Copyright 2018, Elsevier.…”