Condensation mode transition and droplet jumping on microstructured surface

Abstract

Condensation enhancement on the micropillar structured surfaces is studied using a three-dimensional lattice Boltzmann model, and the optimal micropillar configuration is assessed. The impacts brought by varying micropillar geometric parameters on heat transfer and droplet dynamics during dropwise-to-filmwise transition are explored. Increasing micropillar width and spacing or decreasing height accelerates nucleation and improves nucleation density in the dropwise condensation stage, while radial contraction of the liquid film is hindered and the heat transfer area is increased in the filmwise condensation stage. Compared with its plain competitor, the maximum number of the isolated droplets is increased by 525%, the nucleation time is advanced by 57.1% and the heat flux is increased by 187.4% on the optimal micropillar surface. The entire condensation process spanning over nucleation, coalescence and jumping of multiple condensate droplets on the micropillar surface is realized using the present three-dimensional lattice Boltzmann model for the first time. The effects of height and spacing of micropillar arrays on jumping height and velocity are analyzed. The results show that the micropillar height poses little effect on the jumping height and velocity when the micropillar spacing is 0.1. When the micropillar spacing is 0.15, the jumping height and velocity first increase but then decrease with the increase of the micropillar height. Finally, the condensation heat transfer mechanism under different subcooling on the hierarchical surface is analyzed in detail.