Microscopic insight into mechanisms of heat and mass transfer improvement of dropwise condensation on a modified nanopillar surface

Abstract

In this work, a series of molecular dynamics simulations are carried out to explore the mechanisms of heat and mass transport on textured surfaces during the initiation of condensation. The solid fractions of composite nanopillars on textured surface range from 0.13 to 0.35. The addition of nanopillars with φ=0.35 on bare surface results in a 50 % decrease of the total thermal resistance. Increasing surface wettability brings a higher overlap of phonon vibrational density of states between solid and near-surface atoms, and an order magnitude reduction of interfacial Kapitza resistance can be obtained. Also, enhancing temperature (Thot) gives rise to the formation of droplets that exhibits higher solid-liquid viscous force within multi nanostructure cells. The wetting map with respective to the temperature difference and nanostructure spacing shows that the increases of Thot and spacing l facilitates the formation of Wenzel droplets. For Cassie droplets, the highest condensation rate is found for the case of Thot =130 K and l = 30 Å. While both dense and sparsely arranged nanopillar surfaces have higher Wenzel droplet condensation rates. Compared to the cylindrical structure, the cylinder-hemisphere composite structure shows superior condensation performance after droplet approaches the hemisphere region. In addition, the condensation rate on hybrid wettability surface exhibits a 30 % enhancement than that on uniformly hydrophilic surface.