Introduction to Condensation

Abstract

Condensation involves change of phase from the vapor state to the liquid. It is associated with mass transfer, during which vapor migrates towards the liquid-vapor interface and is converted into liquid. Condensation process is initiated by subcooling, a temperature difference between the bulk vapor and the solid surface. Subsequently, energy in the form of the latent heat must be removed from the interfacial region either by conduction and convection through the droplet and conduction through the substrate. This chapter introduces classification and significance of various physical processes in dropwise condensation, while comparing it with the filmwise form of condensation. The importance of surface wettability and equilibrium contact angle on the formation of drops is highlighted. The shape of the drop plays a central role in fixing conduction resistance, the onset of gravitational instability with respect to static equilibrium, as well as its motion over the substrate. Post instability, fresh nucleation ensures that the dropwise condensation process is intrinsically cyclic, with a characteristic timescale, area coverage, and drop size distribution.