Introduction

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. Transport is driven by a pressure reduction that occurs at the phase boundary. Condensation process is initiated by a temperature difference, called subcooling, 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 or convection. Condensation is an essential part of energy conversion, water harvesting, and thermal management systems. Improvement in heat and mass transfer during the phase-change process, therefore, can have beneficial effects. This chapter introduces classification and significance of various physical processes in dropwise condensation. The importance of wettability and 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 instability with respect to static equilibrium, as well as its motion over the substrate. Once large drops move out of the surface, fresh nucleation ensures that the condensation process is cyclic, with a characteristic timescale, area coverage, and drop size distribution. Mathematical modeling of the dropwise condensation process forms the topic of the following chapters.