Menisci evaporation of electrokinetic liquid-film flows within inclined micro-confinements

Abstract

In this article, we consider the electrohydrodynamics of drainage and evaporation induced transport behavior of a liquid meniscus draining along an inclined micro-confinement. The film-flow-hydrodynamics is altered by the application of electrokinetic constraints and directionality either by aiding or opposing the gravity driven flow. This behavior, in turn, morphs the nature of the meniscus formed and the direction and magnitude of the interfacial flow velocity. Consequently, the Stefan flow in the vapor diffusion layer and the thermal gradient across the liquid film are morphed, leading to changed meniscus evaporation kinetics and film dry-out regimes. The film distribution, dry-out lengths, and Nusselt numbers are deduced from a detailed theoretical analysis incorporating the hydrodynamics, heat and mass transfer aspects. We further show that a non-dimensional local film number, of the form ρgsinθδ02/σ, may be proposed to efficiently design and develop such microfluidic systems to obtain desired heat and mass transfer rates within microscale thermofluidic devices. The findings may hold significance for efficient development of evaporative microfluidic systems, reactors, and micro-devices that operate on principles of chemical drying, deposition, and analysis.