Capillary rise and evaporation of a liquid in a corner between a plane and a cylinder: A model of imbibition into a nanofiber mat coating

Abstract

Wetting of surfaces with porous coating is relevant for a wide variety of technical applications, such as printing technologies and heat transfer enhancement. Imbibition and evaporation of liquids on surfaces covered with porous layers are responsible for significant improvement of cooling efficiency during drop impact cooling and flow boiling on such surfaces. Up to now, no reliable model exists which is able to predict the kinetics of imbibition coupled with evaporation on surfaces with porous coatings. In this work, we consider one of possible mechanisms of imbibition on a substrate covered by a nanofiber mat. This is the capillary pressure-driven flow in a corner formed between a flat substrate and a fiber attached to it. The shape and the area of the cross-section occupied by the liquid as well as the capillary pressure change along the flow direction. A theoretical/numerical model of simultaneous imbibition and evaporation is developed, in which viscosity, surface tension and evaporation are taken into account. At the beginning of the process the imbibition length is proportional to the square root of time, in agreement with the Lucas-Washburn law. As the influence of evaporation becomes significant, the imbibition rate decreases. The model predictions are compared with experimental data for imbibition of water-ethanol mixtures into nanofiber mat coatings.

Droplet evaporation on porous fabric materials

“…The power fitting of the plotted data showed that . Chatterjee et al 45 previously demonstrated that the drained volume evolves with time as , following the premise from Washburn’s law when evaporation is not significant during the imbibition and the substrate does not have intrinsic hydrophobic properties 43 , 49 , 50 . Therefore our result corroborates that in the initial moments, the droplet volume loss is dominated by spreading and imbibition.…”

Challenges of Numerical Simulation of Dynamic Wetting Phenomena: A Review

“…Pore-scale models have increasingly become a reliable tool for making predictions of two-phase flows through porous media; see e.g. [87,88]. Direct numerical simulation techniques based on solving the full Navier-Stokes equations provide an accurate solution for pore-scale analysis of multiphase flows in porous media.…”