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.
Highlights
The European Physical Journal Special Topics building components and filters in air conditioning systems and HVAC [1]
The knowledge of wetting behaviour and mechanisms plays a fundamental role in the development of design rules of functional materials, e.g. superhydrophobic surfaces [2], and of porous coatings used for cooling of electronic devices and heat transfer enhancement in spray cooling [3]
In this work a theoretical model is developed which describes simultaneous capillary rise and evaporation in a corner formed between a plane and a cylinder
Summary
The European Physical Journal Special Topics building components and filters in air conditioning systems and HVAC [1]. When a liquid drop encounters a porous layer, the transport of liquid over and within this layer is governed by the physical and chemical properties of liquid and solid in contact, the geometry of the porous structure, and the thickness of the layer. Depending on those properties, different behavior types can been observed, including perfect wetting, partial wetting, non wetting, and liquid imbibition into the layer, both in the direction parallel and normal to the substrate. The topography of the substrate, the geometry and orientation of the pores and geometrical features such as pillars can determine preferential liquid spreading directions and wetting patterns [10]
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