Dynamic Evolution of an Evaporating Liquid Meniscus from Structured Screen Meshes

Abstract

Evaporation from screen mesh is a fundamental phenomenon that plays a vital role in thermal transport devices like heat pipes. Here, a laser scanning confocal microscopy setup has been utilized to study the effect of screen mesh wettability and its surface morphology on the evolution of evaporating liquid menisci from its liquid saturated pores. Stainless steel screen meshes (mesh #100 and #200) that are inherently hydrophobic in nature are turned super-hydrophilic by controlled heat treatment. The heat treatment leads to growth of oxide layer on the wire mesh and a change in surface morphology via formation of microscale pores, which improves the wettability of the screen mesh. The evaporation of liquid meniscus from pores of these untreated and heat-treated meshes is captured through confocal microscopy, and the dynamic evolution of the radius of curvature of the liquid meniscus is evaluated. A simple geometrical model is developed to predict the minimum radius of curvature \((R_{\mathrm{min}})\) of liquid meniscus in mesh pores just before its rupture (pore dryout). Meshes with high wettability, and smaller pore spacing-to-wire diameter ratio, are found to encounter a smaller \(R_{\mathrm{min}}\) before meniscus rupture. In addition, the water pore saturation inventory of the screen meshes are also measured to evaluate the effect of wettability on their water-holding capacity of screen meshes. Increase in screen mesh wettability is found to increase its pore saturation inventory. This increase in mesh pore saturation inventory coupled with the lower \(R_{\mathrm{min}}\) for super-hydrophilic mesh delays the liquid meniscus rupture (mesh dryout), leading to a much longer evaporation timescale for high wettability screen meshes.

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