Formation of a hard surface layer during drying of a heated porous media

Kumar, N and Arakeri, JH and Bobji, MS (2020) Formation of a hard surface layer during drying of a heated porous media. In: PLoS ONE, 15 (2).

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Abstract

We report surface hardening or crust formation, like caking, during evaporation when a porous medium was heated from above using IR radiation. These crusts had higher strength than their closest counterparts such as sandcastles and mud-peels which essentially are clusters of a partially wet porous medium. Observed higher strength of the crusts was mostly due to surface tension between the solid particles, which are connected by liquid bridges (connate water). Qualitative (FTIR) and quantitative (TGA) measurements confirmed the presence of trapped water within the crust. Based on the weight measurements, the amount of water trapped in the crusts was ~1.5; trapped water was also seen as liquid bridges in the SEM images. Further, in the fixed particle sizes case, the crust thickness varied slightly (only 10�20 particle diameters for cases with external heating) while with the natural sand whole porous column was crusted; surprisingly, the crust was also found with the hydrophobic glass beads. Fluorescein dye visualization technique was used to determine the crust thickness. We give a power-law relation between the crust thickness and the incident heat flux for various particle sizes. The strength of the crust decreased drastically with increasing hydrophilic spheres diameter while it increased with higher surface temperature.

Item Type:	Journal Article
Publication:	PLoS ONE
Publisher:	Public Library of Science
Additional Information:	The copyright of this article belongs to Public Library of Science
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	17 Jun 2020 08:06
Last Modified:	17 Jun 2020 08:06
URI:	http://eprints.iisc.ac.in/id/eprint/64827

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