What is it about?
Surface hardening of a porous medium undergoing evaporation of moisture loss. The upper layer of soil becomes hard as is commonly seen when a river runs dry. We explore the physics behind this phenomena.
Photo by Dan Gold on Unsplash
Why is it important?
It is of extreme importance in understanding the soil behaviour connected to the hydrology. Further, once this phenomenon is completely understood, we can devise methods to avoid it.
Read the Original
This page is a summary of: Formation of a hard surface layer during drying of a heated porous media, PLoS ONE, February 2020, PLOS, DOI: 10.1371/journal.pone.0229723.
You can read the full text:
Formation of a hard surface layer during drying of a heated porous media
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.
The following have contributed to this page