The Impact of Corner- and Thick-Film flow on Evaporation: A Micromodel Study

Evaporation from real soils is a rather complex process, where atmospheric processes and internal water-transport and phase-transfer processes interfere each other, often nonlinearly. Coupled surface flow and diffusion from interfering neighboring pores through viscous or turbulent boundary layer determine the upper (atmospheric) boundary condition for the capillary and viscous water flow through the pore network of the porous media.

Recent research studied the influence of corner flow and thin-film flow on the evaporation or drying process. At pore scale these studies use microfluidic setups (Eijkel et al., 2005; Zhao et al., 2016) or micro-models (Zhang et al., 2011; Prat, 2011; Vorhauer et al., 2015; Geistlinger et al., 2019). At REV-scale the studies are based on packed glass beads and sands (Hoogland et al., 2016). Parametrizations of the soil hydraulic functions for the very dry region include corner- and film flow contributions (e.g. Peters et al., 2015).

To the best of our knowledge there is no study of the impact of thick-film flow caused by the roughness of the pore-solid interface on the evaporation (drying) process.

The objective of this paper is to present a comparative study of the two relevant water transport mechanisms corner- and thick-film flow at pore scale using micro-model experiments. The micro-models exhibit the same pore structure, but are different in their surface roughness. This is achieved by producing them based on silicon (smooth surface) and glass ceramics (rough surface). This allows to reduce the complexity of the evaporation process and control the relevant process parameter.

 

[1] Geistlinger, H., Ding, Y., Apelt, B., Schlüter, S., Küchler, M., Reuter, D., et al. (2019). Evaporation study based on micromodel experiments: Comparison of theory and experiment. Water Resources Research, 55, 6653–6672. https://doi.org/10.1029/2018WR024647

[2] Geistlinger, H., & Leuther, F. (2018). Evaporation study for real soils based on HYPROP‐hydraulic functions and micro‐CT‐measured pore‐ size distribution. Vadose Zone Journal, 17(1). https://doi.org/10.2136/vzj2018.02.0041 180041