Impact of Surface Roughness on Evaporation in 2D Micromodels
Yi Ding, Helmut Geistlinger
Abstract
Abstract Evaporation—a key process for water exchange between soil and atmosphere—is controlled by internal water fluxes and surface vapor fluxes. Recent studies demonstrated that the dynamics of the water flow in pore corners and thick‐film flow on the rough pore‐solid interface determine the time behavior of the evaporation rate. A comprehensive experimental study of the combined effect of corner flow (CF) and thick‐film flow (TFF) on evaporation is lacking. Herein, we present a comparative micromodel study of the evaporation process using 2D‐porous media, which exhibit the same stochastic pore structure, but different degree of surface roughness (silicon micromodels with smooth surface and glass‐ceramic micromodels with rough surface). Our study proves both experimentally and theoretically that surface roughness and wettability play a key role for the time and temperature behaviors of the evaporation process. We found a similar behavior up to 42°C regarding the mass loss as a function of time in stage‐2 and a transition to linear t behavior for higher temperatures (61°C) with a high statistical significance (regression coefficients near 1) for both micromodels. Our experimental results elucidate the strong temporal correlation between mass loss and geometric pattern of the unsaturated CF and TFF region. Partial wetting in silicon micromodels causes a weak driving force for CF, whereas complete wetting in glass‐ceramic micromodels causes a strong driving force for TFF. For a consistent description of the time‐dependent mass loss and geometry of the CF/TFF region, the fractality of the evaporation front must be considered. Based on our data, we estimate the film thickness and discover some interesting film‐thinning effect with increasing temperature.