Modeling and analysis of evaporation processes from porous media on the REV scale

Abstract

The dynamics of drying processes from porous media are critically influenced by the intensity of an adjacent free flow and by processes at the interface between free flow and the porous medium. In this paper, the influence of hydraulic properties of a porous medium and of the interaction between fluids and porous medium on the drying dynamics during the capillary-flow dominated stage-1 and transition to the diffusion-dominated stage-2 are studied using a coupled free-flow-porous-medium flow model on the REV scale. We present a detailed model concept that considers mass balance equations, an energy balance equation, and the coupling to the adjacent free flow. Key microscale processes are identified and incorporated in the macroscale description of the evaporation process. Own experimental results are used to illustrate main features of the modeling framework. We demonstrate that the use of a homogeneous distribution of soil parameters without consideration of pore-scale induced nonlinearities in the numerical simulations results in a rather constant drying rate in stage-1, which was not observed for the high evaporative demand in the experiments. To account for the dependency of the drying rate on the surface moisture content, special conditions based on the work of Haghighi et al. (2013) and Schl€ under (1988) are analyzed for their applicability on the REV scale. Typical features of a drying process, such as different stages of the drying rate, could be reproduced.

Numerical modelling of evaporation in a ceramic layer in the tape casting process

“…Numerical results of spatial and temporal evolution for the saturation of water in the porous-media (S w ) as well as mass fraction of vapour in the gas phase (X w,ff g ) are shown in Figure 3. The results are in a good agreement with the ones presented in the similar studies [9,10,11,12,22]. As seen from Figure 3, during the evaporation process, the saturation of the water in the porous medium is decreasing by time.…”

“…The model is implemented in the open source modelling framework DuMux [13]. The model depicts the evaporation process well [7] and it is in a good agreement with the ones presented in the similar studies [9,10,11,12,22].…”

“…where J u n+1,m is the Jacobi matrix calculated by numerical differentiation, Δu is the correction to the primary variables u, and R u n+1,m is the residuum at time level n + 1 and iteration m. The linear problem at each Newton iteration step is solved using the direct linear solver SuperLU [21], and for the time integration, a fully implicit Euler scheme with a heuristic time-step control based on the convergence rate of the Newton solver is used [9,10,11,12,22].…”

Effect of Turbulence and Roughness on Coupled Porous-Medium/Free-Flow Exchange Processes

“…Considering two different domains is desirable from a physical point of view. Because the free-flow processes act on smaller spatial and temporal scales than the porous-medium processes, the two-domain approach allows for the detailed modeling of the free flow while still applying simplifying assumptions to the porous medium (Dahmen et al 2014;Mosthaf et al 2014;Defraeye 2011). These different temporal and spatial scales also motivate different numerical treatments of the subdomains (Rybak et al 2015;Arbogast et al 2007).…”

“…The coupling between the free-flow and porous-medium flow is extremely relevant to evaporation processes from bare soil surfaces. Evaporation from soil surfaces is a vital research subject in the past few years and has been investigated at the pore scale, e.g., (Shahraeeni et al 2012;Assouline et al 2010;Yiotis et al 2007;Laurindo and Prat 1998;Suzuki and Maeda 1968), at the REV scale, e.g., (Trautz et al 2015;Zhang et al 2015;Mosthaf et al 2014 andSchneider-Zapp et al 2010), and at larger scales, e.g., (Vanderborght et al 2010;Shukla andMintz 1982 andPenman 1948).…”