Kinematics in a slowly drying porous medium: Reconciliation of pore network simulations and continuum modeling

Abstract

We study the velocity field in the liquid phase during the drying of a porous medium in the capillarity-dominated regime with evaporation from the top surface. A simple mass balance in the continuum framework leads to a linear variation of the filtration velocity across the sample. By contrast, the instan-taneous slice-averaged velocity field determined from pore network simulations leads to step velocity profiles. The vertical velocity profile is almost constant near the evaporative top surface and zero close to the bottom of the sample. The relative extent of the two regions with constant velocity is dictated by the position of the most unstable meniscus. It is shown that the continuum and pore network results can be reconciled by averaging the velocity field obtained from the pore network simulations over time. This opens up interesting prospects regarding the transport of dissolved species during drying. Also, the study reveals the existence of an edge effect, which is not taken into account in the classical continuum models of drying.

A pore network study of evaporation from the surface of a drying non‐hygroscopic porous medium

“…As discussed in Ref. , this edge effect seems not to be due to the small size of our network but an intrinsic feature of the drying process as qualitatively similar edge effects are also seen in the saturation profiles measured by NMR in real samples, that is, Refs. and .…”

“…As discussed in more details in Ref. , the fact that this period is visible here is a consequence of the relatively small network considered. As can also be seen, the evaporation rate is actually not perfectly constant during the “CRP,” which starts when the saturation is about 0.97, that is, before BT.…”

“…As discussed in Ref. , the capillary regime is characterized by spatially quasi‐uniform saturation profiles during the CRP over almost all the height of network. This is illustrated in Figure with horizontal slice‐averaged saturation.…”

“…In Ref. , we focus on the velocity field induced in the liquid phase during drying, whereas in Ref. we discuss in depth the classical continuum model of drying from comparisons with pore network simulations.…”

Mass and Heat Transport Models for Analysis of the Drying Process in Porous Media: A Review and Numerical Implementation

“…e modeling and numerical simulation of drying in porous media is a topic of great interest in process engineering and has attracted the attention of research institutions for decades. e analysis of absorption or desorption of liquid in general, and of water in particular, finds its application not only in chemical engineering, food processing, and pharmaceuticals but also in electronic packaging, which is becoming more and more important in the area of the Internet of ings [1][2][3][4][5][6][7][8]. Over the years, many works were undertaken to understand the mass and heat transport phenomena during drying.…”