Continuum-Scale Modeling of Liquid Redistribution in a Stack of Thin Hydrophilic Fibrous Layers

Abstract

Macroscale three-dimensional modeling of fluid flow in a thin porous layer under unsaturated conditions is a challenging task. One major issue is that such layers do not satisfy the representative elementary volume length-scale requirement. Recently, a new approach, called reduced continua model (RCM), has been developed to describe multiphase fluid flow in a stack of thin porous layers. In that approach, flow equations are formulated in terms of thickness-averaged variables and properties. In this work, we have performed a set of experiments, where a wet 260-μm-thin porous layer was placed on top of a dry layer of the same material. We measured the change of average saturation with time using a single-sided low-field nuclear magnetic resonance device known as NMR-MOUSE. We have employed both RCM and the traditional Richards equation-based models to simulate our experimental results. We found that the traditional unsaturated flow model cannot simulate experimental results satisfactorily. Very close agreement was obtained by including the dynamic capillary term as postulated by Hassanizadeh and Gray in the traditional equations. The reduced continua model was found to be in good agreement with the experimental result without adding dynamic capillarity term. Moreover, the computational effort needed for RCM simulations was one order of magnitude less than that of traditional models.

Inhomogeneous Distribution of Polytetrafluorethylene in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells

“…This leads to the conclusion that a smaller total amount of PTFE can lead to the same transport characteristics of liquid water through the GDL micro-structure if it is located in the proper regions of the GDL. This result is consistent with the experiments of Tavangarrad et al (2018), who found that liquid water emerging from a hydrophobic layer of porous material does not tend to redistribute very much when it enters a hydrophilic region. Mortazavi and Tajiri (2013) measured contact angles on the surface of Toray GDL.…”

“…Shakerinejad et al (2018) studied GDL performance with the presence of hydrophilic layers inside, using the LB method for their simulations. Tavangarrad et al (2018) experimentally investigated the redistribution of PTFE in a situation where two thin layers of different hydrophobicity were stacked upon each other. Ito et al (2016) applied PTFE to Toray 090 GDLs using different techniques.…”

Liquid water in cathode gas diffusion layers of PEM fuel cells: Identification of various pore filling regimes from pore network simulations

“…However, the lack of length scale separation characterizing the GDLs leads to question the relevance of the classical continuum approach to porous media in the case of GDLs, i.e. [31,32]. Combined with the fact that PNM computations are quite faster than LBM and easy to develop, this has led to the situation that PNM is nowadays the most popular numerical technique to study the https://doi.org/10.1016/j.ijheatmasstransfer.2018.…”

Capillary pressure–saturation curves of thin hydrophilic fibrous layers: effects of overburden pressure, number of layers, and multiple imbibition–drainage cycles

“…Unfortunately, there are several challenges when measuring the unsaturated hydraulic properties of such thin layers. A layer is considered physically thin when the number of pores along its thickness is less than approximately 15 [see Qin and Hassanizadeh,7,8 Ceballos et al, 9 and Tavangarrad et al 10 ], with the thickness of a thin porous layer obviously being much smaller than its planar extent.…”

“…11 Some measurements have been carried out also to determine the P c S ð Þ relationships of thin hydrophilic fabrics used in medical and hygienic absorbent products. 10,20,21 Several modeling studies also exist to estimate the capillary pressure-saturation curves of thin fibrous layers. For example, in a recent study, general expressions for the P c S ð Þ relationship of thin fabrics were developed for a family of fibrous media using a pore morphology methodology.…”