Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

Abstract

Pore network models are powerful tools to simulate invasion and transport processes in porous media. They are widely applied in the field of geology and the drying of porous media, and have recently also received attention in fuel cell applications. Here we want to describe and discuss how pore network models can be used as a prescriptive tool for future water electrolysis technologies. In detail, we suggest in a first approach a pore network model of drainage for the prediction of the oxygen and water invasion process inside the anodic porous transport layer at high current densities. We neglect wetting liquid films and show that, in this situation, numerous isolated liquid clusters develop when oxygen invades the pore network. In the simulation with narrow pore size distribution, the volumetric ratio of the liquid transporting clusters connected between the catalyst layer and the water supply channel is only around 3% of the total liquid volume contained inside the pore network at the moment when the water supply route through the pore network is interrupted; whereas around 40% of the volume is occupied by the continuous gas phase. The majority of liquid clusters are disconnected from the water supply routes through the pore network if liquid films along the walls of the porous transport layer are disregarded. Moreover, these clusters hinder the countercurrent oxygen transport. A higher ratio of liquid transporting clusters was obtained for greater pore size distribution. Based on the results of pore network drainage simulations, we sketch a new route for the extraction of transport parameters from Monte Carlo simulations, incorporating pore scale flow computations and Darcy flow.

Steady-State Water Drainage by Oxygen in Anodic Porous Transport Layer of Electrolyzers: A 2D Pore Network Study

“…Besides fundamental physical studies, PNMs are also used for the parameterization of macroscopic models, e.g. to predict the capillary pressure curve, relative permeability curves, as well as saturation curves [46].…”

“…Pore network models (PNMS) are a type among various pore scale models available, e.g., Lattice Boltzmann models which are mostly available on the scale of one pore. PNMs are discrete models that represent the pore space by a lattice of pores and throats (e.g., [42][43][44][45][46]). In comparison to other methods, which are computationally more expensive in terms of discretization of the physical domain and solving of the governing equations, PNMs can be used to study larger systems computationally more efficiently.…”

“…In comparison to other methods, which are computationally more expensive in terms of discretization of the physical domain and solving of the governing equations, PNMs can be used to study larger systems computationally more efficiently. Besides fundamental physical studies, PNMs are also used for the parameterization of macroscopic models, e.g., to predict the capillary pressure curve, relative permeability curves, as well as saturation curves [46].…”

“…In the absence of dynamic effects, e.g., driven by viscous forces, the entry capillary pressure of pores and throats controls the displacement of liquid (drainage) or gas (imbibition) in such applications [52]. In this work, the quasi-static model from [46] is applied for the simulation of the drainage of water by oxygen.…”

“…After the geometric parameters are specified, active, i.e., invading clusters with their menisci are identified and the maximum liquid pressure is computed within the active clusters using Equation (1). The algorithm then selects the largest accessible throat or pore for gas invasion following the rules specified in Vorhauer et al [46]. As invasion proceeds, entrapped clusters are formed, which are permanently isolated due to the incompressibility of the fluids.…”