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.
Highlights
Pore network models (PNMs) are discrete mathematical models that are basically used to simulate and predict pore scale processes
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
1/VO2 = 1/vO2 A [sμL ], with the slope being the total volume of the pore networks (PNs) in Section 3.1, We have presented a method to study the pore scale transport of oxygen and water through the porous transport layers (PTLs) of water electrolysis cells
Summary
Pore network models (PNMs) are discrete mathematical models that are basically used to simulate and predict pore scale processes. Different types of PNMs are generally distinguished. These are (i) PNMs for quasi-static drainage invasion processes [1,2,3,4], (ii) PNMs for quasi-static imbibition invasion processes [1,3,4,5], (iii) PNMs of drainage with phase transition and diffusion of the vapor (especially applied in drying research) [6,7,8], and (iv) PNMs for the computation of dynamic pore scale fluid flow [9,10,11,12,13]. While the first three approaches usually assume quasi-static invasion of the pore space, the fourth approach considers viscous flow of the liquid phase and dynamic invasion of the pore space. A few models are available that take into account coupled heat and mass transfer [21,22] or that at least consider the invasion and transport processes under non-isothermal conditions [23,24,25]
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