Macroscopic Modeling of Liquid Water in Channel of Jari Cell Based on Detailed Two-Phase CFD

Abstract

In this work, we modeled liquid water behavior in channels based on detailed two-phase CFD for application on Full-Cell scale multiphysics simulation. In our work, in order to execute efficient simulations in full-cell scale, all relevant transport phenomena in PEFC (mass, chemical species, and heat) are considered macroscopic, where the phenomena are coupled with electrochemical reactions. In order to apply this method for conditions in which liquid water is important, two-phase fluid models should be constructed properly.In order to model two-phase flow in channels, we evaluated the relationship between liquid water volume fraction, pressure drop, and liquid water velocity in macroscopic control volume with detailed CFD using OpenFOAM. The calculation target is the JARI cell channel and mesh size is 50 micrometer order. We used the interIsoFoam for the solver, which uses the VOF method for two-phase flow and geometric surface reconstruction method for surface capturing. The relationship is expressed by the table data that shows the relationship between the liquid phase volume fraction and liquid phase velocity or pressure loss multiplier. The table data shows a good representation of the below. Dependency of pressure drop on the water volume fractionDependency of drainage droplet size on the gas flow rateDehydration speed In order to evaluate the obtained models, we calculated PEFC simulations with the models and validated the calculations.In our simulator, in order to estimate the performance of PEFC cells taking all relevant transport phenomena (mass, chemical species, and heat) is solved on the coarse-grained mesh, coupled with electrochemical reactions. The mass transport equation is solved by Darcy’s law, using the distribution of the equivalent hydraulic parameter in flow channels estimated by detailed gas phase CFD. Here mass transport is coupled with heat and chemical species transport equations. Those all transport phenomena are coupled with electrochemical reactions in the MEA. Transport of chemical species and water through the MEA is also considered. Many engineering models are employed in order to consider various transport phenomena, like water up-take into electrolytes and effective transport of oxygen from the gas phase to reaction sites in catalyst layers, etc. Electrochemical reactions are modeled by the Butler-Volmer equation, in the manner of lumped parameter models.The calculation using the derived two-phase model well reproduce the below phenomena. Various Overpotentials difference between drive conditionsDrainage speed difference depending on gas flow ratesLiquid water difference between under the rib and the channelOxygen depletion depending on stoichiometry and liquid water distribution