Two-Phase Modeling and Flooding Prediction of Polymer Electrolyte Fuel Cells

Abstract

A newly developed theory of liquid water transport in hydrophobic gas diffusion layers is applied to simulate flooding in polymer electrolyte fuel cells ͑PEFCs͒ and its effects on performance. The numerical model accounts for simultaneous two-phase flow and transport of species and electrochemical kinetics, utilizing the well-established multiphase mixture formulation to efficiently model the two-phase transport processes. The two-phase model is developed in a single domain, yielding a single set of governing equations valid in all components of a PEFC. The model is used to explore the two-phase flow physics in the cathode gas diffusion layer. Multidimensional simulations reveal that flooding of the porous cathode reduces the rate of oxygen transport to the cathode catalyst layer and causes a substantial increase in cathode polarization. Furthermore, the humidification level and flow rate of reactant streams are key parameters controlling PEFC performance and two-phase flow and transport characteristics. It is also found that minimization of performance limitations such as membrane dry-out and electrode flooding depends not only on material characteristics but also on the optimization of these operating parameters.

Modeling Water Management in Polymer-Electrolyte Fuel Cells

“…However, the difficulty of procuring accurate measurements for GDL properties may be gleaned from the spread in the parameter values. 64,116,133,[157][158][159][160][161] Furthermore, hysteresis and heterogeneities in the medium complicate quantifications and compromise predictive capabilities of macroscopic models with respect to transient phenomena. Microscopic models are thus becoming necessary to elucidate governing flow mechanisms and to predict differences in flow pathways for yet uncharacterized materials or changes due to GDL manufacturing or PEFC design.…”

Characterization of water exchange and two-phase flow in porous gas diffusion materials by hydrogen-deuterium contrast neutron radiography

“…1 Water transport in fuel cell materials is commonly described by two-phase flow models, which take into account the complex transport interactions between liquid and gaseous phases, 1,3-5 and numerous theoretical and experimental reports focusing on two-phase flow have been crucial for understanding the basics of water transport. 3,4,[6][7][8][9][10][11][12][13][14][15][16] In recent years, neutron radiography, 10-13 magnetic resonance imaging, 14 and ͑to a limited extent͒ x-ray imaging [15][16][17] have been applied to visualize liquid water flow in fuel cells. However, until recently, it was not possible to quantify local water transport ͑exchange͒ rates inside fuel cell materials, i.e., the rates at which the accumulated water is exchanged by newly produced water from the cathode, especially under stationary conditions where the local water amount remains almost constant.…”

Multiscale Modeling of Single-Phase Multicomponent Transport in the Cathode Gas Diffusion Layer of a Polymer Electrolyte Fuel Cell

“…CFD treatments are well suited to simulating three-dimensional flow characteristics through complex non-porous structures such as the flow fields of a fuel cell bi-polar plate (BPP) [16], flow through porous regions on a volume-averaged basis [17,18,19] and planar temperature and current density distributions across the surface of the PEFC [20,21]. CFD treatments are not well-suited to simulating electrochemical cross-flow through quasi-porous layers, effects of layer compression/expansion/constraint as this invokes dynamic boundaries, or again flow through actual heterogeneous porous structures of PEFC layers…”