Analysis of a Two-Phase Non-Isothermal Model for a PEFC

Abstract

A non-isothermal, two-phase model for a polymer electrolyte fuel cell ͑PEFC͒ is presented, analyzed, and solved numerically under three different thermal, and two hydrodynamic, modeling assumptions; the consequences of these are then discussed in terms of thermal and water management and cell performance. The study is motivated by recent experimental results that suggest the presence of previously unreported, and thus unmodeled, thermal contact resistances between the components of PEFCs and the discrepancy in the value for the capillary pressure that is used by different authors when modeling the two-phase flow in PEFCs. For the three different thermal assumptions ͑assuming effective heat conductivities, isothermal flow, and interfacial and bulk conductivites͒, liquid saturations of around 10% are obtained at the cathode active layer for 1000 mA cm −2 and a cell voltage of 0.6 V. When lowering the capillary pressure ͑hydrodynamic assumption͒, liquid saturations of almost 30% and locally up to 100% are observed at the active layer of the cathode. At this current density and voltage, temperature differences across the cell of around 9°C are predicted. In addition, the effect of varying clamping pressure within the framework of the model is touched upon. The benefits of the scaling analysis conducted here, to predict correctly, prior to numerical computations, important characteristic cell performance quantities such as current density and temperature drop are also highlighted.

Modeling Water Management in Polymer-Electrolyte Fuel Cells

“…PEFC components are held together with a compressive load to ensure contact between the layers, but the additional force also affects porosity, pore-size distribution, conductivities, and contact resistances. 197,[215][216][217][218][219][220][221][222] Regions under the rib or land are expected to have decreased diffusivities and permeability in the in-plane direction and increased though-plane conductivity due to the vertical compaction of fibers. 219,221 Experimentally, most GDLs exhibit an ideal compression value that balances the benefit from decreasing contact resistance with the penalty of impeding gas and liquid flow.…”

“…Although accounting for clamping effects by tuning contact resistances allows for their quick incorporation into fuel-cell models, 197,219 adjusted contact resistances do not account for deformations nor changes to the internal properties of the GDL.…”

A High Temperature Polymer Electrolyte Membrane Fuel Cell Model for Reformate Gas

“…It was found [8,9] that under the assumption of no liquid water formation, the model consistently overpredicted measured polarization behaviour.…”

Improved modeling and understanding of diffusion-media wettability on polymer-electrolyte-fuel-cell performance

“…The origin of these profiles is due to the complex nature of both the material heterogeneities as well as phenomena such as phase-change-induced (PCI) flow where water moves due to phase transitions. For example, water evaporating and condensing along a temperature gradient can have a large impact on the cell performance [51][52][53][54][55][56][57][58][59], or similarly, during shutdown in a cold-environment, water is predicted and shown to move due to freezing [60][61][62]. Thus, a valuable and predictive macroscopic model must be able to handle changes in the chemical and physical DM structure along with the various dominant transport phenomena.…”