Modeling and Simulations of Multiphysics Phenomena ad Performance in Proton Exchange Membrane Fuel Cells

Sammanfattning: Proton exchange membrane fuel cells (PEMFCs) are considered as the mostpromising alternative power sources with a wide variety of applications owing to their attractive advantages compared to other conventional power sources. During the past decades, the cell performance has been gradually improved. However, the cell performance improvement and cost reduction are still urgently needed due to the requirements of commercialization of PEMFCs.A three-dimensional mathematical model for low temperature proton exchangemembrane fuel cells (LT-PEMFCs) has been developed. The fluid flow, heat andmass transfer inside fuel cells are governed by the mass, momentum, species and energy conservation equations. The transport processes of electrons and protons are determined by the charge conservation equations, and the Butler-Volmer equation and agglomerate model are applied to describe the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) at the anode and cathode catalyst layers (CLs), respectively. In addition, the liquid water formation and transport in porous regions, and water transport through the membrane are taken into account in the mathematical model. For the agglomerate model, the size and structure of the agglomerates are determined by the agglomerate radius (ragg), the volume fraction of ionomer within the agglomerate (Li,agg), and the thickness of the ionomer film over the agglomerate (δi). The effects of agglomerate model parameters on transport characteristics and cell performance are investigated using the developed model. To avoid the reactant gas leakage and minimize the contact resistance, the assembly force is applied on the fuel cell stack, and accordingly the gas diffusion layer (GDL) deformation arises. Fuel cells with interdigitated flow fields under different assembly forces are systematically studied.A three-dimensional mathematical model for high temperature proton exchangemembrane fuel cells (HT-PEMFCs) has also been developed. The fluid flow, heatand mass transfer, and electron and proton transport inside fuel cells are governed by the mass, momentum, species, energy and charge conservation equations. The transport phenomena and performance of fuel cells with different flow fields have been analyzed and compared using the developed model. In addition, the fuel cell with metal foams as flow distributor has also been investigated and compared to the fuel cell with conventional straight channel flow field.Cooling plates of fuel cells aims to avoid overheating, reduce the maximumtemperature and minimize the temperature variations inside fuel cells. A three dimensional model has been adopted to investigate the cooling plates with non-uniform and wavy flow channel designs. The fluid flow and thermal characteristics of various designs have been examined and compared in detail.

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