An Efficient Two-grid Method for a Two-phase Mixed-domain Model of Polymer Exchange Membrane Fuel Cell

AbstractIn this paper, an efficientandfast numerical methodis studiedand implementedfora simplifiedtwo-phasemixed domain model of polymer exchange membrane fuel cell (PEMFC), which fully incorporates both the anode and cathode sides, including the conservation equations of mass, momentum, water vapor concentration, liquid water saturationandwater content.Theproposed numericalalgorithmisbasedonthetwo-grid discretization technique,the combined finite element-upwind finitevolume method and some other appropriate linearization schemes. The original nonlinear partial differential equations are only solved on the coarse grid while the fine grid approximation solution is obtained linearly. Therefore the computational time can be reduced tremendously compared with the traditional one-grid method. Numerical experiments of the two-grid method and conventional method for a two-phase mixed domain fuel cell model are carried out, showing that the presented method is effective and accurate for the numerical simulation of PEMFC

Water dynamics inside a cathode channel of a polymer electrolyte membrane fuel cell.

The present study focuses on the investigation of water dynamics inside a polymer electrolyte membrane fuel cell using two different modelling approaches: Eulerian two-phase mixture and volume of fluid interface tracking models. The Eulerian two-phase mixture model has provided overall information of species distribution inside a fuel cell and identified that the liquid water usually accumulates under the land area. The volume of fluid interface tracking model has then been implemented to investigate the emergence of water droplets from the gas diffusion layer into the cathode channel and the subsequent removal of water from the channel. Further, the effects of the location of water emergence in the cathode channel on the dynamic behavior of liquid water have been investigated. The present study shows that the water emerging into the channel near the side walls greatly reduces the surface water coverage of the channel. In order to control the water path into the channel near side walls, a further discussion has been provided that a gas diffusion layer design based on hydrophilic fibres distributed inside a hydrophobic fibre matrix could provide a precisely controlled water path through the gas diffusion layer

Computational fluid dynamics modelling of PEM fuel cells to investigate transport limitations.

Modern technological advancements in our lifestyle have caused a significant increase in the consumption of energy. With this growing demand, people are more concerned about the rational use of existing limited energy and searching for alternative forms of environmentally friendly energy sources to reduce polluting emissions. Proton Exchange Membrane (PEM) fuel cell has shown and demonstrated that potential to be a suitable alternative power source because of its simplicity of design, load following capabilities, efficiency, feasibility and quick start-up. Although having these splendid advantages, cost and durability of PEM fuel cells are one of the major challenges that needed to be overcome. Three-dimensional single-phase and multi-phase isothermal PEM fuel cell models have been developed to investigate the transport limitations of fresh reactants and its effect on cell performance. The governing equations (continuity, momentum and species transport) with appropriate source terms were solved using computational fluid dynamics (CFD) technique. A user defined function (UDF) code was developed considering source terms for porous zones, effective diffusivity models for species transport inside cells and electrochemical reactions at catalyst layers to predict cell voltage at an average current density. The average current density and net water transfer coefficient, used to calculate the source terms, were calculated using auxiliary equations and linked to the solver through UDFs. Parametric studies were performed to determine the optimal operating conditions and geometrical design of PEM fuel cell. The simulation results show that gas diffusion layer permeability has no effect on cell performance for a value lower than 10-11 m2. GDL porosity is one of the major design parameters which have significant influence on limiting current density, hence on cell performance. Land area width of PEM fuel cell shows influence on cell performance. Low membrane thickness provides higher cell performance and approximately 50% reduction in membrane thickness results approximately 100% improvement in cell performance at high current density of 1.0 Acm-2. Bruggeman correlation was used in most of previous modelling work for explaining the diffusion of species though porous GDL and CL, but this thesis considered other types of effective diffusion models and investigated the effect of diffusion models on cell performance at high current densities. Tomadakis and Sotirchos (1993) anisotropic model produces cell voltage much closer to the experimental values. Therefore, anisotropic diffusion model should be utilized in PEM fuel cell modelling to minimize modelling uncertainties. A two-phase flow, steady-state, three-dimensional PEM fuel cell model considering the phase change effect of water has been developed in the final phase of the thesis. Flooding inside the cell was captured at high current density using the model for a condensation value of 10.0 s-1. Finally, parametric studies were performed based on isotropic and anisotropic GDL permeability cases. Modelling results suggest that isotropic permeability cases have strong influence on cell performance compared to anisotropic cases at high current density

Computational modeling of proton exchange membrane electrolysis cell for hydrogen production

Numerical simulations of electrochemical process for hydrogen production were performed for the purpose of examining the phenomena occurring within the proton exchange membrane (PEM) water splitting cell. A steady-state isothermal two dimensional model of the cell is developed. Finite element method was used to solve the multi-component transport model coupled with flow in porous medium, charge balance and electrochemical kinetics; Parametric studies were performed based on appropriate mass balances, transport, and electrochemical kinetics applied to the cell. It is observed that, as the water on the anode side flows from the inlet to the outlet, the mass fraction of oxygen increases because of the oxidation of oxygen. Similarly, on the cathode side, as the mass fraction of water decreases, the hydrogen mass fraction increases resulting in the formation of hydrogen by reduction of protons. Effects of cell temperature, length of the current collector and thickness of the membrane on the cell performance are examined. As the cell temperature increases, the current density across the cell and mass fraction of hydrogen increases respectively. Increase in thickness of membrane causes a decrease in the cell current density. The current density across the cell tends to increase as the length of the current collector increases

Characterization Techniques and Electrolyte Separator Performance Investigation for All Vanadium Redox Flow Battery

The all-vanadium redox flow battery (VRFB) is an excellent prospect for large scale energy storage in an electricity grid level application. High battery performance has lately been achieved by using a novel cell configuration with advanced materials. However, more work is still required to better understand the reaction kinetics and transport behaviors in the battery to guide battery system optimization and new battery material development. The first part of my work is the characterization of the battery systems with flow-through or flow-by cell configurations. The configuration difference between two cell structures exhibit significantly different polarization behavior. The battery output can be increased by higher electrolyte feed rate, but electrolyte utilization was decreased correspondingly. The battery performance can be largely enhanced by non-wetproofed electrode material. The battery cell with higher vanadium crossover has lower energy efficiency and faster capacity decay in cycling test. Secondly, the state of charge (SOC) monitoring is of great importance for battery management. A SOC monitoring method is developed using UV-Vis spectrometric measurements on VRFB electrolyte solutions. The spectrum of the negative electrolyte is linearly dependent on its SOC. In the positive electrolyte, the nonlinear intensity dependence on SOC appears to be caused by formation of complex vanadium-oxygen ion. The characteristic molar UV-Vis spectrum of the complex vanadium-oxygen ion was separated from that of the pure positive vanadium electrolyte components. The SOC of the positive electrolyte can be then calculated from its UV-Vis spectrum by considering the complex vanadium ion equilibrium. Moreover, the understanding of ionic transport mechanism in the electrolyte separator is critical to reduce internal resistance and vanadium crossover in the battery. The properties of Nafion and sulfonated Alder Diels poly(phelynene) (SDAPP) were investigated after equilibration with different electrolyte compositions. Both sulfuric acid and vanadium ion in the membrane can cause membrane conductivity loss. Vanadium-oxygen ion in membrane can slow down proton mobility via an unknown mechanism. Transmission electron microscope imaging showed that SDAPP is a more homogeneous ion exchange polymer with less phase separation than Nafion. The SDAPP membranes have better ion conducting properties than Nafion because of their higher ionic selectivity