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Similar to other industries, the maritime industry is also facing increasing restrictions on ships regarding pollution control. The research presented in this paper is aimed at studying the pros and cons of alternative fuels followed by a detailed analysis on hydrogen fuel cells (PEMFC) for a particular ship operating in Lisbon, Portugal. Dynamic forces acting on the ship have been studied for a year. Assessing various scenarios based on these results aids ship operators in making informed decisions regarding the future course of action for their existing vessels. These different cases are first: business as usual (diesel engine), second: replacing the diesel engine with a hydrogen hybrid system and, third: replacement of the ship with a new hydrogen hybrid ship. The study is based on the simulation of numerical equations and CFD simulation results. As the result, the second scenario is best suited in both aspects; namely, environmental and economic. [ABSTRACT FROM AUTHOR]

Similar to other industries, the maritime industry is also facing increasing restrictions on ships regarding pollution control. The research presented in this paper is aimed at studying the pros and cons of alternative fuels followed by a detailed analysis on hydrogen fuel cells (PEMFC) for a particular ship operating in Lisbon, Portugal. Dynamic forces acting on the ship have been studied for a year. Assessing various scenarios based on these results aids ship operators in making informed decisions regarding the future course of action for their existing vessels. These different cases are first: business as usual (diesel engine), second: replacing the diesel engine with a hydrogen hybrid system and, third: replacement of the ship with a new hydrogen hybrid ship. The study is based on the simulation of numerical equations and CFD simulation results. As the result, the second scenario is best suited in both aspects; namely, environmental and economic.

A mathematical model of a hydrogen-oxygen (air) fuel cell that takes into account the phenomena of degradation of the cathodic platinum catalyst is presented. For potential cycling from 0.6 to 1.1 V with a scan rate of 0.1 V/s, depending on the platinum loadings, the following factors are found to prevail in the mechanism of electroactive surface degradation: the coalescence of platinum nanoparticles at large loadings and the platinum dissolution/redeposition and diffusion to the membrane at medium and low loadings. Based on mathematical simulation, the data on the discharge curves are calculated. The observed decrease in the discharge characteristics is attributed to the degradation of the catalyst active surface and the increased transport losses during accelerated stress testing. [ABSTRACT FROM AUTHOR]

A developed measurement system for current distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFCs). Currently, there are many issues with the methods to measure current distribution; some of the problems that arise are breaking up the fuel cell component and these measurements are costly. Within this field of work, there is a cost effective method and an easy technique of mapping the current distribution within a fuel cell while not disrupting reactant flow. The physical setup of this method takes a current distribution board and inserts it between an anode flow field plate and a gas diffusion layer. From this layout, the current distribution can be directly measured from the current distribution board. This novel technique can be simply applied to different fuel cell hardware. Further it also can be used in fuel cell stack by inserting multiple current distribution boards into the stack cells. The results from the current distribution measurements and the electrochemical predictions from computational fluid dynamics modeling were used to analyze water transports inside the fuel cell. This developed system can be a basis for a good understanding of optimization for fuel cell design and operation mode. [ABSTRACT FROM AUTHOR]

An improper designed flow field of a polymer electrolyte fuel cell (PEFC) can cause the maldistributions, resulting in the reduction of PEFC performance and lifetime. Although there are several researches investigating the effect of flow field design, the parallel in series flow fields have, however, received a very low attention. In this study, a numerical investigation on the distributions in six different flow field designs over 5 cm 2 PEFC has been systematically carried out using CFD techniques via ANSYS FLUENT software to study the effect of different flow field configurations and number of channels. The results revealed that, for a small-size PEFC, the flow fields with less number of channels provided both a better uniformity and cell performance. Although the number of channels affects the small-size PEFC performance much greater than the flow field geometric configurations, the further investigation revealed that the influence of configurations will be greater as the number of channels increases. In addition, with the same number of channels, the parallel in series flow fields performed better than the multi-channel serpentine flow fields in both uniformity and water management aspects as their geometry provided higher reactant flow velocity. [ABSTRACT FROM AUTHOR]

Abstract: Distributions in the concentration of reactant species in a PEMFC can cause distributions in local current density, temperature, and water content over the area of a PEMFC. These distributions can lead to effects such as flooding and MEA dehydration thus causing stresses in different regions of the fuel cell. Changing flow-field configurations and channel characteristics have been shown to also affect the cell performance and uniformity in distributions. This work investigates how performance and distributions in a baseline laboratory cell prepared by a precise machining method compared with others from alternative manufacturing processes (e.g., stamping, electrochemical etching, hydroforming, etc.). Specifically we examine “typical” variations in the channel width, height, and undercut that may occur with alternatively manufactured metal plates and compare those with sample-to-sample variations that may occur with between laboratory-scale graphite plates. This work will provide fundamental information that can be used to develop tolerance and design principles for manufacturing PEMFC bipolar plates. [Copyright &y& Elsevier]

Abstract: A three-dimensional, two-phase, multi-component model is used to investigate the effects of channel assembled angle on the performance of proton exchange membrane (PEM) fuel cell, including distribution of current density, membrane water content and local temperature. The flow-fields are assembled by single serpentine channels in anode and cathode with intersection angles of 0°, 90°, 180° and 270°, respectively. At high inlet humidity condition each flow-field has its owned strengths. Flow-fields with channel assembled angles of 0°, 90° and 270° show most uniform membrane water content, current density and local temperature distributions, respectively. However, at low inlet humidity condition, flow-field with channel assembled angle of 90° represents highest performance and uniformities in all aspects. Flow-field design for PEM fuel cell should take into account the effects of channel assembled angle on cell performance. [Copyright &y& Elsevier]

Distributions in reactant species concentration in a PEMFC cause distributions in local current density, temperature and water over the area of a PEMFC. These can lead to effects such as flooding or drying of the membrane and cause stresses in different regions of the fuel cell. Changing flow-field configuration, including channel path length, width, or height to distribute the gas more evenly, is one method of minimizing these stresses. This work numerically investigated how serpentine flow-fields with different channel/rib''s cross section areas affect performance and species distributions for both automotive and stationary conditions. Further, the influence of flow direction to performance and its distribution was also reported. The prediction revealed that for stationary condition, narrower channel with wider rib spacing gives higher performance but opposite results when automotive condition is applied. [Copyright &y& Elsevier]

Abstract: Distributions in reactant species concentration in a PEMFC due to local consumption of fuel and local transport of water through the membrane cause distributions in current density, temperature, and water concentration in three dimensions in a PEMFC. These distributions can lead to flooding or drying of the membrane that may shorten the life of an MEA. Changing the cell''s flow-field pattern to distribute the gas more evenly is one method of minimizing these stresses. This paper investigates how 200cm2 serpentine flow-fields with different number of gas paths, and thus different gas path lengths, affect performance and species distribution. The results show how the local temperature, water content, and current density distributions become more uniform for serpentine flow-field designs with shorter path lengths or larger number of channels. These results may be used to develop universal heuristics and dimensionless number correlations in the design of flow-fields and stacks. [Copyright &y& Elsevier]

Abstract: A study is performed to find the optimal operating conditions of hydrogen polymer electrolyte fuel cells using an efficient optimization approach based on validated multi-resolution fuel cell simulation tool developed in house. Through the design of experiment method, a set of designed simulation runs were carried out using the fuel cell simulation tool. Based on the simulation results, an analytic metamodel was then constructed using the radial basis function approach. A feasible sequential quadratic programming scheme was then employed to optimize the metamodel to achieve the global optimal solutions. To illustrate the optimization approach, four control parameters including cell temperature, cathode stoichiometry, cathode pressure, and cathode relative humidity were considered. The optimization objective is defined as the maximization of the overall efficiency of the fuel cell system under ideal or realistic system assumptions. The study shows that different optimal solutions exist for different system assumptions, as well as different current loading levels, classified into small, medium, and large current densities. The approach adopted in this study is generic and can be readily applied to a larger number of control parameters and further to the fuel cell design optimizations. [Copyright &y& Elsevier]

In fuel cell systems, a multitude of coupled physical and chemical processes take place within the assembly: fluid flow, diffusion, charge and heat transport, as well as electrochemical reactions. For design and optimisation purposes, direct numerical simulation of the full three-dimensional (3D) structure (using CFD tools) is often not feasible due to the large range of length scales that are associated with the various physical and chemical phenomena. However, since many fuel cell components such as gas ducts or current collectors are made of repetitive structures, volume averaging techniques can be employed to replace details of the original structure by their averaged counterparts. In this study, we present simulation results for SOFC fuel cells that are based on a two-step procedure: first, for all repetitive structures detailed 3D finite element simulations are used to obtain effective parameters for the transport equations and interaction terms for averaged quantities. Bipolar plates, for example, are characterised by their porosity and permeability with respect to fluid flow and by anisotropic material tensors for heat and charge transport. Similarly one obtains effective values for the Nernst potential and various kinetic parameters. The complex structural information is thereby cast into effective material properties. In a second step, we utilise these quantities to simulate fuel cells in 2D, thereby decreasing the computation time by several orders of magnitude. Depending on the design and optimisation goals, one chooses appropriate cuts perpendicular or along the stack axis. The resulting models provide current densities, temperature and species distributions as well as operation characteristics. We tested our method with the FEM-based multiphysics software NMSeses, which offers the flexibility to specify the necessary effective models. Results of simulation runs for Sulzer HEXIS–SOFC stacks are presented. [Copyright &y& Elsevier]