•Complex CFD model developed for 100 cm2 PEM fuel cell.•Liquid water distribution inside the cell under different operating conditions.•High level of agreement with experimental data obtained via ...neutron imaging.•Co-flow configuration is compared with counter-flow.•Model calibration procedure is outlined and experimental data is provided.
Liquid water distribution inside PEM fuel cell is investigated via interactive combination of CFD analysis and neutron imaging on a single 100 cm2 PEM fuel cell. The analysis is conducted with novel anode flow field designed for improved liquid water removal from the cell at higher currents. Numerical and experimental results show good agreement due to the incorporated experimental structural parameters for the membrane-electrode assembly and properly defined membrane water content parameters in conjunction with electro-osmotic drag and back-diffusion expressions in the numerical model. Methodology for achieving such accurate results is shown in detail in this work and complete lists of numerical parameters are provided for developing such numerical model. The CFD model also incorporates new multiphase model with enhanced heat and mass transfer capabilities for water phase change treatment as well as absorption and desorption modelling. This new approach is used to thoroughly study liquid water distribution inside the cell for dry and humid cases, as well as for co-flow vs. counter-flow configuration while the emphasis is directed towards liquid water distribution inside the porous media where condensation predominantly occurs. The robustness of the developed CFD model is demonstrated in its ability to accurately predict water pooling at lower currents, a phenomenon which could previously be only experimentally observed.
•Lumped model and real-time transient CFD model are compared during a load profile.•Influence of bipolar plate material on temperature is determined.•Influence of operating delta pressure on relative ...humidity inside the stack.•Significant influence of cooling fin re-design on heat transfer is outlined.•Heat transfer between the stack and metal hydride tank is analyzed.
Comprehensive numerical analyses are conducted to study the influence of thermal management on performance of 1 kW edge-cooled proton exchange membrane fuel cell stack without external humidification. The experimental stack and numerical three-dimensional computational fluid dynamics model are characterized by several novelty aspects. Two numerical approaches are considered and compared for a prescribed load profile: (i) lumped model and novel (ii) real-time transient computational fluid dynamics model incorporating realistic modeling of forced air convection on the edge-cooling of the stack. The novelty of the developed computational fluid dynamics model is the capability to give insight in the transient results in only a fraction of time vs. experimental testing (40 min vs. 4 h) and other computational fluid dynamics models of fuel cells which are only capable of steady-state analysis. The developed computational fluid dynamics model is used to study the influence of (i) bipolar plate materials (ii) operating delta pressure along the flow field and (iii) different cooling fin configurations on the water and heat balance inside the stack. The results indicate that (i) maximal and average temperatures of the stack are almost linearly correlated to the thermal conductivity of bipolar plate materials and maximal temperatures can be significantly higher (ii) the operating delta pressure can be manipulated to increase the performance of the stack and (iii) the cooling fin redesign has major influence on the overall temperature uniformity across the stack. Additionally, the heat transfer between the stack and metal hydride tank is studied.
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•A fuel cell unit with 5-fold parallel channel was separated into 5 individual segments.•Pt loading and operating temperature of each segment are controlled separately.•Increasing ...temperature towards outlet improves catalytic activity and reduce water content.•Increasing temperature compensates the loss of catalytic activity due to decreasing Pt loading.•Optimal gradients of Pt loading and temperature achieve homogeneous current density.
Desired electrochemical reaction and mass transport rates vary in the operation of PEM fuel cells due to the inhomogeneous spatial distribution of reactants and products. A segmented fuel cell unit was manufactured and a comprehensive model was developed to study the effect of the graded distributions of platinum loading and operating temperature, to simultaneously save the usage of platinum, improve the cell performance and maintain the homogeneity of current density. The increase of temperature towards the cathode outlet improved the reaction kinetics and reduced the liquid water content along the gas flow direction, which decreased the required platinum loading. A large temperature gradient may lead to membrane/ionomer dehydration and oxygen starvation near the cathode outlet due to the increase in the saturation pressure of vapor and the dilution of the increased vapor content. A systematical design of the gradients of platinum loading and temperature achieved an improved cell performance and saved the usage of Pt-based catalysts without worsening the homogeneity of current density.
An easily machined novel flow field with controllable pressure gradient across adjacent channels was designed and a two dimensional, across‐the‐channel, two‐phase model was developed to study the gas ...transport and water removal of the novel configuration. The effect of channel‐rib width ratio, GDL thickness and pressure gradient on the profiles of oxygen concentration and water saturation within the GDL were investigated. Special attention was paid to the mechanisms of the promoted mass transport and water removal rates under a pressure gradient. The model was validated by experiments with various channel‐rib ratios and GDL thicknesses at different operating pressure. The results revealed that, oxygen concentration was increased, and the water saturation was reduced under the rib with a pressure gradient generated across the adjacent channels. The optimal pressure gradient is between 0.1 to 0.2 atm for the studied channel geometry and configuration. The mechanisms of the improved cell performance were elucidated.
As marine traffic is contributing to pollution, and most vessels have predictable routes with repetitive load profiles, to reduce their impact on environment, hybrid systems with proton exchange ...membrane fuel cells (PEMFC-s) and battery pack are a promising replacement. For this purpose, the new approach takes into consideration an alternative to diesel propulsion with the additional benefit of carbon neutrality and increase of system efficiency. Additionally, in the developed numerical model, control of the PEMFC–battery hybrid energy system with balance of plant is incorporated with repowering existing vessels that have two diesel engines with 300 kWe. The goal of this paper is to develop a numerical model that analyzes and determines an equivalent hybrid ship propulsion system for a known traveling route. The developed numerical model consists of an interconnected system with the PEMFC stack and a battery pack as power sources. The numerical model was developed and optimized to meet the minimal required power demand for a successful route, which has variable loads and sees ships sail daily six times along the same route—in total 54 nautical miles. The results showed that the equivalent hybrid power system consists of a 300 kWe PEMFC stack and battery pack with 424 kWh battery and state of charge varying between 20 and 87%. To power this new hybrid power system, a hydrogen tank of 7200 L holding 284.7 kg at pressure of 700 bar is required, compared to previous system that consumed 1524 kg of diesel and generated 4886 kg of CO2.
Computational fluid dynamics (CFD) study of segmented proton exchange membrane fuel cell (PEMFC) performance has been carried out, based on experimental setup and operating parameters from previous ...studies. Two different temperature boundary conditions were considered – isothermal and, a novel, non-uniform temperature profile calculated from Mollier h-ω chart. Implementation of non-uniform terminal temperature boundary conditions resulted in close to 100% relative humidity along the cathode channel, resulting in improvement of PEMFC performance without the need for external humidification. Model polarization curve and relative humidity distribution along the cathode channel length are in good agreement with experimental results. It was found that different current collector materials, i.e., their thermal conductivity have major influence on temperature, thus on relative humidity distributions along reactant gas channels. The membrane thickness affects the net water transport across the membrane, thus also has influence on temperature and relative humidity distribution along the reactant gas channels.
•Concept of variable temperature field along the cathode channel has been studied.•CFD model of a segmented cell has been calibrated and verified by experimental results.•Close to 100% relative humidity along the cathode channel was achieved without external humidification.•Isothermal and non-uniform boundary conditions have been compared.
An alternative renewable energy concept, i.e. the concept of a solar power plant with short diffuser (SPD), was numerically investigated by more advanced computational fluid dynamics (CFD) model. ...Developed model is characterized by a more sophisticated and streamlined guide vane topology. The main novelty of this work is conducted optimization of the guide vane topology, for a specific novel application related to the alternative renewable energy concept (SPD). Optimization involved determining the required guide vane topology using minimal number of geometry influencing parameters. The objective was to result in vortex genesis and stabilization with respect to the desired circumferential velocity and to minimize the required pressure potential that is necessary for stable operation of the SDP plant. Provided numerical investigation was necessary, and for sure a step forward towards consideration of the experimental plant (which will assume introduction of the turbines). It needs to be taken into account that we deal with complex flow structure that requires gradual numerical investigation, in order to be able to get detail insight in the various influences and processes that can strongly affect SPD operating parameters. The guide vane topology was altered to develop an SPD capable of establishing and maintaining a stable gravitational vortex in pressure ranges which resemble atmospheric vortex phenomena (feasible for development of a compact system, and with maximal velocities in chimney throat regions ranging below 20 m s−1). The study outlines nine cases, each representing the altered guide vane design, where the best case is determined and compared with the available experimental data from other research groups. The comparison indicates that the numerical model, although quite simple, is accurate and robust in predicting the distribution of local velocity and pressure profiles and fit for implementation on wind turbines in order to determine the influence of the installed turbines on the vortex shape and stability in a future study. An important finding is that the swirl ratio can be manipulated by altering the guide vane shape, and it is independent of the Reynolds number (which will be important during the design phase since it can be used as a control strategy for vortex genesis and as a prevention of unintentional genesis regarding additional multiple vortices). The gained numerical results revealed specific operating conditions that will ensure a safer environment around the SPD and that will enable a carbon free electricity production.
•Upgraded numerical model elaborated for alternative renewable energy concept.•Guide vane topology numerically investigated with its effect on vortex features.•Vortex shape and stability analyzed with respect to vane topology.•Numerical results discussed with respect to the critical operating parameters.
The application of newly available technologies in the green maritime sector is difficult due to conflicting requirements and the inter-relation of different ecological, technological and economical ...parameters. The governments incentivize radical reductions in harmful emissions as an overall priority. If the politics do not change, the continuous implementation of stricter government regulations for reducing emissions will eventually result in the mandatory use of, what we currently consider, alternative fuels. Immediate application of radically different strategies would significantly increase the economic costs of maritime transport, thus jeopardizing its greatest benefit: the transport of massive quantities of freight at the lowest cost. Increased maritime transport costs would immediately disrupt the global economy, as seen recently during the COVID-19 pandemic. For this reason, the industry has shifted towards a gradual decrease in emissions through the implementation of “better” transitional solutions until alternative fuels eventually become low-cost fuels. Since this topic is very broad and interdisciplinary, our systematic overview gives insight into the state-of-the-art available technologies in green maritime transport with a focus on the following subjects: (i) alternative fuels; (ii) hybrid propulsion systems and hydrogen technologies; (iii) the benefits of digitalization in the maritime sector aimed at increasing vessel efficiency; (iv) hull drag reduction technologies; and (v) carbon capture technologies. This paper outlines the challenges, advantages and disadvantages of their implementation. The results of this analysis elucidate the current technologies’ readiness levels and their expected development over the coming years.
Variable temperature flow field concept allows maintaining close to 100% relative humidity along the entire flow field of the anode and the cathode side without external humidification using water ...generated during fuel cell operation for internal reactant humidification. This work deals with the experimental validation of the variable temperature flow field concept on a five-segment single cell. The experimental setup provides insight into the membrane water transport, temperature distribution on the current collectors and inside the channels, and the current density distribution along the cell. Variable temperature flow field operation with dry reactants is compared to isothermal operation with partially and fully humidified reactants. The polarization curve comparison shows that the variable temperature flow field operating efficiency is similar or better than the commonly used isothermal configuration with fully humidified reactants. The main contribution of the variable temperature flow field concept, when compared to isothermal operation, is the reduction of the mass transport losses at higher currents, since the generated water is evaporated in the stream of reactants, thereby minimizing the problem of liquid water removal from the cell.
•Segmented fuel cell allowing variable temperature along the channel is constructed.•Temperature and relative humidity along the channel may be tracked in h-x diagram.•Variable temperature along the channel allows operation with dry reactant gases.
A numerical study is conducted to compare the current most popular flow field configurations, porous, biporous, porous with baffles, Toyota 3D fine-mesh, and traditional rectangular flow field. ...Operation at high current densities is considered to elucidate the effect of the flow field designs on the overall heat transfer and liquid water removal. A comprehensive 3D, multiphase, nonisothermal computational fluid dynamics model is developed based on up-to-date heat and mass transfer sub-models, incorporating the complete formulation of the Forchheimer inertial effect and the permeability ratio of the biporous layers. The porous and baffled flow field improves the cell performance by minimizing mass transport losses, enhancing the water removal from the diffusion layers. The baffled flow field is chosen for optimization owing to the simple design and low manufacturing cost. A total of 49 configurations were mutually compared in the design of experiments to show the quantitative effect of each parameter on the performance of the baffled flow field. The results elucidate the significant influence of small geometry modifications on the overall heat and mass transfer. The results of different cases have shown that water saturation can be decreased by up to 33.59% and maximal temperature by 7.91 °C when compared to the reference case which is already characterized by very high performance. The most influencing geometry parameters of the baffles on the cell performance are revealed. The best case of the 49 studied cases is further optimized by introducing a linear scaling factor. Additional geometry modifications demonstrate that the gain in performance can be increased, but at a cost of higher pressure drop and increased design complexity. The conclusions of this work aids in the development of compact and high-performance proton exchange membrane fuel cell stacks.
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