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This work presents the validation carried out for a three dimensional CFD 50 cm2 PEM fuel cell model, particularly focus on the prediction of liquid water distributions within the cell. The CFD model was previously validated against a set of experimental polarization curves, where model results adequately matched the experimental curves. An extension of the validation is presented in this work, by performing a comparison of the local liquid water distributions predicted by the model with the liquid water distributions of the real cell. The experimental measurements were obtained by means of Neutron Imaging, where a set of different cell operating conditions was tested. Although the exact quantitative results are not directly comparable due to differences in the cell setup, qualitative results show a very good agreement between the model results and the water distributions observed in the neutron radiographs. A model validation approach using local variable distributions (such as liquid water in this case) in addition to the integral quantities (i.e. polarization curves) is necessary to ensure the validity of models.

A novel modelling framework for the simulation of the diffusive mass transport limitations occurring at GDL local scale of PEFCs is presented, in particular in relation with the distribution of liquid water in the porous media. The distinctive characteristic of this framework is the fact that the distribution of liquid water is not predicted by the model but it is instead mapped into the simulation model from available experimental measurements, obtained with neutron imaging. The presence of liquid water is thus included in the model as a modifier for the gas diffusion transport, and not directly calculated by the model. This allows for a coupling of experimental measurements and model development that is expected to allow a further progress of highly reliable models for the understanding of local fuel cell phenomena. A 1D cell is analyzed, and the effective diffusion coefficient and the n exponent in the diffusion correction factor is calculated from the results of the combination of modelling and experimental data. An extension of the method for a 2D cell is also introduced.

This paper analyzes safety aspects inside a Fuel Cell vehicle using Computational Fluid Dynamics (CFD) tools. The research considers an introduction of a leak of hydrogen inside the vehicle, and its dispersion for a set of typical ventilation conditions is analyzed. The leak of hydrogen has been modelled according to the properties of hydrogen and depending on the pressure difference between the hydrogen storage tank (200 bar) and the atmosphere. The parameters considered for the simulations are the flow rate of cabin ventilation air and hydrogen’s leak. The results obtained for the hydrogen molar concentration are investigated in different sections of the vehicle. Significant differences between front and rear areas are observed, with higher hydrogen concentrations near the rear ventilation vents. The volume of the vehicle within ignition risk (4–75% hydrogen concentration) is also investigated. Finally, different risk mitigation measures are also proposed.

The turbulent gas-liquid flow field in an industrial 100-m3 stirred tank was calculated by using computational fluid dynamics based on the finite-volume method. Turbulent effects were modeled with the shear stress transport model, and gas-liquid bubbly flow was modeled with the Eulerian-Eulerian approach using the Grace correlation for the drag force interphase momentum transfer. The relative motion between the rotating impeller and the stationary baffled tank was considered by using a multiple frames of reference algorithm. The effects of Rushton and pitched-blade impeller design parameters such as blade geometry, location, and pumping direction on the mixing performance were investigated. It was found that a combination of Rushton turbines with up-pumping pitched-blade turbines provides the best mixing performance in terms of gas holdup and interfacial area density. The approach outlined in this work is useful for performance optimization of biotechnology reactors, as typically found in fermentation processes.

A Computational Fluid Dynamics (CFD) model developed for a 50 cm 2 Fuel Cell with parallel and serpentine flow field bipolar plates was presented in an article published in the International Journal of Hydrogen Energy 35 (2010) 11,533–11,550 [1] . The experimental validation details were presented as well in an article published in the International Journal of Hydrogen Energy 35 (2010) 11,437–11,447 [2] . A good agreement between numerical results and experimental measurements were obtained except for the high current density region where mass-transport limitations dominate the voltage loss. This short communication presents an update on the last simulations performed, where an improved prediction of the polarization curve is obtained. The physical and computational aspects of the reasons underlying the improvement of the results are discussed.

AC impedance or electrochemical impedance spectroscopy (EIS) is becoming a fundamental technique used by researchers and scientists in proton exchange membrane (PEM) fuel cell analysis and development. In this work, in situ impedance measurements are presented for a series of operating conditions in a 50 cm 2 fuel cell. The electrode charge transfer resistance was determined from the corresponding arcs of the Nyquist diagrams. The analyses were performed for H 2 /O 2 and H 2 /air operation at different stoichiometric factors and reactant gases humidification. Characteristic time scales of charge transfer processes at the different operating conditions were estimated from the corresponding Bode plots. These values were used for a non-dimensional analysis of the different fuel cell electrochemical and transport processes, namely electrochemical reaction versus GDL reactant transport. Fuel cell adapted Damkholer numbers are thus presented, where the results indicate that the GDL diffusion transport is the limiting process for the cases under analysis, especially when air is used as oxidant. Additional analysis of channel convective mass transport versus GDL diffusive mass transport is also presented.

The work and conclusions gained from the analysis of five new underground interchange buildings ongoing in Madrid, Spain, is presented. An additional study was performed for a typical two-level interchange building, and the methodology and results are presented in this paper. First, different ventilation and air conditioning strategies have been analyzed. The main goal is to find the most efficient design in order to maintain pollutants concentration and temperatures below the designed values, at minimum investment and operation costs. Different strategies have been modelled and compared using a Computational Fluid Dynamics (CFD) code, taking into account the buses circulation and the different pollution and heat sources. The final solution developed is based on a physical separation between the island area and the dock area. Conclusions on the efficiency of the different design strategies and possible pitfalls are presented. Secondly, different fire scenarios are analyzed. The main goal is to check whether the fire fighting measures planned, such as mechanical ventilation and a curtains system to define smoke sectors are able to cope with a fire emergency situation. A model for the bus fire has been developed, including heat release and smoke production. The main results presented are temperature fields, visibility and smoke concentration.

This work presents a Computational Fluid Dynamics (CFD) model developed for a 50 cm 2 fuel cell with parallel and serpentine flow field bipolar plates, and its validation against experimental measurements. The numerical CFD model was developed using the commercial ANSYS FLUENT software, and the results obtained were compared with the experimental results in order to perform a model validation. A single parameter, namely the reference exchange current density, was fitted to calibrate the model results. All other model parameters were determined from technical data sheets, literature survey, or experimental measurements. A discussion on different validation issues and model parameters is provided. The results of the numerical model show a good agreement with the experimental measurements for the different bipolar plates and range of operating conditions analysed. However, inaccuracies in the results in the mass-transport polarization region were observed, presumably when liquid water in the channels produces a blockage effect that cannot be modelled with the multiphase flow model currently implemented.

This work presents experimental performance results for a 50 cm 2 Polymer Electrolyte Membrane (PEM) Fuel Cell, including polarization curves and Electrochemical Impedance Spectroscopy (EIS) analysis of the Fuel Cell. EIS results were used for the determination of the cell ohmic resistance as well as charge transfer resistances under different operating conditions. Different combinations of operating conditions and bipolar plate designs were analysed. In particular, the effect of the cathode oxygen concentration, reactant gases humidification, and bipolar plate (BP) design were assessed. Butler–Volmer (BV) kinetic parameters such as the charge transfer coefficient were also determined from Tafel plots. The electronic contact resistances were measured for both Bipolar Plate designs, and the membrane protonic resistances were calculated. Its dependence on the BP flow field design and operating conditions is addressed. The results obtained in this work are aimed both at gaining insight into the fundamental processes determining the fuel cell performance, and at determining parameters needed for Computational Fuel Cell Dynamics (CFCD) numerical simulations.

In the present work, a computational model based on an Eulerian–Eulerian approach was used for the simulation of the transient two-phase flow in a rectangular partially aerated bubble column. Superficial gas velocities (UG) ranging from 0.24 to 2.30 cm/s were used throughout both the experiments and the simulations. The calculated results were verified by comparing them with experimental data including measurements of gas hold-up, plume oscillation period (POP) and Sauter mean bubble diameter. The study shows the effect of mesh refinement, time-step and physical model selection, the latter regarding the role of bubble size distribution and non-drag forces, on the computational results. According to the results presented here, the representation of bubble populations using multiple size groups (MUSIG model) instead of a single group improves the prediction of the experimental parameters under study. Additionally, the results obtained after including the virtual mass force term do not differ considerably from those obtained including only the drag force. On the contrary, as a consequence of introducing the lift force term into the model, the gas hold-up is overestimated and a non-symmetric bubble plume oscillation appears, a fact that is not experimentally observed.

An event in November 2007 in Asco-1 nuclear power plant (NPP) in Spain, originated the release of a significant amount of active metallic particles through the discharge stack. Particles were dispersed and deposited in roofs and neighbouring areas within the NPP controlled area. However, the event was not detected until March 2008. More than 1,300 active points with radioactive particles were found, 94 % located inside the double fenced controlled area and 6 % within the exclusion area; 5 particles were found out of the exclusion area. To provide additional insights on the potential consequences of the release, a computational fluid dynamics (CFD) code, ANSYS-CFX-11, has been used to investigate the near-range atmospheric dispersion and deposition of the particles. The purpose of the analysis was to assess the distance travelled by particles of different sizes. A very detailed model of the site was built, taking into account the buildings and the terrain features including the river valley and the surrounding hills. The modelled domain was $$3.2 \times 5.2\, \mathrm{km}$$ , with the atmospheric layer up to 4 km height. The atmospheric conditions recorded during the different periods of time between November 2007 and January 2008 were classified into 37 representative categories. In general, the distribution of the particles found was adequately reproduced by the numerical model. Particles larger than $$100\,{\upmu }$$ m could not travel beyond the double fence. Particles between $$\mathrm{50\;and\;100}\,{\upmu }$$ m could have been deposited mainly within the exclusion area, with a small probability of travelling farther. Smaller particles could have travelled beyond, but also should have been deposited in the nearby area, while the majority of particles found are larger, thus indicating that the size of the released particles should be above $$50\,{\upmu }$$ m. The detailed CFD simulation allowed answering relevant questions concerning the possibility of having an impacted region larger than the exclusion area.

The thermal conductivity of the polymer electrolyte membrane (PEM) of fuel cells is an important property affecting the overall cell performance. However, very few studies or fuel cell models include the dependence of this property on temperature and humidification conditions. In addition, no detailed studies have been reported for the quantitative understanding of how this property influences important aspects of the cell such as performance, water management, and membrane durability. This work presents results of a sensibility study performed for different membrane thermal conductivities, analyzing the influence of this parameter on the main cell response variables. The work has been performed with the aid of a computational fluid dynamics (CFD) model developed for a 50 cm2 fuel cell with serpentine flow field bipolar plates, previously validated against experimental measurements. The results show to what extent the cell performance, water management, and durability issues such as MEA temperature gradients are influenced by the membrane thermal conductivity, especially at high current densities, leading up to a 50% increase in the cell electric power at 1000 mA/cm2 when the thermal conductivity of the membrane is set to 0.26 W/(m K) instead of to the base value of 0.13 W/(m K).

Polymer Electrolyte Membrane Fuel Cells (PEMFC) have attracted significant interest during the last few decades, as they are considered to be one of the most promising alternative clean power generation devices for portable, mobile and stationary applications. However, different technological barriers such as cost, durability, or heat and water management, are limiting the implementation of fuel cell systems into the global energy markets, and therefore significant research efforts and investments are being carried out. Fuel cells are devices where electrochemical reactions transform chemical energy available in fuels into electrical energy. Fuel cells are not limited by the thermodynamic restrictions of conventional power generation systems, such as the Carnot efficiency, meaning that fuel cells can be operated with higher efficiency for energy conversion. Additionally, the environmental impact is low as no combustion processes occurs and no pollutants are generated (U.S. Department of Energy [DOE], 2004). A typical fuel cell power system consists of different components: Single cells, where the electrochemical reactions occur. Stacks, consisting of the necessary number of cells electrically connected to provide the required power capacity. The balance of plant, or additional equipment to provide fuel and oxidants with the appropriate conditions, thermal management, electric power conditioning, and other functions. Single or unit cells are the core of a fuel cell. They convert the chemical energy contained in a fuel into electrical energy, via electrochemical reactions. The basic configuration of a fuel cell consists of an electrolyte layer or membrane in contact with an anode and a cathode on either side. In a PEM fuel cell, hydrogen is continuously supplied to the anode or negative electrode, and an oxidant, often oxygen or air, is also continuously supplied to the cathode or positive electrode. Electrochemical reactions occur at the electrodes, generating an electric current through the electrolyte thus driving the corresponding electric current that performs the electric work on the load. At the anode, hydrogen is fed to the cell and a reaction takes place at the catalyst layer