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As part of the European Commission research project DIY4U focused on the development of machinery to be installed in supermarket allowing customers to define their customized detergent according to their needs. These machines will mix the detergent components (surfactant, fatty acid, water, perfume, etc.) already in the detergent canister as sold to consumers. To avoid long waiting times for customers, and to obtain a product with good quality and consistency, mixing must be very efficient. A mixing process with rotation and displacement by means of rotating the canister around an axis below the canister bottom has been checked by means of Computational Fluid Dynamics (CFD) tools after validation of one case with lab results. This is a new approach for liquid detergents, as commonly is a powder detergent production process. The mixing process has been simulated for 39 different combinations of components mass fraction percentages and the mixing quality observed during the mixing period. A response surface obtained from these simulations has been developed to be included in a Digital Twin, this being a task within this DIY4U project. The results show that this system is very efficient, taking a few seconds to develop a complete mixing. Also, the mixing time differences are quite small, requiring all customers to wait just few seconds independently of their detergent formulation.

The goal of the review series on the H2 economy is to highlight the current status, major issues, and opportunities associated with H2 production, storage, transportation, distribution and usage in various energy sectors. In particular, Part I discussed the various H2 (grey and green) production methods including the futuristic ones such as photoelectrochemical for small, medium, and large-scale applications. Part II of the H2 economy review identifies the developments and challenges in the areas of H2 storage, transportation and distribution with national and international initiatives in the field, all of which suggest a pathway for establishing greener H2 society in the near future. Currently, various methods, comprising physical and chemical routes are being explored with a focus on improving the H2 storage density, capacity, and reducing the cost. H2 transportation methods by road, through pipelines, and via ocean are pursued actively in expanding the market for large scale applications around the world. As of now, compressed H2 and its transportation by road is the most realistic option for the transportation sector.

This work presents the development of liquid-cooled industry-scale bipolar plates for improved water management in PEM Fuel Cells. The methods used for the design development are based on Computational Fluid Dynamics (CFD) modelling and simulation, and Neutron Radiography experiments to analyse liquid water distributions within the cell for different operating conditions. A novel 140 cm2 bipolar plate was designed and manufactured on 0.1 mm thick stainless steel using pre-coated strip steel. CFD modelling carried out for the novel design predicted a significant improvement in terms of cell performance, as well as a more uniform temperature distribution within the membrane. Liquid water distributions were later analysed by neutron radiography experiments, defining a set of different operating conditions (current density, stoichiometry, inlet gases dew point, and cell temperature). Electrochemical and neutron radiography results are presented for all cases and the influence of the operating conditions is discussed. Liquid water distributions within the cell are also analysed and compared against the CFD model results obtained. The influence of the gas flow configuration (reactant gases and cooling water) is clearly observable in the results.

In this study, 3-D numerical simulations are conducted for single-phase flow and conjugate heat transfer in mini-channel heat sinks subjected to constant heat flux. The effects of using different gallium alloys (EGaInSn, EGaIn, GaSn, and GaIn) and various substrate materials (copper alloy, aluminum, tungsten, and silicon) on the temperature distribution, pumping power, pressure drop, maximum heat flux, and the total thermal resistance are comprehensively investigated for a series of Reynolds number (300–1900). Among all coolants considered, it is found that EGaIn reduces the flow resistance most efficiently. It is also found that the substrate material’s conductivity significantly influences the thermal resistance of the mini-channel. The higher conductivity leads to lower thermal resistance. In addition, when comparing to other gallium alloys, the GaIn alloy with higher thermal conductivity and specific heat shows better thermal performance. Finally, numerical results of the pumping power and pressure drop for gallium alloys are compared and discussed with the prediction by analytical correlations.

Energy enthusiasts in developed countries explore sustainable and efficient pathways for accomplishing zero carbon footprint through the H2 economy. The major objective of the H2 economy review series is to bring out the status, major issues, and opportunities associated with the key components such as H2 production, storage, transportation, distribution, and applications in various energy sectors. Specifically, Part I discussed H2 production methods including the futuristic ones such as photoelectrochemical for small, medium, and large-scale applications, while Part II dealt with the challenges and developments in H2 storage, transportation, and distribution with national and international initiatives. Part III of the H2 economy review discusses the developments and challenges in the areas of H2 application in chemical/metallurgical industries, combustion, and fuel cells. Currently, the majority of H2 is being utilized by a few chemical industries with >60% in the oil refineries sector, by producing grey H2 by steam methane reforming on a large scale. In addition, the review also presents the challenges in various technologies for establishing greener and sustainable H2 society., Highlights • Industrial applications of H2 with a focus on decarbonization of industry. • H2 usage through fuel cells for mobile and stationary applications. • Combustion of H2 in internal combustion engines and gas turbines. • Major challenges and opportunities towards realizing H2 economy.

The efforts on energy system decarbonization and improved sustainable energy efficiency in developed countries led energy enthusiasts to explore alternative highly effective pathways in accomplishing these goals. Specifically, the transition from hydrocarbon to H2 economy using fuel cells and H2 technologies is a sustainable and favorable approach forward in meeting stationary, transportation, industrial, residential, and commercial sectors. This review in three Parts brings out the capability of H2 for enabling an energy revolution through much-needed flexibility in renewable energy resources. The review identifies the developments and challenges within the H2 generation, storage, transportation, distribution, and usage - as well as applications along with national and international initiatives in the field, all of which suggest a pathway for a greener H2 society. The review also highlights the opportunities and challenges in major energy sectors for H2 technologies. Part I of the series highlights the importance of H2 economy and initiatives from various agencies, and presents several H2 generation methods.

Fuel cells are electrochemical devices that convert the chemical energy stored in fuels (hydrogen for polymer electrolyte membrane (PEM) fuel cells) directly into electricity with high e ciency. Fuel cells are already commercially used in di erent applications, and significant research e orts are being carried out to further improve their performance and durability and to reduce costs. Experimental testing of fuel cells is a fundamental research activity used to assess all the issues indicated above. The current work presents original data corresponding to the experimental analysis of the performance of a 50 cm2 PEM fuel cell, including experimental results from a load cycling dedicated test. The experimental data were acquired using a dedicated test bench following the harmonized testing protocols defined by the Joint Research Centre (JRC) of the European Commission for automotive applications. With the presented dataset, we aim to provide a transparent collection of experimental data from PEM fuel cell testing that can contribute to enhanced reusability for further research. Ministerio de Ciencia, Innovación y Universidades de España ENE2017-91159-EXP Ministerio de Economía y Competitividad UNSE15-CE2962

This work presents the application of CFD (Computational Fluid Dynamics) to the unsteady gas transport modelling in the cathode side of a Polymer Electrolyte Membrane (PEM) fuel cell during an AC impedance test. The CFD model development and results during AC impedance experiments for 1D and 2D cases are presented and discussed. The effect of liquid water was considered by modelling scenarios with saturated (according to water profiles obtained experimentally) and dry Gas Diffusion Layers (GDL). It was observed that the magnitude of the transient variations of the oxygen concentration within the GDL is dependent on the frequency of the AC signal during the test, given the differences between the diffusion characteristic time and the oxygen consumption characteristic time. For the 2D model where the differences under-the-rib to under-the-channel can be analysed, it was verified that oxygen concentration is much higher under the channel, however the amplitude of the oscillations during AC testing are significantly higher under the rib. When comparing saturated and dry GDLs for both models, it was verified that oxygen concentrations are higher for dry GDLs, but the amplitude of the oscillations is however higher for saturated GDLs.

An appropriate degree of mixing in molten salt tanks for Thermal Energy Storage (TES) in Concentrated Solar Power Plants (CSPPs) is required in order to ensure the safe operation of the tank. Otherwise, cooling due to thermal heat losses is prone to result in a high thermal stratification of the salts and eventually local solidification. In this work, the mixing performance of different configurations of ejectors is investigated by means of Computational Fluid Dynamics (CFD). A set of different ejector configurations has been resolved, modifying the number of ejectors, flow direction, and ejector angle. The best configurations are identified, where the highest fluid circulation capacity is achieved by 10 ejectors directing the jet flow in the tangential direction with an inclination angle of 0° with respect to the tank bottom surface. This is increasing the fluid circulation capacity of the tank by more than 100% with respect to the usual configuration implemented in such tanks (ejectors directed to the tank central vertical axis, at 30° angle). In addition, such configuration ensures an enhanced flow circulation in the bottom part of the tank (with an increase of more than 6 times in the flow velocity in the lower section of the tank), reducing the risk of local salt solidification due to heat loss through the bottom surface. However, the shortest mixing times (95% and 99%) are achieved by the configuration with 10 ejectors pumping flow towards the central tank axis with an inclination angle of 0°.

An advanced energy conversion catalyst comprising pristine carbon-nanotubes and conductive polyaniline polymer successfully synthesized and characterized for high temperature and non-humidified polymer electrolyte membrane fuel cells. The fabricated polyaniline-based catalyst shown a good distribution of platinum nanoparticles (Pt-NPs), and displayed an electrochemical surface area of 645 cm2/mgPt. The catalyst indicated remarkable catalytic activity towards the oxygen reduction reaction (ORR). The overpotential of ORR, the open-circuit voltage, and the power density of the polyaniline-based catalyst declined by a 30 mV, increased by a 50 mV, and enhanced by 26.5%, respectively, when compared to the polybenzimidazole-based catalyst. The impedance measurements have emphasized the improved catalytic activity and the enhanced fuel cell performance of the polyaniline-based catalyst, showing a remarkable reduction of 45% in the charge transfer resistance. This study revealed the advantages of using polyaniline as an anchor to improve the Pt-catalytic activity, opening the door for the wide applications of hydrogen energy.

Promising proton exchange membranes comprising a nitrogen-rich and a high molecular weight poly[2,2′-(bipyridyl)-bibenzimidazole] (BipyPBI) polymer as a substrate and graphene oxide (GO) as a filler were successfully fabricated. The synergism of GO on the membrane physicochemical properties, including the acid doping level, acid retention capability, water uptake, swelling degree, mechanical properties, proton conductivity, oxidative stability, and the hydrogen permeability was studied. The results of the study confirmed the fabrication of mechanically robust and highly conductive proton exchange membranes. Regarding the phosphoric acid (PA) doping level, the BipyPBI/GO membrane reached 17 mol of PA per monomeric unit of BipyPBI (an increase of around 69% in PA-doping level compared to the bare BipyPBI membrane). The proton conductivity at 60 °C under anhydrous conditions increased from 0.002 S cm−1 to 0.019 S cm−1 (around 10-folds increase) when 4 wt% of GO was incorporated into the BipyPBI matrix. In addition, the conductivity reached 0.045 S cm−1 at 140 °C. The activation energy of the proton conduction decreased from 45.6 kJ mol−1 for the bare BiPyPBI to 12 kJ mol−1 for the composite membranes, indicating an improved proton mobility where the GO worked as a carrier-bridge for a smooth proton transfer into the polymer matrix. Furthermore, the H2 permeability reached 1.3 Barrer at 140 °C, indicating the fabrication of tightly-packed membranes. These results provide a very promising membrane for fuel cell applications.

A commercial 50 cm2 PEM fuel cell with serpentine flow fields was operated at 2.0 bar (a) and 60 °C with different relative humidity (RH) values for the inlet reactants (a matrix of 3 RH for anode and 3 RH for cathode). Between each test the cell was decompressed and liquid water was thus flushed out. The liquid water build-up and the time evolution during each experiment were recorded by means of Neutron Imaging. A qualitative and quantitative analysis of the results is presented in this work. It was observed that the dynamics of water build-up comprises three main stages, where the major difference is the liquid water accumulation rate. The onset location for the water appearance in the flow field channels was found to be determined by the flow field design, gravity and gas flow direction along the serpentine path. The time evolution of the water progressive accumulation along the flow field channels and cell active area is discussed.

This work presents a method for the analysis of sand-loaded air flow erosion in heritage sites by means of Computational Fluid Dynamics (CFD). This is intended for cases where particle loaded air flow represents a significant contribution to the erosion process. An investigation of the wind erosion over the heritage site of Baelo Claudia, near Tarifa in Spain, is developed in order to present the method. The site is located directly on the beach by the Mediterranean Sea, on one of the windiest locations in South Europe. The presence of large amounts of sand from the beach in such a windy area is making the site extremely prone to suffer from erosion, as evidenced by the present state of one of the most well-known items in the site, the “Cardo of the Columns”. In this study, a CFD model of the “Cardo of the Columns” area, including the terrain features has been developed. The wind has been modelled according to the statistics available of wind velocity and direction for the site, and sand particles have been included in the simulation by means of the Lagrangian Particle Tracking model. The effect of the sand particles over the columns has been modelled with the erosion model from Finnie. Based on simple in situ measurements and assumptions, an erosion rate of 3.55 kg/year has been calculated, which represents a 30% of the total initial mass of the columns. The constants of the CFD erosion model have been calibrated so that results match the theoretical predictions of the erosion rate. In addition, the erosion-caused damage prediction is predicted for evaluating the state of the columns in the next 50 and 100 years, and potential remedial measures such as the installation of wind baffle are evaluated with the aid of the CFD model.

Computational Fluid Dynamics (CFD) has been firmly established as a fundamental discipline to advancing research on energy engineering. The major progresses achieved during the last two decades both on software modelling capabilities and hardware computing power have resulted in considerable and widespread CFD interest among scientist and engineers. Numerical modelling and simulation developments are increasingly contributing to the current state of the art in many energy engineering aspects, such as power generation, combustion, wind energy, concentrated solar power, hydro power, gas and steam turbines, fuel cells, and many others. This review intends to provide an overview of the CFD applications in energy and thermal engineering, as a presentation and background for the Special Issue “CFD Applications in Energy Engineering Research and Simulation” published by Processes in 2020. A brief introduction to the most significant reviews that have been published on the particular topics is provided. The objective is to provide an overview of the CFD applications in energy and thermal engineering, highlighting the review papers published on the different topics, so that readers can refer to the different review papers for a thorough revision of the state of the art and contributions into the particular field of interest.

This paper presents a computational fluid dynamics (CFD) analysis of the air and temperature distribution in a representative railway vehicle, with the objective of evaluating passengers' thermal comfort. The CFD model developed is featuring the wagon geometry in detail including air diffusers geometry, passengers, and luminaires. A set of different scenarios are studied, covering occupancy levels, state of the doors and windows (open/closed), inlet temperature, and air diffuser design. The results show a clear influence of the air supply system and design geometry on comfort, as local velocities well above 1 m/s were obtained for the original design. A new diffuser design proposed clearly improved the velocity field distribution enhancing passengers' thermal comfort. Exhaust vents are also presenting high velocities, which are significantly reduced down to 2 m/s when windows are open. It is observed that thermal comfort is not appropriate when air inlet temperature is conditioned to 19 °C, especially for the original diffuser design.

Terrestrial laser scanning is a widely used technology to digitise archaeological, architectural and cultural heritage. This allows for modelling the assets’ real condition in comparison with traditional data acquisition methods. This paper, based on the case study of the basilica in the Baelo Claudia archaeological ensemble (Tarifa, Spain), justifies the need of accurate heritage modelling against excessively simplified approaches in order to support structural safety analysis. To do this, after validating the 3Dmeshing process frompoint cloud data, the semi-automatic digital reconstitution of the basilica columns is performed. Next, a geometric analysis is conducted to calculate the structural alterations of the columns. In order to determine the structural performance, focusing both on the accuracy and suitability of the geometric models, static and modal analyses are carried out by means of the finite element method (FEM) on three different models for the most unfavourable column in terms of structural damage: (1) as-built (2) simplified and (3) ideal model without deformations. Finally, the outcomes show that the as-built modelling enhances the conservation status analysis of the 3D heritage city (in terms of realistic compliance factor values), although further automation still needs to be implemented in the modelling process.

This study presents the Computational Fluid Dynamics (CFD) thermal design and experimental tests results for a multi-tubular solar reactor for hydrogen production based on the ferrite thermochemical cycle in a pilot plant in the Plataforma Solar de Almer&iacute, a (PSA). The methodology followed for the solar reactor design is described, as well as the experimental tests carried out during the testing campaign and characterization of the reactor. The CFD model developed for the thermal design of the solar reactor has been validated against the experimental measurements, with a temperature error ranging from 1% to around 10% depending on the location within the reactor. The thermal balance in the reactor (cavity and tubes) has been also solved by the CFD model, showing a 7.9% thermal efficiency of the reactor. CFD results also show the percentage of reacting media inside the tubes which achieve the required temperature for the endothermic reaction process, with 90% of the ferrite pellets inside the tubes above the required temperature of 900 &deg, C. The multi-tubular solar reactor designed with aid of CFD modelling and simulations has been built and operated successfully.

This work presents an experimental analysis of the time constants associated to diffusion and electrochemical processes in a 50 cm2 Polymer Electrolyte Membrane (PEM) fuel cell. The experimental techniques and results include polarization curves and Electrochemical Impedance Spectroscopy (EIS) analysis of the fuel cell, where the time constants are determined from the analysis of the Distribution of Relaxation Times (DRT). EIS results are also used to determine the cell ohmic resistance, where High Frequency Resistance (HFR) values are calculated from the Nyquist plots. A wide range of operating conditions of the fuel cell are analysed, including back pressure (0.5 bar–1 bar), cell temperature (55 °C, 65 °C, 75 °C), reactant gases relative humidity (30%, 60%, 90%), cathode stoichiometry (λc 2.5–3.5), and oxygen concentration (air and pure oxygen). The effect of the operating conditions on the time constants are discussed, and Damkohler number is introduced and discussed.

This work presents the operating conditions optimization of a 50 cm 2 PEM fuel cell using a one dimensional analytical model previously validated against experimental data for a comprehensive set of different operating conditions of cell temperature, pressure, reactants relative humidity and cathode stoichiometry. The analytical model is used to predict the operating conditions that provide the maximum (and the minimum) power output of the given PEM fuel cell for every value of current intensity. Thus, a maximum performance polarization curve is developed where the operating conditions are not fixed for every current intensity, but modified in order to provide the maximum possible power output for every value of current intensity. The obtained operating conditions have been tested in the real cell showing a good agreement between experimental and modeling results where the maximum error is below 2% for the case of maximum power and 3% for the case of minimum power. The comparison shows that the power output using the operating conditions for the curve of maximum power is about 100% higher than using the curve of minimum power.

This work presents the main steps for the development of a Computational Fluid Dynamics (CFD) model to evaluate the performance of a solar tubular reactor design from the thermal point of view. In this paper a detailed description of the methodology is presented step by step. A simplified reactor design, which consists of a cubical cavity with a single tube, has been selected as base case to illustrate the different models and parameters which take part in the CFD simulations. This base case represents a solar tubular reactor for hydrogen production by means of ferrite thermochemical cycle. The accurate modeling of heat transfer to the packed bed in the interior of the tube is presented, including the effect of the radial distribution of porosity within the porous media. According to the type of reactor and the operating conditions, models and model parameters are analyzed and selected in order to solve the simulation balancing accuracy and required computational time, and the main results are presented. To conclude, the methodology is presented as a powerful tool to identify weaknesses in the design of solar tubular reactor. In addition, the reactor performance at different operating conditions can be evaluated.

A commercial 50 cm2 polymer electrolyte membrane (PEM) fuel cell with serpentine flow fields was operated at 2.0 bar and 60 °C with two orientations of the flow field channels with respect to gravity, i.e. horizontal and vertical channels. A 3 × 3 test matrix of anode and cathode reactants relative humidity was used for the performance assessment of the cell in both orientations. The cell performance and operating data, including cell voltage and resistance, were measured, and neutron radiographs were recorded during the entire operation in order to gain knowledge of the liquid water distributions within the cell for both orientations. A quantitative analysis of the results is presented in this work, comparing the cell operation for both flow field orientations. It is observed that the configuration with horizontal cathode flow field channels presents a better cell performance, and less amount of liquid water blocking the flow field channels. Thus, the results show that the selection of the cell orientation has an influence on the final performance, and it is therefore, a design parameter to be considered for a real application. The differences in the cell water content are quantitatively analyzed and discussed.

This work presents a one dimensional analytical model developed for a 50 cm2 PEM (polymer electrolyte membrane) fuel cell with five-channel serpentine flow field. The different coupled physical phenomena such as electrochemistry, mass transfer of hydrogen, oxygen and water (two phases) together with heat transfer have been solved simultaneously. The innovation of this work is that the model has been validated with two different variables simultaneously and quantitatively in order to ensure the accuracy of the results. The selected variables are the cell voltage and the water content within the membrane MEA (Membrane Electrode Assembly) and GDL (gas diffusion layers) experimentally measured by means of neutron radiography. The results show a good agreement for a comprehensive set of different operating conditions of cell temperature, pressure, reactants relative humidity and cathode stoichiometry. The analytical model has a relative error less than 3.5% for the value of the cell voltage and the water content within the GDL + MEA for all experiments performed. This result presents a new standard of validation in the state of art of PEM fuel cell modeling where two variables are simultaneously and quantitatively validated with experimental results. The developed analytical model has been used in order to analyze the behavior of the PEM fuel cell under different values of relative humidity.

In this work, a comprehensive experimental analysis on the performance of a 50 cm2 polymer electrolyte membrane (PEM) fuel cell is presented, including experimental results for a dedicated load cycling test. The harmonized testing protocols defined by the Joint Research Centre (JRC) of the European Commission for automotive applications were followed. With respect to a reference conditions representative of automotive applications, the impact of variations in the cell temperature, reactants pressure, and cathode stoichiometry was analyzed. The results showed that a higher temperature resulted in an increase in cell performance. A higher operating pressure also resulted in higher cell voltages. Higher cathode stoichiometry values negatively a ected the cell performance, as relatively dry air was supplied, thus promoting the dry-out of the cell. However, a too low stoichiometry caused a sudden drop in the cell voltage at higher current densities, and also caused significant cell voltage oscillations. No significant cell degradation was observed after the load cycling tests. Ministerio de Ciencia, Innovación y Universidades de España ENE2017-91159-EXP Ministerio de Economía y Competitividad UNSE15-CE2962

Bipolar Plate design is one of the most active research fields in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) development. Bipolar Plates are key components for ensuring an appropriate water management within the cell, preventing flooding and enhancing the cell operation at high current densities. This work presents a literature review covering bipolar plate designs based on nature or biological structures such as fractals, leaves or lungs. Biological inspiration comes from the fact that fluid distribution systems found in plants and animals such as leaves, blood vessels, or lungs perform their functions (mostly the same functions that are required for bipolar plates) with a remarkable efficiency, after millions of years of natural evolution. Such biomimetic designs have been explored to date with success, but it is generally acknowledged that biomimetic designs have not yet achieved their full potential. Many biomimetic designs have been derived using computer simulation tools, in particular Computational Fluid Dynamics (CFD) so that the use of CFD is included in the review. A detailed review including performance benchmarking, time line evolution, challenges and proposals, as well as manufacturing issues is discussed.

AIP Conference Proceedings, 2033, Nov. 2018, Article number 130013-1-130013-9 This study presents a comparison of the experimental tests and CFD results for a multi-tubular solar reactor for hydrogen production in a pilot plant in the Plataforma Solar de Almería. This paper describes the methodology used for the solar reactor design and the experimental tests carry out during the testing and characterization campaign of the plant. The CFD model which has been used to design the solar reactor has been validated with an error around 10%. CFD simulations also allow to solve the thermal balance in the reactor (cavity and tubes) and to calculate the percentage of reacting media inside the tubes which achieve the required temperature for the process. The temperature in the thermocouples is around 1200 °C for the experimental data and a 90% of the ferrite inside the tube is above 900 °C. The multi-tubular solar reactor, which has been design with CFD techniques, has been built and operated successfully. Ministerio de Ciencia e Innovación, Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2008-2011 Fondo Europeo de Desarrollo Regional IPT-2011-1323-920000 Fondos FEDER Andalucía 2007-2013 Proyecto RNM 6127

Spanish company Ajusa Hydrogen Technologies and the Thermal Engineering Group at the University of Sevilla are completing a research project named AGUAPEM (Research on water management in PEM Fuel Cells and optimisation of their power systems), funded by the Spanish Ministry of Science, Innovation and Universities.

An experimental investigation of the performance and contamination of low and high temperature PEMFCs (polymer electrolyte membrane fuel cells) operating with different concentrations of CO2 at the anode inlet is presented. 50 cm2 MEAs are used in the investigation: Nafion membranes with catalyst Pt loading 0.5 mg cm−2 for both anode and cathode for the low temperature cell, and Celtec P1000 PBI MEAs with catalyst loading 0.75 mg cm−2 in anode and 1 mg cm−2 in cathode for the high temperature cell. An analysis of the relative humidity influence in the contamination process for low temperature polymer electrolyte membrane fuel cells and the temperature effect for both low and high temperature operation range are also investigated in this work. The results show that the performance loss is larger than expected if only a dilution effect were considered, so that a real contamination process occurs in the cell when CO2 is fed to the anode, due to the RWGS (reverse water gas shift) reaction. This contamination effect is analysed and quantified by comparing the polarization curves of the contaminated cell with the ones corresponding to the cell operating with pure hydrogen, following the method described in section 2. The overpotentials for different current densities, CO2 concentrations, relative humidity, and cell temperatures are presented and discussed for both types of fuel cells. Two different regeneration processes (anode feeding with pure H2 and with air) are also presented and discussed. The analysis of the effectiveness of each regeneration strategy also supports that CO produced via the RWGS reaction is adsorbed onto the catalyst.

A 50 cm 2 commercial PEM fuel cell has been used to investigate the effects of a set of different operating conditions on the resulting liquid water distributions in the cell. A comprehensive matrix of operating conditions was analyzed, varying the reactants relative humidity (anode and cathode), cathode stoichiometry, and cell current density. Neutron imaging was used to determine the liquid water distributions within the cell for each operating condition. The obtained neutron radiographs were post-processed and analyzed in order to assess the effects of the different operating conditions. Cell voltage and cell resistance (High Frequency Resistance) were also monitored during the experiments and included in the analysis. Overall, the well-known water distributions corresponding to serpentine flow fields were observed, featuring a progressive water accumulation along the gas flow and towards the outlet port. Cathode channels were showing water accumulation. It was found that the cathode relative humidity had a much larger effect on the cell water content and overall performance than the anode relative humidity for this particular cell.

Molten salts consisting of 60% sodium nitrate and 40% potassium nitrate have been used successfully as a thermal energy collection and storage fluid in different solar thermal plants. However, the relatively high melting point of this mixture (221 °C) represents an important risk of local solidification in the operation of the solar power plants during standby periods. In this work, a computational fluid dynamics (CFD) model is developed to analyze the cooling process of representative state-of-the-art molten salt thermal storage tanks during these standby periods. A comprehensive set of operating conditions is analyzed, covering both hot and cold storage tanks, charging levels, and heat losses. Results show that the onset of local crystallization is highly influenced by the tank charging level. While the risk is relatively high in the case of the minimum charging level, in the case of maximum charging level the risk is minimal as it would require a very long standby period. To summarize the results, this work presents a safe charging level calculation, as a function of the operation temperature and the expected standby duration, which could be used as part of an appropriate operational strategy to avoid the risk of freezing for long standby periods. The model assumptions, the different configurations studied and their results are presented and discussed in detail.

We present a method for distinguishing liquid water content in the different layers of a polymer electrolyte fuel cell (“anode flow channels”, “cathode flow channels”, and “GDL/MEA”) from through-plane neutron imaging. The method is based on sudden decompression of the anode and cathode sides of a cell in two separate steps. The decompression induces a strong purging effect with effective liquid water removal from the flow channels, without affecting the gas diffusion layers (GDL) and membrane electrode assembly (MEA). The water in the flow channels is imaged by the differences of water distribution before and after the corresponding purges, and the water remaining after the purges is considered to be GDL/MEA water. The method is valid both for qualitative and quantitative analysis. A validation of the method is presented in this work, including results obtained for a 50 cm2 commercial PEFC. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0511506jes] Ministerio de Economía y Competitividad (España) PTQ-11-04703 Programa específico FP7 Capacidades FP7- 284522

A computational fluid dynamics (CFD) analysis of air distribution in a representative railway vehicle equipped with a heating, ventilation, air conditioning (HVAC) system is presented in this paper. Air distribution in the passenger’s compartment is a very important factor to regulate temperature and air velocity in order to achieve thermal comfort. A complete CFD model, including the car’s geometry in detail, the passengers, the luminaires, and other the important features related to the HVAC system (air supply inlets, exhaust outlets, convectors, etc.) are developed to investigate eight different typical scenarios for Northern Europe climate conditions. The results, analyzed and discussed in terms of temperature and velocity fields in different sections of the tram, and also in terms of volumetric parameters representative of the whole tram volume, show an adequate behavior from the passengers’ comfort point of view, especially for summer climate conditions.