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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.

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

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.

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.

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.

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.

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.

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.

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

Bipolar plates (BPs) are one of the most important components in Proton Exchange Membrane Fuel Cells (PEMFC) due to the numerous functions they perform. The objective of the research work described in this paper was to develop a simplified and validated method based on Computational Fluid Dynamics (CFD), aimed at the analysis and study of the influence of geometrical parameters of BPs on the operation of a cell. A complete sensibility analysis of the influence of dimensions and shape of the BP can be obtained through a simplified CFD model without including the complexity of other components of the PEMFC. This model is compared with the PEM Fuel Cell Module of the FLUENT software, which includes the physical and chemical phenomena relevant in PEMFCs. Results with both models regarding the flow field inside the channels and local current densities are obtained and compared. The results show that it is possible to use the simple model as a standard tool for geometrical analysis of BPs, and results of a sensitivity analysis using the simplified model are presented and discussed. Junta de Andalucía P08-TEP-4309