Analytical approach to ground heat losses for high temperature thermal storage systems

A new approach to estimate the heat loss from thermal energy storage tank foundations is presented. Results are presented through analytical correlations based on numerical solutions for the steady-state heat conduction problem for thermal energy slab-on-grade tanks with uniform insulation. Model results were verified with other well-established benchmark problems with similar boundary conditions and validated with experimental data with excellent agreement. In addition to the TES foundation heat loss, new correlations for the maximum temperature and for the radial evolution of the temperature underneath the insulation layer are also provided, giving important information related to the tank foundation design. The correlated variables are of primordial importance in the tank foundation design because, due to the typical high operating storage temperatures, an inappropriate tank foundation insulation would lead not only to a not desired loss of energy but also to an inadmissible increase of the temperatures underneath the insulation layer, affecting the structural stability of the tank. The proposed correlations provide a quick method for the estimation of total tank foundation heat losses and soil maximum temperature reached underneath the insulation layer, saving time, and cost on the engineering tank foundation design process. Finally, a comprehensive parametric analysis of the variables of interest is made and a set of cases covering a wide range of tank sizes, insulation levels, depths to water table, and storage temperatures are solved

Experimental and numerical Investigation on the design of a bioinspired PEM fuel cell

Proton exchange membrane fuel cells (PEMFCs) are promising energy devices that directly convert chemical energy of fuels such as hydrogen to useful work with negligible environmental impact and high efficiency. The channel geometry of the Bipolar Plate (BP) has a considerably impact on the PEMFC performance. BP designs based on nature-inspired structures such as leaves, lungs or sponges have been explored to date with success but have not yet achieved their full potential. With the objective of researching new flow field designs with enhanced operation, this work presents an experimental analysis of a novel bioinspired design of the channels of a PEMFC. Starting from a CFD fluid flow analysis of different novel initial biomimetic designs, the most promising one was selected, manufactured and tested experimentally. Experimental results comprise polarization and power curves for a comprehensive set of operating conditions. Results were analysed and compared against a reference parallel-serpentine model. Results indicated that the proposed novel biomimetic design is particularly suited for improving water management at high reactants humidity reaching out a peak power a 6.0% higher in comparison with the reference design. Future research should further develop novel design variants and analyze water distribution within the channels

Dataset and mesh of the CFD numerical model for the modelling and simulation of a PEM fuel cell

A CFD mesh corresponding to a Proton Exchange Membrane Fuel Cell (PEMFC) with an active area of 50 cm2, serpentine channels and cross-flow field distribution is presented. The mesh was developed using ANSYS ICEM CFD hexa (v12.0) and it is divided into 3D regions corresponding to the different components of the fuel cell: bipolar plates (anode and cathode), gas diffusion layers (GDLs), catalytic layers (CLs) and membrane. The mesh was generated following Best Practice Guidelines, and mesh quality parameters are reported including minimum cell angle or maximum aspect ratio amongst others. Mesh independence results were checked in the corresponding CFD model and simulation of an experimental fuel cell ANSYS FLUENT with the PEM Fuel Cell module. Simulation results were also validated with the experimental data available from a fuel cell test bench for a set of different operating conditions. The experimental validation provides credibility to the CFD model and supports the use of the proposed mesh for fuel cell research, ensuring accurate results and enabling further validation works an

Parametric Investigation Using Computational Fluid Dynamics of the HVAC Air Distribution in a Railway Vehicle for Representative Weather and Operating Conditions

This article belongs to the Special Issue Engineering Fluid Dynamics. http://www.mdpi.com/journal/energies/special_issues/eng_fluid_dynA 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 condition

Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified

Voltage distribution analysis and non-uniformity assessment in a 100 cm2 PEM fuel cell stack

In this study, a comprehensive set of experimental tests were carried out to investigate individual cell voltage and temperature deviation under different operating conditions in a fuel cell stack. Five key operating conditions were considered: temperature, pressure, anode and cathode relative humidity, and cathode stoichiometry. Different configurations of reactant flow within the stack were also investigated. A 100 cm2 7-cell stack was used for the experiments, and voltage and temperature measurements were taken for each individual cell. Both ANOVA and range analysis method were used to evaluate the results. The findings showed that the performance of the external cells was consistently lower than that of the central ones since its temperature, the parameter that most affected performance, was also lower due to heat losses. Additionally, voltage deviation increased with temperature deviation. The study also revealed that stack performance was improved by an increase in temperature, pressure and cathode stoichiometry, whereas the effect of anode and cathode humidity was not so significant in the studied range. Furthermore, gravity played a clear role in water management, hindering the removal of condensed water for flow configurations where reactant gases were fed from the bottom interfaces of the stack

Dataset and mesh of the CFD numerical model for the modelling and simulation of a PEM fuel cell

A CFD mesh corresponding to a Proton Exchange Membrane Fuel Cell (PEMFC) with an active área of 50 cm2, serpentine channels and cross-flow field distribution is presented. The mesh was developed using ANSYS ICEM CFD Hexa (v12.0) and it is divided into 3D regions corresponding to the different components of the fuel cell: bipolar plates (anode and cathode), gas difusión layers (GDLs), catalytic layers ((CLs) and membrane. The mesh was generated following Best Practice Guidelines. Mesh independence results was checked in the corresponding CFD model and simulation of a experimental fuel cell ANSYS FLUENT with the PEM Fuel Cell module. Simulation results were also validated with the experimental data available from a fuel cell test bench for a set of different operating conditions. The experimental validation provides credibility to the CFD model and supports the use of the proposed mesh for fuel cell research, ensuring accurate results and comparison of different designs and operating conditions using numerical simulations.Se presenta un mallado CFD correspondiente a una pila de combustible de membrana de intercambio de protones (PEMFC) con un área activa de 50 cm2, canales en forma de serpentín y distribución de campo de flujo cruzado. La malla se desarrolló utilizando ANSYS ICEM CFD Hexa (v12.0) y está dividida en regiones 3D correspondientes a los diferentes componentes de la pila de combustible: placas bipolares (ánodo y cátodo), capas de difusión de gases (GDLs), capas catalíticas (CLs) y membrana. El mallado se generó siguiendo “Best Practice Guidelines”. Los resultados Los resultados de independencia de malla se comprobaron utilizando el modelo CFD y la simulación de una pila de combustible a través de ANSYS FLUENT con el módulo “PEM Fuel Cell”. Los resultados de la simulación también fueron validados con los datos experimentales disponibles de una banco de ensayos de pilas de combustible para diferentes conjuntos de condiciones de funcionamiento. La validación experimental proporciona credibilidad al modelo CFD y apoya el uso de la malla propuesta para la investigación de pilas de combustible, garantizando resultados precisos y la comparación de diferentes diseños y condiciones de funcionamiento mediante simulaciones numéricas.1. Mallado CFD de pila de combustible PEMv1.

Experimental dynamic load cycling and current density measurements of different inlet/outlet configurations of a parallel-serpentine PEMFC

Proton-exchange membrane fuel cells (PEMFCs) in the transport sector require specific design and durability, and stable and reliable performance under varying cycling loads. In this study, experimental dynamic load cycling (DLC) tests and current density mapping (CDM) measurements of local current densities and temperatures were performed for different inlet/outlet configurations of reactants in a parallel-serpentine PEMFC. Results were analyzed in terms of the polarization and power curves and the DLC tests, indicating that the Inverse Hydrogen Flow configuration performed best. However, the differences with respect to the other inlet/outlet configurations (Normal Flow, Inverse Air Flow and Inverse Flow) were not significant with maximum relative voltage and power densities differences below 5% in the polarization and power curves. Also results of the experimented inlet/outlet configurations during the DLCs were similar, with maximum differences in terms of energy during the cycle below 10% comparing the best configuration (Inverse Hydrogen Flow) with the worst. CDM measurements showed an inverse bell-shaped distribution with higher current density values in the external part of the bipolar plate and lower values in the central part and a highly homogeneous temperature distributions in all configurations.VII PPIT from the University of SevilleThe Research, Technology and Innovation Centre (CITIUS) of the University of Sevill