Consistent modeling of a single PEM fuel cell using Onsager's principle

In this paper a novel approach is proposed for a three-dimensional (3D) modeling of a High Temperature Exchange Membrane Fuel Cell (HTPEMFC). This new modeling is based on Onsager's principle of minimum energy dissipation that is applicable for near equilibrium and coupled irreversible systems. In particular, for low conductivity membranes, this leads to a one directional proton movement through the membrane. The resulting equations are numerically solved for a real single cell geometry, using a 3D finite volume discretization. Results are analyzed and validated against experimental data

Consistent behavior of Eulerian Monte Carlo fields at Low Reynolds Numbers

A slightly different version of the Eulerian Monte Carlo method (EMC) (Valiño, Flow Turbul. Combust. 60, 157–172, (1998)) is presented in this paper. The EMC method is an effective stochastic numerical approach to solve the Probability Density Function (PDF) of reacting species in turbulent flows. In contrast with the original formulation, the spurious Wiener term associated with the molecular diffusion is removed, by splitting the micro-mixing into mean gradient and fluctuating contributions. The evolution of the EMC fields representing the PDF in the proposed formulation is then consistent in the laminar limit: the EMC fields follow the same standard convection-diffusion equation, without any stochastic terms

Comparison of economic performance of lead-acid and li-ion batteries in standalone photovoltaic energy systems

Standalone renewable energy systems usually incorporate batteries to get a steady energy supply. Currently, Li-ion batteries are gradually displacing lead-acid ones. In practice, the choice is made without previous comparison of its profitability in each case. This work compares the economic performance of both types of battery, in five real case studies with different demand profiles. For each case, two sets of simulations are carried out. In one of the sets, the energy demand is supplied by a standalone photovoltaic system and, in the other one, by a standalone hybrid photovoltaic-diesel system. Through optimization processes, the economic optimum solutions are obtained. In addition, sensitivity analyses on various parameters have been carried out, seeking the influence in favor of one or another type of battery. The results show that if the type of battery is changed, to achieve the economic optimum the entire system must be resized. In some cases, the economic optimum is reached with Li-ion and in others with lead-acid batteries, depending on the demand profiles. Thus, both types of batteries can be profitable options in standalone energy systems, with a greater tendency to lead-acid in fully photovoltaic systems and to Li-ion in hybrids. The price reductions that would make Li-ion the only choice is quantified. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Parameter characterization of HTPEMFC using numerical simulation and genetic algorithms

This paper develops a novel approach to the parameterisation of high temperature exchange membrane fuel cells (HTPEMFC) with limited and non-invasive measurements. The proposed method allows an effective identification of electrochemical parameters for three-dimensional fuel cell models by combining computational simulation tools and genetic algorithms. To avoid each evaluation undertaken by the optimisation method involving a complete computational simulation of the 3D model, a strategy has been designed that, thanks to an iterative process, makes it possible to decouple the fluid dynamic resolution from the electrochemistry one. Two electrochemical models have been incorporated into these tools to describe the behaviour of the catalyst layer, Butler-Volmer and spherical aggregate. For each one, a case study has been carried out to validate the results by comparing them with empirical data in the first model and with data generated by numerical simulation in the second. Results show that, from a set of measured operating conditions, it is possible to identify a unique set of electrochemical parameters that fits the 3D model to the target polarisation curve. The extension of this framework can be used to systematically estimate any model parameter in order to reduce the uncertainty in 3D simulation predictions. © 2021 The Author(s

Experimental results and modelling of humidity control strategies for greenhouses in continental and coastal settings in the Mediterranean region. II: Modelling of strategies

Strategies for humidity control —with and without heating— were evaluated via simulations performed with apreviously developed model (see accompanying paper, this issue, part I). With heating, the best strategy combined theuse of a humidity setpoint with step control of the roof window, increasing the ventilation in line with the outsidetemperature. Without heating, the best strategy again combined the use of a humidity setpoint with step control of theroof window, but required ventilation to be increased in line with the inside air temperatur

Brain transcriptomics of agonistic behaviour in the weakly electric fish Gymnotus omarorum, a wild teleost model of non-breeding aggression

Differences in social status are often mediated by agonistic encounters between competitors. Robust literature has examined social status-dependent brain gene expression profiles across vertebrates, yet social status and reproductive state are often confounded. It has therefore been challenging to identify the neuromolecular mechanisms underlying social status independent of reproductive state. Weakly electric fish, Gymnotus omarorum, display territorial aggression and social dominance independent of reproductive state. We use wild-derived G. omarorum males to conduct a transcriptomic analysis of non-breeding social dominance relationships. After allowing paired rivals to establish a dominance hierarchy, we profiled the transcriptomes of brain sections containing the preoptic area (region involved in regulating aggressive behaviour) in dominant and subordinate individuals. We identified 16 differentially expressed genes (FDR < 0.05) and numerous genes that co-varied with behavioural traits. We also compared our results with previous reports of differential gene expression in other teleost species. Overall, our study establishes G. omarorum as a powerful model system for understanding the neuromolecular bases of social status independent of reproductive state

Joint PDF modelling of turbulent flow and dispersion in an urban street canyon

The joint probability density function (PDF) of turbulent velocity and concentration of a passive scalar in an urban street canyon is computed using a newly developed particle-in-cell Monte Carlo method. Compared to moment closures, the PDF methodology provides the full one-point one-time PDF of the underlying fields containing all higher moments and correlations. The small-scale mixing of the scalar released from a concentrated source at the street level is modelled by the interaction by exchange with the conditional mean (IECM) model, with a micro-mixing time scale designed for geometrically complex settings. The boundary layer along no-slip walls (building sides and tops) is fully resolved using an elliptic relaxation technique, which captures the high anisotropy and inhomogeneity of the Reynolds stress tensor in these regions. A less computationally intensive technique based on wall functions to represent boundary layers and its effect on the solution are also explored. The calculated statistics are compared to experimental data and large-eddy simulation. The present work can be considered as the first example of computation of the full joint PDF of velocity and a transported passive scalar in an urban setting. The methodology proves successful in providing high level statistical information on the turbulence and pollutant concentration fields in complex urban scenarios.Comment: Accepted in Boundary-Layer Meteorology, Feb. 19, 200

Superficial radiotherapy as haemostatic treatment in breast cancer

Poster Session [EP-1661] Purpose or Objective Breast cancer is a common pathology in which o = 25% in tumor size and absence of bleeding was observed. Conclusion Surface radiotherapy is a treatment modality that should be taken into account in patients with breast cancer who present bleeding as a consequence of local tumor growth, given that this is a treatment comfortable for the patient, non invasive and increases the quality of patient’s life

Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an Octocopter

An in-situ calibration of a logarithmic periodic dipole antenna with a frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of a radio station system used for detection of cosmic ray induced air showers at the Engineering Radio Array of the Pierre Auger Observatory, the so-called Auger Engineering Radio Array (AERA). The directional and frequency characteristics of the broadband antenna are investigated using a remotely piloted aircraft (RPA) carrying a small transmitting antenna. The antenna sensitivity is described by the vector effective length relating the measured voltage with the electric-field components perpendicular to the incoming signal direction. The horizontal and meridional components are determined with an overall uncertainty of 7.4^{+0.9}_{-0.3} % and 10.3^{+2.8}_{-1.7} % respectively. The measurement is used to correct a simulated response of the frequency and directional response of the antenna. In addition, the influence of the ground conductivity and permittivity on the antenna response is simulated. Both have a negligible influence given the ground conditions measured at the detector site. The overall uncertainties of the vector effective length components result in an uncertainty of 8.8^{+2.1}_{-1.3} % in the square root of the energy fluence for incoming signal directions with zenith angles smaller than 60{\deg}.Comment: Published version. Updated online abstract only. Manuscript is unchanged with respect to v2. 39 pages, 15 figures, 2 table