Experimental decoupling of single cell polarization losses

Trabajo presentado al V Iberian Symposium on Hydrogen, Fuel Cells and Advanced Batteries celebrado en Tenerife (España) del 5 al 8 de julio de 2015.The decoupling of the current sweep with the Ohmic resistance is a very powerful tool to determine the magnitude of the voltage losses inside of a fuel cell. In a time frame of seconds, the fuel cell can be diagnosed and critical information on the state of the membrane, catalyst and diffusion layer can be assessed. The losses determined by this technique are the Ohmic, mass transport and activation. With this technique flooding and dry can be isolated and degradation studies can be made. Finally, this technique can be applied to a real system were this data can be used to improve control strategies for performance and durability when integrated in to a model based controller.This work is partially funded by the Spanish national MICINN project DPI2011-25649, as well as by the 7th Framework Programme of the European Commission in the context of the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) through the project PUMA-MIND FP7 303419.Peer Reviewe

Water transport study in a high temperature proton exchange membrane fuel cell stack

A study of water transport in a high temperature phosphoric acid doped polybenzimidazole (PBI) membrane fuel cell stack is reported. Tests with different stoichiometries of dry cathode and different humidity levels of anode are performed. It is found that water transport across the membrane electrode assembly (MEA) is noteworthy and that water vapor partial pressure on the anode outlet is almost always higher than on the cathode outlet, even when using dry hydrogen. The water transport is a strong function of current density but it also depends on stoichiometry and humidity level. In a series of tests with dry nitrogen on one side and humid nitrogen on the other side, the membrane's water permeability coefficient is determined to be 2.4 × 10-13 mol s-1 cm-1 Pa-1 at 160 °C which is more than an order of magnitude higher than the values previously reported in the literature. Also, the results indicate that the permeability coefficient might be relative humidity dependent and could even be somewhat higher than the value reported here, but further investigation is needed. The experimental findings are reproduced and explained with a 2D steady state computational fluid dynamics (CFD) model. Internal water transport profiles across the membrane and along the gas flow channels are presented and discussed.This work is partially funded by the project of CICYTDPI2011-25649 MICINN. Finally, the authors highly appreciate the support of the Institut de Robòtica i Informàtica Industrial in enabling a research stay of Dario Bezmalinović at the Fuel Cell Laboratory in Barcelona.Peer Reviewe

Identification of PEM fuel cells based on support vector regression and orthonormal bases

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Polymer Electrolyte Membrane Fuel Cells (PEMFC) are efficient devices that convert the chemical energy of the reactants in electricity. In this type of fuel cells, the performance of the air supply system is fundamental to improve their efficiency. An accurate mathematical model representing the air filling dynamics for a wide range of operating points is then necessary for control design and analysis. In this paper, a new Wiener model identification method based on Support Vector (SV) Regression and orthonormal bases is introduced and used to estimate a nonlinear dynamical model for the air supply system of a laboratory PEMFC from experimental data. The method is experimentally validated using a PEMFC system based on a ZB 8-cell stack with Nafion 115 membrane electrode assembliesPeer ReviewedPostprint (author's final draft

Modelling of solid oxide electrolizer and hydrogen leak estimation

Solid Oxide Elecyrolizers (SOEC) are electrochemical devises that produce hydrogen from water using the energy of an electric power source. SOEC operate at high temperatures (around 800ºC) and have efficiencies around 53% [1]. One of the most interesting scenarios of SOEC use is the storage of energy in hydrogen form when renewable power sources do not match the load. Because of this, it is important to study the dynamic behavior of SOEC systems in order to know their ability to adapt to changing power profiles. Different works describe SOEC models in the literature, as reviewed in [2], but time dependent models are scarse [3] and very few of the models are experimentally validated. This work presents a dy-namic model of a SOEC implemented in MATLAB Simulink and its match with experimental data. One important issue in SOEC stacks is hydrogen leak, which aggravates with ageing and is mostly caused by the high operating temperatures. The analysis of the experimental data of this work suggested hydrogen leak. Based on the SOEC thermal model, a methodology to quantify the flow of hydrogen that is leaked out is proposed and applied to the experimental system.Postprint (published version

Intravenous bisphosphonate-related osteonecrosis of the jaws: influence of coadjuvant antineoplastic treatment and study of buccodental condition

Objectives: To determine whether coadjuvant antineoplastic treatment can influence the number and size of bone exposures among patients with intravenous bisphosphonaterelated osteonecrosis of the jaws (iBRONJ), and to analyze the buccodental condition of these patients. Material and methods: The study sample comprised 67 patients with iBRONJ, 53 patients without iBRONJ receiving treatment with intravenous bisphosphonates, and 36 healthy subjects. In all three groups, measurements were made of the CAO index and of resting whole saliva and stimulated whole saliva. In the patients with iBRONJ, the size (cm) and number of bone exposures were recorded. The data obtained were subjected to analysis of variance (ANOVA), the Mann-Whitney U-test, and multivariate logistic regression analysis. Results: A total of 57.6% of the patients presented single bone exposure, 25.4% presented two, and 17% more than two exposures. The mean exposure size was 2.3±1.9 cm. Neither the bivariate analysis nor the multivariate multiple regression analysis found coadjuvant antineoplastic treatment to exert a statistically significant effect upon the number and size of bone exposures. On the other hand, there were statistically significant differences among the three study groups in relation to the CAO index (p=0.02) and the number of missing teeth (p=0.00). The resting whole saliva and stimulated whole saliva levels were similar in the three groups, though the patients with osteonecrosis of the jaws showed comparatively lower SWS levels. Conclusions: Coadjuvant antineoplastic treatment alone appears to exert no influence upon the size and number of bone exposures in iBRONJ. The patients with this disease show a higher CAO index and a larger number of missing teeth

Ewing sarcoma of the oral cavity. A review

A review is made of the clinical, diagnostic, therapeutic and survival characteristics of Ewing sarcoma (ES) of the oral cavity. A systematic literature search was carried out, with restrictions referred to time (1960-2014), language (English and Spanish) and type of study (case reports, letters, datasets, reviews). The following MeSH terms and boolean operators were used: Ewing AND Sarcoma AND [tongue, jaw, maxilla, cheek, condyle OR temporomandibular, floor AND mouth, gum OR gingiva, palate OR palatal, lip, uvula, head AND neck]. Seventy-one cases of ES of the oral cavity were documented from 53 articles. The main differences versus ES of other locations were a younger age at manifestation, a shorter time from symptoms onset to diagnosis, and swelling as the most frequent clinical manifestation versus swelling and pain in the rest of disease locations. The way in which ES manifests in the oral cavity is varied and comprises dental displacement (19.7%), dental mobility (7%), root reabsorption (5.6%), destruction of the dental follicle (4.2%), premature exfoliation (4.2%) and paresthesia of the chin (2.8%). Metastatic neck adenopathies appear in 11.3% of the cases. Significant differences in survival are observed between patients with a complete diagnosis of ES (hematoxylin-eosin staining, PAS positivity, CD99 positivity) and those with an incomplete diagnosis. Ewing sarcoma of the oral cavity presents a series of specific features that distinguish it from ES of other locations

Water transport study in high temperature proton exchange membrane fuel cell stack

A study of water transport in a high temperature phosphoric acid doped polybenzimidazole (PBI) membrane fuel cell stack is reported. Tests with different stoichiometries of dry cathode and different humidity levels of anode are performed. It is found that water transport across the membrane electrode assembly (MEA) is noteworthy and that water vapor partial pressure on the anode outlet is almost always higher than on the cathode outlet, even when using dry hydrogen. The water transport is a strong function of current density but it also depends on stoichiometry and humidity level. In a series of tests with dry nitrogen on one side and humid nitrogen on the other side, the membrane's water permeability coefficient is determined to be 2.4 × 10-13 mol s-1 cm-1 Pa-1 at 160 °C which is more than an order of magnitude higher than the values previously reported in the literature. Also, the results indicate that the permeability coefficient might be relative humidity dependent and could even be somewhat higher than the value reported here, but further investigation is needed. The experimental findings are reproduced and explained with a 2D steady state computational fluid dynamics (CFD) model. Internal water transport profiles across the membrane and along the gas flow channels are presented and discussed.Peer ReviewedPostprint (author’s final draft

Differences in clinical variables and risk factors between patients with osteoarthritis and osteoarthrosis of the temporomandibular joint (TMJ)

Objective: To study differences in risk factors and clinical variables between a group of patients with osteoarthritis and a group with osteoarthrosis of the temporomandibular joint. Material and methods: Thirty-five patients (32 women and 3 men) (mean age 53±18 years), 21 (60%) with a diagnosis of osteoarthrosis (mean age 54.7±20.2 years) and 14 (40%) with a diagnosis of osteoarthritis (mean age 51.7±16.9 years), were studied. The two groups were compared with each other and also with the group of 164 patients with temporomandibular joint pathology from which they were drawn. An evaluation was made of the demographic variables, risk factors (parafunctions, posterior occlusal contacts, sleep disturbances and psychoactive medication), clinical manifestations (pain, joint sounds, limitation of mandibular movements) and panoramic X-ray and magnetic resonance imaging alterations. Results: None of the studied variables showed statistically significant differences between osteoarthritis and osteoarthrosis. Age was significantly older among the patients with osteoarthritis/osteoarthrosis than in the general group of patients with temporomandibular joint pathology (36.9±17.2) (F=20.1; p=0.000). The time from appearance of the symptoms to medical consultation (35.9±41.8 months) was significantly longer in patients with osteoarthritis (F=3.95; p=0.049). The number of posterior occlusal contacts (5.2±3.0), maximum aperture (32.5±6.5 mm), and the frequency of parafunctions (42.9%) were significantly lower in the group of patient with osteoarthritis (F=6.2 p=0.01; F=4.45 p=0.04; χ2 =4.85 p=0.03) than in the group of patients with temporomandibular joint pathology from which they were drawn. Conclusions: No epidemiological or clinical differences were observed between osteoarthritis and osteoarthrosis, though both processes - particularly osteoarthritis - showed differences with respect to the group of patients with temporomandibular joint pathology from which they were drawn

An adaptive power split strategy with a load disturbance compensator for fuel cell/supercapacitor powertrains

Electric vehicles powered by fuel cell and supercapacitor hybrid power sources are of great interest. However, the power allocation between each power source is challenging and the DC bus voltage fluctuation is relatively significant in cascaded PI control schemes. This paper develops a power control strategy with an adjustable cut-off frequency, using an artificial potential field, to adaptively split the load current between the fuel cell and the supercapacitor under various load conditions. The adaptive cut-off frequency is calculated by cutting the load frequency spectrum with an allocation ratio that changes with the supercapacitor state of charge. Therefore, the relatively lower frequency portion of the load current is provided by the fuel cell and the supercapacitor handles the higher frequency portion. To enhance the control performance of the DC bus voltage regulation against the load disturbance, a load disturbance compensator is introduced to suppress the DC bus voltage fluctuation when the load variation occurs, which is implemented by a feed-forward controller that can compensate the load current variation in advance. The effectiveness of the proposed strategy is validated by extensive experiments