1,745,661 research outputs found
Fuel processor - PEM fuel cell systems for energy generation
No full textIn the last few years, increasing attention has been paid to PEM fuel cells, as promising device for decentralized energy production, both in stationary and automotive field, thanks to high compactness, low weight (high power-to-weight ratio), high modularity, good efficiency and fast start-up and response to load changes. The high efficiencies that can be obtained with a PEM fuel cell, however, require a high purity hydrogen feed at the anode. Hydrogen, though, is not a primary source, but it is substantially an energy carrier, that can be stored, transported and employed as gaseous fuel, however, it needs to be produced from other sources. The main hydrogen source is actually represented by hydrocarbons, through classical Steam Reforming or Partial Oxidation industrial scale processes. However, the limitation of hydrogen storage and transport due to its chemico-physical properties has pushed toward the concept of decentralized hydrogen production; in this way, the hydrogen source, such as methane, is distributed through pipelines to the small-scale plant, installed nearby the users, and the hydrogen produced in situ is fed directly to the energy production system, avoiding hydrogen storage and transportation. In this sense, research is oriented toward the optimization of the decentralized hydrogen production unit, generally named as fuel processor, for residential and automotive applications, for achieving fuel conversion into hydrogen with high efficiencies and high compactness.
Since the efficiency of the integrated fuel processor – fuel cell system strongly depends on system configuration and on the heat integration, a system analysis of the most promising configurations is performed, in order to identify the best solution for energy production in a PEM fuel cell system. Analysis of global system efficiency of fuel processor – PEM fuel cell systems is performed by means of the software AspenPlus®, with identification of best configuration and best operating conditions.
Moreover, since the application of fuel processor – PEM fuel cell system is foreseen for small and medium scale, an important characteristic that must me associated to the high efficiency is the compactness of the system. The PEM fuel cell, indeed, is generally characterized by high efficiency and compactness, therefore, in order to keep its standard, also the fuel processor coupled with it must be efficient and as compact as possible. In order to have an idea of the encumbrance of the reactors, a detailed mathematical model for fixed bed reactors was developed in this work, in order to size and compare conventional fixed bed reactor and membrane catalytic reactors. The software employed was Mathematica®
Estudo teórico e experimental de célula-combustível tipo pem e perspectivas de aplicação em sistemas de geração distribuída
Get PDFDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica.Células-combustível se apresentam como alternativas promissoras para acionamento primário em sistemas de geração ou cogeração de energia. Caracterizam-se pela conversão direta da energia química do combustível em energia elétrica, o que geralmente lhes confere eficiência superior aos acionadores primários convencionais utilizados para geração termoelétrica. Dentre os diversos tipos de células-combustível existentes, as Células-Combustível do tipo Membrana de Troca de Prótons, comumente chamadas de PEMFC ou simplesmente células PEM, estão em crescente estágio de desenvolvimento. Como seu eletrólito é um polímero sólido e sua temperatura de operação é em torno de 80ºC, são adequadas para aplicação automobilística e em sistemas portáteis de geração de energia elétrica (celulares, laptops, etc). Atualmente, devido a outras características favoráveis tais como, tamanho compacto, baixo peso, partida rápida, longa vida útil dos "stacks" (blocos) e capacidade de trabalhar em regime descontínuo e com altas densidades de corrente, sua aplicabilidade foi estendida para os sistemas de geração distribuída de energia elétrica. O presente trabalho tem como objetivo avaliar experimentalmente a influência dos parâmetros de operação sobre o desempenho de uma célula-combustível tipo PEM de 15 W de potência, de fabricação brasileira e em operação no LabCET. A partir dos resultados obtidos, ações foram implementadas de forma a melhorar o desempenho desta célula-combustível. Trabalho complementar foi também realizado para avaliar a aplicabilidade dessa tecnologia como sistema compacto de geração de energia elétrica. Nesta etapa, foi realizada uma análise termoeconômica preliminar de uma célula PEM de 30 kW, comparando os resultados com valores obtidos de duas bancadas experimentais existentes no LabCET, uma constituída de uma microturbina de 28 kW e outra constituída por um motogerador de 30 kW, ambos operando com gás natural veicular
Análise e desenvolvimento de modelo de transporte de massa visando a aplicação em células a combustível tipo PEM
Get PDFTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2012O atual cenário mundial na área de energia demanda o desenvolvimento tecnológico de alternativas sustentáveis, e de menor impacto ambiental. O uso eficiente de fontes de energia renováveis para a produção de energia elétrica em sistemas descentralizados e isolados, bem como para o setor de mobilidade, destaca-se como um ingrediente capaz de mitigar a agressão ambiental dos sistemas de energia. A célula a combustível é um dispositivo eletroquímico que converte diretamente a energia interna de ligação química de combustíveis em energia elétrica e calor com alta eficiência global, ausência de ruído e emissões. O elevado custo de desenvolvimento destes sistemas sugere que estratégias que combinem medições e previsões teóricas apresentem a maior chance de atingir os desenvolvimentos necessários. O principal objetivo da presente tese é desenvolver uma teoria para o transporte de massa em uma célula a combustível tipo PEM a partir de uma análise fenomenológica com base nos fundamentos do transporte de massa multicomponente, multifásico em meios porosos. O modelo tem por objetivo prever o comportamento do transporte elétrico e de massa com uma formulação adequada. Para este fim, foram revisadas as escalas de comprimento característicos dos diferentes componentes e fenómenos dentro da célula a combustível visando determinar as relações entre os processos termodinâmicos, eléctricos e eletroquímicos em uma célula de combustível tipo PEM. Foi revisada a grande quantidade de informações sobre teoria, modelagem e simulação da célula a combustível tipo PEM, a fim de classificar os diferentes modelos, ressaltar sua aplicabilidade e definir as necessidades de melhoria. A curva de polarização de um sistema de célula de combustível foi medida com o objetivo de identificar os fenómenos que controlam o transporte e a fenomenologia química, avaliar a aplicabilidade dos modelos globais disponíveis e determinar a ordem de grandeza dos parâmetros característicos globais da operação da célula de combustível. Então, foram revisadas as teorias fundamentais de transporte de massa e carga em duas fases, em fluxo multicomponente em meios porosos, focando na base do continuo e da termodinâmica para o tratamento de Maxwell-Stefan do transporte de massa. Finalmente, foi proposto um modelo fenomenológico geral para transferência de massa e carga aplicável às células a combustível tipo PEM. O modelo foi comparado com outros modelos da literatura e alguns problemas mais simples fundamentais foram resolvidos.Abstract : The present world energy scenario requires the development of alternative and sustainable energy sources and conversion systems that also result in an overall smaller impact in the environment. The efficient use of renewable energy sources for the production of electrical power in decentralized and isolated systems, as well as for the mobility sector, stands out as a possible ingredient to mitigate the environmental aggression from energy systems. Fuel cells are electrochemical devices that convert internal energy of chemical bond in electricity and heat power in an efficient, noiseless and lower emissions form. The relative high cost of system development suggests that a combined measurement, theoretical and simulation effort is the way to achieve the required breakthroughs. The main objective of the present thesis is to develop a theory for mass transport in a PEM fuel cell from a phenomenological analysis based on the fundamentals of the multicomponent, multiphase mass transport in porous media. The model aims at predicting the electric and mass transport behaviors with a formulation suitable for solution with current computational resources. To this end, the characteristic length scales of the different components and phenomena within the fuel cell were revised aiming at determining the relations between thermodynamic, electric and electrochemical processes in a PEM fuel cell. The vast amount of information on PEM fuel cell theory, modeling and simulation was reviewed with a view to classify the different models, point out their applicability and define the needs for further improvements. The polarization curve for a fuel cell system was measured with the purpose of identifying the controlling transport and chemical phenomena, assess the applicability of the available lumped models and to determine the orders of magnitude of global parameters characteristic of the fuel cell operation. Then, the fundamental theories of mass and charge transport in two-phase, multicomponent flow in porous media were reviewed, focusing on the continuum and thermodynamic basis for the Maxwell-Stefan treatment of mass transport. Finally, a general phenomenological model for mass and charge transfer applicable to PEM fuel cells was proposed, compared to other models from the literature and a few simpler fundamental problems were solved
PEM fuel cells: theory and practice
No full textDemand for fuel cell technology is growing rapidly. Fuel cells are being commercialized to provide power to buildings like hospitals and schools, to replace batteries in portable electronic devices, and as replacements for internal combustion engines in vehicles. PEM (Proton Exchange Membrane) fuel cells are lighter, smaller, and more efficient than other types of fuel cell. As a result, over 80% of fuel cells being produced today are PEM cells. This new edition of Dr. Barbir's groundbreaking book still lays the groundwork for engineers, technicians and students better than any other resource, covering fundamentals of design, electrochemistry, heat and mass transport, as well as providing the context of system design and applications. Yet it now also provides invaluable information on the latest advances in modeling, diagnostics, materials, and components, along with an updated chapter on the evolving applications areas wherein PEM cells are being deployed. Comprehensive guide covers all aspects of PEM fuel cells, from theory and fundamentals to practical applicationsProvides solutions to heat and water management problems engineers must face when designing and implementing PEM fuel cells in systemsHundreds of original illustrations, real-life engineering examples, and end-of-chapter problems help clarify, contextualize, and aid understanding.Demand for fuel cell technology is growing rapidly. Fuel cells are being commercialized to provide power to buildings like hospitals and schools, to replace batteries in portable electronic devices, and as replacements for internal combustion engines in vehicles. PEM (Proton Exchange Membrane) fuel cells are lighter, smaller, and more efficient than other types of fuel cell. As a result, over 80% of fuel cells being produced today are PEM cells. This new edition of Dr. Barbir's groundbreaking book still lays the groundwork for engineers, technicians and students better than any other resource, covering fundamentals of design, electrochemistry, heat and mass transport, as well as providing the context of system design and applications. Yet it now also provides invaluable information on the latest advances in modeling, diagnostics, materials, and components, along with an updated chapter on the evolving applications areas wherein PEM cells are being deployed. Comprehensive guide covers all aspects of PEM fuel cells, from theory and fundamentals to practical applicationsProvides solutions to heat and water management problems engineers must face when designing and implementing PEM fuel cells in systemsHundreds of original illustrations, real-life engineering examples, and end-of-chapter problems help clarify, contextualize, and aid understanding.Includes bibliographical references and index.Print version record.Elsevie
The State of the Art in Fuel Cell Condition Monitoring and Maintenance
Get PDFFuel cell vehicles are considered to be a viable solution to problems such as carbon emissions and fuel shortages for road transport. Proton Exchange Membrane (PEM) Fuel Cells are mainly used in this purpose because they can run at low temperatures and have a simple structure. Yet to make this technology commercially viable, there are still many hurdles to overcome. Apart from the high cost of fuel cell systems, high maintenance costs and short lifecycle are two main issues need to be addressed. The main purpose of this paper is to review the issues affecting the reliability and lifespan of fuel cells and present the state of the art in fuel cell condition monitoring and maintenance. The Structure of PEM fuel cell is introduced and examples of its application in a variety of applications are presented. The fault modes including membrane flooding/drying, fuel/gas starvation, physical defects of membrane, and catalyst poisoning are listed and assessed for their impact. Then the relationship between causes, faults, symptoms and long term implications of fault conditions are summarized. Finally the state of the art in PEM fuel cell condition monitoring and maintenance is reviewed and conclusions are drawn regarding suggested maintenance strategies and the optimal structure for an integrated, cost effective condition monitoring and maintenance management system
Degradations and Improvements in PEM Fuel Cell Materials: A Computational Study
Get PDFThe advantages of Proton Exchange Membrane (PEM) fuel cells include lower operating temperature than other fuel cells and size small enough to fit into a car. Improving the cost and durability of PEM fuel cell materials is a hot topic of research today.
The Nafion membrane and cathode catalysts are two areas where PEM fuel cells have issues of cost, durability, and efficiency. In order to improve these materials, researchers need a better understanding of the detailed mechanisms for basic operation and degradation. Computational quantum mechanics has improved in recent years to the point where it can provide accurate potential energy maps of reactions that are difficult to determine by laboratory experiments alone. With the basic understanding of mechanisms, experimentalists can make educated predictions of ways to improve fuel cell materials.
Experimental studies suggest that Nafion degradation is caused by generation of trace radical species (such as OH●, H●) when in the presence of H2, O2, and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H2 (or H+) and O2 in the presence of the Pt catalyst. We find that OH● can be generated in trace amounts on the Pt surface from HOOH and OOHad. Next, we look at various ways in which the OH● can attack the Nafion sidechains or endgroups on the backbone.
Researchers are looking for ways to replace the Pt cathode catalyst, due to the preciousness of Pt and the low efficiency of the oxygen reduction reaction (ORR) on Pt, among other things. Alloying Pt with non-precious Co greatly increases the ORR efficiency. However, Pt3Co was reported to not withstand long-cycle testing due to the migration of Co metals onto the catalyst surface and leaching of Co into the electrolyte. To overcome these challenges, we first study Pt3Co to find out what makes these alloys so special in improving fuel cell efficiency, as well as what causes degradation to occur. Then, we apply the principles we learned in proposing improved fuel cell alloy catalysts.</p
Experimental validation of equilibria in fuel cells with dead-ended anodes
Get PDFThis paper investigates the nitrogen blanketing front during the dead-ended anode (DEA) operation of a PEM fuel cell. Surprisingly the dynamic evolution of nitrogen and water accumulation in the dead-ended anode (DEA) of a PEM fuel cell arrives to a steady-state suggesting the existence of equilibrium behavior. We use a multi-component model of the two-phase one-dimensional (along-the-channel) system behavior to analyze and exploit this phenomenon. Specifically, the model is first verified with experimental observations, and then utilized for showing the evolution towards equilibrium. The full order model is reduced to a second-order ordinary differential equation (ODE) with one state, which can be used to predict and amalyse the surprising but experimentally observed steady state DEA behavior
Currículo y programación en educación especial
No full textEl multimedio le permite observar ejemplos de trabajo (videos), le proporciona información que complementa los contenidos del curso y le posibilita la realización de actividades interactivas que pretenden reforzar los nuevos conocimientosEste disco es parte del curso Currículo y programación en educación especial (código 2003), cuyo propósito es ofrecer conocimientos del currículo vigente a la luz de los principios que orientan la educación especial para que, en la práctica docente, pueda realizar las adaptaciones necesarias, demostrando dominio en la programación y manejo de las diferencias individuales.Universidad Estatal a Distancia de Costa Ric
Study of PEM electrolysis: compressibility, leakage and benchmark materials
No full textopenIn termini di sostenibilità e impatto ambientale, l’elettrolisi dell’acqua a membrana a scambio protonico (Proton Exchange Membrane Water Electrolysis, PEMWE) è considerata una delle tecnologie che contribuiranno alla produzione efficiente e versatile di idrogeno verde a partire da fonti energetiche rinnovabili. All’interno di una cella PEM, la distribuzione ottimale della pressione di bloccaggio è fondamentale per garantire alte prestazioni di cella. Infatti, la connessione ottimale tra tutti gli elementi della cella è uno dei criteri di progettazione più importanti. Oltre a questo, la compressione dell’idrogeno, volta ad uno stoccaggio efficiente, è una parte fondamentale della catena di approvvigionamento dell'idrogeno verde. L'elettrolisi dell'acqua ad alta pressione può alleviare questo problema garantendo la produzione di un gas già compresso all'interno dell'elettrolizzatore stesso, eliminando così la necessità di un compressore di idrogeno esterno con conseguente abbattimento dei costi.
In questo studio sono stati studiati gli effetti della pressione di bloccaggio sulla resistenza di contatto elettrico, sulla tenuta e sulle performance finali di una cella PEM avente area attiva di 25 cm2, variando gli spessori dei componenti di cella. Si sono messi a punto diversi assemblaggi tramite i quali è stato possibile raggiungere una resistenza di contatto elettrico minima di 216,40 mΩ∙cm2 e una densità di corrente massima di 2,552 A∙cm-2 (a 2,20 V) applicando una pressione di bloccaggio di 3,9 MPa, ad una temperatura operativa di 80°C a pressione atmosferica. Per di più è stato dimostrato che lavorare a pressione differenziale di 30 bar (lato catodico), ottenendo tassi di perdita accettabili (inferiori a 10-3 mbar∙l∙s-1) ed evitando, al contempo, possibili cedimenti strutturali della membrana, non è un compito facile. Le celle assemblate mostravano evidenti problemi di trasporto di massa e di calo di performance nel tempo. Questi fenomeni sono stati studiati e indagati mediante l’analisi di curve di polarizzazione (V-I) e l’impiego della spettroscopia elettrochimica ad impedenza (EIS). Questo lavoro ha permesso di dimostrare quanto la pressione di bloccaggio di cella, in relazione allo spessore e alla compressibilità dei materiali, sia un parametro molto importante in grado di influenzare direttamente le performance elettrochimiche e la tenuta dell’elettrolizzatore. Inoltre, si è provato quanto la messa a punto di un protocollo di test volto a valutare sin dal principio gli aspetti relativi alla tenuta dei fluidi e allo spessore dei componenti di cella sia estremamente importante.In terms of sustainability and environmental impact, Proton Exchange Membrane Water Electrolysis (PEMWE) is considered one of the technologies that will contribute to the efficient and versatile production of green hydrogen from renewable energy sources. Within a PEM cell, optimal distribution of clamping pressure is crucial to ensure high cell performance. In fact, the optimal connection between all cell components is one of the most important design criteria. In addition, hydrogen compression, aimed at efficient storage, is a fundamental part of the green hydrogen supply chain. High-pressure water electrolysis can alleviate this issue by ensuring the production of already compressed gas within the electrolyzer itself, thereby eliminating the need for an external hydrogen compressor and reducing costs.
This study investigated the effects of clamping pressure on electrical contact resistance, sealing, and final performance of a PEM cell with an active area of 25 cm2 by varying the thicknesses of cell components. Various assemblies were developed, allowing the achievement of a minimum electrical contact resistance of 216.40 mΩ∙cm2 and a maximum current density of 2.552 A∙cm-2 (at 2.20 V) by applying a clamping pressure of 3.9 MPa at an operating temperature of 80°C and atmospheric pressure. Furthermore, it was demonstrated that working at a differential pressure of 30 bar (on the cathodic side), achieving acceptable leakage rates (lower than 10-3 mbar∙l∙s-1), and avoiding potential structural membrane failures is not an easy task. The assembled cells exhibited evident mass transport issues and performance degradation over time. These phenomena were studied and investigated using polarization curves (V-I analysis) and electrochemical impedance spectroscopy (EIS). This work demonstrated how the clamping pressure, in relation to the thickness and compressibility of materials, is a highly influential parameter directly affecting the electrochemical performance and sealing of the electrolyzer. Additionally, the development of a testing protocol aimed at evaluating fluid sealing aspects and cell component thickness from the outset was proven to be extremely important
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