Optimalno korištenje energije sa socijalnog aspekta (Osvrt na esej Ivana Illicha Energy and Equity)

U eseju Energy and Equity Ivan Illich razrađuje tezu da svaki sustav, proces ili ljudska aktivnost raste ili se odvija do određenog praga nakon kojeg daljnji rast ili daljnje aktivnosti postaju kontraproduktivne. Illich ilustrira svoju tezu na primjeru transporta. Razvoj tehnike omogućuje sve veće brzine transportnih sredstava, no ljudi u prosjeku provode više vremena u transportu nego nekad. Dakle, brzina ne mora nužno značiti uštedu na vremenu. Upravo je brzina, a s tim povezana i potrošnja energije, ključan čimbenik koji čini transport socijalno destruktivnim jer izaziva društveno raslojavanje na one koji je mogu i ne mogu priuštiti. Budući da je stalan rast potrošnje energije nemoguć iz fizičkih, ekoloških i socijalnih razloga, Ivan Illich vidi budućnost čovječanstva u postindustrijskom društvu tehnološke zrelosti, oslobođenom obilja i ovisnosti o potrošnji

Experimental diagnostics and modeling of inductive phenomena at low frequencies in impedance spectra of proton exchange membrane fuel cells

Representation of fuel cell processes by equivalent circuit models, involving resistance and capacitance elements representing activation losses on both anode and cathode in series with resistance representing ohmic losses, cannot capture and explain the inductive loop that may show up at low frequencies in Nyquist diagram representation of the electrochemical impedance spectra. In an attempt to explain the cause of the low-frequency inductive loop and correlate it with the processes within the fuel cell electrodes, a novel equivalent circuit model of a Proton Exchange Membrane (PEM) fuel cell has been proposed and experimentally verified here in detail. The model takes into account both the anode and the cathode, and has an additional resonant loop on each side, comprising of a resistance, capacitance and inductance in parallel representing the processes within the catalyst layer. Using these additional circuit elements, more accurate and better fits to experimental impedance data in the wide frequency range at different current densities, cell temperatures, humidity of gases, air flow stoichiometries and backpressures were obtained

PEM fuel cells: theory and practice

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.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

Proton exchange membrane fuel cells

Includes bibliographical references and index.xvii, 518 p. :Suitable for engineers, technicians and students, this title covers fundamentals of design, electrochemistry, heat and mass transport, as well as provides the context of system design and applications. It covers various aspects of (Proton Exchange Membrane) PEM fuel cells, from theory and fundamentals to practical applications. "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 cell

D5.3: Condition monitoring and health assessment of PEM fuel cells

A novel equivalent circuit model is made by adding additional resonance loops comprising of a resistance, capacitance and inductance, for both anode and cathode, representing mass transport and resistive losses within the catalyst layer. Such a model is able to match and explain low frequency inductance observed in all Electrochemical Impedance Spectroscopy measurements taken during durability tests. The model was used to monitor the state of health of a fuel cell exposed to a controlled accelerated stress test. The results indicate that resistance, capacitance and inductance representing the cathode catalyst layer change dramatically during the accelerated stress test, and this shows good agreement with the findings of the periodic diagnostic tests

D5.1: Analysis of Degradation Mechanisms

PEM fuel cells degrade over time. The loss of cell potential is the most obvious symptom of degradation. Degradation may affect either one of the four major losses in fuel cells, namely activation polarization, ohmic losses, concentration polarization and hydrogen crossover losses. The report first addresses these symptoms, and then degradation mechanisms of different fuel cell components are discussed, namely catalyst and catalyst layer, membrane, and gas diffusion layer. For each of these some mitigation strategies are discussed. For each of degradation mechanism the key stressors are identified and standardized accelerated test protocols are presented. Experiments that were conducted at FESB with the goal of gaining practical experience and understanding of underlying degradation mechanisms. Two series of experiments were conducted with two of the most severe stressors, namely prolonged exposure to open circuit voltage, and potential cycling

FUELCELL2005 -74037 PRESSURE DROP ON THE CATHODE SIDE OF A PEM FUEL CELL AS A DIAGNOSTIC TOOL FOR DETECTION OF FLOODING AND DRYING CONDITIONS

ABSTRACT An increase in pressure drop on the cathode side of PEM fuel cell is a reliable indicator of PEM fuel cell flooding. Flooding, i.e., liquid water accumulation inside the cell causes a rather erratic cell potential behavior -steady voltage drops followed by sudden voltage increases. The pressure drop in this case behaves similarly, i.e., increases as the water accumulates, and drops as the water is expulsed from the cell, however with an obvious and detectable upward trend. In an opposite case of fuel cell drying, the cell potential steadily decreases as the ionic resistance increases, while the pressure drop initially decreases as the last of the liquid water is being expulsed, and thereafter remains constant. By monitoring both pressure drop and cell resistance in an operational fuel cell stack it was possible to reliably diagnose either flooding or drying conditions inside the stack, which were intentionally created by adjusting the humidification and stack temperatures. Pressure drop, therefore, may be used to define a control strategy, i.e. to make decisions on corrective actions. In most cases, the pressure drop is a linear function of flow rate when a single phase (gas) is flown through a fuel cell since the flow is well in the laminar regime. When the gas starts to carry water droplets, such as the case when the fuel cell operates with fully saturated gases, the pressure drop departs from linearity. In addition, slugs of water, possibly present inside the fuel cell passages, create unsteady conditions