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1
Kerekes, Rudolf. „Electrolyte flow rate control for Hydrogen Bromine Flow Batteries“. Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263240.
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The need for energy storage solutions became more significant with the increasing penetration of renewable energy sources in the electricity grid. In the last decades, the flow batteries have gained increasing attention. They have several advantages compared to the conventional battery technologies. Among these, the Hydrogen Bromine Flow Batteries offer a low cost energy storage solution by using globally abundant materials, since Hydrogen and Bromine can be found in large quantities in the oceans. This study was conducted to find out the relation between electrolyte flow rate and electrochemical cell performance and to give a suggestion for dynamic flow rate control to maximize the battery system performance. First, a theoretical model was built to describe the behaviour of the system in various conditions. However, the lack of information of the parameters led the research towards experimental analysis. A small scale system with cell power range of 10 to 14 W and pump power range of 2.6 to 6.8 W was built for the experiments to analyse the cell power at different flow rate values (122 ml/min, 185 ml/min and 230 ml/min). Also, the aim was to observe the gains of using dynamic flow rate (122 ml/min and 230 ml/min used at specific periods of the cycles). The results show that for small scale systems there is no net positive energy gain due to the small power of the battery compared to the power of the pump. However, there were improvements found in battery capacity with 28 % increase, and in Coulombic efficiency with 2.47 % increase, if the largerflow rate was used. Furthermore, a 55% pumping energy saving was reached if the dynamic flow rate was used instead of constant maximum flow rate. In addition, a large scale system was designed, which would be able to integrate a PID control concept for dynamic flow rate control in kW scale batteries. Further work will be required for building and testing the proposed large scale system, which tend to model a commercial size Hydrogen Bromine Flow Battery.Behovet av energilagringslösningar blev mer betydande med den ökande penetrationen av förnybara energikällor i elnätet. Under de senaste decennierna har flödesbatterierna fått ökad uppmärksamhet. De harflera fördelar jämfört med konventionella batteriteknologier. Då väte och brom finns i stora mängder i haven, erbjuder vätebromflödesbatterier en billig lösning för energilagring genom att använda globalt rikligt förekommande material. Denna studie genomfördes för att ta reda på sambandet mellan elektrolytflödeshastighet och elektrokemisk cellprestanda och för att ge ett förslag för dynamisk flödeshastighetskontroll för att maximera batterisystemets prestanda. Först byggdes en teoretisk modell för att beskriva systemets beteende under olika förhållanden. Emellertid ledde bristen på information om parametrarna forskningen mot experimentell analys. Ett småskaligt system med celleffektintervall från 10till 14 W och pumpeffektintervall på 2.6 till 6.8 W byggdes för experimenten för att analysera celleffekten vid olika flödeshastighetsvärden (122 ml / min, 185 ml / min och 230 ml / min). Syftet var också att observera vinsterna med att använda dynamisk flödeshastighet (122 ml / min och 230 ml / min använd vidspecifika perioder av cyklerna). Resultaten visar att för småskaliga system finns det ingen nettopositiv energivinst på grund av batteriets lilla effekt jämfört med pumpens effekt. Det fanns emellertid förbättringari batterikapacitet med en ökning på 28% och i Coulombic effektivitet med en ökning på 2.47% om den större flödeshastigheten användes. Det uppnåddes även en energibesparing på 55% om den dynamiska flödeshastigheten användes istället för konstant maximal flödeshastighet. Dessutom utformades ett storskaligt system som skulle kunna integrera ett PID-kontrollkoncept för dynamisk flödeshastighetskontroll i kW-skalbatterier. Ytterligare arbete kommer att krävas för att bygga och testa det föreslagna storskaliga systemet, som tenderar att modellera ett kommersiellt vätebromflödesbatteri.
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Feser, Joseph P. „Convective flow through polymer electrolyte fuel cells“. Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.77 Mb., 93 p, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1428199.
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Chivengwa, Tapiwa. „Microchannel flow fields for polymer electrolyte fuel cells“. Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/13674.
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Fuel cell technology represents an efficient and relatively quiet way of generating electricity. Among the various types of fuel cells, the polymer electrolyte fuel cell (PEFC) is the leading candidate for portable, automotive and more recently stationary applications. One of the key challenges affecting both the performance and durability of low temperature PEFCs is water management. Various water management strategies in PEFCs have been employed to date ranging from manipulation of operating conditions, fuel cell component design and flow field design to name a few. The optimisation of the flow field design for water removal has primarily focused on the use of flow channels which are in the minichannel range. This study investigated the use of a microchannel flow field design (channel hydraulic diameters of less than or equal to 200 ìm) for a low temperature PEFC. Specifically it focused on the effect of using a microchannel design on overall fuel cell performance, pressure drop and the cell voltage behaviour over time. In addition the effect of different operating conditions was also investigated. The overall aim was to develop a more comprehensive understanding of the use of a microchannel based flow field system with specific focus on water management. Fuel cell testing of two different flow field designs, namely a microchannel design and a more conventional commercial minichannel design, was performed in a single cell set up. Two operating conditions, cathode flow rate and cell compression, were varied and the effect on overall fuel cell performance and limiting current was investigated. Several diagnostic measurements including polarization curve, high frequency resistance, electrochemical impedance spectroscopy, pressure drop co-efficient and cell voltage monitoring were conducted to understand the water management behaviour and trends in the two different aforementioned flow field designs.
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Elfrink, Gideon. „Computer simulations of an all-organic electrolyte flow-battery“. Thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-438609.
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Melane, Xolani. „Visualisation of electrolyte flow fields in an electrolysis cell“. Diss., University of Pretoria, 2015. http://hdl.handle.net/2263/57492.
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The performance and efficiency of an electrochemical system with gas evolution can be related to the mass transfer effects which are influenced by the resulting two-phase flow. The aim of this investigation was to develop a better understanding in the effects of current density, anode height and inter-electrode spacing on the electrolyte flow patterns and to validate Computational Fluid Dynamic (CFD) model predictions of the electrolyte flow patterns. The CFD model was developed in a previous study and was applied to the experimental rig developed for this study, in which the electrolysis of copper sulphate was studied.
A direct flow visualisation technique was used as the method of investigation in the experimental work. To facilitate the visual observation of the electrolyte flow patterns, O2 gas bubbles evolved on the anode surface were used as the flow followers to track the electrolyte flow patterns. At the bottom of the anode where there was no gas evolution, polyamide seeding particles (PSP) were used as the flow followers. A Photron FASTCAM SA4 high speed camera with a capability of recording up to 5000 fps was used to record the electrolyte flow patterns and circulation. The Photron FASTCAM Viewer (PFV) camera software was used for the post analysis of the recordings and for measuring bubble size, bubble speed and the speed of the PSP tracking particles.
The experimental results were then compared with the results obtained from the CFD model simulation in order to validate the CFD model. The electrolysis cell was approximated by a simplified planar two-dimensional domain. The fluid flow patterns were assumed to be affected only by the change in momentum of the two fluids. To simplify the model, other physical, chemical and electro-magnetic phenomena were not modelled in the simulation. The Eulerian multiphase flow model was used to model the multiphase flow problem investigated.
The flow fields observed in the experiments and predicted by the model were similar in some of the positions of interest. The gas bubble flow field patterns obtained in the experiment and model were similar to each other in Position A (the top front of the anode), C (the area at the bottom of the cell below the anode), and D (the gap between the anode and the diaphragm), with the only exception being Position B (slightly above the anode top back). The experimental results showed an accumulation of the smaller gas bubbles in Position B with a resulting circulation loop across that region. On the other hand, the model predictions did not show this gas bubble accumulation and circulation in Position B.
All the flow patterns predicted for the electrolyte flow illustrated similar flow patterns to the ones observed in the experimental results, including the circulation loop in Position B. The bubble speeds measured at Position A in the experimental work had a reasonable agreement with the bubble speeds predicted by the model. The error between the two results ranged from 6% to 29% for the various cases which were tested.
An increase in the current density generated more gas bubbles which resulted in an increase in the bubble speed. Increasing the anode height increased the amount of gas bubbles generated as well as bubble speed while the bubble speed was decreased with an increasing inter-electrode distance.Dissertation (MEng)--University of Pretoria, 2015.
tm2016
Chemical Engineering
MEng
Unrestricted
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Leahy, Scott B. „Active Flow Control of Lab-Scale Solid Polymer Electrolyte Fuel Cells“. Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5188.
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The effects of actively pulsing reactant flow rates into solid polymer electrolyte fuel cells were investigated in this thesis. First, work was conducted to determine the magnitude of voltage response to pulsed reactant flow on a direct hydrogen proton exchange membrane (PEM) cell. The effects of pulsed reactant flow into a direct methanol fuel cell (DMFC) were then considered.
The PEM work showed substantially greater response to pulsed air flow than to pulsed fuel flow. It was found that several parameters affect the magnitude of cell response to active flow control (AFC). Increasing current load, increasing the magnitude of flow oscillation, decreasing the frequency of oscillation, and decreasing the average level of excess reactant supplied were found to maximize both the level of voltage oscillations and the decrease in cell power from steady state performance. Greater response to pulsed oxidant flow is believed to have been observed due to effects brought about by changes in membrane humidity.
In contrast, pulsed fuel flow showed the greatest response in the study of DMFC technology. In this case, time averaged cell voltage was found to increase as the time averaged fuel flow rate was reduced. The increase in average cell power is the result of a reduction in methanol crossover; sustainable increases of up to 6% in power output were measured. The parameters found to effect the increase in cell power observed include the frequency of oscillation and the time-averaged NOSfuel. Pulsed air flow on the DMFC did not show any such rise in voltage, supporting the hypothesis that a reduction in methanol crossover is the phenomenon which brings about enhanced performance.
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Takeuchi, Junichi. „Experimental investigation of magnetohydrodynamic turbulent pipe flow of aqueous electrolyte solution“. Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1835497681&sid=3&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Duranti, Mattia. „Bromine-Based Electrolyte Properties for a Semi-Organic Redox Flow Battery“. Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/276465.
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Redox Flow Batteries are chemical based energy storage systems that accumulate energy in liquid electrolytes. Dissolved redox active substances undergo redox reactions in an electrochemical cell and so charge and discharge a battery. Recently, the introduction of organic materials as electrolytes raised research interest. Electrolytes that operate with the bromine/bromide redox couple are interesting due to their high energy density and fast reversible kinetics. They are used in combination with several anodic chemistries (e.g. Zinc, Hydrogen, Quinone), including organic materials.Due to the corrosive and volatile nature of bromine, practical electrolytes use Bromine Complexing Agents (BCAs) in order to bind bromine in a less volatile form and deal with safety issues. These additives have a strong influence on the battery’s operation by influencing the concentration of redox active species, the cell voltage and the electrolyte conductivity. Nevertheless, very little is known about the real properties of aqueous acidic bromine electrolytes, both in pure dilution and in presence of BCAs, which influence on the electrolyte is not predictable so far.
The aim of this PhD project is to provide a comprehensive understanding of the behavior of an electrolyte based on bromine and bromide, with particular reference to the one used in semi-organic flow batteries. Along this work an analysis on the performance of a AQDS-Bromine flow battery cell was executed and an extensive study on the physico-chemical behavior of the positive electrolyte was
developed. A review of the flow battery technology and of the metrics and methods available for diagnostics was firstly performed as a basis to define macro characteristics,such as State of Charge (SoC) and State of Health (SoH). The cycling behavior of an AQDS-Bromine flow battery was investigated by cell tests and possible degradation mechanisms have been highlighted and explained by interpretation of electrochemical measurements. Following, a broad characterization of the bromine-based electrolyte was performed, producing extended experimental data on physico-chemical properties and a modeling framework for the prediction of the electrolyte behavior.
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Prifti, Helen Chemical Sciences & Engineering Faculty of Engineering UNSW. „Electrolyte and membrane studies of the novel vanadium bromide redox flow cell“. Awarded by:University of New South Wales. Chemical Sciences & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41478.
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The novel Vanadium Bromide (V/Br) redox flow cell employs a V (III)/V (II) couple in the negative half-cell and a Br/Br2 couple in the positive half-cell, with hydrobromic acid and hydrochloric acid as the supporting electrolyte. This study evaluated the chemical and electrochemical properties of the electrolytes and assessed experimental and commercial membranes for use in the V/Br flow cell. A number of techniques were employed to characterise the composition of the V/Br flow cell electrolytes. During charge, the conductivity of the positive half-cell electrolyte increased, whilst the density and viscosity increased. The reverse was observed for the negative half-cell. The UV-visible spectra of the electrolytes showed characteristic peak wavelengths of the vanadium oxidation states and provided and insight into the halogenated species forming during the operation of the V/Br flow cell. The electrochemical properties of the electrolytes were also examined using cyclic voltammetry. NMR studies examined the relationships between the 35CI and 79Br nuclei in the presence of halide and paramagnetic vanadium ions. It was established that the SOC and performance of the V/Br flow cell can be measured by changes in slllectral chemical shifts and line widths. Small-scale cycling experiments were conducted to evaluate the performance of ion exchange membranes in the V/Br redox flow cell. Of the membranes evaluated, a number were not suitable for use due to high membrane resistances or low chemical stability. The perfluorinated Nafion?? and Gore Select?? ion exchange membranes proved to be the most chemically inert and showed low resistances. The Gore Select?? membranes did however exhibit blistering during extended cycling. The chemical stability and cycling performance of the HiporeTM microporous separator showed promise for future studies to optimise the selectivity and ion exchange capacity of the membrane. Tests of membrane ion exchange capacity, diffusivity and conductivity mirrored the properties displayed in the cell cycling experiments. Results suggested that the structural characteristics of the membrane (including functionality and crosslinking) greatly influenced membrane properties and performance. Tests of long term stability showed a negative change in membrane properties. These changes did not however reflect measured changes during cell cycling experiments.
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Kramer, Denis. „Mass transport aspects of polymer electrolyte fuel cells under two-phase flow conditions“. Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:bsz:105-6973937.
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Die Visualisierung und Quantifizierung von Flüssigwasseransammlungen in Polymerelektrolytmembran-Brennstoffzellen konnte mittels Neutronenradiographie erreicht werden. Dank dieser neuartigen diagnostischen Methode konnte erstmals die Flüssigwasseransammlung in den porösen Gasdiffusionsschichten direkt nachgewiesen und quantifiziert werden. Die Kombination von Neutronenradiographie mit ortsaufgelösten Stromdichtemessungen bzw. lokaler Impedanzspektroskopie erlaubte die Korrelation des inhomogenen Flüssigwasseranfalls mit dem lokalen elektrochemischen Leistungsverhalten. Systematische Untersuchungen an Polymerelektrolyt- und Direkt-Methanol-Brennstoffzellen verdeutlichen sowohl den Einfluss von Betriebsbedingungen als auch die Auswirkung von Materialeigenschaften auf die Ausbildung zweiphasiger Strömungen.
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Kramer, Denis. „Mass transport aspects of polymer electrolyte fuel cells under two-phase flow conditions“. Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=984745246.
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Najibi, Seyed Hesam. „Heat transfer and heat transfer fouling during subcooled flow boiling for electrolyte solutions“. Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/773/.
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Kramer, Denis. „Mass transport aspects of polymer electrolyte fuel cells under two-phase flow conditions“. Freiberg : TU Bergakademie Freiberg, Fakultät Maschinenbau, Verfahrens- und Energietechnik, 2007. https://fridolin.tu-freiberg.de/archiv/html/MaschinenbauKramerDenis697393.html.
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Zhu, Huanfeng. „Experimental and Theoretical Aspects of Electrode Electrolyte Interfaces“. Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1259680393.
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Thesis(Ph.D.)--Case Western Reserve University, 2010Title from PDF (viewed on 2009-12-30) Department of Chemistry Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Ding, Yulong. „Numerical simulations of gas-liquid two-phase flow in Polymer Electrolyte Membrane fuel cells“. Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42648.
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Water management in PEM fuel cells has received extensive attention for its key role in fuel cell operation. Several water management issues have been identified that needed further investigation, i.e., droplet behaviour on the GDL surface, two-phase flow patterns in gas flow channels, impact of two-phase flow on PEM fuel cell performance, impact of flow mal-distribution on PEM fuel cell performance, and mitigation of flow maldistribution. In this work, those issues were investigated based on simulations using computational fluid dynamics (CFD) method.
Using the Volume of Fluid (VOF) two-phase flow model, droplet behaviour and two-phase flow patterns in mini-channels were identified consistently in both simulations and experimental visualizations. The microstructure of the GDL was found to play a significant role in the formation of local two-phase flow patterns, and the wettability of both GDL and channel wall materials greatly impacted on the two-phase flow patterns.
A novel 1+3D two-phase flow and reaction model was developed to study the impact of two-phase flow on PEM fuel cell performances. The existence of two-phase flow, especially the slug flow, in gas flow channels was found to be detrimental to the fuel cell performance and stability. Uneven liquid flow distribution into two parallel gas channels significantly reduces the fuel cell output voltage because of the induced severe non-uniform gas distribution, which should be avoided in the operation due to its negative effect on the fuel cell performance and durability.
Finally, several maldistribution mitigation methods were tested in the simulation. It was found that utilizing narrow communication channels or adding gas inlet resistances could effectively reduce the gas flow maldistribution.
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Friess, Brooks Regan. „Development of radial flow channel for improved water and gas management of cathode flow field in polymer electrolyte membrane fuel cell“. Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/40365.
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This thesis presents an innovative radial flow field design for PEMFC cathode flow plates. This new design, which is in the form of a radial field, replaces the standard rectangular flow channels in exchange for a set of flow control rings. The control rings allow for better flow distribution and use of the active area. The radial flow field was constructed with aluminum and plated with gold for superior surface and conductive properties. These materials were selected based on the results obtained from the performance of the standard flow channels of serpentine and parallel constructed of hydrophilic gold and hydrophobic graphite materials. The new flow field design provides a competitive performance compared to the current standard serpentine and parallel flow fields in a dry-air-flow environment. The polarization curves for a dry cathode reactant flow, however, shows excessive membrane drying with the radial design. Humidifying the air flow improves the membrane hydration while the fuel cell with the innovative radial flow field produces a higher limiting current density compared to other channel designs, even the serpentine flow field. The water removal and mass transport capacity of the radial flow field was proven to be better than parallel and serpentine. This performance increase was achieved while maintaining the pressure drop nearly half of the pressure drop measured in the serpentine flow fields. The initial results for this design show promising performance and further optimization and simplification of the design should improve the performance and allow for simpler manufacturing processes.
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Tranter, Thomas George. „A study of water management in polymer electrolyte fuel cells : compression effect on multiphase flow“. Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/16086/.
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One of the main obstacles to overcome regarding the uptake of renewable energy technologies, specifically wind and solar energy, is their intermittency. Current energy storage techniques are costly and in-efficient. Fuel cells are a promising candidate for future energy storage, as part of an integrated system combining renewable energy with hydrogen production as the storage vector with reconversion. The Polymer Electrolyte Fuel Cell (PEFC) has the greatest potential for use with micro-generated renewable power and is suitable for the widest range of applications. Hence it has received a great deal of attention from research institutions and industry over the last few decades. However, they suffer performance limitations due to flooding by liquid water in the porous components forming the electrodes of the cell. Two numerical investigations utilising different methods to probe multiphase transport in porous media, and one experimental investigation into the flow through partially saturated porous media, are presented. The porous media under investigation are typical materials for PEFC gas diffusion layers (GDLs), and the influence of compression of the material on the multiphase transport is investigated. In addition, a further study assessing the suitability of pore-scale capillary pressure models for predicting multiphase flow behaviour is included as a final research chapter.
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Burkholder, Michael B. „Nonlinear Analysis, Control, and Modeling of the Two-Phase Flow Dynamics in Polymer Electrolyte Fuel Cells“. Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/618.
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Polymer electrolyte fuel cells (PEFCs) generate clean, renewable power from hydrogen and oxygen with a byproduct of water. When the liquid water produced at the cathode is improperly removed, PEFCs experience unstable operation and power loss. Current techniques for cathode water removal result in excessive parasitic loads on the PEFC that contribute to high system costs. This thesis explores ways to improve the efficiency of PEFC cathode water management by developing a fundamental understanding of the dynamical stability of two-phase air and water ow in parallel cathode microchannels through experiments, analysis, and modeling. The dynamics of an experimental PEFC under varying degrees of cathode water removal were characterized by nonlinear invariants indicative of dynamical complexity and stability, the correlation dimension and Kolmogorov entropy. It was found that low-current operating conditionsm suffer from chaotic instability and performance loss due to cathode flooding. In order to detect and control dynamical instability in real time, a computationally-efficient reduced order Lyapunov exponent was formulated to indicate stability related to cathode water content. A stabilizing control algorithm was developed using feedback from real-time computation of the reduced order Lyapunov exponent of the PEFC voltage to trigger lowcost cathode pressure pulses. The control was demonstrated to stabilize flooding conditions with minimal parasitic expense for water removal. Two-phase air-water ow structures were visualized and pressure drops were measured in ex-situ microchannels under varying levels of transience. The pressure drops and their fluctuations were characterized with average values and fractal statistics, respectively, across air and water ow rates and ow regimes of relevance in PEFC operation. Dynamic pressure drop hysteresis was observed and measured, most likely for the first time. The statistical experimental results were used to develop a dynamical model of a PEFC cathode flow field with two-phase ow in parallel microchannels. The model included experimental values for two-phase pressure drops, a 1D + 1 PEFC model for water generation, and fractional Brownian motion for two-phase pressure uctuations. The model was used to understand ow maldistribution and Ledinegg instability in PEFC cathod flow fields, and to highlight methods for optimizing PEFC water management.
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Virk, M. S. „Numerical analyses of proton electrolyte membrane fuel cell's performance having a perforated type gas flow distributor“. Thesis, Coventry University, 2009. http://curve.coventry.ac.uk/open/items/6eb010bc-d336-930c-de60-2c9c24b64516/1.
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This thesis presents a compendium of work related to performance analyses of a proton electrolyte membrane (PEM) fuel cell with two novel design configurations. The finite element based numerical analysis has been carried out to solve the numerical transport models involved in a PEM fuel cell coupled with the flow in a porous medium, charge balance, electrochemical kinetics and membrane water content. The scope of this research work focuses on improving the performance of the PEM fuel cell by optimizing the thermo-fluid properties of the reactant species instead of analysing the complex electro-chemical interactions. Two new design configurations have been numerically analyzed; in the first design approach, a perforated-type gas flow distributor is used instead of a conventional gas flow distributor such as a serpentine, straight or spiral shape; the second design approach examines the effect of reactant flow pulsation on the PEM fuel cell performance. Results obtained from the numerical analyses were also compared with the experimental data and a good agreement was found. Performance of the PEM fuel cell with a perforated-type gas distributor was analyzed at different operating and geometric conditions to explore the merits of this new design configuration. Two-dimensional numerical analyses were carried out to analyze the effect of varying the different operating parameters; threedimensional numerical analyses were carried out to study the variation of different geometric parameters on overall performance of the new design configuration of the PEM fuel cell. The effects of the reactant flow pulsation on the performance of PEM fuel cell were analyzed using a two-dimensional numerical approach where both active and passive design configurations were numerically simulated to generate the pulsations in the reactant flow. The results showed a considerable increase in overall performance of the PEM fuel cell by introducing pulsations in the flow.
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Hays, Daniel George. „Testing of an Axial Flow Moisture Separator in a Turbocharger System for Polymer Electrolyte Membrane Fuel Cells“. Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7134.
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Proton exchange membrane (PEM) fuel cells, with low operating temperatures and high power density, are a reasonable candidate for use in mobile power generation. One large drawback to their use is that their fuel reformer requires not only fuel but also water, thereby requiring two separate reservoirs to be available. PEM fuel cells exhaust enough water in their oxidant stream to potentially meet the needs of the fuel reformer. If this water could be recovered and routed to the fuel reformer it would markedly increase the portability of PEM fuel cells.
The goal of this research was to test a previously designed axial flow moisture separator. The separator was employed in a test bed which utilized compressed, heated air mixed with steam to simulate the oxidant exhaust conditions of a 25 kW PEM fuel cell. The simulated exhaust was saturated with water. The mixture was expanded through the turbine side of an automotive turbocharger, which dropped the temperature and pressure of the mixture, causing water to condense, making it available for separation. The humid air mixture was passed over an axial flow centrifugal separator and water was removed from the flow.
The separator was tested in a variety of conditions with and without passing chilled water through the separator. The axial separator was tested independently, with a flow straightener preceding it, and with a commercially available centrifugal moisture separator in series following it. It was shown that cooling makes a significant impact on the separation rate while adding a flow straightener does not. Separation efficiencies of 19% on average were experienced without cooling, while efficiencies of 50% were experienced with 3.1 kW of cooling. The separation efficiency of the two moisture separators combined was found to be 31.7% which is 165% that of the axial separator alone under uncooled conditions.
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Haase, Stefan [Verfasser]. „Experimental investigations and numerical evaluations of the flow distribution in polymer electrolyte membrane fuel cells / Stefan Haase“. München : Verlag Dr. Hut, 2016. http://d-nb.info/110387215X/34.
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Wang, Yuhua. „Conductive Thermoplastic Composite Blends for Flow Field Plates for Use in Polymer Electrolyte Membrane Fuel Cells (PEMFC)“. Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2893.
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This project is aimed at developing and demonstrating highly conductive, lightweight, and low-cost thermoplastic blends to be used as flow field bipolar plates for polymer electrolyte membrane (PEM) fuel cells. The research is focused on designing, prototyping, and testing carbon-filled thermoplastic composites with high electrical conductivity, as well as suitable mechanical and process properties.
The impact of different types of fillers on the composite blend properties was evaluated, as well as the synergetic effect of mixtures of fill types within a thermoplastic polymer matrix. A number of blends were produced by varying the filler percentages. Composites with loadings up to 65% by weight of graphite, conductive carbon black, and carbon fibers were investigated. Research results show that three-filler composites exhibit better performance than single or two-filler composites.
Injection and compression molding of the conductive carbon filled polypropylene blend was used to fabricate the bipolar plates. A Thermal Gravimetric Analysis (TGA) was used to determine the actual filler loading of composites. A Scanning Electron Microscope (SEM) technique was use as an effective way to view the microstructure of composite for properties such as edge effects, porosity, and fiber alignment. Density and mechanical properties of conductive thermoplastic composites were also investigated. During this study, it was found that 1:1:1 SG-4012/VCB/CF composites showed better performance than other blends. The highest conductivity, 1900 S/m in in-plane and 156 S/m in through plane conductivity, is obtained with the 65% composite. Mechanical properties such as tensile modulus, tensile strength, flexural modulus and flexural strength for 65% 1:1:1 SG-4012/VCB/CF composite were found to be 584. 3 MPa, 9. 50 MPa, 6. 82 GPa and 47. 7 MPa, respectively, and these mechanical properties were found to meet minimum mechanical property requirements for bipolar plates. The highest density for bipolar plate developed in this project is 1. 33 g/cm³ and is far less than that of graphite bipolar plate.
A novel technique for metal insert bipolar plate construction was also developed for this project. With a copper sheet insert, the in-plane conductivity of bipolar plate was found to be significantly improved. The performance of composite and copper sheet insert bipolar plates was investigated in a single cell fuel cell. All the composites bipolar plates showed lower performance than the graphite bipolar plate on current-voltage (I-V) polarization curve testing. Although the copper sheet insert bipolar plates were very conductive in in-plane conductivity, there was little improvement in single cell performance compared with the composite bipolar plates.
This work also investigated the factors affecting bipolar plate resistance measurement, which is important for fuel cell bipolar plate design and material selection. Bipolar plate surface area (S) and surface area over thickness (S/T) ratio was showed to have significant effects on the significance of interfacial contact resistances. At high S/T ratio, the contact resistance was found to be most significant for thermoplastic blends. Other factors such as thickness, material properties, surface geometry and clamping pressure were also found to affect the bipolar plate resistance measurements significantly.
23
Borah, Deepjyoti Verfasser], Werner [Akademischer Betreuer] [Lehnert und Lorenz [Akademischer Betreuer] Singheiser. „Two-phase flow in porous transport layers of polymer electrolyte membrane electrolysers / Deepjyoti Borah ; Werner Lehnert, Lorenz Singheiser“. Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/1241891540/34.
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Caston, Terry Brett. „Design of a gas diffusion layer for a polymer electrolyte membrane fuel cell with a graduated resistance to flow“. Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34790.
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Due to escalating energy costs and limited fossil fuel resources, much attention has been given to polymer electrolyte membrane (PEM) fuel cells. Gas diffusion layers (GDLs) play a vital role in a fuel cell such as (1) water removal, (2) cooling, (3) structural backing, (4) electrical conduction and (5) transporting gases towards the active catalyst sites where the reactions take place. The power density of a PEM fuel cell in part is dependent upon how uniform the gases are distributed to the active sites. To this end, research is being conducted to understand the mechanisms that influence gas distribution across the fuel cell. Emerging PEM fuel cell designs have shown that higher power density can be achieved; however this requires significant changes to existing components, particularly the GDL. For instance, some emerging concepts require higher through-plane gas permeability than in-plane gas permeability (i.e., anisotropic resistance) which is contrary to conventional GDLs (e.g., carbon paper and carbon cloth), to obtain a uniform gas distribution across the active sites. This is the foundation on which this thesis is centered. A numerical study is conducted in order to investigate the effect of the gas permeability profile on the expected current density in the catalyst layer. An experimental study is done to characterize the effects of the weave structure on gas permeability in woven GDLs. Numerical simulations are developed using Fluent version 6.3.26 and COMSOL Multiphysics version 3.5 to create an anisotropic resistance profile in the unconventional GDL, while maintaining similar performance to conventional GDL designs. The effects of (1) changing the permeability profile in the in-plane and through-plane direction, (2) changing the thickness of the unconventional GDL and (3) changing the gas stoichiometry on the current density and pressure drop through the unconventional GDL are investigated. It is found that the permeability profile and thickness of the unconventional GDL have a minimal effect on the average current density and current density distribution. As a tradeoff, an unconventional GDL with a lower permeability will exhibit a higher pressure drop. Once the fuel cell has a sufficient amount of oxygen to sustain reactions, the gas stoichiometry has a minimal effect on increases in performance. Woven GDL samples with varying tightness and weave patterns are made on a hand loom, and their in-plane and through-plane permeability are measured using in-house test equipment. The porosity of the samples is measured using mercury intrusion porosimetry. It is found that the in-plane permeability is higher than the through-plane permeability for all weave patterns tested, except for the twill weave with 8 tows/cm in the warp direction and 4 tows/cm in the weft direction, which exhibited a through-plane permeability which was 20% higher than the in-plane permeability. It is also concluded that the permeability of twill woven fabrics is higher than the permeability of plain woven fabrics, and that the percentage of macropores, ranging in size from 50-400 µm, is a driving force in determining the through-plane permeability of a woven GDL. From these studies, it was found that the graduated permeability profile in the unconventional GDL had a minimal effect on gas flow. However, a graduated permeability may have an impact on liquid water transport. In addition, it was found that graduating the catalyst loading, thereby employing a non-uniform catalyst loading has a greater effect on creating a uniform current density than graduating the permeability profile.
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Khakdaman, Hamidreza. „A Two Dimensional Model of a Direct Propane Fuel Cell with an Interdigitated Flow Field“. Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22732.
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Increasing environmental concerns as well as diminishing fossil fuel reserves call for a new generation of energy conversion technologies. Fuel cells, which convert the chemical energy of a fuel directly to electrical energy, have been identified as one of the leading alternative energy conversion technologies. Fuel cells are more efficient than conventional heat engines with minimal pollutant emissions and superior scalability. Proton Exchange Membrane Fuel Cells (PEMFCs) which produce electricity from hydrogen have been widely investigated for transportation and stationary applications.
The focus of this study is on the Direct Propane Fuel Cell (DPFC), which belongs to the PEMFC family, but consumes propane instead of hydrogen as feedstock. A drawback associated with DPFCs is that the propane reaction rate is much slower than that of hydrogen. Two ideas were suggested to overcome this issue: (i) operating at high temperatures (150-230oC), and (ii) keeping the propane partial pressure at the maximum possible value. An electrolyte material composed of zirconium phosphate (ZrP) and polytetrafluoroethylene (PTFE) was suggested because it is an acceptable proton conductor at high temperatures. In order to keep the propane partial pressure at the maximum value, interdigitated flow-fields were chosen to distribute propane through the anode catalyst layer.
In order to evaluate the performance of a DPFC which operates at high temperature and uses interdigitated flow-fields, a computational approach was chosen. Computational Fluid Dynamics (CFD) was used to create two 2-D mathematical models for DPFCs based on differential conservation equations. Two different approaches were investigated to model species transport in the electrolyte phase of the anode and cathode catalyst layers and the membrane layer. In the first approach, the migration phenomenon was assumed to be the only mechanism of proton transport. However, both migration and diffusion phenomena were considered as mechanisms of species transport in the second approach. Therefore, Ohm's law was used in the first approach and concentrated solution theory (Generalized Stefan-Maxwell equations) was used for the second one. Both models are isothermal.
The models were solved numerically by implementing the partial differential equations and the boundary conditions in FreeFEM++ software which is based on Finite Element Methods. Programming in the C++ language was performed and the existing library of C++ classes and tools in FreeFEM++ were used. The final model contained 60 pages of original code, written specifically for this thesis.
The models were used to predict the performance of a DPFC with different operating conditions and equipment design parameters. The results showed that using a specific combination of interdigitated flow-fields, ZrP-PTFE electrolyte having a proton conductivity of 0.05 S/cm, and operating at 230oC and 1 atm produced a performance (polarization curve) that was (a) far superior to anything in the DPFC published literature, and (b) competitive with the performance of direct methanol fuel cells. In addition, it was equivalent to that of hydrogen fuel cells at low current densities (30 mA/cm2).
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Zhu, Wei. „Molecular dynamics simulation of electrolyte solution flow in nanochannels and Monte Carlo simulation of low density CH 3 Cl monolayer on graphite“. Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1072284612.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xiv, 90 p.; also includes graphics. Includes abstract and vita. Advisor: Sherwin J. Singer, Dept. of Chemistry. Includes bibliographical references (p. 86-90).
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Laska, Claudius Alexander [Verfasser], Karl J. J. [Akademischer Betreuer] Mayrhofer und Wolfgang [Akademischer Betreuer] Schuhmann. „Development of a scanning flow cell system with dynamic electrolyte change for fully automated parameter screening / Claudius Alexander Laska. Gutachter: Karl J. J. Mayrhofer ; Wolfgang Schuhmann“. Bochum : Ruhr-Universität Bochum, 2015. http://d-nb.info/1079843752/34.
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Modiba, Portia. „Electrolytes for redox flow battery systems“. Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/3999.
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Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010.Electrochemical behaviour of Ce, Fe, Cr,V and Mn in the presence of DTPA, EDTA, EDDS, NTA ligands were investigated by using cyclic voltammetry, a rotating disc electrode and electrochemical impedance spectroscopy for use in redox flow battery (RFB) systems. RFB is currently used for energy storage, the vanadium, which is used in most of the RFB’s, however suffers from species crossover and sluggish reactions, which limit the lifetime of the battery. These various ligands and metal complexes mentioned above where all examined to identify the suitable and favoured electrolyte that can be used for a RFB system. Kinetic parameters such as potential, limiting current, transfer coefficient, diffusion coefficients, and rate constants were studied. RDE experiments confirmed that the parameters measured by CV are similar under hydrodynamic conditions and can be used to determine the kinetic parameters of the redox couples. The use of DTPA as a ligand for complexation of Ce(IV) gave more favourable results compared to other ligand with various metal complexes used in this study [1-3]. The results of kinetic studies of Ce(IV)–DTPA complex shows promise as an electrolyte for a redox flow battery. The separation of V(IV)/(V), Fe (III)/(IV),Cr(III)/(IV),Mn (III)/(IV) and Ce(III)/(IV) with various ligands (EDTA, EDDS, NTA and DTPA) were also investigated using capillary electrophoresis. To understand the speciation of these metal complexes as used in this study and particularly the vanadium, for the reason that it has a complicated (V) oxidation state. The charge/discharge performance of all electrolytes used in this work was determined and a high voltage achieved when Ce-DTPA was used, and it is compared to that of the vanadium electrolyte currently in use. This was evaluated with systems studied previously. Therefore, Ce-DTPA will be a suitable electrolyte for redox flow battery systems.
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Skoglund, Emil. „A NUMERICAL MODEL OF HEAT- AND MASS TRANSFER IN POLYMER ELECTROLYTE FUEL CELLS : A two-dimensional 1+1D approach to solve the steady-state temperature- and mass- distributions“. Thesis, Mälardalens högskola, Framtidens energi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-55223.
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Methods of solving the steady state characteristics of a node matrix equation system over a polymer electrolyte fuel cell (PEFC) were evaluated. The most suitable method, referred to as the semi-implicit method, was set up in a MATLAB program. The model covers heat transfer due to thermal diffusion throughout the layers and due to thermal advection+diffusion in the gas channels. Included mass transport processes cover only transport of water vapor and consist of the same diffusion/advection schematics as the heat transfer processes. The mass transport processes are hence Fickian diffusion throughout all the layers and diffusion+advection in the gas channels. Data regarding all the relevant properties of the layer materials were gathered to simulate these heat- and mass transfer processes.Comparing the simulated temperature profiles obtained with the model to the temperature profiles of a previous work’s model, showed that the characteristics and behavior of the temperature profile are realistic. There were however differences between the results, but due to the number of unknown parameters in the previous work’s model it was not possible to draw conclusions regarding the accuracy of the model by comparing the results.Comparing the simulated water concentration profiles of the model and measured values, showed that the model produced concentration characteristics that for the most part alignedwell with the measurement data. The part of the fuel cell where the concentration profile did not match the measured data was the cathode side gas diffusion layer (GDL). This comparison was however performed with the assumption that relative humidity corresponds to liquid water concentration, and that this liquid water concentration is in the same range as the measured data. Because of this assumption it was not possible to determine the accuracy of the model.
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Miller, Mallory A. „FUNDAMENTAL FLOW BATTERY STUDIES: ELECTRODES AND ELECTROLYTES“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case148224641339497.
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Chakrabarti, B. K. „Investigation of Electrolytes for a Novel Redox Flow Battery“. Thesis, University of Manchester, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522622.
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Bae, C. H. „Cell design and electrolytes of a Novel Redox flow battery“. Thesis, University of Manchester, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509374.
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Mallinson, Sarah L. „Tailoring electrolytes and ion permeable membranes for potential redox flow battery applications“. Thesis, University of Surrey, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616326.
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Energy storage is a solution to the problem of renewable energy intermittency. The vanadium redox flow battery (VRFB) is one such energy storage technology, allowing energy to be stored electrochemically in vanadium electrolytes until required. The advantages of VRFBs include independently scalable energy and power characteristics, high reliability and long life time. The broad aim of this work was to investigate the main problems VRFBs currently present: 1. temperature stability of the vanadium electrolyte, and 2. chemical stability and vanadium cation permeability issues of the ion permeable separator membrane. It was determined that the concentrations of vanadium and sulfuric acid in the electrolyte have a greater impact on thermal stability than the presence of additives. Decreasing the sulfuric acid concentration, improves cold temperature stability of the vanadium electrolyte without impeding stability at elevated temperature.
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Escalante, García Ismailia Leilani. „Fundamental and Flow Battery Studies for Non-Aqueous Redox Systems“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1425046485.
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Huang, Zhifeng [Verfasser]. „Organic redox-active flow batteries enabled by aqueous ionic liquid electrolytes / Zhifeng Huang“. Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1219068624/34.
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Lee, Juhan [Verfasser], und Volker [Akademischer Betreuer] Presser. „Redox electrolytes for non-flow electrochemical energy storage / Juhan Lee ; Betreuer: Volker Presser“. Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2018. http://d-nb.info/117121281X/34.
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Zhang, Yonglai [Verfasser], und Rolf [Akademischer Betreuer] Hempelmann. „Ionic liquids based aqueous electrolytes for redox flow batteries / Yonglai Zhang ; Betreuer: Rolf Hempelmann“. Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://d-nb.info/1194928528/34.
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Zhang, Yonglai Verfasser], und Rolf [Akademischer Betreuer] [Hempelmann. „Ionic liquids based aqueous electrolytes for redox flow batteries / Yonglai Zhang ; Betreuer: Rolf Hempelmann“. Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://d-nb.info/1194928528/34.
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Schrage, Briana Rae. „Ferrocenes and Isoindolines as Reagents for Redox Flow Battery Electrolytes and Moieties in Chromophores, Chelates, and Macrocycles“. University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1621518169239914.
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Akcali, Fikri. „Experimental Investigation Of Flow Separation From Rigid Walls With Salient Edges“. Master's thesis, METU, 2004. http://etd.lib.metu.edu/upload/1097971/index.pdf.
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This thesis presents the experimental results on the formation of flow separation from a rigid wall with a salient edge. In the case of automotive vehicles or aircrafts with rear cargo compartment doors, such salient edges are at the origin of separated wake flows resulting in increased drag and other disturbing effects. Recent studies of Ahmed et al. (1984) on simplified geometries showed the strong influence of the slant angle on the flow separations. In this study, the geometry is further simplified to examine the flow separation under two-dimensional conditions. The experimental configuration consists
of a fixed horizontal front panel and an attached rear panel with variable slant angle. The experiments were carried out in a low speed water channel to analyze the flow structure by flow visualization techniques. The hydrogen bubble technique nd PIV measurements are used to obtain both qualitative and quantitative information on the flow structure. The electrolytic precipitation technique is used to analyze the flow separation in more detail. The slant angle varied between 0 and 35 degrees while the Reynolds numbers of the model was fixed to 24800 and 50500. As a function of slant angle and Reynolds number, two different types of flow separation were observed: boundary layer separation due to adverse pressure gradient and the so called &ldquoinertial separation&rdquo
at the edge singularity. Future strategies to control the formation of the wake flow highly depend on the very different flow structure of these two types of separation.
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Thakore, Vaibhav. „Nonlinear dynamic modeling, simulation and characterization of the mesoscale neuron-electrode interface“. Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5529.
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Extracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron-microelectrode cleft. This has made it difficult to correlate the extracellularly recorded signals with the intracellular signals recorded using conventional patch-clamp electrophysiology. For bringing about an improvement in the signal-to-noise ratio of the signals recorded on the extracellular microelectrodes and to explore strategies for engineering the neuron-electrode interface there exists a need to model, simulate and characterize the cell-sensor interface to better understand the mechanism of signal transduction across the interface. Efforts to date for modeling the neuron-electrode interface have primarily focused on the use of point or area contact linear equivalent circuit models for a description of the interface with an assumption of passive linearity for the dynamics of the interfacial medium in the cell-electrode cleft. In this dissertation, results are presented from a nonlinear dynamic characterization of the neuroelectronic junction based on Volterra-Wiener modeling which showed that the process of signal transduction at the interface may have nonlinear contributions from the interfacial medium. An optimization based study of linear equivalent circuit models for representing signals recorded at the neuron-electrode interface subsequently proved conclusively that the process of signal transduction across the interface is indeed nonlinear. Following this a theoretical framework for the extraction of the complex nonlinear material parameters of the interfacial medium like the dielectric permittivity, conductivity and diffusivity tensors based on dynamic nonlinear Volterra-Wiener modeling was developed. Within this framework, the use of Gaussian bandlimited white noise for nonlinear impedance spectroscopy was shown to offer considerable advantages over the use of sinusoidal inputs for nonlinear harmonic analysis currently employed in impedance characterization of nonlinear electrochemical systems. Signal transduction at the neuron-microelectrode interface is mediated by the interfacial medium confined to a thin cleft with thickness on the scale of 20-110 nm giving rise to Knudsen numbers (ratio of mean free path to characteristic system length) in the range of 0.015 and 0.003 for ionic electrodiffusion. At these Knudsen numbers, the continuum assumptions made in the use of Poisson-Nernst-Planck system of equations for modeling ionic electrodiffusion are not valid. Therefore, a lattice Boltzmann method (LBM) based multiphysics solver suitable for modeling ionic electrodiffusion at the mesoscale neuron-microelectrode interface was developed. Additionally, a molecular speed dependent relaxation time was proposed for use in the lattice Boltzmann equation. Such a relaxation time holds promise for enhancing the numerical stability of lattice Boltzmann algorithms as it helped recover a physically correct description of microscopic phenomena related to particle collisions governed by their local density on the lattice. Next, using this multiphysics solver simulations were carried out for the charge relaxation dynamics of an electrolytic nanocapacitor with the intention of ultimately employing it for a simulation of the capacitive coupling between the neuron and the planar microelectrode on a microelectrode array (MEA). Simulations of the charge relaxation dynamics for a step potential applied at t = 0 to the capacitor electrodes were carried out for varying conditions of electric double layer (EDL) overlap, solvent viscosity, electrode spacing and ratio of cation to anion diffusivity. For a large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appears to be purely an effect of nanoscale confinement. Results from these simulations are then discussed in the context of the dynamics of the interfacial medium in the neuron-microelectrode cleft. In conclusion, a synergistic approach to engineering the neuron-microelectrode interface is outlined through a use of the nonlinear dynamic modeling, simulation and characterization tools developed as part of this dissertation research.Ph.D.
Doctorate
Physics
Sciences
Physics
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Vukasin, Julien. „Modélisation des transferts de masse et de chaleur dans une cellule d'électrolyse de production de fluor“. Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT132.
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Modélisation des transferts de masse et de chaleur dans une cellule d'électrolyse de production de fluor. La production de fluor par électrolyse est une étape clé de la conversion de l’uranium dans l’industrie nucléaire. Afin d’optimiser ce procédé, les travaux de thèse décrits dans ce manuscrit se sont concentrés sur deux axes : le développement d’un modèle numérique de l’électrolyseur et l’étude du phénomène d’hyperpolarisation cathodique néfaste pour le bon fonctionnement de la cellule. Un modèle couplant plusieurs physiques (thermique avec solidification, diphasique, électrocinétique) a été développé et des essais expérimentaux ont été menés afin d’acquérir, d’une part, certaines propriétés physiques de l’électrolyte nécessaires aux simulations (conductivité thermique et capacité thermique à pression constante) et, d’autre part, des données expérimentales permettant de qualifier le modèle obtenu. Ce travail de modélisation a abouti à l’obtention d’un modèle 3D fiable couplant les physiques citées précédemment, ceci à l’échelle d’un pilote R&D semi-industriel. L’impact de la solidification de l’électrolyte sur le transfert de chaleur a également pu être simulé pour la première fois. Ces essais ont également permis de fournir des premières explications sur le phénomène d’hyperpolarisation cathodique en dressant des tendances claires quant à l’influence de certains paramètres de contrôle de l’électrolyseur comme le titre HF et la température de consigneComputer modeling of heat transfer and mass transfer in an electrolytic cell for production of fluorineElectrolytic production of fluorine is a key step in uranium conversion for the nuclear industry. In order to improve this process, the work described in this dissertation aims at two main objectives: to build a numerical simulation of the electrolysis cell and to understand the cathodic hyperpolarization effect which lowers the productivity of the cell. A model coupling several physics (heat transfer with solidification, two-phase flow, electrokinetics) has been developed and experiments were made in order to evaluate unknown physical properties of the electrolyte (thermal conductivity and heat capacity at constant pressure). Experimental data were also acquired in order to assess the capacity of the model to simulate various phenomena occurring inside the cell. Eventually, a reliable 3D model of a semi-industrial R&D cell coupling the physics above mentioned has been obtained. The negative impact of the solidification of the electrolyte on the cooling system was simulated for the first time. Thanks to these experiments, it was also possible to determine the major trends which drive the cathodic hyperpolarization effect. The influence of HF mass fraction and temperature on this phenomenon was clearly shown
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Soreefan, Aurelie M. „Development of an original laboratory prototype for a field tritium detector containing a PEM electrolyzer, mounted in series with a gas flow proportional counter“. Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1246565666/.
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Baumann, Lars. „Improved system models for building-integrated hybrid renewable energy systems with advanced storage : a combined experimental and simulation approach“. Thesis, De Montfort University, 2015. http://hdl.handle.net/2086/11103.
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The domestic sector will play an important role in the decarbonisation and decentralisation of the energy sector in the future. Installation numbers of building-integrated small-scale energy systems such as photovoltaics (PV), wind turbines and micro-combined heat and power (CHP) have significantly increased. However, the power output of PV and wind turbines is inherently linked to weather conditions; thus, the injected power into the public grid can be highly intermittent. With the increasing share of renewable energy at all voltage levels challenges arise in terms of power stability and quality. To overcome the volatility of such energy sources, storage technologies can be applied to temporarily decouple power generation from power consumption. Two emerging storage technologies which can be applied at residential level are hydrogen systems and vanadium-redox-flow-batteries (VRFB). In addition, the building-integrated energy sources and storage system can be combined to form a hybrid renewable energy system (HRES) to manage the energy flow more efficiently. The main focus of this thesis is to investigate the dynamic performance of two emerging energy storage technologies, a hydrogen loop composed of alkaline electrolyser, gas storage and proton exchange membrane (PEM) fuel cell, and a VRFB. In addition, the application of building-integrated HRES at customer level to increase the self-consumption of the onsite generated electricity and to lower the grid interaction of the building has been analysed. The first part deals with the development of a research test-bed known as the Hybrid Renewable Energy Park (HREP). The HREP is a residential-scale distributed energy system that comprises photovoltaic, wind turbine, CHP, lead acid batteries, PEM fuel cell, alkaline electrolyser and VRFB. In addition, it is equipped with programmable electronic loads to emulate different energy consumption patterns and a charging point for electric vehicles. Because of its modular structure different combinations of energy systems can be investigated and it can be easily extended. A unified communication channel based on the local operating network (LON) has been established to coordinate and control the HREP. Information from the energy systems is gathered with a temporal resolution of one second. Integration issues encountered during the integration process have been addressed. The second part presents an experimental methodology to assess the steady state and dynamic performance of the electrolyser, the fuel cell and the VRFB. Operational constrains such as minimum input/output power or start-up times were extracted from the experiments. The response of the energy systems to single and multiple dynamic events was analysed, too. The results show that there are temporal limits for each energy system, which affect its response to a sudden load change or the ability to follow a load profile. Obstacles arise in terms of temporal delays mainly caused by the distributed communication system and should be considered when operating or simulating a HRES at system level. The third part shows how improved system models of each component can be developed using the findings from the experiments. System models presented in the literature have the shortcoming that operational aspects are not adequately addressed. For example, it is commonly assumed that energy systems at system level can respond to load variations almost instantaneously. Thus, component models were developed in an integrated manner to combine theoretical and operational aspects. A generic model layout was defined containing several subsystems, which enables an easy implementation into an overall simulation model in MATLAB®/Simulink®. Experimental methods were explained to extract the new parameters of the semi-empirical models and discrete operational aspects were modelled using Stateflow®, a graphical tool to formulate statechart diagrams. All system models were validated using measured data from the experimental analysis. The results show a low mean-absolute-percentage-error (<3%). Furthermore, an advanced energy management strategy has been developed to coordinate and to control the energy systems by combining three mechanisms; statechart diagrams, double exponential smoothing and frequency decoupling. The last part deals with the evaluation, operation and control of HRES in the light of the improved system models and the energy management strategy. Various simulated case studies were defined to assess a building-integrated HRES on an annual basis. Results show that the overall performance of the hydrogen loop can be improved by limiting the operational window and by reducing the dynamic operation. The capability to capture the waste heat from the electrolyser to supply hot water to the residence as a means of increasing the overall system efficiency was also determined. Finally, the energy management strategy was demonstrated by real-time experiments with the HREP and the dynamic performance of the combined operation has been evaluated. The presented results of the detailed experimental study to characterise the hydrogen loop and the VRFB as well as the developed system models revealed valuable information about their dynamic operation at system level. These findings have relevance to the future application and for simulation studies of building-integrated HRES. There are still integration aspects which need to be addressed in the future to overcome the proprietary problem of the control systems. The innovations in the HREP provide an advanced platform for future investigations such as electric-vehicles as decentralised mobile storage and the development of more advanced control approaches.
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Khodayari, Mehdi [Verfasser]. „Fuel Cells, Metal/Air Batteries : characterization of dual thin-layer flow through cell and determination of solubility and diffusion coefficient of oxygen in aqueous and non-aqueous electrolytes / Mehdi Khodayari“. Bonn : Universitäts- und Landesbibliothek Bonn, 2015. http://d-nb.info/1077290101/34.
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Safa, Meer. „3D study of non-metallic inclusions by EEmethod and use of statistics for the estimationof largest size inclusions in tool steel“. Thesis, KTH, Materialvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93770.
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The control of non-metallic inclusions is very important for the improvement of performance during the application of tool steel. This present study was performed to see the effect of changing of some process parameters during the vacuum degassing of the melt and how these changing parameters affects the characteristics of inclusions in tool steel. The main parameters that were changed during the vacuum degassing were the change of induction stirring, argon flow rate from both the plug 1 and 2 and different ladle ages for different heat. Electrolytic extraction method was used to observe the morphology and characteristics of inclusions as a 3 dimensional view in tool steel. Four lollipop samples from four different heats were used for the experiment and all the samples were after vacuum (AV) degassing. In this study four different types of inclusions were found and they are classified as type 1, 2, 3 and 4. Of them type 1 inclusion was the major one with mostly spherical shaped. This study shows that among the three parameters, induction stirring has the biggest effect for the total number of inclusions per volume in the sample than the other two parameters Heat 4A showed the lowest number of inclusions per volume comparing with the other heats. The main reason behind this can be said that the induction stirring was the lowest comparing with the other heats with moderate argon flow and ladle age of 12. Extreme value analysis was used in this study to predict the probability of getting largest size inclusions in a certain volume of the metal. For the prediction of the largest inclusion size, both the electrolytic extraction (3D) and cross-sectional (2D) method was used. Later in this study comparison was done to determine the accuracy of both the methods and it is concluded that for the type 1 inclusions electrolytic extraction method shows almost similar trend with cross-sectional method and electrolytic extraction method shows better accuracy for the prediction of largest size inclusions than the cross-sectional method. Electrolytic Extraction method is also applicable for the prediction of largest size inclusions for multiple types of inclusions.
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Horvath, A. Elisabet. „The effects of cellulosic fiber charges on polyelectrolyte adsorption and fiber-fiber interactions“. Doctoral thesis, Stockholm : Department of Fibre and Polymer Technology, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4158.
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Boissonneau, Patrick. „Propulsion MHD en eau de mer : étude des couplages hydrodynamique-électrochimie-électromagnétisme“. Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10079.
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La magnetohydrodynamique (mhd) permet de realiser des propulseurs a reaction fournissant des flux d'eau de mer a grande vitesse sans helice ni piece mecanique en mouvement. En appliquant a un ecoulement d'eau de mer des champs magnetique et electrique, on produit directement au sein de l'ecoulement des forces electromagnetiques (laplace) qui propulsent le navire. Malheureusement l'eau de mer est un electrolyte : le passage des courants amenes par des electrodes entraine une electrolyse non desiree. Le travail presente se consacre a l'etude des couplages suivants : - influence de l'hydrodynamique parietale sur l'electrochimie de l'eau de mer - influence du degagement de micro-bulles sur la couche limite turbulente - determination des courants et des forces au sein de l'ecoulement les parties experimentales reposent sur la confrontation des mesures sur electrodes de platine en cellule d'electrolyse avec des mesures sur electrodes de titane platine en ecoulement reel. Nous avons associe aux mesures traditionnelles electriques et electrochimiques, l'analyse de la production de bulles (electrolyse) et de ses consequences sur l'ecoulement (velocimetrie granulometrie laser doppler & visualisation). Les parties theoriques, touchant l'electrochimie, font une synthese des connaissances et permettent d'identifier les mecanismes dominants et d'expliquer les resultats experimentaux. La partie calcul numerique, concernant le couplage : ecoulement/champs electromagnetiques, repose sur la confrontation de resultats de modeles globaux dedies avec des simulations faites a l'aide de fluent, logiciel commercial (volumes finis 2d).
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Aubras, Farid. „Contribution à l’étude de l’influence des régimes bi-phasiques sur les performances des électrolyseurs de type PEM basse pression : approche numérique, analytique et expérimentale“. Thesis, La Réunion, 2018. http://www.theses.fr/2018LARE0011/document.
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Les électrolyseurs à membrane échangeuse de protons basse pression (E-PEMs) apparaissent comme une solution efficace et durable pour la production d’hydrogène. Cette technologie pourrait permettre de pallier l’intermittence des énergies renouvelables (notamment solaire et éolien) en convertissant l’énergie électrique produite en énergie chimique (hydrogène). Durant ces travaux de thèse, trois aspects ont été développés : une approche analytique, une approche numérique, ainsi que approche expérimentale. Ces trois approches ont permis de comprendre l’influence du mélange bi-phasique eau/oxygène à l’anode du système sur les performances électrochimiques des E-PEMS ainsi que déterminer les paramètres opérationnels et intrinsèques qui impactent les performances des E-PEMs. À propos de l'approche expérimentale, des mesures d'impédance électrochimique ainsi que des courbes de polarisation ont été réalisées sur deux différentes cellules d'électrolyseurs de type PEM basse pression (la cellule ITW power de l'Electrochimical innovation Lab (UCL) et la cellule réversible Q-URFC du Laboratoire d'Énergétique, d'Électronique et Procédés (LE2P). À propos de la modélisation numérique, Le modèle expérimentale conjugue une approche multi-échelle macroscopique 2D et mésoscopique 1D. Ce modèle prend en compte le transfert de matière, le transfert de chaleur, les réactions électrochimiques anodique et cathodique et le transfert de charges présents dans le cœur des E-PEMs. D’un point de vue mésoscopique, une attention particulière a été portée sur l’influence des régimes bi-phasiques anodiques (régime de bulles coalescées (BC régime) et régime de bulles non coalescées (NCB régime) sur le transfert de matière à l’anode et sur l’humidification de la membrane. Ces travaux démontrent et confirment l’hypothèse que la transition du NCB régime vers le CB régime augmente le transfert de matière anodique, diminue la résistance ohmique de la membrane et améliore l’efficacité des E-PEMs. À propos de la modèle analytique, l’étude analytique explore une approche adimensionnelle de l'assemblage membrane électrode (AME) en régime stationnaire et isotherme. À l’échelle locale, en 1D, les équations prises en compte sont la conservation du courant dans l’AME, les réactions électrochimiques au sein des couches actives et le transfert de matière à travers la membrane. La résolution a permis d’obtenir des expressions analytiques des surtensions aux électrodes, de la chute ohmique et de la teneur en eau dans la membrane. L’approche adimensionnelle a permis de quantifier analytiquement les sources d’irréversibilités (chute ohmique, surtensions d’activations anodique et cathodique, et de la surtension induite par le bouchonnement des canaux anodiques) respectivement pour les faibles densités de courant, les moyennes densités de courant et les hautes densités de courant. En outre, ce modèle analytique peut être implémenté dans une boucle de contrôle commande. Ces travaux de thèse proposent une contribution à la compréhension du fonctionnement des E-PEMs basse pression en général, et en particulier de l'impact des régimes bi-phasiques sur leurs performances électro-chimiquesBased on proton conduction of polymeric electrolyte membrane (PEM) technology, the water electrolysis (PEMWE) offers an interesting solution for efficiency hydrogen production. During the electrolysis process of water in PEMWE, the anodic side is the place where the water is splitting into oxygen, protons and electrons. The aim of this study is to recognize the link between two-phase flows (anode side) and cell performance under low pressure conditions. We have developed three approaches: the analytical approach and the numerical approach validated by the experimental data. For the numerical model, we have developed a two-dimensional stationary PEMWE model that takes into account electro-chemical reaction, mass transfer (bubbly flow), heat transfer and charges balance through the Membrane Electrodes Assembly (MEA). In order to take into account the changing electrical behavior, our model combines two scales of descriptions: at microscale within anodic active layer and MEA scale. The water management at both scales is strongly linked to the slug flow regime or the bubbly flow regime. Therefore, water content close to active surface areas depends on two-phase flow regimes. Our simulation results demonstrate that the transition from bubble to slug flow in the channel is associated with improvement in mass transport, a reduction of the ohmic resistance and an enhancement of the PEMWE efficiency. Regarding the analytical model, we have developed a one-dimensional stationary isothermal PEMWE model that takes into account electro-chemical reaction, mass transfer and charges balance through the Membrane Electrodes Assembly (MEA). The analytical approach permit to obtain mathematical solution of the activation overpotential, the ohmic losses and the bubbles overpotential respectively for the low current density, the middle current density and the high current density. This approach quantify the total overpotential of the cell, function of the operational and intrinsic numbers. In terms of perspective, the analytical model could be used for the diagnostic of the electrolyzer PEM
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Tung, Cheng-hsiang, und 董成祥. „Study on Flow Field of Electrolyte of Water Electrolysis“. Thesis, 2008. http://ndltd.ncl.edu.tw/handle/bd54dz.
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碩士國立中央大學
能源工程研究所
96
In order to probe into the effect of electrolyte fluid field on electrolysis, magnetite and water pump are used to let 1M KOH electrolyte generating vortex and internal flow in the electrobath. The experimental results are discussed to understand the interaction between electrolyte fluid field and electrolysis. At first, in the part of vortex flow, the vortex are ranged among 0RPM~1100RPM and the applied voltages are ranged among 2V~5V.When the rotation rate is 100RPM, the experimental results show that there is a maximum current density enhancement about 3.4%.In addition, as the rotation rate is among 100RPM and 1100RPM,the current density decreases. Moreover, at the rotation rate of 400RPM, the current density is minimum. In the part of internal flow, the circulating rates of electrolyte are ranged among 0ml/s~65ml/s and the applied voltages are ranged among 2v~5v. The electrolyte flows in either parallel or normal to the electrodes. The experimental results show that there is a maximum current density enhancement about 23%, and the best circulating rate of electrolyte occurres for every current density. There are no difference in current density between parallel flow and crossed flow. The biggest difference between vortex flow and internal flow is that the circulation generated by the vortex will drag the electrolysis gases from escaping from the electrobath, and this causes serious polarization phenomenon that does not occur in internal flow.