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Hidrodinâmica do escoamento nos canais catódicos de uma célula a combustível de membrana polimérica condutora de prótons; Hydrodynamics flow channels in the cathode of a proton exchange membrane fuel cell

Skoda, Sandro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 27/08/2014 PT
Relevância na Pesquisa
66.22%
Este trabalho tem por objetivo estudar as regiões dos canais catódicos de uma célula a combustível de membrana polimérica condutora de prótons PEM unitária, em que há acúmulo de água e os padrões de escoamento desta água nos canais, bem como as condições de operação em que isto ocorre. Esta água acumulada nos canais catódicos tem duas origens distintas, a saber: 1. água produzida na reação de redução do oxigênio no sítio catalítico do cátodo, 2. água de condensação formada a partir do vapor de água proveniente do umidificador de oxigênio. O arranjo experimental desenvolvido permitiu a perfeita visualização dos fenômenos; a saber: iniciando-se com gotículas que emergem da camada de difusão gasosa do cátodo, passando estas gotículas a se aglutinarem por um processo de coalescimento aumentando de tamanho até formarem um filme nas paredes dos canais. Em continuidade a este processo há um adensamento do filme com a formação de bolsões (slugs) de água líquida que ocupam a área de passagem do oxigênio nos canais. O bloqueio da passagem do oxigênio pelo bolsão de água líquida no canal impede que o oxigênio alcance os sítios catalíticos da camada catalítica do cátodo onde ocorre a reação de redução do oxigênio...

Estudos de eletrocatalisadores  baseados em Pt, Mo e W como ânodos tolerantes ao CO em célula a combustível de membrana trocadora de prótons (PEMFC); Study of Pt, Mo and W based electrocatalysts as CO tolerant anodes in proton exchange membrane fuel cell (PEMFC)

Hassan, Ayaz
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/02/2015 PT
Relevância na Pesquisa
66.17%
Elevada tolerância ao CO e alta estabilidade são necessário para o eletrocatalisador anódico de células a combustível de membrana protônica (PEMFC) para o melhoramento do desempenho do sistema operando com combustível reformado. Neste trabalho eletrocatalisadores suportados em carbono e carbetos (carbetos de molibdênio e tungstênio) foram estudados para a reação de oxidação de hidrogênio (ROH), a tolerância ao CO e a estabilidade no ânodo de PEMFC. Os materiais investigados incluem: PtMo/C, PtMo/C tratado-termicamente, Pt/Mo2C/C, PtMo/Mo2C/C, PtW/C, Pt/WC/C e Pt/C. As diferenças na morfologia dos eletrocatalisadores foram caracterizadas por redução com temperatura programada (TPR), difração de raios-x (XRD), microscopia eletrônica de transmissão (MET), energia dispersiva de raios-x (EDX), espectroscopia de absorção de raios-x (XAS), microscopia eletrônica de varredura (MEV) e espectroscopia de dispersão de comprimento de onda (WDS). As características e as atividades eletroquímicas dos electrocatalisadores foram avaliadas para ROH e tolerância ao CO por medidas de curvas de polarização em célula unitária e voltametria cíclica, sob a forma de elétrodos de difusão de gás. Espectrometria de massa (EMS) "on-line" e experimentos de stripping de CO foram realizados para avaliar o mecanismo de tolerância ao CO dos eletrocatalisadores. Voltametria cíclica conduzida até 5000 ciclos voltamétricos foi realizada para avaliar a estabilidade dos eletrocatalisadores. Tanto o eletrocatalisador de PtMo suportado em carbono e tratado a 600ºC...

Estudo dos parâmetros operacionais de uma célula a combustível de glicerol direto utilizando uma membrana de polibencimidazol impregnada com ácido fosfórico (PBI/H3PO4) ou 1-hexil-3-metilimidazol trifluorometanosulfo; Study of the operating parameters of a direct glycerol fuel cell using a polibenzimidazole membrane impregnated with phosphoric acid (PBI/H3PO4) or 1-hexyl-3-methylimidaolium trifluoromethanesulfonate (PBI/HMI-Tf)

Barrientos, Wilner Valenzuela
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/07/2015 PT
Relevância na Pesquisa
66.19%
Com o aumento da população mundial, o desenvolvimento de novas fontes e conversores de energia tornou-se uma necessidade. As células a combustível mostram-se como uma alternativa viável devido principalmente a duas razões, sua alta eficiência e a utilização de combustíveis renováveis. No presente trabalho se estuda a influência da temperatura de operação e o conteúdo de álcali no combustível sobre a densidade de potencia para uma célula a combustível de glicerol direto. Como combustível foi utilizado uma solução de glicerol:KOH (1M:xM, x=0, 1, 3, 5), como membranas foram utilizados filmes de polibencimidazol impregnado com ácido fosfórico (PBI/H3PO4, relação molar 1:11) ou 1-hexil-3-metilimidazol trifluorometanosulfonato (PBI/HMI-Tf relação molar 1:1.5), e finalmente, nano partículas de Pt suportadas em carbono (60% w/w) como catalizador no ânodo e no cátodo. Em geral, o incremento da temperatura e conteúdo de álcali no combustível mostra um efeito favorável na densidade de potencia do sistema. Numa célula a combustível unitária de glicerol direto utilizando membranas de PBI/ H3PO4 e PBI/HMI-Tf foram obtidas densidades de potencia de 0.54mW.cm-2 a 175°C e 0.599mW.cm-2 a 130°C, respectivamente...

Study of fuel cell co-generation systems applied to a dairy industry

Leal, E. M.; Silveira, J. L.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 102-108
ENG
Relevância na Pesquisa
66.18%
This paper presents a methodology for the study of a molten carbonate fuel cell co-generation system. This system is applied to a dairy industry of medium size that typically demands 2100 kW of electricity, 8500 kg/h of saturated steam (P = 1.08 MPa) and 2725 kW of cold water production. Depending on the associated recuperation equipment, the co-generation system permits the recovery of waste heat, which can be used for the production of steam, hot and cold water, hot and cold air. In this study, a comparison is made between two configurations of fuel cell co-generation systems (FCCS). The plant performance has been evaluated on the basis of fuel utilisation efficiency and each system component evaluated on the basis of second law efficiency. The energy analysis presented shows a fuel utilisation efficiency of about 87% and exergy analysis shows that the irreversibilities in the combustion chamber of the plant are significant. Further, the payback period estimated for the fuel cell investment between US$ 1000 and US$ 1500/k-W is about 3 and 6 years, respectively. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Celulas a combustivel a gas de biomassa : modelagem de sistemas e comparação com turbinas a gas; Fuel cell to biomass gas : modelling of systems and comparison with gas turbines

Alexandre Sordi
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/02/2007 PT
Relevância na Pesquisa
66.23%
O objetivo desse trabalho foi a modelagem de sistemas de células a combustível (CaCs) operando com o gás de gaseificação de biomassa. Dois tipos de CaCs foram consideradas no estudo: a PEMFC (Proton Exchange Membrane Fuel Cell) e a SOFC (Solide Oxide Fuel Cell). A primeira opera com hidrogênio de alta pureza e a concentração permissível de monóxido de carbono no gás combustível é de 10 _mol.mol-1; então, o sistema deve conter módulos de reforma e purificação da mistura gasosa. A segunda, devido à alta temperatura de operação, pode usar a mistura gasosa diretamente sem restrição quanto ao monóxido de carbono. A metodologia consistiu na análise termodinâmica dos sistemas modelados, visando determinar as irreversibilidades nos processos e as eficiências de primeira e segunda lei; isto foi feito considerando misturas gasosas produzidas por diferentes processos de gaseificação. O estudo demonstrou a importância de um reator de reforma para o desempenho exergético do sistema PEMFC. Neste, respectivamente as eficiências de primeira e de segunda lei variaram de 39% a 41% e de 26% a 31%, a máxima eficiência de segunda lei ocorre quando o gás de gaseificação apresenta menor fração molar de nitrogênio. Para o sistema SOFC as respectivas eficiências variaram de 48% a 51% e de 34% a 39%. A comparação com o sistema de turbina a gás demonstrou que este é superior em eficiência quando opera em ciclo STIG e o reator de gaseificação é pressurizado. Por outro lado o sistema SOFC é o mais eficiente se as turbinas operarem em ciclo simples e com gaseificador pressurizado; The objective of this work was to model fuel cell systems with biomass gasification gas. Two types of fuel cells were considered in the study: PEMFC (Proton Exchange Membrane Fuel Cell) and SOFC (Solide Oxide Fuel Cell). The first uses high-purity hydrogen and the maximum carbon monoxide concentration in the fuel gas it is 10 _mol.mol-1. Therefore...

MEA degradation in PEM Fuel Cell : a joint SEM and TEM study

Silva, R. A.; Hashimoto, T.; Thompson, G. E.; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em 10/11/2011 ENG
Relevância na Pesquisa
66.18%
One of the important factors determining the lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is membrane electrode assembly (MEA) degradation and failure. The lack of effective mitigation methods is largely due to the currently very limited understanding of the underlying mechanisms for mechanical and chemical degradations of fuel cell MEAs. This work reports on the effect of 1500 h operation of an eight-cell stack Portuguese prototype low power fuel cell. A performance decrease of 34%, in terms of maximum power, was found at the end of testing period. A post-mortem analysis by SEM and TEM was done for most cells of the fuel cell. Loss of the PTFE ionomer in the anode and cathode catalytic layers; morphological changes in the catalyst surfaces such as loss of porosity and platinum aggregation, deformation on the MEA components (anode, cathode and membrane) were identified. Others, like delamination and cracking were also detected. Catalyst migration and agglomeration on the interface of the electrodes was observed at cells 2, 4, 6 and 7. A platinum band was also detected on the membrane at 2 μm apart from the anode of cell 4. In some cases, dissolution occurred with re-deposition of the platinum particles with facet

Water management in a passive direct methanol fuel cell

Oliveira, V. B.; Falcão, D. S.; Rangel, C. M.; Pinto, A. M. F. R.
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artigo de Revista Científica
Publicado em //2013 ENG
Relevância na Pesquisa
66.17%
Passive direct methanol fuel cells (DMFCs) are under development for use in portable applications because of their enhanced energy density in comparison with other fuel cell types. The most significant obstacles for DMFC development are methanol and water crossover because methanol diffuses through the membrane generating heat but no power. The presence of a large amount of water floods the cathode and reduces cell performance. The present study was carried out to understand the performance of passive DMFCs, focused on the water crossover through the membrane from the anode to the cathode side. The water crossover behaviour in passive DMFCs was studied analytically with the results of a developed model for passive DMFCs. The model was validated with an in-house designed passive DMFC. The effect of methanol concentration, membrane thickness, gas diffusion layer material and thickness and catalyst loading on fuel cell performance and water crossover is presented. Water crossover was lowered with reduction on methanol concentration, reduction of membrane thickness and increase on anode diffusion layer thickness and anode and cathode catalyst layer thickness. It was found that these conditions also reduced methanol crossover rate. A membrane electrode assembly was proposed to achieve low methanol and water crossover and high power density...

Experiment and numerical simulation on the performance of a kw-scale molten carbonate fuel cell stack

Yu,L. J.; Ren,G. P.; Jiang,X. M.; Yuan,J. Q.; Cao,G. Y.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2007 EN
Relevância na Pesquisa
66.18%
A high-temperature molten carbonate fuel cell stack was studied experimentally and computationally. Experimental data for fuel cell temperature was obtained when the stack was running under given operational conditions. A 3-D CFD numerical model was set up and used to simulate the central fuel cell in the stack. It includes the mass, momentum and energy conservation equations, the ideal gas law and an empirical equation for cell voltage. The model was used to simulate the transient behavior of the fuel cell under the same operational conditions as those of the experiment. Simulation results show that the transient temperature and current and power densities reach their maximal values at the channel outlet. A comparison of the modeling results and the experimental data shows the good agreement.

Thermodynamic simulation of biomass gas steam reforming for a solid oxide fuel cell (SOFC) system

Sordi,A.; Silva,E. P. da; M. Neto,A. J.; Lopes,D. G.; Pinto,C. S.; Araújo,P. D.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2009 EN
Relevância na Pesquisa
66.17%
This paper presents a methodology to simulate a small-scale fuel cell system for power generation using biomass gas as fuel. The methodology encompasses the thermodynamic and electrochemical aspects of a solid oxide fuel cell (SOFC), as well as solves the problem of chemical equilibrium in complex systems. In this case the complex system is the internal reforming of biomass gas to produce hydrogen. The fuel cell input variables are: operational voltage, cell power output, composition of the biomass gas reforming, thermodynamic efficiency, electrochemical efficiency, practical efficiency, the First and Second law efficiencies for the whole system. The chemical compositions, molar flows and temperatures are presented to each point of the system as well as the exergetic efficiency. For a molar water/carbon ratio of 2, the thermodynamic simulation of the biomass gas reforming indicates the maximum hydrogen production at a temperature of 1070 K, which can vary as a function of the biomass gas composition. The comparison with the efficiency of simple gas turbine cycle and regenerative gas turbine cycle shows the superiority of SOFC for the considered electrical power range.

Microstructured electrolyte membranes to improve fuel cell performance

Wei, Xue (1982 - ); Yates, Matthew Z.
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xx, 153 leaves; Illustrations:ill.
ENG
Relevância na Pesquisa
66.19%
Thesis (Ph. D.)--University of Rochester. Dept. of Chemical Engineering, 2011.; Fuel cells, with the advantages of high efficiency, low greenhouse gas emission, and long lifetime are a promising technology for both portable power and stationary power sources. The development of efficient electrolyte membranes with high ionic conductivity, good mechanical durability and dense structure at low cost remains a challenge to the commercialization of fuel cells. This thesis focuses on exploring novel composite polymer membranes and ceramic electrolytes with the microstructure engineered to improve performance in direct methanol fuel cells (DMFCs) and solid oxide fuel cells (SOFCs), respectively. Polymer/particle composite membranes hold promise to meet the demands of DMFCs at lower cost. The structure of composite membranes was controlled by aligning proton conducting particles across the membrane thickness under an applied electric field. The field-induced structural changes caused the membranes to display an enhanced water uptake, proton conductivity, and methanol permeability in comparison to membranes prepared without an applied field. Although both methanol permeability and proton conductivity are enhanced by the applied field, the permeability increase is relatively lower than the proton conductivity improvement...

Modelling the Effect of Liquid Water Transport on PEM Fuel Cell Performance

VEYRET Damien
Fonte: Ulf Bossel, European Fuel Cell Forum Publicador: Ulf Bossel, European Fuel Cell Forum
Tipo: Contributions to Conferences Formato: CD-ROM
ENG
Relevância na Pesquisa
66.21%
Water management is essential for PEM (Proton Exchange Membrane) fuel cell performance. Nafion® based membranes in fuel cells operating up to 90°C demand high hydration levels to exhibit good proton conductivity. However, too much of water present in fuel cell electrodes and GDLs (Gas Diffusion Layer) may lead to pore-blockage preventing efficient gas and water transport to and from reaction sites. Experimentally, water transport is difficult to quantify. In-situ visualization techniques usually do not distinguish regions of water production, condensation, and blockage during fuel cell operation. CFD (Computational Fluid Dynamics) modelling however can overcome this drawback because at the same time water and gas transport, electrochemical reactions and electric conduction can be simulated. In this paper a water transport model for PEM fuel cells is described and the effect of water transport for different flow field designs and different operation conditions (e.g. inlet gas humidity) on fuel cell performance are studied.; JRC.DDG.F.2-Cleaner energy

Towards a Membrane Electrode Assembly for a Thermally Regenerative Fuel Cell

Skerritt, Mark
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
66.23%
The thermally regenerative fuel cell (TRFC) concept that is analyzed is a polymer electrolyte membrane fuel cell (PEMFC), powered by the electro-oxidation of H2 and the electro-reduction of propiophenone. The main products of this fuel cell should be 1-phenyl-1-propanol and electricity. The 1-phenyl-1-propanol should then be converted back to propiophenone, while hydrogen is regenerated by using waste heat and a metal catalyst (Pd/SiO2). The first objective was to find a compatible polymer that would work as either an ionomer/binding agent and as a membrane in the membrane electrode assembly (MEA) of the TRFC. This was achieved by checking the compatibility of each polymer with 1-phenyl-1-propanol and propiophenone (the alcohol-ketone pair). Catalyst coated gas diffusion layers or catalyst coated membranes were made to test the stability of the polymers in the catalyst bed when exposed to the alcohol-ketone pair. If the polymer was compatible with the alcohol-ketone pair, MEAs were constructed using this polymer. The second objective was to test these MEAs inside a H2/propiophenone fuel cell that would prove the concept of our envisioned TRFC. It was found that the only polymer that was stable in the alcohol-ketone pair was mPBI (m-phenylene polybenzimidazole). The mPBI had to be doped with H3PO4 to enable H+ conductivity. Unfortunately...

Fuzzy logic based energy management strategy for a fuel cell/battery/ultra-capacitor hybrid ship

ZHU, Lisi; PENG, Dongkai; HAN, jingang; WANG, Tianzhen; TANG, Tianhao; CHARPENTIER, Jean-Frederic
Fonte: IEEE Publicador: IEEE
EN
Relevância na Pesquisa
66.2%
In this paper, energy management strategy based on fuzzy logic is proposed for a fuel cell hybrid ship, combining proton exchange membrane fuel cell (PEMFC), battery and ultra-capacitor (UC). This hybrid system aims to optimize power distribution among each energy unit. The simulation model of the fuel cell hybrid power system is established in the MATLAB/SIMULINK simulation environment. The fuzzy logic energy strategy is verified by simulation according to the typical drive cycle of ship. The simulation results show that the proposed energy management strategy is able to satisfy power required by the ship, reduce the dynamic load of fuel cell, maintain the state of charge (SOC) of battery and SOC of the UC, and optimize the performance, fuel economy and efficiency of the hybrid system; The research is supported by the program of the National Natural Science Foundation (No.61304186 and No.51007056).

Characterization of two-phase flow in a transparent PEM fuel cell using simultaneous anode and cathode visualization and digital image processing

Sergi, Jacqueline
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
66.24%
Proton exchange membrane (PEM) fuel cells have emerged as a potential alternative to internal combustion engines in order to curb dependency on fossil fuels and reduce harmful CO2 emissions. Water management has been identified as a key research area for the advancement of PEM fuel cell technology, especially as it affects the purge protocol prior to cell shutdown. The presence of water in the cell is necessary to sustain membrane hydration, but the accumulation of excess liquid water, referred to as flooding, can lead to increased mass transport losses and reductions in performance and durability. In this work, a technique was developed to characterize the two-phase flow in the anode and cathode flow field channels simultaneously using a transparent fuel cell with dual-visualization capability. The transparent fuel cell used in this work was designed to represent actual full scale automotive fuel cell geometry. A video processing algorithm was developed to automatically detect dynamic and static liquid water present in the gas channels and generate relevant quantitative information. The water coverage ratio is introduced as a parameter to capture the time-averaged flow field water content information through recorded video sequences. The algorithm also yields information pertaining to the distribution of water among different two-phase flow structures. The water coverage ratio and distribution metrics were employed in comparing the performance of Freudenberg and Toray gas diffusion layers (GDLs) from a water management perspective...

Robust control strategies for hybrid solid oxide fuel cell systems

Allag, Tahar
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Relevância na Pesquisa
66.23%
Solid Oxide Fuel Cell (SOFC) systems are electrochemical energy conversion devices characterized by the use of solid oxide as the electrolyte. They operate at high temperatures (between 800± ¡ 1000±C). Mitigating fuel starvation and improving load-following capability of SOFCs are conflicting control objectives. In this thesis, this issue is addressed using a hybrid SOFC ultra-capacitor configuration. The fuel cell is controlled by incorporating a steady-state property of fuel utilization into an input-shaping framework. Two comprehensive control strategies are developed. The first is a Lyapunov-based nonlinear control and the second is a standard H-infinity robust control. Both strategies additionally control the state of charge (SOC) of the ultra-capacitor that provides transient power compensation. A hardware-in-the-loop test-stand is developed where the proposed control strategies are verified. An investigation to improve the hybrid fuel cell system by incorporating a lithium-ion battery as an additional power source is conducted. Combining both battery and ultra-capacitor with a fuel cell is potentially a winning combination especially for high power applications. A novel SOC estimation method for lithium-ion battery is investigated. Based on the combined ultra-capacitor battery hybrid system...

Effect of temperature on the in-plane permeability of the gas diffusion layer of a PEM fuel cell

Banerjee, Rupak
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
66.23%
Proton Exchange Membrane (PEM) Fuel Cells convert hydrogen into water by causing electrochemical reaction with oxygen, producing an electric current which can be used to power electric motors. This is seen as a viable alternative to the Internal Combustion Engine which operates on fossil fuels and is often blamed for contribution to the global climate change. Due to the low temperature operation, compared to other forms of fuel cells, it is possible to adapt the PEM Fuel Cell for automotive application. By running on hydrogen, the PEM Fuel Cell promises to enable a clean mode of transport. Water vapor transport inside the fuel cell takes place by two primary mechanisms: diffusion and permeability. Diffusion is important in the through-plane direction, whereas permeability is most important in the in-plane direction. Some work has been done to measure the permeability; it has been correlated with the porosity. However, the work has focused on the permeability at room temperature for ease of measurement. The PEM fuel cell works most efficiently between 60⁰C and 95⁰C. In this work, we direct our efforts at verifying whether there is any change in permeability in the in-plane direction with change of temperature. The in-plane permeability has been measured at 25⁰C...

Assessment of bio-fuel options for solid oxide fuel cell applications

Lin, Jiefeng
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Dissertação
EN_US
Relevância na Pesquisa
66.29%
Rising concerns of inadequate petroleum supply, volatile crude oil price, and adverse environmental impacts from using fossil fuels have spurred the United States to promote bio-fuel domestic production and develop advanced energy systems such as fuel cells. The present dissertation analyzed the bio-fuel applications in a solid oxide fuel cell-based auxiliary power unit from environmental, economic, and technological perspectives. Life cycle assessment integrated with thermodynamics was applied to evaluate the environmental impacts (e.g., greenhouse gas emission, fossil energy consumption) of producing bio-fuels from waste biomass. Landfill gas from municipal solid wastes and biodiesel from waste cooking oil are both suggested as the promising bio-fuel options. A nonlinear optimization model was developed with a multi-objective optimization technique to analyze the economic aspect of biodiesel-ethanol-diesel ternary blends used in transportation sectors and capture the dynamic variables affecting bio-fuel productions and applications (e.g., market disturbances, bio-fuel tax credit, policy changes, fuel specification, and technological innovation). A single-tube catalytic reformer with rhodium/ceria-zirconia catalyst was used for autothermal reformation of various heavy hydrocarbon fuels (e.g....

Characterization of mass transport processes to enable PEM fuel cell start-up from low temperatures

Harris, Daniel I.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
66.3%
A PEM fuel cell assembly requires the simultaneous delivery of reactants to the electrodes of multiple cells in order to produce electrical power. The mass transport of reactants to the electrode surfaces is complicated by the presence of liquid water during operation in low temperature environments. The water transport characteristics of an operational fuel cell were experimentally determined to build a low ambient temperature control strategy for a full scale automotive application. Two key topics for fuel cell control are covered: (a) purge of the fuel cell at shutdown, and (b) the fuel cell stack power management during freeze-start. After a PEMFC system is shut down, excess liquid water is often present in the MEA and flow field. Upon exposure to sub-freezing temperatures, this water can block the flow of reactants to the cell and prevent the fuel cell system from operating. To mitigate the effects of residual water in the fuel cell, this study tests the effects of various parameters during shutdown purge on freeze-start reliability. Both cell orientation and water content in the membrane-electrode assembly (as inferred by measurement of high frequency resistance) were shown to influence freeze-start reliability. The transport of product water away from the cell electrodes during start-up is significantly limited at lower temperatures (below about 45 °C)...

Robust adaptive control for a hybrid solid oxide fuel cell system

Snyder, Steven
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
66.19%
Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices. They offer a number of advantages beyond those of most other fuel cells due to their high operating temperature (800-1000 ° C), such as internal reforming, heat as a byproduct, and faster reaction kinetics without precious metal catalysts. Mitigating fuel starvation and improving load-following capabilities of SOFC systems are conflicting control objectives. However, this can be resolved by the hybridization of the system with an energy storage device, such as an ultra-capacitor. In this thesis, a steady-state property of the SOFC is combined with an input-shaping method in order to address the issue of fuel starvation. Simultaneously, an overall adaptive system control strategy is employed to manage the energy sharing between the elements as well as to maintain state-of-charge of the energy storage device. The adaptive control method is robust to errors in the fuel cell's fuel supply system and guarantees that the fuel cell current and ultra-capacitor state-of-charge approach their target values and remain uniformly, ultimately bounded about these target values. Parameter saturation is employed to guarantee boundedness of the parameters. The controller is validated through hardware-in-the-loop experiments as well as computer simulations.

Comparative bioelectricity generation from waste citrus fruit using a galvanic cell, fuel cell and microbial fuel cell

Khan,Abdul Majeed; Obaid,Muhammad
Fonte: Journal of Energy in Southern Africa Publicador: Journal of Energy in Southern Africa
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2015 EN
Relevância na Pesquisa
66.22%
This article demonstrates the new approaches for the generation of bioelectricity from waste citrus fruit using direct a galvanic cell (DGC), an indirect galvanic cell (IDGC), a conventional fuel cell (CFC) and a microbial fuel cell (MFC). The citrus fruit was used as whole for the preparation of DGC and their juices for the preparation of IDGC, CFC and MFC. The performance and bioelectrical parameters obtained were compared. The voltage found to be increased by increasing the number of cells in a series while, the current remains constant. Whereas the voltage remains constant and the current found to be increased with increasing the number of cells in parallel sequence. The power output of three units of citrus fruit connected together in a series found to be sufficient to turn on the LED light bulb in all cases. The result showed that lemons have the maximum power output by the DGC and MFC method, whereas grapefruit showed the maximum power output by IDGC, and thus considered as the best citrus fruit. Addition of NaCl solution in DGC and IDGC slightly increased the values of power output. The power output of citrus fruit was also determined by CFC and MFC before and after the inoculation of Escherichia coli. The detailed microscopic analysis of all the samples was carried out. It is found that all MFCs have higher power output as compared to their counterpart CFCs. However...