This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management. Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained. A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved. Keywords:Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis.

<p>This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management.</p><p>Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained.</p><p>A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved.</p><p><b>Keywords:</b>Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis.</p>

A presente proposta visa examinar a formação histórica do conceito de célula visual. Pretendemos delimitar o estudo ao caso das células fotorreceptoras (cones e bastonetes). Em meados da década de 1860 a teoria vigente sobre o processo perceptivo era a das energias específicas dos nervos proposta por Johannes Müller (1801-1858) e desenvolvida posteriormente por Hermann Von Helmholtz (1821-1894). Examinaremos em nossa pesquisa a formação do conceito de tipos específicos de células nervosas associadas aos processos perceptivos (o foco do trabalho são as células do sistema visual). Esse debate envolve a formação dos conceitos de córtex visual, sistema visual, informação nervosa e célula nervosa. O período examinado será o entorno das duas últimas décadas do século XIX (décadas de 1880 e 1890), período em que Ferruccio Tartuferi (1852-1925) propõe a constituição híbrida da retina em 1887 e é marcada também pela formulação da teoria neuronal (teoria formulada principalmente pelo espanhol Santiago Ramón y Cajal) / The objective of the present study is to examine the historical formation of the visual cell concept, focussing on the the study of photoreceptor cells (cones and rods). In the mid-1860s, the current theory about the perceptual process was that of the specific energies of nerves proposed by Johannes Müller (1801-1858) and later developed by Hermann Von Helmholtz (1821-1894). Our research will examine the formation of the concept of specific types of nerve cells associated with perceptual processes (the focus of the work are the cells of the visual system). This debate involves the formation of the concepts of visual cortex, visual system, nervous information and nerve cell. The period examined will be the last two decades of the nineteenth century (1880s and 1890s), a period in which Ferruccio Tartuferi (1852-1925) proposed the hybrid constitution of the retina in 1887 and also marked by the formulation of neuronal theory mainly by the Spaniard Santiago Ramón y Cajal

A presente proposta visa examinar a formação histórica do conceito de célula visual. Pretendemos delimitar o estudo ao caso das células fotorreceptoras (cones e bastonetes). Em meados da década de 1860 a teoria vigente sobre o processo perceptivo era a das energias específicas dos nervos proposta por Johannes Müller (1801-1858) e desenvolvida posteriormente por Hermann Von Helmholtz (1821-1894). Examinaremos em nossa pesquisa a formação do conceito de tipos específicos de células nervosas associadas aos processos perceptivos (o foco do trabalho são as células do sistema visual). Esse debate envolve a formação dos conceitos de córtex visual, sistema visual, informação nervosa e célula nervosa. O período examinado será o entorno das duas últimas décadas do século XIX (décadas de 1880 e 1890), período em que Ferruccio Tartuferi (1852-1925) propõe a constituição híbrida da retina em 1887 e é marcada também pela formulação da teoria neuronal (teoria formulada principalmente pelo espanhol Santiago Ramón y Cajal) / The objective of the present study is to examine the historical formation of the visual cell concept, focussing on the the study of photoreceptor cells (cones and rods). In the mid-1860s, the current theory about the perceptual process was that of the specific energies of nerves proposed by Johannes Müller (1801-1858) and later developed by Hermann Von Helmholtz (1821-1894). Our research will examine the formation of the concept of specific types of nerve cells associated with perceptual processes (the focus of the work are the cells of the visual system). This debate involves the formation of the concepts of visual cortex, visual system, nervous information and nerve cell. The period examined will be the last two decades of the nineteenth century (1880s and 1890s), a period in which Ferruccio Tartuferi (1852-1925) proposed the hybrid constitution of the retina in 1887 and also marked by the formulation of neuronal theory mainly by the Spaniard Santiago Ramón y Cajal