Thermodynamics of Fuel Cells

Winkler, Wolfgang; Nehter, Pedro

doi:10.1007/978-1-4020-6995-6_2

Cited by 18 publications

(21 citation statements)

References 5 publications

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“…(14)- (15), respectively. E 0 for carbon monoxide decreases with increased temperature, but it is not temperature dependent for methane, due to a constant molar number of products and reactants [21][22]. In this study only eqns.…”

Section: Electrochemical Reactionsmentioning

confidence: 99%

“…The amount of heat generated due to electrochemical reactions can be calculated as [25]: (22) where n is the molar flux density [mol/(m 2 s)] and 'S r entropy change of the reaction (-50.2 J/(K mol)), calculated from data in [26]. The concentration polarizations are specified as [23]: where p i,TPB stands for the partial pressure at three phase boundary (TPB) and p i,b the partial pressure at the interface between gas channel and electrode.…”

Section: Electrochemical Reactionsmentioning

confidence: 99%

“…The electromotive force (reversible open-circuit voltage, E OCV ) is determined by the difference in the thermodynamic potentials of the electrode reactions [21][22][23]. When a hydrogen-steam mixture is used as fuel, it can be calculated by the Nernst equation [23]:…”

Section: Electrochemical Reactionsmentioning

confidence: 99%

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Modeling Validation and Simulation of an Anode Supported SOFC Including Mass and Heat Transport, Fluid Flow and Chemical Reactions

Andersson

Yuan

Sundén

et al. 2011

ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology

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Fuel cells are electrochemical devices that directly transform chemical energy into electricity, which are promising for future energy systems, since they are energy efficient and, when hydrogen is used as fuel, there are no direct emissions of greenhouse gases. The cell performance depends strongly on the material characteristics, the operating conditions and the chemical reactions that occur inside the cell. The chemical-and electrochemical reaction rates depend on temperature, material structure, catalytic activity, degradation and the partial pressures for the different species components. There is a lack of information, within the open literature, concerning the fundamentals behind these reactions. Experimental as well as modeling studies are needed to reduce this gap.In this study experimental data collected from an intermediate temperature standard SOFC with H 2 /H 2 O in the fuel stream are used to validate a previously developed computational fluid dynamics model based on the finite element method. The developed model is based on the governing equations of heat and mass transport and fluid flow, which are solved together with kinetic expressions for internal reforming reactions of hydrocarbon fuels and electrochemistry. This model is further updated to describe the experimental environment concerning cell design. Discussion on available active area for electrochemical reactions and average ionic transport distance from the anodic-to the cathodic three-phase boundary (TPB) are presented. The fuel inlet mole fractions are changed for the validated model to simulate a H 2 /H 2 O mixture and 30 % pre-reformed natural gas. Keywords: SOFC, Modeling, Validation, Active Area, IonicTransport Distance, COMSOL Multiphysics INTRODUCTION AND PROBLEM STATEMENTFuel cells (FCs) are promising due to advantages of higher efficiency and lower emissions of SO X , NO X and CO 2 than conventional power generation [1]. The solid oxide fuel cell (SOFC) is a high temperature fuel cell, which operates at 600-1000 ºC [2]. This temperature allows SOFCs to operate with different types of fuels from both fossil and renewable sources. It opens a way for an easier transition from conventional power generation with hydrocarbon based fuels to fuel cells with possibility for different fuels, especially SOFCs. Due to the increasing global awareness of that energy usage affects the environments, the interest of renewable energy has increased. SOFCs are generally more tolerant to contaminants than other fuel cells and the possibility to internally (as well as externally) reform the fuel make them interesting for renewable energy resources [1].Numerical results of SOFC models are only approximations of real conditions and the validation is an important and necessary step in the development of reliable and accurate computational models. A range of validity can be established between the developed model and experimental

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Section: Electrochemical Reactionsmentioning

confidence: 99%

Section: Electrochemical Reactionsmentioning

confidence: 99%

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Modeling Validation and Simulation of an Anode Supported SOFC Including Mass and Heat Transport, Fluid Flow and Chemical Reactions

Andersson

Yuan

Sundén

et al. 2011

ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology

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“…When a hydrogen-8 steam mixture is used as fuel, it can be calculated by the Nernst equation (eqn (9)) [19][20]. [21] and it is recommended to replace this expression in future extensions of our model to include the impact from hydrocarbons.…”

Section: Ion and Electron Transport As Well As Electrochemical Reactionsmentioning

confidence: 99%

Comparison of humidified hydrogen and partly pre-reformed natural gas as fuel for solid oxide fuel cells applying computational fluid dynamics

Andersson

Nakajima

Shimizu

et al. 2014

International Journal of Heat and Mass Transfer

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“…Note that the tortuosity for ion and electron transport differs from the tortuosity for gas-phase transport. (14)) [16][17]. The electromotive force for carbon monoxide as fuel is presented in eqn (16) [18].…”

Section: Ion and Electron Transportmentioning

confidence: 99%

Grading the Amount of Electrochemical Active Sites along the Main Flow Direction of an SOFC

Andersson

Yuan

Sundén

2012

J. Electrochem. Soc.

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A fully coupled computational fluid dynamics (CFD) approach based on the finite element method, in two-dimensions, is developed to describe a solid oxide fuel cell (SOFC). Both hydrogen and carbon monoxide are considered as electrochemical reactants within the anode. The dimensionless number of electrochemical active sites (EAS), the pore radius (indirectly proportional to the particle radius) and the active area-to-volume ratio available for methane reforming are graded, along the main flow direction, to equalize the current density distribution. Previous studies available in the open literature only considered grading in the direction normal to the main flow direction, in terms of porosity and tortuosity. It is found that grading the active area-to-volume ratio available for methane reforming increases the OCV along the main flow direction. It is concluded that an optimized graded EAS reduces the need of air flow rate with 21%, with the same outlet temperatures as for the ungraded case.

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Thermodynamics of Fuel Cells

Cited by 18 publications

References 5 publications

Modeling Validation and Simulation of an Anode Supported SOFC Including Mass and Heat Transport, Fluid Flow and Chemical Reactions

Modeling Validation and Simulation of an Anode Supported SOFC Including Mass and Heat Transport, Fluid Flow and Chemical Reactions

Comparison of humidified hydrogen and partly pre-reformed natural gas as fuel for solid oxide fuel cells applying computational fluid dynamics

Grading the Amount of Electrochemical Active Sites along the Main Flow Direction of an SOFC

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