scholarly journals CFD Modeling: Different Kinetic Approaches for Internal Reforming Reactions in an Anode-Supported SOFC

2011 ◽  
Vol 8 (3) ◽  
Author(s):  
Hedvig Paradis ◽  
Martin Andersson ◽  
Jinliang Yuan ◽  
Bengt Sundén
Keyword(s):  
Fuel Cells ◽  
Reaction Rate ◽  
Experimental Studies ◽  
Reaction Rates ◽  
Transport Processes ◽  
Cfd Modeling ◽  
Chemical Compositions ◽  
Internal Reforming ◽  
Shift Reaction ◽  
Reforming Reactions

Fuel cells are electrochemical devices that convert chemical energy into electricity. Solid oxide fuel cells (SOFCs) are a particularly interesting type because they can reform hydrocarbon fuels directly within the cell, which is possible, thanks to their high operating temperature. The purpose of this study is to develop an anode-supported SOFC theoretical model to enhance the understanding of the internal reforming reactions and their effects on the transport processes. A computational fluid dynamics approach, based on the finite element method, is implemented to unravel the interaction among internal reforming reactions, momentum, and heat and mass transport. The three different steam reforming reaction rates applied were developed and correlated with experimental studies found in the literature. An equilibrium rate equation is implemented for the water-gas shift reaction. The result showed that the reaction rates are very fast and differ quite a lot in size. The pre-exponential values, in relation to the partial pressures, and the activation energy affected the reaction rate. It was shown that the anode structure and catalytic composition have a major impact on the reforming reaction rate and cell performance. The large difference between the different activation energies and pre-exponential values found in the literature reveals that several parameters probably have a significant influence on the reaction rate. As the experiments with the same chemical compositions can be conducted on a cell or only on a reformer, it is important to reflect over the effect this has on the kinetic model. To fully understand the effect of the parameters connected to the internal reforming reaction, microscale modeling is needed.

CFD Modeling Considering Different Kinetic Models for Internal Reforming Reactions in an Anode-Supported SOFC

2010 ◽  
Author(s):  
Hedvig Paradis ◽  
Martin Andersson ◽  
Jinliang Yuan ◽  
Bengt Sunde´n
Keyword(s):  
Fuel Cells ◽  
Kinetic Models ◽  
Reaction Rate ◽  
Experimental Studies ◽  
Reaction Rates ◽  
Transport Processes ◽  
Cfd Modeling ◽  
Internal Reforming ◽  
Partial Pressures ◽  
Shift Reaction

Fuel cells are electrochemical devices that transform chemical energy into electricity. Solid oxide fuel cells (SOFCs) are particularly interesting because they can handle the reforming of hydrocarbon fuels directly within the cell. This is possible due to their high operating temperature. The purpose of this study is to develop an anode-supported SOFC model, to enhance the understanding of the internal reforming and effects on the transport processes. In this study, a CFD approach, based on the finite element method, was implemented for the analysis to unravel the interaction between internal reforming, momentum, heat and mass transport. COMSOL Multiphysics is used to analyze the effects of different global kinetic models available for the steam reforming reaction. The three different reaction rates applied in this study were developed and correlated through experimental studies found in the literature. An equilibrium equation is implemented for the reaction rate for the water-gas shift reaction. The partial pressures and the related reaction order of the pressure are found to affect the reaction rate.

Simulation of Surface Reactions and Multiscale Transport Processes in a Composite Anode Domain Relevant for Solid Oxide Fuel Cells

2013 ◽  
Vol 10 (2) ◽  
Author(s):  
Jinliang Yuan ◽  
Guogang Yang ◽  
Bengt Sunden
Keyword(s):  
Fuel Cells ◽  
Solid Oxide Fuel Cells ◽  
Gas Phase ◽  
Gas Flow ◽  
Surface Reactions ◽  
Transport Processes ◽  
Solid Oxide ◽  
Oxide Fuel ◽  
Internal Reforming ◽  
Reforming Reactions

There are various transport phenomena (gas-phase species, heat, and momentum) occurring at different length scales in anode-supported solid oxide fuel cells (SOFCs), which are strongly affected by catalytic surface reactions at active triple-phase boundaries (TPBs) between the void space (for gas), Ni (catalysts for electrons), and YSZ (an electrolyte material for ions). To understand the multiscale chemical-reacting transport processes in the cell, a three-dimensional numerical calculation approach (the computational fluid dynamics (CFD) method) is further developed and applied for a composite domain including a porous anode, fuel gas flow channel, and solid interconnect. By calculating the rate of microscopic surface-reactions involving the surface-phase species, the gas-phase species/heat generation and consumption related to the internal reforming reactions have been identified and implemented. The applied microscopic model for the internal reforming reactions describes the adsorption and desorption reactions of six gas-phase species and surface reactions of 12 surface-adsorbed species. The predicted results are presented and analyzed in terms of the gas-phase species and temperature distributions and compared with those predicted by employing the global reaction scheme for the internal reforming reactions.

scholarly journals CFD Modelling of a Hydrogen/Air PEM Fuel Cell with a Serpentine Gas Distributor

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 564
Author(s):  
Alessandro d’Adamo ◽  
Matteo Riccardi ◽  
Massimo Borghi ◽  
Stefano Fontanesi
Keyword(s):  
Fuel Cells ◽  
Proton Exchange Membrane ◽  
Catalyst Layer ◽  
Active Surface ◽  
Reaction Rates ◽  
Transport Processes ◽  
Proton Exchange ◽  
Sustainable Mobility ◽  
Cfd Modelling ◽  
Gas Distributor

Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.

Oscillations, glow and ignition in carbon monoxide oxidation in an open system. I. Experimental studies of the ignition diagram and the effects of added hydrogen

1985 ◽  
Vol 397 (1812) ◽  
pp. 21-44 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Open System ◽  
Reaction Rate ◽  
Experimental Studies ◽  
Reaction Rates ◽  
Step Change ◽  
Stable Node ◽  
Stationary States ◽  
Show Evidence ◽  
Oxidation Of Carbon Monoxide

The oxidation of carbon monoxide in equimolar mixtures (CO + O 2 ) has been studied in a well-stirred open system (0.5 dm 3 ) at vessel temperatures in the range 700-840 K, and reactant pressures up to 100 Torr ( ca . 13.3 kPa) at a mean residence time of 8.5 s. Stationary states are established and oscillatory states sustained indefinitely in this system. The effect of small quantities of added hydrogen is studied by a carefully controlled, continuous supplement to the principal reactants. Four different modes of reaction (I-IV) have been characterized, and conditions for their occurrence mapped on a reactant pressure-vessel temperature ( p - T a ) ignition diagram. Most boundaries are quite sharp, and some show evidence of hysteresis. Close to the axes, reaction is slow, non-luminous and non-oscillatory (I). Within a first broad promontory (II) reaction is accompanied by steady luminescence. Crossing the boundary is not accompanied by a step change in reaction rate, but there is a change in character from stable node (in I) to stable focus (in II). Auto-oscillatory luminescence occurs in a closed region (III) wholly within the promontory II. The effects of adding hydrogen on all these modes is to increase the reaction rates markedly and to make them non-isothermal; the boundaries between I, II and III are not as greatly affected. However, systems to which more than 0.10% H 2 have been added also display a new mode, of oscillatory ignition. This appears at first in a region (IV) of high temperatures and pressures but as more H 2 is increased its realm expands and it eventually dominates the ignition diagram, invading the region of luminescence and soon obliterating the oscillatory part completely.

Transport Phenomena Analysis in Proton Exchange Membrane Fuel Cells

2005 ◽  
Vol 127 (12) ◽  
pp. 1363-1379 ◽  
Author(s):  
Hongtan Liu ◽  
Tianhong Zhou ◽  
Ping Cheng
Keyword(s):  
Experimental Investigation ◽  
Fuel Cells ◽  
Fuel Cell ◽  
Proton Exchange Membrane ◽  
Transport Phenomena ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Transport Processes ◽  
Proton Exchange ◽  
Exchange Membrane

The objective of this review is to provide a summary of modeling and experimental research efforts on transport phenomena in proton exchange membrane fuel cells (PEMFCs). Several representative PEMFC models and experimental studies in macro and micro PEMFCs are selected for discussion. No attempt is made to examine all the models or experimental studies, but rather the focus is to elucidate the macro-homogeneous modeling methodologies and representative experimental results. Since the transport phenomena are different in different regions of a fuel cell, fundamental phenomena in each region are first reviewed. This is followed by the presentation of various theoretical models on these transport processes in PEMFCs. Finally, experimental investigation on the cell performance of macro and micro PEMFC and DMFC is briefly presented.

CFD Analysis and Parameter Study of Transport Processes with Catalytic Reactions in Anodes of Solid Oxide Fuel Cells

2011 ◽  
Vol 347-353 ◽  
pp. 3310-3316
Author(s):  
Chao Yang ◽  
Guo Guang Yang ◽  
Dan Ting Yue ◽  
Jin Liang Yuan
Keyword(s):  
Fuel Cells ◽  
Model Simulation ◽  
Reaction Rates ◽  
Transport Processes ◽  
Solid Oxide ◽  
Parameter Study ◽  
Oxide Fuel ◽  
Cfd Model ◽  
Internal Parameters ◽  
Working Processes

Solid oxide fuel cell (SOFC) is one of most promising types of fuel cells with advantages of high efficiencies, flexibility of usable fuel types. The performance of SOFC is strongly affected by cell overall parameters, e.g., temperature, pressure, reaction rates, etc. But it is very difficult to validate internal parameters distributions and complex physical processes by experimental method. The CFD model simulation has been proved an effective method for SOFC research. In this work, a 3D CFD model is developed to simulate the working processes in SOFC’s anode. The objective of this work is to study the effects of the parameters such as temperature, permeability, pores radius and elementary surface reaction rate on the working processes, by coupling the transport processes such as mass, momentum and thermal energy with the chemical reactions of gas- and surface-phase species based on catalyst surface coverage.

Simulation and Analysis of Multi-scale Transport Phenomena and Catalytic Reactions in SOFC Anodes

2010 ◽  
Vol 5 (1) ◽  
Author(s):  
Jinliang Yuan
Keyword(s):  
Gas Phase ◽  
Transport Processes ◽  
Ni Catalyst ◽  
Surface Phase ◽  
Fuel Gas ◽  
Multi Scale ◽  
Internal Reforming ◽  
Physical Phenomena ◽  
Porous Anode ◽  
Reforming Reactions

Solid oxide fuel cell (SOFC) has been considered as one of the most efficient power generation devices for the coming decades. There are various physical phenomena appearing in SOFC in multi-length and -time scales, such as multi-component gas-phase species/charge flow, thermal energy and mass transfer. Meanwhile, generation and consumption of gas- and surface-phase species together with electric current production are involved at various active sites. Catalytic reforming reactions of hydrocarbon fuels in SOFC anode are strongly coupled with the transport processes making the physical phenomena more complicated.An effective SOFC electrode design is to correctly balance each of the transport processes and the involved reactions. To deeply understand the multi-scale chemical reactions and transport processes in the anode, a fully three-dimensional numerical calculation method (CFD approach) is further developed and applied. The calculated domain includes the porous anode, fuel gas flow channel and the solid interconnects.By calculating fractions of Ni catalyst vacancies and surface-phase species coverages, the gas-phase species/heat generation and consumption related to the internal reforming reactions of methane and the electrochemical reactions of hydrogen have been implemented. The variable thermal-physical properties and transport parameters of the fuel gas mixture have also been taken into account. Furthermore, the heat transfer due to the fuel gas diffusion is implemented into the energy balance based on multi-component diffusion models. A multi-step heterogeneous steam reforming reaction mechanism based on the micro and detailed reaction mechanisms of Ni/YSZ is employed in this study. The surface reactions include 42 irreversible elementary ones accounting for the steam reforming, the water-gas shift reforming and Boudouard reactions. This microscopic reaction model describes the adsorption and desorption reactions of 6 gas-phase species and surface reactions of 12 surface-adsorbed species.The predicted results show that the catalytic reactions take place at most regions of the porous anode, and a gradual CH4 distribution profile and incomplete CH4 conversion at the anode exit are observed. Transport processes of the fuel gas-phase species and temperature distribution are affected by both the internal reforming reactions and the electrochemical reaction. Parameter studies reveal that both low operating temperature and big permeability can increase the available nickel catalyst surface fraction in the anode. Such detailed reaction scheme is much more complicated to incorporate in SOFC modelling but helpful to predict surface-phase species profiles over Ni-catalyst surfaces.

Eclogitization kinetics of continental granulites : quantification and implications

2020 ◽  
Author(s):  
Marie Baisset ◽  
Loic Labrousse ◽  
Alexandre Schubnel
Keyword(s):  
Rheological Behavior ◽  
Reaction Rate ◽  
Experimental Studies ◽  
Reaction Rates ◽  
First Order ◽  
Piston Cylinder ◽  
Ductile Flow ◽  
Convergence Zones ◽  
Kinetics Of ◽  
Type Apparatus

<p><span>When implicated in convergence zones, granulites of the lower continental crust are expected to eclogitize at depth.When exposed in the field such units show a bimodal rheological behavior between fracturing of the protolith rock (granulites) and ductile flow of the transformed parts (eclogites). It seems therefore that a competition exists between the rate at which the rocks are loaded in stress and the rate at which they transform, i.e. the overall eclogitization kinetics. The aim of the work presented here is to quantify the kinetics of the metamorphic reactions involved in eclogitization by estimating the reaction rates in plagioclase-bearing assemblages<span>  </span>submitted to different P-T conditions over different time spans. For this, experiments have been performed in piston-cylinder apparatus on aggregates derived from natural granulites. Special attention is paid to the location where nucleation starts and how it propagates in and between the grains. In this prospect, the presence of garnet and cpx in the plagioclase matrix is a first order control on the reaction process. This work follows previous experimental studies (e.g. Shi et al., 2017, Incel et al., 2018) which show that reaction-enhanced embrittlement may be key for fracturing at high pressure. It has been proposed that transient properties of the rocks induced by the very beginning of the reaction (e.g. volume change, small grain size nucleation products) can lead to brittle instabilities. As we assume that the rheological behavior of the crust is controlled by a competition between reaction rate and strain rate, experiments involving deformation of granulites while undergoing eclogitization are required. Preliminary results performed on Griggs-type apparatus, which constitutes the best tool for that, will also be presented.</span></p>

scholarly journals Modeling Analysis of Different Renewable Fuels in an Anode Supported SOFC

2010 ◽  
Author(s):  
Martin Andersson ◽  
Hedvig Paradis ◽  
Jinliang Yuan ◽  
Bengt Sunde´n
Keyword(s):  
Fuel Cells ◽  
Molar Fraction ◽  
Energy System ◽  
Reaction Rates ◽  
Inlet Temperature ◽  
Fuel Composition ◽  
Initial Fuel ◽  
Sustainable Energy System ◽  
Shift Reaction ◽  
The Right

It is expected that fuel cells will play a significant role in a future sustainable energy system. They are energy efficient, fuel can be produced nearly locally and, when a renewable fuel such as ethanol, methanol and biogas is used, there are no net emissions of greenhouse gases. Fuel cells have during recent years various progresses, but the technology is still in the early phases of development, however the potential is enormous. In this study a CFD approach (COMSOL Multiphysics) is employed to investigate effects of different fuels such as biogas, pre-reformed methanol, ethanol and natural gas. The fuel composition and inlet temperature are varied to study the effect on temperature distribution, molar fraction distribution and reforming reaction rates within a singe cell for an intermediate temperature solid oxide fuel cell (IT-SOFC). The developed model is based on the governing equations of heat-, mass- and momentum transport, which are solved together with global reforming kinetics. The result shows that the heat generation within the cell depends mainly on the initial fuel composition and the inlet temperature. The water-gas shift reaction proceeds to the right as hydrogen is consumed and water generated in the electrochemical reactions at the anodic three-phase boundaries.

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