| 1. |
- Yuan, Jinliang, et al.
(författare)
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Gas Flow and Heat Transfer Analysis for an Anode Duct in Reduced Temperature SOFCs
- 2003
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Ingår i: Fuel Cell Science, Engineering and Technology. - 0791836681 ; , s. 209-216
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Konferensbidrag (refereegranskat)abstract
- In this study, a fully three-dimensional calculation method has been further developed to simulate and analyze various processes in a thick anode duct. The composite duct consists of a porous layer, the flow duct and solid current connector. The analysis takes the electrochemical reactions into account. Momentum and heat transport together with gas species equations have been solved by coupled source terms and variable thermo-physical properties (such as density, viscosity, specific heat, etc.) of the fuel gases mixture. The unique fuel cell conditions such as the combined thermal boundary conditions on solid walls, mass transfer (generation and consumption) associated with the electrochemical reaction and gas permeation to / from the porous electrode are applied in the analysis. Results from this study are presented for various governing parameters in order to identify the important factors on the fuel cell performance. It is found that gas species convection has a significant contribution to the gas species transport from / to the active reaction site; consequently characteristics of both gas flow and heat transfer vary widely due to big permeation to the porous layer in the entrance region and species mass concentration related diffusion after a certain distance downstream the inlet.
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| 2. |
- Huang, Zhe, 1986, et al.
(författare)
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Characterization and application of forced cooling channels for traction motors in HEVs
- 2012
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Ingår i: 2012 20th International Conference on Electrical Machines, ICEM 2012; Marseille; France; 2 September 2012 through 5 September 2012. - 9781467301428 ; , s. 1212-1218, s. 1212-1218
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Konferensbidrag (refereegranskat)abstract
- This paper presents the characterization of forced cooling channels with three different shapes which are applied in traction motors mounted in Hybrid Vehicles (HEVs) or Zero Emission Vehicles (ZEVs). Generally, there are two different positions of forced cooling channels in electric motors. One way is by drilling holes or cutting cooling channels inside the housing, which is called indirect cooling approach. The other way is to cut the cooling channels at the edges of housing or/and stator back to form direct cooling channels, where the coolant is in direct contact with the hot stator back. In both cases, choosing suitable shapes of cooling channels are necessary. In this paper, both heat transfer coefficient hf and pump power Wpump are calculated. The dimensional parameters are easily understood and also used for further thermal analysis of the completed machine by either Finite Element Analysis (FEA) or lumped parameter approaches. In addition, the dimensionless parameters Nusselt number Nu and Darcy friction factor f are evaluated with the aim to understand the characterizations for different channels. These parameters are easily used for further cooling channels optimization. In the end, the thermal analyses for a stator segment with three different shaped channels are carried on by applying the calculated results from Computational Fluid Dynamics (CFD) simulations.
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| 3. |
- Yuan, Jinliang
(författare)
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Computational Analysis of Gas Flow and Heat Transport Phenomena in Ducts Relevant for Fuel Cells
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis concerns modeling, simulation and numerical analysis of heat and mass transport, and fluid flow in ducts of both solid oxide fuel cells (SOFCs) and proton exchange membrane fuel cells (PEMFCs). The unique fuel cell boundary conditions (thermal, mass) for the flow ducts in fuel cells are identified and applied. Various duct configurations have been studied, such as rectangular and trapezoidal cross sections, composite geometries including porous layer, flow duct and solid current inter-collector (-connector). Numerical simulations of fully developed / developing laminar flow and heat transfer have been presented with various Gr*, Re, Rem, aspect ratio (b/h) and base angle at electrolyte supported SOFC boundary conditions. It was verified that the mass injection through one wall increases the friction factor f and decreases the Nusselt number Nu; the mass suction decreases f but Nu increases. Onset of deviation of friction factor and heat transfer from pure forced convection is caused by the formation of a vortex. It was verified that the number of vortices and enhancement of f and Nu depends mainly on the magnitude of Ratio of Gr*/Re2. For the same design, combined effects of mass transfer and buoyancy force have been simulated for various Grashof number Gr*, mass suction rate Rem and Reynolds number Re. It was found that onset of gas flow and heat transfer from pure forced convection is caused by combined effects of the formation of vortices associated with buoyancy and downward flow with mass suction. The mass suction can advance the onset of instability for the combined flow For the same design, combined effects of mass transfer and buoyancy force have been simulated for various Grashof number Gr*, mass suction rate Rem and Reynolds number Re. It was found that onset of gas flow and heat transfer from pure forced convection is caused by combined effects of the formation of vortices associated with buoyancy and downward flow with mass suction. The mass suction can advance the onset of instability for the combined flow relative to pure forced convection flow at all Reynolds numbers. The effect of combined flow on the friction factor is less significant than on the heat transfer. From the simulated velocity distribution in the PEMFC composite ducts, it was found that the velocity in the porous diffusion layer is only about a few percent of that in the gas flow duct, and secondary flows caused by mass transfer can be clearly found in both diffusion layer and gas flow duct. It was also found, among the parameters studied, that permeability and thermal conductivity ratio have a significant impact on f and Nu for both cathode and anode ducts at a fixed porous layer configuration. It has been revealed that the values of fRe and Nu vary widely in anode-supported SOFC ducts, where the thickness of the porous layer is large. fRe decreases from that of pure duct flow and has a low value due to the permeation effects in the entrance. By varying one or more of the characteristic ratios identified in this study, effects of permeation and secondary flow on the gas flow and heat transfer have been investigated in terms of fRe and Nu. A uniform fRe in the main flow direction can be achieved through appropriate adjustment of the flow parameters or / and duct configuration. Based on the concentration prediction, it has been found that gas species transport from/to the reaction site is mainly dominated by mass convection in the entrance region and by species mass concentration associated diffusion after a certain distance downstream the inlet; The position for occurrence of this change depends on several parameters, e.g., the current density.
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| 4. |
- Johansson, Erik O., et al.
(författare)
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Modeling of a non-periodic boundary condition with entrance and exit in dissipative particle dynamics
- 2015
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Ingår i: ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2015, collocated with the ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. - 9780791856871
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Konferensbidrag (refereegranskat)abstract
- Dissipative particle dynamics (DPD) have been widely used for the simulations of dynamics of both simple and complex fluids at nano/micro scales. In these simulations, periodic boundaries are usually employed in the main flow direction and the characterization of the flow and heat transfer is based on fully developed conditions. In the real nano/micro-fluidic devices, however, there are entrances and exits and the flow and temperature fields are not the same at different positions, making the periodic boundary conditions ill-suited due to problems with conservation of energy and momentum. This is the motivation of the present study to generate the non-periodic boundary condition having an entrance and an exit in the the DPD system and study the heat transfer characteristics in the entrance region. In this study, the entrance and exit regions are modelled for simulations of the flow in a parallel-plate channel based on the available methodology originally introduced for molecular dynamics. In this methodol-ogy, a body force acts on the DPD particles at the entrance region of the solution domain to generate the entrance region. This is region is so-called pump region. Also, a region to initiate the DPDe temperature was located followed by the pump region. Forced convection heat transfer of water flowing through a parallel-plate channel with constant wall temperature was simulated using this method. The simulations were implemented for different body forces in the pump region. The results were evaluated in terms of velocity, temperature and number density distributions in the channel and showed the effects of the compressibility of the DPD fluid and random movement (or Brownian motion). In addition, the Reynolds and Nusselt numbers were calculated to investigate their effects on the heat transfer characteristics at the entrance region.
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| 5. |
- Alhelfi, Ali Kadhim Hadi, et al.
(författare)
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Modeling of Spherical Gas Bubble Oscillation in Acoustic Pressure Field
- 2013
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Ingår i: Proceedings Of The 8th International Conference on Multiphase Flow, 2013.
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Konferensbidrag (refereegranskat)abstract
- Different applications of high power ultrasound in industry and medical applications are based on the propagation and collapse of acoustic cavitation bubbles. This paper presents an enhanced numerical model and simulated results of formation and collapse of a single bubble in a liquid for two cases: bubble with uniform pressure and a bubble with variable pressure inside. For the two cases, both heat transfer inside the bubble and heat transfer to the surrounding liquid are taken into account. Various fundamental properties of oscillating bubbles in ultrasonic acoustic field, such as pressure, temperature and velocity fields inside the bubble under the influence of time-dependent acoustic pressure, have been investigated and the results show that neglecting the pressure gradient inside the bubble affects considerably the bubble dynamics.
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| 6. |
- Alhelfi, Ali Kadhim Hadi, et al.
(författare)
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Solid Oxide Fuel Cell Auxiliary Power Units for Heavy Duty Trucks
- 2012
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Ingår i: Proceedings Of The ASME 10th Fuel Cell Science, Engineering, and Technology Conference, 2012. ; , s. 317-325
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Konferensbidrag (refereegranskat)abstract
- This paper explores the potentials of solid oxide fuel cells (SOFCs) as 3 kW auxiliary power units for trucks and military vehicles operating on diesel fuel. Various issues are discussed, e.g., the requirements and specifications for the unit as well as the advantages, challenges, and development issues for SOFCs in such applications. System design and analysis are carried out. The major component of the system is the fuel cell stack. The calculations are performed for two voltage systems 12/14 V and 36/42 V, respectively. The influences of others parameters like the mass flow rates of air and gases, water production and heat production are also evaluated for the two voltage systems.
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| 7. |
- Andersson, Daniel, et al.
(författare)
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Dynamic Modeling Of A Solid Oxide Fuel Cell System In Modelica
- 2010
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Ingår i: Proceedings of the Asme 8th International Conference on Fuel Cell Science, Engineering, and Technology 2010, Vol 2. - 9780791844052 ; 2, s. 65-72
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Konferensbidrag (refereegranskat)abstract
- In this study a dynamic model of a solid oxide fuel cell (SOFC) system has been developed. The work has been conducted in a cooperation between the Department of Energy Sciences, Lund University, and Mode Ion AB using the Modelica language and the Dymola modeling and simulation tool. Modelica is an equation based, object oriented modeling language, which promotes flexibility and reuse of code. The objective of the study is to investigate the suitability of the Modelica language for dynamic fuel cell system modeling. A cell electrolyte model including ohmic, activation and concentration irreversibilities is implemented and verified against simulations and experimental data presented in the open literature. A ID solid oxide fuel cell model is created by integrating the electrolyte model and a ID fuel flow model, which includes dynamic internal steam reforming of methane and water-gas shift reactions. Several cells are then placed with parallel flow paths and connected thermally and electrically in series. By introducing a manifold pressure drop, a stack model is created. The stack model is applied in a complete system including an autothermal reformer, a catalytic afterburner, a steam generator and heat exchangers. Four reactions are modeled in the autothermal reformer; two types of methane steam reforming, the water-gas shift reaction and total combustion of methane. The simulation results have been compared with those in the literature and it can be concluded that the models are accurate and that Dymola and Modelica are tools well suited for simulations of the transient fuel cell system behaviour.
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| 8. |
- Andersson, Martin, et al.
(författare)
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3D modeling of an anode supported SOFC using FEM and LBM
- 2014
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Ingår i: ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology collocated with the ASME 2013 Heat Transfer Summer Conference and the ASME 2013 7th International Conference on Energy Sustainability. - 9780791855522
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Konferensbidrag (refereegranskat)abstract
- Solid oxide fuel cells (SOFCs) are promising as energy producing device, which at this stage of its development will require extensive analysis and benefit from numerical modeling at different time-and length scales. In this study, two models based on finite element method (FEM) and Lattice Boltzmann model (LBM), respectively, are evaluated and compared for an anode-supported SOFC. First, a 3D model is developed based on the FEM, using COMSOL, of a single SOFC operating at an intermediate temperature range. Heat, gas-phase species, momentum, ion and electron transport are implemented and coupled to the kinetics of the electrochemical reactions. Secondly, a 3D model of the porous anode of a SOFC is developed using LBM to investigate the effects of electrochemical reactions on the transport processes at microscale for 3 components (H 2, H2O and O2-). Parallel computing in Python is employed through the program Palabos to capture the active microscopic catalytic reaction effects on the heat and mass transport. It is found that LBM can be effectively used at a mesoscale ranging down to a microscale and proven to effectively take care of the interaction between the fluid particles and the walls of the porous media. The 3D LBM model takes into account the transport of oxygen ions within the solid particles of the SOFC anode. Both the oxygen ions and the hydrogen are mainly consumed by the reaction layer. One of the improvements in this study compared to our previous (FEM) models is the captured 3D effects which was not possible in 2D. High current density spots are identified, where the electron transport distance is short and the oxygen concentration is high. The relatively thin cathode results in a significant oxygen mole fraction gradient in the direction normal to the main flow direction.
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| 9. |
- Andersson, Martin, et al.
(författare)
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Analysis of Microscopic Anode Structure Effects on an Anode-Supported SOFC Including Knudsen Diffusion
- 2011
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Ingår i: SOFC12. - : The Electrochemical Society. ; 35, s. 1799-1809
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Konferensbidrag (refereegranskat)abstract
- In this study a two dimensional CFD (COMSOL Multiphysics) is employed to study the effect of anode microscopic structures on the transport phenomena and reactions for an anode-supported solid oxide fuel cell (SOFC). FCs can be considered as energy devices, involving multiple processes, such as (electro-) chemical reactions, heat exchange, gas- and ionic transport. All these complex processes are strongly integrated, needing modeling as an important tool to understand the couplings between mass-, heat-, momentum transport and chemical reactions. For the porous material, the Knudsen diffusion is taken into account in this study. The chemical- and electrochemical reaction rates depend on temperature, material structure, catalytic activity, degradation and partial pressure among others. It is found that the anode thickness and also the anode pore size need to be optimized to achieve high cell efficiency, when the Knudsen diffusion effects are included.
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| 10. |
- Andersson, Martin, et al.
(författare)
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Catalyst Materials and Catalytic Steam Reforming Reactions in SOFC Anodes
- 2010
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Ingår i: International Green Energy Conference.
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Konferensbidrag (refereegranskat)abstract
- It is expected that fuel cells will play a significant role in a future sustainable energy system. They are energy efficient and fuel can be produced nearly locally. There are no net emissions of greenhouse gases when a renewable fuel such as ethanol, methanol, biogas and hydrogen is used. Fuel cells reached during the latest years various progresses, but the technology is still in the early phases of development, however the potential is enormous. The reforming reaction of hydrocarbons (e.g., methane) is a key one for an effective solid oxide fuel cell (SOFC) operation. This reaction could either be described by global kinetics or by elementary surface reaction kinetics. When a global approach is applied, the reaction rates depend on temperature, partial pressures, activation energy and the pre-exponential factor. Note that the last two mentioned parameters are normally calculated from experimental data. Different detailed reaction mechanisms (considering elementary surface kinetics) are developed, but there is a disagreement considering the involved reaction pathways, rate-limiting steps and intermediate species. It is found that detailed kinetics of the reforming reaction is important for design and development of new effective catalytic materials. A thermodynamical analysis tells that nickel and ruthenium are suitable catalytic materials for the methane steam reforming reactions.
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