| 1. |
|
|
| 2. |
- Andersson, Martin, et al.
(författare)
-
Modeling Analysis of Different Renewable Fuels in an Anode Supported SOFC
- 2011
-
Ingår i: Journal of Fuel Cell Science and Technology. - ASME. ; 8:3
-
Tidskriftsartikel (refereegranskat)abstract
- Background. It is expected that fuel cells will play a significant role in a future sustainable energy system, due to their high energy efficiency and possibility to use renewable fuels. Fuels, such as biogas, can be produced locally close to the customers. The improvement for fuel cells during the last years has been fast, but the technology is still in the early phases of development, however the potential is enormous. Method of approach. A CFD approach (COMSOL Multiphysics) is employed to investigate effects of different fuels such as biogas, pre-reformed methanol, ethanol and natural gas. The effects of fuel inlet composition and temperature are studied in terms of 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 reaction kinetics. Results. The result shows that the heat generation within the cell depends mainly on the initial fuel composition and the inlet temperature. This means that the choice of internal- or external reforming has a significant effect on the operating performance. Conclusions. The anode structure and catalytic characteristic have a major impact on the reforming reaction rates and also on the cell performance. It is concluded that biogas, methanol and ethanol are suitable fuels in a SOFC system, while more complex fuels need to be externally reformed.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Gabrielaitiene, Irena, et al.
(författare)
-
Dynamic Temperature Simulation in District Heating Systems in Denmark Regarding Pronounced Transient Behaviour
- 2011
-
Ingår i: Journal of Civil Engineering and Management. - Taylor & Francis Group. - 1392-3730. ; 17:1, s. 79-87
-
Tidskriftsartikel (refereegranskat)abstract
- A dynamic performance of district heating systems was analysed with an emphasis on temperature profile distortion throughout a heating system network. Therefore, a modelling approach (the so-called node method) developed at the Technical University of Denmark was applied. For comparison purposes, commercial TERMIS software was also used in this work. Typical supply conditions were investigated in the considered district heating systems in Denmark. Large and sudden temperature changes in supply temperature were depicted in the district heating system in Madumvej while the pronounced transient supply conditions of temperature wave were exhibited in the district heating system in Naestved. Time-dependent consumer data from the district heating systems were applied to compare the results obtained from modelling approaches. Based on the analysis of temperature wave propagation through the network, it was noted that temperature wave spread unevenly on different locations of the network.
|
|
| 6. |
- Khan, Munir, et al.
(författare)
-
Analysis of multi-phase transport phenomena with catalyst reactions in polymer electrolyte membrane fuel cells - A review
- 2011
-
Ingår i: Journal of Power Sources. - Elsevier Science BV. - 0378-7753. ; 196:19, s. 7899-7916
-
Forskningsöversikt (refereegranskat)abstract
- A review is presented for two-phase modeling approaches to study various transport processes and reactions in polymer electrolyte membrane (PEM) fuel cells along with some experimental work. It has been noted that water management is still one of the least accurate modeled phenomena. The lackness in complete descriptive models for water management inside PEM fuel cells can be attributed to the complexity of the phenomena, lack of empirical or measured data and non-availability of apt governing equations. Another discrepancy found in present models is the proper validation of the numerical work as it has been observed that mere comparison with V-I curve can sometimes lead to misguided conclusions. Additionally, keeping in mind the multi-scale nature of a PEM fuel cell. application of the Lattice Boltzmann (LB) method has also been reviewed in this work and it was noticed that LB methods offer bright perspective at meso-scale by incorporating details of local structure. Furthermore, a brief description of the catalyst layer models is also presented with some technological developments at nano-scale to improve the physio- and electro-chemical properties. A test case for a 2D PEM cathode is also simulated for different operating voltages to predict the water saturation effects. (C) 2011 Elsevier B.V. All rights reserved.
|
|
| 7. |
- Khan, Munir, et al.
(författare)
-
Analysis of multiphase tranport phenomena in PEMFCs by incorporating microscopic model for catalyst layer structure
- 2011
-
Konferensbidrag (refereegranskat)abstract
- The catalyst layer (CL) in polymer electrolyte membrane (PEM) fuel cells is one of the key components regulating the overall performance of the cell. In PEM fuel cells, there are two CLs having identical composition for hydrogen oxidation (HO) and oxygen reduction (OR) reactions. There are four phases inside the CL, namely: carbon, Pt particles, ionomer and voids. In this work, a micro-model of the cathode CL has been developed mathematically using finite volume (FV) technique to reconstruct the local structure and further investigate the transport phenomena of reactants and product species, ions and electrons by incorporating the above stated phases at the cathode side only, due to the fact that the OR reactions are the rate limiting as compared to HO reaction. The 3D CL has been reconstructed based on a regularly distributed sphere’s method with dimensions 4:14:14:1 μm3. Platinum particles combined with carbon spheres (C/Pt) are regularly placed in the domain, an ionomer layer of a given thickness is extruded from the sphere surfaces. The C/Pt, ionomer and void distribution, as well as Address all correspondence to this author. (munir.khan@energy.lth.se) the triple phase boundary (TPB) are analysed and discussed. A microscopic model has been developed for water generation and species transport including Knudsen diffusion through the voids and the proton transport in the ionomer has been included here to aim for the rigorousness of the work. In addition, the electrochemical reactions have been simulated on the surface of Pt particles fulfilling the TBP conditions.
|
|
| 8. |
- Khan, Munir, et al.
(författare)
-
Water saturation modeling in polymer electrolyte membrane (PEM) fuel cells using a validated approach
- 2011
-
Konferensbidrag (refereegranskat)abstract
- In this work, a 3D model of a PEM fuel cell has been developed for water saturation and its effects using a validated approach considering the internal movement of water across the membrane. For different operating levels, it was found that at lower current densities, the maximum saturation occurs faraway region from the air inlet because of the decrease in ability of air to evaporate the liquid water, while at higher current densities, a shift in the maximum value is noticed towards the inlet region due to increase in electro-chemical reaction rate and the electro-osmotic drag. Apart from water saturation shift at different load conditions, it is also observed that the liquid water tends to accumulate at the interface of the inlet channel and the porous media. Considering the movement of water across the membrane, a linear profile for back diffusion was observed with increasing current density because of higher water content at the cathode. For the electro-osmotic drag, the increase is observed to follow the rate of increase of the electro-chemical reactions and becomes approximately constant at higher current density due to the concentration losses where the electro-chemical reaction rate is limited due to the physical characteristics of the agglomerates. Although the rise trend of the back diffusion and electro-osmotic drag followed a dissimilar pattern, the net transport was calculated to be towards the anode side suggesting that the water content at the cathode side increases with increasing current density, hence causing more problems for the PEM fuel cells in terms of water management.
|
|
| 9. |
- Paradis, Hedvig, et al.
(författare)
-
CFD Modeling: Different Kinetic Approaches for Internal Reforming Reactions in an Anode-Supported SOFC
- 2011
-
Ingår i: Journal of Fuel Cell Science and Technology. - ASME. ; 8:031014
-
Tidskriftsartikel (refereegranskat)abstract
- 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 are 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 CFD approach, based on the finite element method, is implemented to unravel the interaction between internal reforming reactions, momentum, heat and mass transport. The three different steam reforming reaction rates applied were developed and correlated to 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 the size. The pre-exponential values, in relation to the partial pressures, and the activation energy was affected the reaction rate. It was shown that the anode structure and catalytic composition have a major impact on the reforming reaction rate and on the cell performance. The large difference between the different activation energies and pre-exponential values found in the literature reveals that several parameters probably have significant influence on the reaction rate. As the experiments with the same chemical compositions can be conducted on a cell or only 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, micro scale modeling is needed.
|
|
| 10. |
- Paradis, Hedvig, et al.
(författare)
-
Comparative Analysis of Different Renewable Fuels for Potential Utilization in SOFCs
- 2011
-
Ingår i: International Journal of Energy Reserach. - 1099-114X. ; 35
-
Tidskriftsartikel (refereegranskat)abstract
- Fuel cells are promising due to advantages with higher energy conversion efficiency and lower emissions of SOX, NOX and CO2 than conventional power systems. Solid oxide fuel cell (SOFC) is a high temperature fuel cell, which operates at 600-1000 ºC. The high operating temperature and the anode material allow SOFCs to operate with different types of fuels from both fossil and renewable sources due to their general higher tolerance to contaminants than other fuel cells. It opens up for an easier transition from conventional power generation with hydrocarbon-based fuels to hydrogen energy by fuel cells. Due to the increasing global awareness of how energy production and utilization affect the environment, the interest of use of renewable energy has increased and fuel cells have the potential to be a part of a sustainable solution. Attractive fuels, which are considered in this study, are methanol, ethanol, di-methyl-ether, ammonia and biogas. It is concluded that it is feasible for SOFCs to handle all the studied fuels. An analysis of the fuels at the same temperature (298 K and 1000 K) is conducted and evaluates the heat required for each mole H2 converted. It shows that methane is possibly more efficient as it uses twice as much heat as methanol and DME do. More advanced methods to investigate surface reactions are prospected to contribute, in combination with better catalysts, to more efficient reforming of the fuels.
|
|
