| 1. |
- Andersson, Martin, et al.
(författare)
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Chemical reacting transport phenomena and multiscale models for SOFCs
- 2008
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Ingår i: Advanced Computational Methods and Experiments in Heat Transfer. - 9781845641221 ; X, s. 69-79
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Konferensbidrag (refereegranskat)abstract
- Electrochemical reactions at the anode triple phase boundary (TPB) proceed on the basis of the fuel concentration, which depends on transport processes within the porous anode and the heterogeneous reforming chemistry. Microscale modeling is needed to describe these interactions with an acceptable accuracy. The aim of this article is to investigate if it is possible to use a multiscale approach to model solid oxide fuel cells (SOFCs) and combine the accuracy at microscale with for example the calculation speed at macroscale to design SOFCs, based on a clear understanding of transport phenomena and functional requirements. A literature review is made to find out what methods can be used to model SOFCs and also to sort these models after length scale. Couplings between different methods and length scales, i.e., multiscale modeling, are outlined. The SOFC microscale model corresponds in many cases to the atom or molecular level, such as Lattice Bolzmann Method, Density Functional Theory, Molecular Dynamics, Dusty Gas Model, Ficks Model and Stefan-Maxwell Model. SOFC modeling in the mesoscale can be done with Kinetic Monte Carlo. Macroscale models match to the global flow field. Finite Element Method and Finite Volume Method are used to model SOFCs in the macroscale. Multiscale modeling is a promising tool for fuel cell research. COMSOL Multiphysics, based on the Finite Element Method as well as FLUENT, based on the Finite Volume Method, can be used to couple different physical models at different scales. Multiscale modeling increases the understanding for detailed transport phenomena, and can be used to make a correct decision on the specific design and control of operating conditions. It is expected that the development- and production cost will decrease as the understanding of complex phenomena increases.
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| 2. |
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| 3. |
- Gylys, J., et al.
(författare)
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Pecularities of heat transfer from in-line tube bundles to upward aqueous foam flow
- 2008
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Ingår i: Advanced Computational Methods and Experiments in Heat Transfer X. - 9781845641221
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Konferensbidrag (refereegranskat)abstract
- Four in-line tube bundles with different geometry were investigated for establishing their performance in terms of heat transfer enhancement. Two-phase aqueous foam was used as a coolant. Such coolant was considered, because our previous research showed that large heat transfer intensity may be reached even at small mass flow rate of the foam. Spacing among the centres of the tubes across the first in-line tube bundle was 0. 03 m and spacing along the bundle was 0. 03 m. In the second case spacing among the centres of the tubes across the bundle was 0. 03 m; spacing along the bundle was 0. 06 m. In the third case spacing was accordingly 0. 06 and 0. 03 and in the last case spacing was accordingly 0. 06 m and 0. 06 m. During an experimental investigation it was determined a dependence of heat transfer intensity on flow parameters. The investigation of heat transfer from the bundle to upward vertical foam flow was provided for three different values of foam volumetric void fractions β=0. 996÷0. 998. The velocity of the foam flow was changed from 0. 14 to 0. 30 m/s. The heat transfer coefficient varied from 200 to 2000 W/(m2K) for the above mentioned foam flow parameters.
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| 4. |
- Selimovic, Faruk, et al.
(författare)
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Numerical simulation of fluid flow in a monolithic exchanger related to high temperature and high pressure operating conditions
- 2008
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Ingår i: Advanced Computational Methods and Experiments in Heat Transfer X. - 9781845641221 ; 61, s. 25-35
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Konferensbidrag (refereegranskat)abstract
- The purpose of this work is the enhancement of performance by a new design of monolithic heat exchangers under steady-state operating conditions. Heat transfer phenomena and hydrodynamics have been studied and visualized by computational fluid dynamics (CFD). Further, a simple gas distribution system has been analyzed in purpose to find the best performance of the exchanger. To achieve this, 3D simulations of air flow were performed. One of characteristics of monolithic structures is the low pressure drop and high heat transfer coefficient. This is because they operate in the laminar flow regime and have high compactness. However, some experimental studies show that when two fluids are introduced into monolith channels, the manifolds cause severe pressure losses. Therefore, in this work, turbulent flow regime at low Reynolds numbers has been investigated to find the difference and better understanding of these structures, which are of interest in high temperature applications today. The simulation shows that the pressure drop of the gas flow distributor is a key parameter affecting the heat transfer in the exchanger channels.
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| 5. |
- Sterner, Dirk, et al.
(författare)
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Predictive modelling of heat and mass transfer in hamburger patties
- 2002
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Ingår i: Seventh International Conference on Advanced Computational Methods in Heat Transfer. Heat Transfer VII. - 1853129062 ; 4, s. 283-292
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Konferensbidrag (refereegranskat)abstract
- This study concerns fundamental analysis and predictive modelling of heat and mass transfer in frozen hamburger patties cooked in a double-sided contact fryer. Mathematical and physical models are formulated and further developed to enable improved understanding of the transport processes and reveal the influence of essential parameters. Prediction and analysis of practical situations with heating are investigated. The coupled governing partial differential equations are solved by a finite difference technique. In particular, the boundary conditions are treated carefully. The mathematical and physical models, the governing equations and the boundary conditions are presented in detail and special care is taken in the frozen region. The numerical method is briefly described. Results from a few simulations are reported. Parametric studies were carried out by changing the contact heat transfer coefficient, effective thermal conductivity for the core, effective specific heat in the core, the initial freezing temperature, diffusion coefficient and the mass fraction of ice. The calculated cooking time was found to be most influenced by the effective thermal conductivity and effective specific heat. in the core and the heat transfer coefficient, in descending order of importance
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| 6. |
- Wang, Q., et al.
(författare)
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Design Optimization and Performance Prediction of Compact Heat Exchangers
- 2014
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Ingår i: Emerging Topics in Heat Transfer: Enhancement and Heat Exchangers. - 9781845648183 - 9781845648190 ; , s. 301-319
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Bokkapitel (refereegranskat)abstract
- Applications of genetic algorithms (GAs) and artificial neural networks (ANNs) in thermal engineering have received much attention. Compact heat exchangers (CHEs) have special merits of high-performance and compactness and are widely used in various applications of energy and power engineering. This chapter demonstrates optimization design of a plate-fin heat changer and performance prediction of three kinds of tube-fin heat exchangers by a GA and an ANN, respectively. The successful applications of optimization and prediction of CHEs suggest that GAs and ANNs have strong ability of intelligent design and prediction of CHEs.
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| 7. |
- Wang, Qiuwang, et al.
(författare)
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Preface
- 2014
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Ingår i: Emerging Topics in Heat Transfer: Enhancement and Heat Exchangers. - 9781845648183 - 9781845648190
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Bokkapitel (refereegranskat)
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| 8. |
- Xie, G., et al.
(författare)
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Heat Transfer Enhancement of a Gas Turbine Blade-Tip Wall
- 2014
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Ingår i: Emerging Topics in Heat Transfer: Enhancement and Heat Exchangers. - 9781845648190 ; , s. 67-88
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Bokkapitel (refereegranskat)abstract
- The blade-tip region encounters high thermal loads because of the hot gas leakage flows. A common way to cool blade tips is to design serpentine passages with 180 degrees turn with the blade-tip walls inside the turbine blades. Improved internal convective cooling is therefore required to increase blade-tip lifetime. This chapter summarizes the heat transfer enhancement of an internal blade-tip wall having pins, dimples and protrusions, and the influence of guide ribs and pins material. It is found that the pinned tip exhibits best performance to improve the blade-tip cooling. However, when considering the added mechanical stress, making dimples is a more suitable way especially at low Reynolds numbers. Properly designed guide ribs might reduce the pressure loss.
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| 9. |
- Yuan, Jinliang, et al.
(författare)
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Analysis of Water Condensation and Two-phase Flow in a Channel Relevant for Plate Heat Exchangers
- 2006
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Ingår i: Advanced Computational Methods in Heat Transfer IX. - 1845641760 ; 53, s. 351-360
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Konferensbidrag (refereegranskat)abstract
- Water vapor condensation and two-phase flow appear in plate heat exchangers being used as condensers. Analysis of water phase change and flow dynamics is an important but complicated task due to large change in water physical/transport properties across the water liquid-vapor interface boundary. In particular, a singular-link behaviour in Navier-Stokes (N-S) equations is present due to the large step change in the density when computational simulation methods are applied. Conventional methods using ensemble averaged parameters such as void fraction are impossible to be applied to cases where high-resolution calculations and detailed analysis are required. In this study, a computational fluid dynamics (CFD) approach is presented for analysis of water vapor condensation and two-phase flow in a channel relevant for plate heat exchanger parallel plates. The developed model is based on the governing equations which are directly solved for the entire single- and two-phase fields. The water phase change and two-phase flow are treated by employing a water liquid-phase fraction factor based on the total enthalpy in each computational cell. The factor is defined as the ratio of the total enthalpy differential to the latent heat of condensation. The density, viscosity and conductivity of the two-phase region are calculated and updated based on the calculated value of the liquid-phase fraction factor until a converged result is reached. It is revealed that, among others, the inlet vapor velocity has significant effects on the water phase change and two-phase flow in the channel, in terms of liquid-water fraction factor distribution.
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| 10. |
- 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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