| 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. |
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| 3. |
- Jia, Rongguang, et al.
(författare)
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Impingement cooling in a rib-roughened channel with cross-flow
- 2001
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Ingår i: International Journal of Numerical Methods for Heat & Fluid Flow. - : Emerald. - 1758-6585 .- 0961-5539. ; 11:7, s. 642-662
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Tidskriftsartikel (refereegranskat)abstract
- A numerical investigation to determine the velocity and heat transfer characteristics of multiple impinging slot jets in rib-roughened channels in the presence of cross-flow has been carried out. Fluid flow is modeled using an explicit algebraic stress model. A simple eddy diffusivity and a generalized gradient diffusion hypothesis are applied for the modeling of turbulent heat fluxes. The computations are validated against available experimental fluid flow and heat transfer data. Different size and arrangement of jets and ribs are considered in detail, while the Reynolds numbers of a jet and the channel inlet are fixed at 6,000 and 14,000, respectively. Results show that the ratio (B/W) between the size of the jets and ribs is most important. An explanation is that the ribs inhibit the motion of eddies by preventing them from coming very close to the surface when B/W is low, e.g. B/W = 1, although the ribs will increase the turbulence intensity. This blockage limited the heat transfer enhancement effect of the ribs and impinging jets.
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| 4. |
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| 5. |
- Jia, Rongguang, et al.
(författare)
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Numerical assessment of different turbulence models for slot jet impinging on flat and concave surfaces
- 2002
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Ingår i: American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI. ; 3 B, s. 815-822
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Konferensbidrag (refereegranskat)abstract
- A numerical study has been carried out for slot jet impinging on flat and concave surfaces. Five turbulence models are employed for the predictions of these strongly strained turbulent flows, namely linear eddy viscosity model (LEVM), low-Re explicit algebraic Reynolds stress model (EASM) and three different V2F models. A bounded formulation for Cμ was also introduced to account for the better prediction of the wall jet development. The studied Reynolds numbers vary from 8,000 to 20,000, and nozzle-to-surface distance (H) is in the range of 1 [less-than or equal to] H/B [less-than or equal to] 8. Detailed comparison is made between the results from the models and available experimental data to test the ability of the models in predicting these fluid flow and heat transfer problems.
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| 6. |
- Jia, Rongguang, et al.
(författare)
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Numerical investigation of impingement cooling in ribbed ducts due to jet arrays
- 2003
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Ingår i: Journal of Enhanced Heat Transfer. - 1563-5074. ; 10:3, s. 243-255
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Tidskriftsartikel (refereegranskat)abstract
- A numerical investigation of impingement heat transfer and fluid flow in a rectangular two-pass duct was carried out. The impingement wall was smooth or with periodically mounted square ribs. A multiblock parallel CFD code was employed for the calculation. The turbulence modeling was treated by applying a low Reynolds number turbulence eddy viscosity model (LEVM) and a V2F model. First, the calculations were validated against available experimental data in a two-pass duct where the impingement wall was smooth. Then, jets impinging on ribbed walls were simulated. The distance from the nozzle to the impingement wall was fixed at four nozzle diameters (d). The square rib width was set as 0.5 d. The duct inlet Reynolds number was fixed at 10,000. Results show that the presence of ribs was favorable for the heat transfer enhancement on the impingement wall, but not for the side wall.
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| 7. |
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| 8. |
- Rokni, Masoud, et al.
(författare)
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A study on turbulent flow characteristics in ducts of relevance for heat exchangers
- 2004
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Ingår i: International Journal of Transport Phenomena. - 1540-0069. ; 6:3, s. 225-226
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Tidskriftsartikel (refereegranskat)abstract
- The performance of an explicit algebraic stress model with a cubic equation for closure constants is assessed in predicting the turbulent flow dynamics of ducts relevant for heat exchangers. The use of a cubic equation allows elimination of any damping functions in the tensor representation for the Reynolds stresses and thereby improves prediction of turbulent stresses theoretically. The methodology used here allows for prediction of Cm in any spatial points and eliminates the use of damping functions in the turbulent viscosity. A flow parameter, which characterizes the flow type from plane strain and plane shear to elliptical flows, is used to prescribe the flow type in the ducts under consideration. In all cases, isothermal conditions are imposed on the duct walls, and the turbulent heat fluxes are modeled using a new bounded quadratic generalized gradient-diffusion type model. In addition, the calculated results are compared with existing experimental data and satisfactory results are obtained. A comparison of velocity and temperature contours is shown in order to study the effect of waviness on flow/heat dynamics.
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| 9. |
- Rokni, Masoud, et al.
(författare)
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An explicit WET-type model for the turbulent scalar fluxes
- 2002
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Ingår i: Advances in Fluid Mechanics. AFM 2002. Fourth International Conference. - 1853129100 ; , s. 55-64
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Konferensbidrag (refereegranskat)abstract
- A new explicit WET model for the turbulent heat fluxes is derived and developed from the transport equation of the scalar passive flux. In order to study the performance of the model itself, all other turbulent quantities are taken from a DNS channel flow data-base and thus the error source has been minimized. This anisotropic eddy diffusivity model can be solved with a two-equation model for the temperature field based on the temperature variance and its dissipation rate. The model can theoretically be used for a range of Prandtl numbers or a range of different fluids. The results are compared with the DNS channel flow and fairly good agreement is achieved
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| 10. |
- Rokni, Masoud, et al.
(författare)
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Calculation of turbulent fluid flow and heat transfer in ducts by a full Reynolds stress model
- 2003
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Ingår i: International Journal for Numerical Methods in Fluids. - : Wiley. - 1097-0363 .- 0271-2091. ; 42:2, s. 147-162
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Tidskriftsartikel (refereegranskat)abstract
- A computational method has been developed to predict the turbulent Reynolds stresses and turbulent heat fluxes in ducts by different turbulence models. The turbulent Reynolds stresses and other turbulent flow quantities are predicted with a full Reynolds stress model (RSM). The turbulent heat fluxes are modelled by a SED concept, the GGDH and the WET methods. Two wall functions are used, one for the velocity field and one for the temperature field. All the models are implemented for an arbitrary three-dimensional channel. Fully developed condition is achieved by imposing cyclic boundary conditions in the main flow direction. The numerical approach is based on the finite volume technique with a non-staggered grid arrangement. The pressure-velocity coupling is handled by using the SIMPLEC-algorithm.. The convective terms are treated by the van Leer scheme while the diffusive terms are handled by the central-difference scheme. The hybrid scheme is used for solving the e equation. The secondary flow generation using the RSM model is compared with a non-linear k-epsilon model (non-linear eddy viscosity model). The overall comparison between the models is presented in terms of the friction factor and Nusselt number. Copyright (C) 2003 John Wiley Sons, Ltd.
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