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Numerical Investigation of Mixed Convection in AGRs By Amir Keshmiri
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Numerical Investigation of
Mixed Convection in AGRs
ByBy
Amir KeshmiriAmir Keshmiri
Supervisors:Supervisors: Prof. Dominique Laurence and Dr. Mark Cotton Prof. Dominique Laurence and Dr. Mark Cotton
School of Mechanical, Aerospace & Civil Engineering (MACE)School of Mechanical, Aerospace & Civil Engineering (MACE)
The University of ManchesterThe University of Manchester
Internal Seminar at the University of Manchester – 07/11/2007Internal Seminar at the University of Manchester – 07/11/2007
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OutlineOutline
• Introduction to AGRs
• Ascending/Descending Flows
• The Geometry Studied
• Some Results
• Conclusions
• Future Work
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[http://gt-mhr.ga.com]
[http://www.gen-4.org]
Advanced Gas-Cooled ReactorsAdvanced Gas-Cooled Reactors (AGRs) (AGRs)
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[The Safety of the AGR by J M Bowerman (1982)]
Advanced Gas-Cooled ReactorsAdvanced Gas-Cooled Reactors (AGRs) (AGRs)
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Advanced Gas-Cooled ReactorsAdvanced Gas-Cooled Reactors (AGRs) (AGRs)
[The Safety of the AGR by J M Bowerman (1982)]
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Ascending/Descending Flows; Ascending/Descending Flows; Enhancement/Impairment of Heat TransferEnhancement/Impairment of Heat Transfer
2w
4qgDGr
8.0425.34108
PrReD
DGrBo
UD
D Re
ehD
Nu
pCPr
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Solution MethodsSolution Methods
• In-House Code (CONVERT)In-House Code (CONVERT)
• Commercial CFD Package (STAR-CD)Commercial CFD Package (STAR-CD)
• Industrial Code (Code_Saturne)Industrial Code (Code_Saturne)
• or
• Radius=0.1 m
• Ascending Flow
• Constant Heat Flux BC
• ‘Boussinesq’ Approximation
180Reτ 5300ReD
Key Features of the Flow ProblemKey Features of the Flow Problem
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The Governing EquationsThe Governing Equations
0)(1
z
W
r
rV
r
Continuity:
zt gTTr
Wr
rr
dz
dpW
zrVW
rr
)0
2
(1)(1
)()(1
Momentum:
r
Tr
rrWT
zrVT
rr t
t )Pr
(1
)()(1
Energy:
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The Geometry Used in ‘CONVERT’The Geometry Used in ‘CONVERT’
RUN1=‘approximate turbulent flow’
RUN2=‘fully developed flow’
R Marching
• An in-house Fortran77 Code, ‘CONVERT’ (for Convection in Vertical Tubes)
• Finite Volume/Finite Difference Code
• Parabolic governing equations i.e. Marching problem
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RANS ResultsRANS Results
The Turbulence Models Tested by CONVERT :
• Launder-Sharma k-ε model [1]
• Cotton-Ismael k-ε-S model [2]
• Suga NLEVM [3]
The Results are validated against:
• DNS of You et al (2003) [4]
• LS of Kim et al (2006) [5]
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The analysis focuses on 4 cases:
• Gr/Re^2=0.000 Forced Convection
• Gr/Re^2=0.063 Early onset Mixed Convection
• Gr/Re^2=0.087 Laminarization
• Gr/Re^2=0.241 Recovery
RANS ResultsRANS Results
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Gr/Re^2=0 – Forced ConvectionGr/Re^2=0 – Forced Convection
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Gr/Re^2=0 – Forced ConvectionGr/Re^2=0 – Forced Convection
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Gr/Re^2=0 – Forced ConvectionGr/Re^2=0 – Forced Convection
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Gr/Re^2=0 – Forced ConvectionGr/Re^2=0 – Forced Convection
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Gr/Re^2=0.087 – LaminarizationGr/Re^2=0.087 – Laminarization
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Gr/Re^2=0.087 – LaminarizationGr/Re^2=0.087 – Laminarization
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Gr/Re^2=0.087 – LaminarizationGr/Re^2=0.087 – Laminarization
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Gr/Re^2=0.087 – LaminarizationGr/Re^2=0.087 – Laminarization
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Budgets of Turbulent Kinetic EnergyBudgets of Turbulent Kinetic Energy
Gr/Re^2=0.087Gr/Re^2=0.087Gr/Re^2=0.0Gr/Re^2=0.0
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Heat Transfer Enhancement/ImpairmentHeat Transfer Enhancement/Impairment
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Heat Transfer Enhancement/ImpairmentHeat Transfer Enhancement/Impairment
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Heat Transfer Enhancement/ImpairmentHeat Transfer Enhancement/Impairment
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Nu and Cf DevelopmentsNu and Cf Developments
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Nu and Cf DevelopmentsNu and Cf Developments
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Effects of Reynolds NumberEffects of Reynolds Number
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Effects of Reynolds NumberEffects of Reynolds Number
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ConclusionsConclusions
• Mixed convection in an ascending flow in a heated pipe, is a very complex phenomenon, despite its simplicity; Thus requires more research.
• Most of the turbulence models successfully predict the flow field at relatively low heat loading i.e. small Gr/Re^2
• Only very few turbulence models (only Linear k-ε) can predict the Re-laminarization Phenomena.
• There is a close agreement between the results of Code_Saturne and STAR-CD for the tested models.
• The relatively more advanced turbulence models, such as Non-Linear k- of Suga and V2f models are observed to suffer from convergence problems at high Gr/Re^2.
• The few available DNS data are not sufficient to carry out in depth validation of the RANS models, particularly at the maximum heat transfer impairment point.
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• Development of Code_Saturne by implementing some advanced wall functions such as Analytical and Numerical Wall Functions.
• Cross examination of Code_Saturne with TEAM and STREAM Codes.
• Testing more complex geometries such as rib roughened surfaces, etc.
Future WorkFuture Work
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AcknowledgementsAcknowledgements
This work was carried out as part of the TSEC programme KNOO and as such we are grateful
to the EPSRC for funding under grant EP/C549465/1
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ReferencesReferences
[1] Launder, B.E. and Sharma, B.I., 1974, “Application of the energy dissipation model of turbulence to the calculation of flow near a spinning disc”, Lett. Heat Mass Transfer, 1, pp. 131-138.
[2] Cotton, M.A., Ismael, J.O., 1998, “A strain parameter turbulence model and its application to homogeneous and thin shear flows”, Int. J. Heat Fluid Flow 19, pp. 326–337.
[3] Craft, T.J., Launder, B.E. and Suga, K. 1996, “Development and application of a cubic eddy-viscosity model of turbulence”, Int. J. Heat Fluid Flow, 17, pp. 108-115
[4] You, J., Yoo, J.Y. and Choi. H., 2003, “Direct Numerical Simulation of Heated Vertical Air Flows in Fully Developed Turbulent Mixed Convection”, Int. J. Heat Mass Transfer, 46, pp.1613-1627
[5] Kim, W.S., Jackson, J.D. and He, S. (2006), “Computational Investigation into Buoyancy-Aided Turbulent Flow and Heat Transfer to Air in a Vertical Tube”, Turbulence, Heat and Mass Transfer, 5, (Hanjalić, K., Nagano, Y. and Jakirlic, S. (Editors))
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THE ENDTHE ENDTHANK YOUTHANK YOU