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Numerical Investigation of Mixed Convection in AGRs By Amir Keshmiri

Internal Seminar at the University of Manchester – 07/11/2007. Numerical Investigation of Mixed Convection in AGRs By Amir Keshmiri Supervisors: Prof. Dominique Laurence and Dr. Mark Cotton School of Mechanical, Aerospace & Civil Engineering (MACE) The University of Manchester. Outline.

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Numerical Investigation of Mixed Convection in AGRs By Amir Keshmiri

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  1. Internal Seminar at the University of Manchester – 07/11/2007 Numerical Investigation of Mixed Convection in AGRs By Amir Keshmiri Supervisors: Prof. Dominique Laurence and Dr. Mark Cotton School of Mechanical, Aerospace & Civil Engineering (MACE) The University of Manchester

  2. Outline • Introduction to AGRs • Ascending/Descending Flows • The Geometry Studied • Some Results • Conclusions • Future Work

  3. [http://www.gen-4.org] [http://gt-mhr.ga.com] Advanced Gas-Cooled Reactors (AGRs)

  4. [The Safety of the AGR by J M Bowerman (1982)] Advanced Gas-Cooled Reactors (AGRs)

  5. Advanced Gas-Cooled Reactors (AGRs) [The Safety of the AGR by J M Bowerman (1982)]

  6. Ascending/Descending Flows; Enhancement/Impairment of Heat Transfer

  7. or • Radius=0.1 m • Ascending Flow • Constant Heat Flux BC • ‘Boussinesq’ Approximation Key Features of the Flow Problem • Solution Methods • In-House Code (CONVERT) • Commercial CFD Package (STAR-CD) • Industrial Code (Code_Saturne)

  8. Continuity: Momentum: Energy: The Governing Equations

  9. The Geometry Used in ‘CONVERT’ • An in-house Fortran77 Code, ‘CONVERT’ (for Convection in Vertical Tubes) • Finite Volume/Finite Difference Code • Parabolic governing equations i.e. Marching problem

  10. RANS 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]

  11. RANS Results 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

  12. Gr/Re^2=0 – Forced Convection

  13. Gr/Re^2=0 – Forced Convection

  14. Gr/Re^2=0 – Forced Convection

  15. Gr/Re^2=0 – Forced Convection

  16. Gr/Re^2=0.087 – Laminarization

  17. Gr/Re^2=0.087 – Laminarization

  18. Gr/Re^2=0.087 – Laminarization

  19. Gr/Re^2=0.087 – Laminarization

  20. Budgets of Turbulent Kinetic Energy Gr/Re^2=0.0 Gr/Re^2=0.087

  21. Heat Transfer Enhancement/Impairment

  22. Heat Transfer Enhancement/Impairment

  23. Heat Transfer Enhancement/Impairment

  24. Nu and Cf Developments

  25. Nu and Cf Developments

  26. Effects of Reynolds Number

  27. Effects of Reynolds Number

  28. Conclusions • 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.

  29. Future Work • 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.

  30. Acknowledgements 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

  31. References [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))

  32. THE END THANK YOU

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