The Effect of Plugging Tubes on the Gas Mixing in AGR Boilers

1. The Effect of Plugging Tubes on the Gas Mixing in AGR Boilers Alastair West 1st Year EngD student

2. Outline • Background to the Problem • Overall Objectives of Research • Use of Code_Saturne • Future Developments

3. Background • 30 years of AGR operation have lead to boiler tubes being ‘plugged’ in order to prevent leakage into the primary circuit • Adverse effect on the spread of stream temperatures within the boiler tubes and therefore on the stability at low loads • Effect will deteriorate with time, threatening the scheduled lifetime of the AGRs

4. Overall Objective • Current boiler code (HEBMIX) is a design-specific lumped-parameter code using potentially inaccurate mixing data when plugged tubes are considered • Provide a sensible computer-based predictive model of the effect of tube plugging into the existing boiler code for designs at Hinkley Pt B and Hunterson B

5. Boiler Geometry

6. Experimental Data • Configuration suggests extremely good CO2 mixing • Distinct sideways drift of the peak on each successive temperature profile curve • Predicted overall swirling motion inside the boiler casing.

7. Predicted Swirl

8. Initial Calculations • Square in-line configurations of different pitch (longitudinal and transverse pitch are equal) (1.4, 1.5 & 1.6) • Include heat transfer prediction • Deduce best performing turbulence model • Validate with LES data from Afgan and experimental data from Aiba, 1982

9. Mesh

10. Future Extensions • Coarsen mesh in order to include all 22 tube rows and unit casing, whilst still capturing the secondary flow and blank tube effects • Does this change from initial flow calculations with periodic boundary conditions?

11. Long-term Developments • Implement Analytical or Numerical Wall Function treatments in order to compute • Use conjugative heat transfer • Implement improvements to the current lumped-parameter boiler code (HEBMIX)

12. Improvements on an unsteady eddy viscosity model with stress-strain lag sensitivity Neil Ashton 1st Year PhD student

13. Background • A eddy viscosity model based on the SST model with an added transport equation to model the stress-strain lag was developed by Revell (2006) • This model will be developed further and implemented with the Phi-alpha model of Billard (2009) to see if this brings any improvements over the current SST model which it is based upon. • Work will be undertaken to understand the benefits of the SST model against the Phi-α with the aim of making the C_as model of Revell more robust and suitable for a range of flows

14. Current Work I am currently getting to grips with Code Saturne, by running several test cases including Channel flow at various Reynolds numbers and a NACA0012 airfoil at high incidence. Further test cases will be an oscillating channel flow and a diffuser in the short term. With more complex cases relating the motorsport section being in the long term. I haven’t been using the GUI as I wanted to get to grips with the subroutines, and also because I will need a good knowledge of these before I can implement any improvements to these models.

15. NACA0012

16. Future work The C_as model of Revell is currently implemented in the 1.1 version of Saturne and thus my task this summer will be to update this to the current 1.4 version. This will be a big task to someone who is relatively new to Saturne and this is way I am getting to grips with Saturne via test cases first to gain an further understanding before getting into the many subroutines which will need updating. The use of this model in a hybrid RANS/LES scheme is something which could be investigated in the future depending on how well the new model performs.

17. Thank you