Modelling of In-Line Tube Banks inside Advanced Gas-Cooled Reactor Boilers

  • James Blackall

Student thesis: Phd


This doctoral thesis concerns itself with the simulations of turbulent fluid flows with heat transfer about serpentine tube boiler geometries, with the aim of developing the tools necessary to tackle research questions put forward by the EDF Energy R&D UK Centre with regard to their continued use beyond their original decommissioning date in a safe manner. This is in support of the Plant Lifetime Extension, or PLEX, scheme currently being implemented by EDF to safely lengthen the operational lifespan of their Advanced Gas-Cooled Reactor (AGR) fleet, which provide a significant portion of the UK’s energy demands, without large-scale reactor deployments to replace them. Among the key components that ageing affects most significantly are the serpentine boiler systems used by some of the newer AGR designs, where fatigue and corrosion damage have forced operators to plug individual tube platens to prevent feedwater escaping and coming into contact with the graphite core. The primary coolant is CO 2 , which is heated by the reactor core before coming into thermal contact with the boiler tubes, producing steam. The flow domain is an in-line tube bank with alternating longitudinal pitch, and so this report utilises Code Saturne, a general-purpose Computational Fluid Dynamics package developed by the wider EDF R&D teams, on an idealised square in-line tube bank validation case assuming flow periodicity, along with supporting software packages. Chapter 1 contains a discussion on AGR technology, introduces the problem definition, and the main research outcomes expected by EDF Energy by the doctorate’s end. Chapter 2 documents a review of pertinent literature concerning flows about cylinders and tube banks, and the heat transfer processes which occur across them. Chapter 3 outlines the software packages and the methods used to simulate fluid problems via the Finite Volume Method, along with the reasons for their selection. Chapter 4 is entirely dedicated to turbulence modelling and explores in detail many of the strategies used to account for it, though it is not exhaustive. Chapter 5 introduces the concept and underlying reasoning behind the Analytical Wall Function (AWF) of Suga et al. (2006), which enables the possibility of improved near-wall behaviour for high-Reynolds number turbulence modelling approaches and an extension to account for augmented surface roughness. Chapter 5 also documents precisely how this AWF modelling approach has been implemented in Code Saturne for the first time as part of this research work. Chapter 6 presents the methodology behind simulating a square in-line tube bank using flow periodicity, and the results obtained from 2D and 3D appraisals using Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) approaches, with temperature operating as a passive scalar while thermal fluid properties are held constant, both with and without the AWF implementation. Chapter 7 addresses a similar methodology, except on a problem of greater interest to the application, a spanwise-periodic platen geometry consisting of four tube platens with ten passes through the flow domain, with confining walls, where tube blanking is represented and the properties of carbon dioxide can now vary freely with temperature. Attempts are made also to definitively quantify the effect of blanking and augmented roughness on impairments of heat transfer through the system, to give some indication as to its safe operational lifespan. Finally, the conclusions from each chapter are presented, along with a discussion on potential avenues for further exploration. Appendices A and B list some of the more lengthy formulations and derivations used within the AWF implementation respectively, while Appendix C contains some supplementary results from Chapter 7 not critical to the discussion taking place there. The findings here indicate that in a worst-case scenario, at current reactor capacity, approximately 30% of heat tra
Date of Award31 Dec 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorHector Iacovides (Supervisor) & Juan Uribe Torres (Supervisor)

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