Thermal-Hydraulic Analysis in Support to the Integrated Circulation Experiment ICE

1. Thermal-Hydraulic Analysis in Support to the Integrated Circulation ExperimentICE Presentedby Vincent Moreau CRS4, Energy & Environment Program WP 4.5 meeting FZR 22-06-2006

2. Objectives • support to the experiment • Check pre-sizing • Propose pre-sizing • Help understanding • Get confidence with CFD tool • Show it gives results at least as good as 1D analysis • Find its place between 1D analysis and experiment • Possibility to inquire on details • Allow to explore geometrical assembly not analyzable in 1D

3. ToolStar-CD software suite ( Version 4, beta)Allowing • Enhanced meshing capability: access to complex 3D geometry • Velocity field: evaluation of corrosion risk • Temperature field: onset of freezing, melting or evaporation • Pressure field: onset of cavitation • Conjugated (between fluid and solid) Heat transfer: Heat removal of electrically heated pin • Multi-stream: Heat Exchanger • Free Surface (with strong limitation): Beam target position • Two-phase flow (idem): Gas-lift pump

4. Three different simulations • Heat removal of an electrically heated pin bundle • Two-phase flow separation at the gas-lift pump top • Heat Exchanger characterization

5. Simulation 1:Heat Removal of an electrically heated Pin Bundle • Objective: • Check 1D pre-sizing • Check/Set up CFD tool • Main Features: • Extrusion of a 2D geometry • Temperature field • Heat source • Conjugated Heat Transfer

6. Simulation 2:Two-phase flow separation at the gas-lift pump top • Objective: • Propose consistent precise geometry • Avoid large gas transfer in the Heat Exchanger • Ensure that “free surface” is not necessary for the Heat Exchanger simulation • Main Features: • Complex Geometry • Two-phase flow • Multiple pressure boundaries

7. Simulation 3: Heat Exchanger characterization • Objective: • Check 1D pre-sizing • Check consistency of the connector sizing • Avoid large local velocity • Avoid Hot/Cold points • Check that “free surface” is not a necessary tool • Main Features: • Complex Geometry • Conjugated Heat transfer • Multi-stream (14)

8. Free-Surface in Star-CD V4 • Implementation based on VOF method with “contracting” sharp density interface tracking convective scheme • Force Unsteady Flow simulation • Force Upwind differencing for the convective scheme • Difficult to initialise • Stable for density ratio about 1000 but unstable for density ratio about 10000, typical of Air-LBE at 1Atm => To avoid unless critically necessary, specially for steady flows

9. Two-phase flows in Star-CD V4 • Eulerian approach: two interconnected continua • Permit Steady State Simulation • Force Upwind differencing for the convective scheme • Difficult to initialise often giving long convergence time • Unstable for large density ratio if the heavy phase volume fraction a goes to zero, unless the light phase viscosity is largely increased, which in turn gives unrealistic profiles • On pressure boundaries, both phases flow must be oriented the same, may be sometimes unphysical (low velocity gas exit). • Avoid unless critically necessary, Carefully avoid that a goes to 0 somewhere

10. Physical Properties Thermo-physical Properties of LBE in function of temperature [°C]. Thermo-physical Properties of Steel in function of temperature [°C].

11. Simulation 1:Heat Removal of an electrically heated Pin Bundle • Geometry Main Features: • Extrusion of a 2D geometry • Hexagonal Geometry => only 1/12th of domain to simulate • Heat source as heat flux at the boundary • Conjugate Heat Transfer on only one pin to check equivalence of wall temperature representation • No heat transfer through (lacking) solid parts (conservative shortcut)

12. Mesh and Flow features Domain: 1m high, radius about 4 cm, pin diameter 8.2 mm PbBi inlet on bottom: upward velocity 2. m/s, temperature 300 C, Reynolds  40000. Turbulence intensity 5% and length scale 0.1 mm. PbBi outlet on top. Two lateral symmetry planes. Fixed temperature 300 C with resistance 10-3 m2 K/W on the external wall. Fixed heat flux such as to get 106W/m2 on the active pin walls for a total of 800/12 kW. Adiabatic on the inactive half-pin wall. Numerical schemes and turbulent models: StarCD MARS TVD scheme and k-e model RNG variant. Stationary Calculation, SIMPLE algorithm. Table : main characteristics on the pin mesh

13. Simulation 1: main results • Bundle correctly sized • Star-CD and Fluent give very similar results • Maximum temperature and velocity under control

14. Velocity field Uniform inlet velocity main not be really consistent with the experiment

15. Simulation 2:Two-phase flow separation at the gas-lift pump top Objective: • Propose consistent precise geometry • Avoid large gas transfer in the Heat Exchanger • Ensure that “free surface” is not necessary for the Heat Exchanger simulation Main Features: • Complex Geometry • Rather small bounding dimensions • Two-phase flow • Multiple pressure boundaries Shortcuts: • Gas phase incompressible • Gas density 10kg/m3

16. Simulation 2: Proposed Geometry • Relatively large connector (10 cm Diameter) • Small penetration of the connector inside the expansion tube • Large penetration of the riser in the expansion tube • Slanted cut to allow expansion and hide connector

17. Simulation 2: Mesh • Initial objective was to have the gas phase completely separated on the top • Small penetration of the connector inside the expansion tube • Large penetration of the riser in the expansion tube • Slanted cut to allow expansion and hide connector • Numerical outlets, large pressure outlets being unstable • Unstructured base and extrusion • Mesh: 286 000 Cells

18. Simulation 2: Results Gas Volume Fraction, Bubble Diameter 1mm Gas Volume Fraction, Bubble Diameter 3mm

19. Simulation 2: Results LBE Velocity, Bubble Diameter 3mm Gas Velocity, Bubble Diameter 3mm

20. Simulation 3: Heat Exchanger characterization • Objective: • Check 1D pre-sizing • Check consistency of the connector sizing • Avoid large local velocity • Avoid Hot/Cold points • Check that “free surface” is not a necessary tool • Main Features: • Complex Geometry • Conjugated Heat transfer • Multiple pressure boundaries • Multi-Stream (14) • Shortcuts : • Single phase flow • Half domain (for now) • No free surface • k(T91) fixed at 28.5

21. Simulation 3: Mesh (1/3) • No penetration of the connector inside the Hex • 14 Stream (1 LBE, 13 Water) • Unstructured base and extrusion • Unstructured connector “stuck” to the extrusion mesh • Mesh: 1.15E6 Cells: LBE: 5.4E5, Steel: 2.5E5 (3 rows),Water: 3.6E5

22. Simulation 3: Mesh (2/3)

23. Simulation 3: Mesh (3/3)

24. Simulation 3: Mesh (4/4)

25. Simulation3: Main results • Simulation converges fast with UD, but keep high mass residual with MARS: to be investigated (buoyancy ?) • Heat Exchanged: • Global 4.5E5 W (Half Domain) • Single pipe Minimum: 3.20E4 W • Single Pipe Maximum: 3.73E4 W • Maximum velocity: 1.4 m/s, pipe in front of the connector • Pressure variation on surface: 1500 Pa (~1.5 cm) • Maximum velocity close to the surface: 0.47 m/s • Minimum LBE Temperature (Wall): 198 C • Maximum Water Temperature (Wall): 265 C (Boiling at 188 C)

26. Simulation3: Temperature fields

27. Simulation3: Velocity field

28. Conclusion • 1D pre-sizing has been globally confirmed • Proposed riser design avoid almost all gas transfer in the Hex. • High Water wall temperature may need a larger connector or partial boiling must be taken into account. • Reason of high residual with MARS scheme (Hex simulation) must be found and possibly put under control.

29. Perspectives • Give a definitive Riser-connector design • Full (360 degrees) Hex simulation • Test also AISI 316L • Possibility to tune each water channel flow independently for incidental test