Correlations for the Plate Divertor and Update on the GT Helium Test Facility

1. Correlations for the Plate Divertor and Update on the GT Helium Test Facility M. Yoda, S. I. Abdel-Khalik, D. L. Sadowski, B. H. Mills, and J. D. Rader G. W. Woodruff School of Mechanical Engineering

2. Research Goals Goals • Evaluate thermal performance of gas-cooled divertor designs in support of the ARIES team • Estimate maximum heat flux that can be accommodated by divertor and coolant pumping power requirements for various divertor designs • Develop methods for extrapolating dynamically similar experiments with different coolants to helium at prototypical conditions • Provide design guidance and develop correlations that can be used in system codes • Determine how divertor thermal performance will be affected by changes in material and coolant temperature limits ARIES Meeting (1/13)

3. Approach • Conduct experiments that span non-dimensional parameters at prototypical conditions • Design and fabricate instrumented test sections that closely match divertor geometry • Match nondimensional coolant flow rate (Reynolds number Re) and fraction of heat removed at cooled surface by conduction, vs. convection (ratio of divertor to coolant thermal conductivities κ) • Vary test section material and/or coolant (including high-temperature He) to match κ • Measure cooled surface temperatures and pressure drop  Nusselt number Nu, loss coefficient KL as a function of Re and κ • Develop power-law correlations for Nu, KL • Extrapolate to prototypical conditions to determine for given material and coolant temperature limits ARIES Meeting (1/13)

4. Plate-Type Divertor • Cools large areas: ~500 modules to cover the O(100 m2) divertor • Accommodates heat fluxes up to 10 MW/m2 without exceeding Tmax 1300 °C, max 400 MPa[Wang et al. 09] • Experiments performed on a single He-cooled flat • plate (HCFP) module using air at prototypical Re • [Hageman et al. 11] 100 cm W armor 20 ARIES Meeting (1/13)

5. Thermal Conductivity Ratio Experiments on HEMP-like and HEMJ-like modules performed with air, helium, and argon at same Re Experimental data and numerical simulations  fraction of heat conducted through the side walls of the divertor (vs. removed by coolant at cooled surface) varies with coolant, divertor material Effect characterized by ratio of divertor to coolant thermal conductivities κ ks / k: ks evaluated at average cooled surface temperature , k evaluated at average coolant temperature Objective: Improve previous correlations for plate-type divertor, a leading candidate for the ARIES study Modify previous correlations obtained for air that only considered Re effects to include κ Perform numerical simulations of HCFP 5 ARIES Meeting (1/13)

6. Numerical Model • Simulate 3D numerical half-model of GT HCFP • ~3 million unstructured tetrahedral cells: ANSYS Workbench • Numerical simulations: ANSYS Fluent 14 • Realizable k-ε turbulence model with standard wall functions • Adiabatic boundary condition on all walls except the heated surface • Simulate air, He and Ar cooling brass and WL10 • Re = 1.3104, 3.1104, 4.7104 •  = 340, 750, 5000 (expts.), 7000 ARIES Meeting (1/13)

7. HCFP Numerical Model • Average heat transfer coefficients based on average heat flux determined using control-volume energy balance • Average Nusselt number • Validate simulations by experimental data: at prototypical Re, values from simulations within 5% of experimental results • Following previous work, assume a power-law correlation: ARIES Meeting (1/13)

8. Nusselt Number • Simulations show depends on κandRe • Experiments (brass/air): • κ≈ 5000 •  κ≈ 7000 (brass/Ar) • κ≈ 5000 (brass/air) • κ≈ 750 (stainless/air) •  κ≈ 750 (brass/He) • κ≈ 340 (prototypical) 0 2 4 6 ARIES Meeting (1/13)

9. Nu Correlation • Use multilinear regression to fit numerical predictions and experimental data to power law •  = 3407000 • New correlation significantly reduces • for plate-type divertor at prototypical conditions 0 1 2 3 4 5 ARIES Meeting (1/13)

10. GT Helium Loop • Objective: evaluate thermal performance of various divertor designs at prototypical conditions • Dynamic similarity requires matching   use He • Only American facility at present • Current status / Experimental timeline • Provides helium at mass flow rates up to 10 g/s, temperatures up to 400 °C, pressures ~10 MPa • Leak tested at 10 MPa, ~30°C over >24 h with negligible loss of He • Heat fluxes  3 MW/m2 with oxy-acetylene torch over ~1 cm2 area • February 13: Brass HEMJ test section:   950, Re <3104 (vs. prototypical value of 2.1104 ) • March 13: Tungsten-alloy HEMJ test section:   600, Re <6.2104 (vs. prototypical value of 2.1104 ) ARIES Meeting (1/13)

11. He Loop Schematic He source tanks Electric heater Recuperator Buffer tanks • Charge evacuated loop with He from 41.3 MPa source tank • Buffer tanks minimize compressor pulsation • Adjust with bypass • Heat He with electric heater and recuperator • Recuperator recovers heat from He exiting test section Bypass Cooler Test section Vacuum pump He inlet Reciprocating compressor ARIES Meeting (1/13)

12. GT He Loop • Single-stage reciprocating compressor: delivers 10 g/s helium at ~10 MPa and ~50°C • Electrically heat He before test section • After hot He passes through test section, recuperator and cooler reduce He temperatures to <50 °C before compressor Compressor ARIES Meeting (1/13)

13. Summary Updated Nusselt number correlation for plate-type divertor , vs. New correlation suggests maximum heat transfer accommodated by plate-type divertor at prototypical conditions will be significantly less than that predicted by original correlation  may need fins to improve thermal performance Planning experiments with stainless steel test section/air:   750 Generalized design charts GT helium test loop will start experiments on HEMJ-like test section next month Brass, then W-alloy, test sections Designing heaters to increase incident heat flux to 6 MW/m2 ARIES Meeting (1/13)