HIGH HEAT FLUX AND CRITICAL HEAT FLUX (CHF) TESTS IN SUPPORT TO ITER HHFC by F.Escourbiac With the contributions of : J.Schlosser, N.Vignal, V.Cantone, M.Missirlian, M.Richou, R.Guigon * Association EURATOM-CEA, France J.L. Jouvelot, S.Constans, I.Bobin * AREVA-NP industry, Le Creusot, France J.Boscary * Association FZJ, Germany M.Merola * ITER Organization, Cadarache, France B. Riccardi * Fusion For Energy, Barcelona, Spain Experimental work was supported by the European Communities Slide 1
INTRODUCTION Vplasma= 25 m3 In powerfull fusion machines, the HHFC have to sustain HHF of 10-20 MW/m2 R=2.715m R=2.22m When cooled by water in the subcooled boiling regime, typically -40 bar, 100-140 C, the critical heat f lux is a concern In addition with thermal design rules on armour or joint temperatures (not reported in this talk), it is necessary to estimate the margin to critical heat flux for any design of HHFC ITER VT Objective of this talk : to come back on the notion of CHF to review the EU studies and to assess the CHF margin of the ITER Divertor CEA-EURATOM Slide 2
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF margin : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 3
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 4
THE CHF TESTS Principle Sweeping frequency: up to 10 khz (b) 90% of the power in a < 1.5 mm disc. diameter (a) 4 mm 4 mm (c) Main facility for CHF tests: FE200 (electron beam 200 kw) in Le Creusot, France (flexible pressurized water loop : 20-40 bar, up to 6 kg/s, 20-220 C) Slide 5
THE CHF TESTS Increase power step by step * measure Absorbed Heat Flux (AHF) PW Coolant circuit High Heat Flux 23 2 * Infrared monitoring 790 C Up to sudden temperature excursion 800 700 600 500 400 0 T Pyr2 ( C) Shot 2576 8.1 5.0 10.9 10.3 9.8 11.2 100 0 500 t (s) Low-temperature pyrometers vs time during one shot (absorbed flux in MW/m² is given in red) (destruction of component in a few 100 ms if gun not stopped) 520 Infra-red picture at steady state 970 C 525 Infra-red picture, transient OUTPUT : Absorbed CHF (ACHF) Slide 6
THE CHF TESTS CHF is often used for Burn-out, ACHF, ICHF, WCHF More precisely, when Burn-out is detected during HHF testing : * ACHF : Absorbed Critical Heat Flux is measured by calorimetry ACHF = QC p (T out -T in )/(w x L) Heat Flux Heat Flux * ICHF : Incident Critical Heat Flux is derived from ACHF taking account radiation (width) Tin L (length) Tout ICHF = ACHF + Radiated Heat Flux * WCHF : Wall Critical Heat Flux is calculated by Finite Element modeling WCHF = ICHF x Pf ICHF s WCHF 0 WHF=F(s) s(mm) πr Slide 7
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 8
A LONG CHF TESTING STORY 1992-95 Investigation of various smooth/swirl tubes diameters 1996 Investigations of cooling concept (swirl rod insert, double smooth and swirl tubes, HV tubes) CEA 3a-5b CEA 3a-3,4,5 CEA 3a-1,2 AF1 ID/OD 11/16 AF3 ID/OD 18.6/22 1.5 1.5 2.4 13 10 13 10 15 10 25 27 15 15 17 27 27 CEA 3e-1,2,3 1.5 CEA 3b 2.5 CEA 3f-1,2 2.5 DSM2 10 ID DST2/DST4 Tr = 2 and 4 HV1/HV3 17 14 19 18 21 18 19 23 24 25 27 27 3 3 4 5 1.5 27 3 20 3 (copper alloy tubes : Glidcop, CuCrZr) Slide 9
A LONG CHF TESTING STORY 1997 : Study of twist ratio and tape thickness ST2 ST08 2 2 1998 : monoblock PRODIV1 4.5 CFC material 23 Tape thick.: 2 mm Twist ratio: 2, 3 or 4 23 Tape thick.: 0.8 mm Twist ratio: 2, 3 or 4 28 23 CFC monoblock, Glidcop tube Tape thickness: 2 mm Twist ratio: 2 2001 : Study on hypervapotron as an alternative solution to the monoblock concept 3 4 5 1.5 27 3 20 3 40 50 2002 : investigation of CFC monoblocks mock-ups width and tube diameter 23 28 33 33 10/12 ID/OD 10/12 ID/OD 10/12 ID/OD 12/15 ID/OD > 200 CHF values have been obtained Slide 10
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 11
CHF RESULTS Influence of thermalhydraulics parameters ICHF (MW/m²) 60 50 40 20 10 Série9 Série8 ST2 5 m/s ST2 10m/s ST2 15m/s ST4 5m/s ST4 10m/s ST4 15m/s 15 m/s 10 m/s 5 m/s ST4 CHF with T sat -T bulk (K) (subcooling) * Means : CHF with Tsat (water pressure) * Means : CHF if Tbulk (water temperature) ICHF (MW/m²) 0 60 50 40 20 10 0 Série8 Série7 Série9 HV1 5m/s HV1 10m/s HV1 15m/s HV3 5m/s HV3 10m/s HV3 15m/s 15 m/s 10 m/s 5 m/s HV3 40 60 80 100 120 140 160 180 T sat -T bulk (K) CHF with water flow rate (The lines show the CEA-Tong75 correlation described later) Slide 12
CHF RESULTS Influence of the swirl tape design : twist ratio CHF results Mock-up Geometry Twist Ratio ICHF (MW/m 2 ) flat peaked Thick tapes 2 ST22 2 32.2 36.6 ST23 23 3 27.1 28.4 ST24 4 21.1 24.3 Thin tapes 2 ST082 2.0 35.0 ST083 23 3 31.2 26.7 ST084 4 17.5 27.8 (3.5 MPa, Tsub,out=100 C, V=12m/s, ID = 10 mm) CHF if twist ratio 20 40 Twist ratio 2 Twist ratio 3 Twist ratio 4 Slide 13
CHF RESULTS Influence of the swirl tape design : thickness CHF results Mock-up Geometry Twist Ratio ICHF (MW/m 2 ) flat peaked Thick tapes 2 ST22 2 32.2 36.6 ST23 23 3 27.1 28.4 ST24 4 21.1 24.3 Thin tapes 2 ST082 2.0 35.0 ST083 23 3 31.2 26.7 ST084 4 17.5 27.8 (3.5 MPa, Tsub,out=100 C, V=12m/s, ID = 10 mm) CHF if twist ratio CHF with thickness tape 20 40 2 mm Twist ratio 2 Twist ratio 3 Twist ratio 4 0.8 mm Slide 14
CHF RESULTS Influence of the incident heat flux axial profile CHF results Mock-up Geometry Twist Ratio ICHF (MW/m 2 ) flat peaked Thick tapes 2 ST22 2 32.2 36.6 ST23 23 3 27.1 28.4 ST24 4 21.1 24.3 Thin tapes 2 ST082 2.0 35.0 ST083 23 3 31.2 26.7 ST084 4 17.5 27.8 (3.5 MPa, Tsub,out=100 C, V=12m/s, ID = 10 mm) CHF if twist ratio CHF with thickness tape CHF with peaked axial heat flux Incident Heat Flux (MW/m²) 20 40 2 mm Twist ratio 2 Twist ratio 3 Twist ratio 4 0.8 mm 20 ITER 15 Transient Reference Case 10 FE200 Peaked Profile 5 X(cm) 0-20 0 20 40 60 80 Slide 15
CHF RESULTS Influence of geometry ICHF ( MW/m²) 25 20 15 10 5 0 Subcooling ~120 C Axial Velocity ~4 m/s peak. unif. 20 40 50 60 Width (mm) ICHF (MW/m 2 ) 40 35 25 20 15 20 25 35 Width (mm) Subcooling ~100 C Axial velocity ~10 m/s ID/OD 10/12 uniform ID/OD 10/12 peaked ID/OD 12/15 uniform 27 40 50 CHF if width 23 28 33 33 10/12 ID/OD 10/12 ID/OD 10/12 ID/OD 12/15 ID/OD Slide 16
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 17
HEAT TRANSFER EVALUATION Development of correlations Convective regime : Sieder Tate Nu = f ST x 0.027 Re 0.8 H Pr 1/3 (µ b /µ w ) 0.14 h con = k Nu / D h, f ST =1.15 if twisted tape; 1 if not Subcooled boiling regime : Thom-CEA T w - T sat = 22.65 (10-6 Φ w ) 0.357 e (-P.10-5 /87) 1/2.8 Comparison between the different correlations using B. & R. method Slide 18
HEAT TRANSFER EVALUATION Validation of subcooled boiling regime correlation with swirl tubes 100 ST22 ST22R ST24 2 TH7 thermocouples 1.7 5 23 5 7 TH8 Jens & Lottes 1/4 Thom-CEA 1/2.8 wall heat flux ( MW/m 2 ) 10 ST082 Thom 1/2 1 T wall - T sat (K) 10 100 Slide 19
HEAT TRANSFER EVALUATION Validation of full set of correlations with swirl tubes 2 TH7 thermocouples 1.7 7 TH8 600 550 500 Comparison between thermocouples and FE calculations 5 23 5 temperature ( C ) 450 400 350 0 250 200 TH7 2 mm from heated surface TH8 7 mm from heated surface 150 Step wise increase of EB gun power up to CHF 100 0 5 10 15 20 25 3 Int. HHFC Workshop, Dec. 10-12, 2008, incident UCSD, heat flux ( CA, MW / m 2 ) Slide 20
HEAT TRANSFER EVALUATION Validation of heat transfer evaluation : hypervapotron 6.6 Tsurf ( C) 00 2500 2000 TSEFEY-M 1500 FE200 1000 20 MW/m² T( C) 136 500 258 35 bar, 120 C, 9 m/s 381 0 504 0 10 20 40 626 AHF (MW/m²) 749 871 Tth ( C) 994 1120 1240 1360 Slide 21
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 22
CHF PREDICTION F TONG75H calculated from CEA-TONG75 correlation Bo Hcrit =1.84 (D H /D o ) Re H -0.6 [1 + 0.00216(P/Pc) 1.8 Re H -0.5.Ja] F TONG75H = Bo Hcrit.ρ.V.i fg (Re H = VD H / ν taking account swirl presence) WCHF : estimated with application of a corrective factor extrapolated from tests WCHF = C f. F TONG75H C f : depends on the geometry, the promoter and the heat flux profile (range 1,2 2,2, precision +/- 20%) CHF margin = WCHF /max.whf max.whf being calculated with design values Slide 23
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 24
CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CHF is a concern near the strike point on the CFC monoblocks (lower part of the VT) Heat loads : * Nominal : 10 MW/m², 400 sec. * Transient : 20 MW/M², 10 sec. Design Erosion during lifetime 18 5-7 Potential Imperfection of bonding (defect) CFC or W θ θ Cu CuCrZr 28 28 ID/OD 10/12 mm θ : Location, θ : Extension CFC, W or Cu : Interface Slide 25
APPLICATION TO ITER DIVERTOR CHF margin estimation max WHF (MW/m²) 40 35 25 20 15 (radiation included) CFC IHF Defect CHF thickness Margin 18 mm 7 mm max Wall Heat Flux (loading 20 MW/m²; 10 sec.) CFC 7 mm ; loc. 45 CFC 7 mm ; loc. 0 CFC 18 mm ; loc. 45 CFC 18 mm ; loc. 0 0 20 40 60 Extension defect θ 10 MW/m², SS No 3,5 yes 3,8 20 MW/m², 10 No 2,2 sec yes 2,0 10 MW/m², SS No 3,5 yes 3,3 20 MW/m², 10 No 1,6 sec yes 1,4 Defect centred at 0 can protect from CHF! 500 2400 (K) OUTPUT : Lowest margin to CHF = 1.4 Slide 26
OUTLINE THE CHF TESTS A LONG CHF TESTING STORY CHF RESULTS HEAT TRANSFER EVALUATION CHF PREDICTION CHF MARGIN : APPLICATION TO THE ITER DIVERTOR CONCLUSIONS Slide 27
CONCLUSIONS The actively cooled plasma facing components have to sustain HHF of 10-20 MW/m2 Cooled by water in the subcooled boiling regime, the critical heat flux is a concern Several CHF studies in Europe during since more 15 years investigated various cooling concepts at various cooling conditions. More than 200 values of CHF have been obtained. Critical Heat Flux prediction and heat transfer correlations were developed during these studies This methodology already used for the design of the HHFC of water cooled controlled fusion machines such as Tore Supra and W7-X Stellerator was applied to ITER Vertical target divertor, this gives a CHF margin of 1.4, the current state of the art Slide 28
Additional information Slide 29
ZOOM ON NUKIYAMA S BOILING CURVE Different design, different limits NUKIYAMA S BOILING CURVE Swirl tube ACHF ~ local CHF ( no transition boiling, except at low velocity [Marshall]) Hypervapotron ACHF > local CHF ( there is transition boiling in normal conditions) Forced Convection Wall Heat Flux Subcooled Nucleate Boiling Partial Boiling ONB Fully Developed Boiling local CHF CHF Wall Temperature Transition Boiling Film Boiling Swirl Hypervapotron tube Slide
FE200 FACILITY ELECTRON BEAM : 180 kw at steady state (200 kw, t<10s) advanced sweeping system (10 khz, +/-10 ) 0.1 sec. to 6000 sec. VACUUM CHAMBER 8 m3, mockups up to 2 m WATER LOOP : heat exchanger 0 kw Pressurized water loop (3.9 MPa) 50 to 2 C, 6 kg/s, 0.7 MPa DIAGNOSTICS : IR, CCD devices 2 pyrometers thermocouples data acquisition Co-operated by CEA Framatome Since 1992 in Le Creusot, France more than 100 components tested Slide 31
DEFINITIONS i fg : latent heat of vaporization [J.kg -1 ] P c : critical pressure of water (221 bars) Ja = (ρ f /ρ g ).[(i sat -i)/i fg ]: Jacob number µ: dynamic viscosity [kg.m -1.s -1 ] D 0 : reference diameter (12.7 mm = 0.5 inch) Slide 32
COMPARISON OF SWIRL TUBE AND HYPERVAPOTRON CHF (MW/m²) 40 35 25 20 15 10 5 0 (P = 35 bar, Dtsubout = 120 C) 16 14 12 27 10 10 8 23 6 4 2 0 0 5 10 15 20 25 35 40 DP (bar/m) Higher pressure drop for swirl tube but it is about only 21% of the total pressure drop Both swirl and HV tubes meet the ITER requirements kg/s/m 2 Slide 33