Based on the paper FT/P5-35 for 21st IAEA Fusion Energy Conference 16 - 21 October, Chengdu, China Lithium Free-Surface Flow and Wave Experiments H.Horiike 1), H.Kondo 1), H.Nakamura 2), S.Miyamoto 1), N.Yamaoka 1), T.Muroga 3) 1) Graduate School of Engineering, Osaka University, Osaka, Japan 2) Japan Atomic Energy Agency, Ibaraki, Japan 3National Institute for Fusion Science, Gifu, Japan e-mail : [email protected] Introduction Back Ground IFMIF ( International Fusion Materials Irradiation Facility ) - Liquid Li Target Item Deuterium beam energy / current Averaged heat flux Aim of this study Investigation of the flow dynamics - Surface fluctuation of the target - Measurement technique - Engineering issues Beam deposition area on Li jet Jet width / thickness Jet velocity Nozzle geometry 40MeV / 250mA Remarks 125mA nominal x 2 beams 1 GW/m2 0.2 m x 0.05 m 0.26 m / 0.025 m 15 m/s Double-reducer Nozzle contraction ratio 10 Curvature of back wall 0.25 m Wave amplitude of Li-free surface ~ 1 mm Flow rate of Li 130 l/s Inlet Temperature of Li 250oC Vacuum pressure 10-3 Pa Materials Reference from IFMIF Home Page http://insdell.tokai-sc.jaea.go.jp/IFMIFHOME/i_target_en.html Specification RAF steel or 316SS range: 10 - 20 m/s based on Shima’s model 4 x 2.5 at Li free surface (back wall) 2 Outline of Osaka Univ. Li Loop Main loop : Test section, Void separation tank, EMP and EMF. The total length : 40 m Daughter loop : Cold Trap, EMP and EMF Free-Surface Test Section Void separation tank 1/2.5 scaled model of IFMIF Li target Dump tank Li Ingot Electro-Magnetic Pump ALIP type EMP < 700 l/min In a pit Li inventory : 420 litter In a pit 3 Outline of Free-Surface Test Section Nozzle Nozzle and Flow Channel Shima’s model ×2 ( Two convergent sections ) Hight : 10mm, Width : 70mm ( 1/2.5 scale ) made of SS304 Straight Flow Channel Viewing ports Viewing ports and Shutter 4 Electro-Contact Probe apparatus Fluctuations were measured on Li free surface with using an Electro-Contact Probe apparatus ・ Two needles mechanically fixed move together, but electrically independent ・ Electric motor cylinder to move the needles : 0.1 mm step Set on the second viewing port (on the beam axis) 175 mm from the nozzle needle 1 : 16 mm from the side wall needle 2 : 35 mm (at the center of flow) Electro-Contact Probe Detection circuit 5 Measured Time Series Signals Probes were moved with 0.1mm step, while recording voltage signals. No contact - Recording time : 20 sec - Sampling freq : 48 kHz ( using PCM recorder) (a) 11.44mm from wall Higher than the Li free surface contact contacts were rare ( almost no contact) Middle of the surface contacts made frequently Lower than the Li free surface (b) 11.04mm contacts were rare ( almost contact ) Schematic of contacts (c) 10.74mm at 10 m/s Center of flow 6 Shapes of Li surface waves Contact frequency and contact time rate were defined and calculated statistically from electric signals Contact frequency : Number of changes between contact and no-contact per unit time Contact time rate : The quotient of total contact period divided by recording time (a) 5m/s (b) 10m/s (c) 15m/s 7 Average thickness and max wave amplitude Average thickness of the flow Height at maximum contact frequency ( = center of the fluctuation ) - in the lower velocity of 1 to 5 m/s, the thickness shows a peak at ~ 4m/s - in the velocity 5 to 10 m/s, the thickness continuously increased gradually. - in thr velocity of more than 11 m/s, the thickness decreased to 10mm which equals the depth of nozzle throat. Amplitude of the fluctuation defined as half height between “no contact” and “full contact”. - the amplitude increased with flow velocity - in the velocity more than 12 m/s, the amplitude seems to be saturated. - the amplitude was 2 mm at 15 m/s. 8 Visual observation of the surface Stroboscopic photography of the Li surface at 175mm downstream from the nozzle exit (second viewing port) (a) 2 m/s (b) 3 m/s (c) 5 m/s (d) 7 m/s (e) 10 m/s (f) 15 m/s 9 Boundary layer thickness along the nozzle wall and at the nozzle exit Momentum thickness d2 along the nozzle was calculated [1] Nozzle coordinate 1. velocity distribution along the nozzle wall ( potential model ) 2. Development of laminar boundary layer ( method of Waltz ) Momentum thickness 3. Transition to turbulent ( Re d2 > 420 ) Transition to turbulent 3. Development of turbulent boundary layer ( method of Buri ) 4. Relaminarization ( acceleration parameter K ) Boundary layer thickness D at the nozzle exit was estimated from the momentum thickness DD D 2d 2 /(0.664)2 [1] K. Itoh et al., “Free-surface shear layer instabilities on a high-speed liquid jet”, Fusion Technol. 37 (2000) 74-88 10 Non-dimensional amplitude Experimental results of the amplitude was summarized to non-dimensional form, non-dimensional amplitude : A/D against Weber number : We Weber number was defined as U0 r D WeD T 2 . where T: surface tension, r: density, U0 : mean velocity The non-dimensional amplitude was well predicted by square of We A / D 0.278 We D 0.443 We D 0.00495 2 It is noted that the saturation above We of 5.5 is observed. 11 Summary Experiment study on IFMIF liquid Li target was carried out with using a 1/2.5 scale test channel. Surface fluctuation of the target flow was measured by electrocontact probe apparatus. As a result, - Time series signals were represented by contact frequency. - Waves of Gaussian like profiles were observed. - Average thickness of the flow, and maximum amplitude of surface fluctuation were plotted as a function of the velocity. - The amplitude was described by non-dimensional form of We number. This showed that the amplitude was well predicted by square of We number, and it began to saturate above velocity of 12-13m/s. 12
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