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, Japan2) Japan Atomic Energy Agency, Ibaraki, Japan

3National Institute for Fusion Science, Gifu, Japan

e-mail : horiike@nucl.eng.osaka-u.ac.jp

Based on the paper FT/P5-35for 21st IAEA Fusion Energy Conference 16 - 21 October, Chengdu, China

2

Introduction

Item Specification Remarks

Deuterium beam energy / current

40MeV / 250mA  125mA nominal x 2 beams

Averaged heat flux 1 GW/m2

Beam deposition area on Li jet

0.2 m x 0.05 m

Jet width / thickness 0.26 m / 0.025 m

Jet velocity 15 m/s range: 10 - 20 m/s

Nozzle geometry Double-reducer based on Shima’s model

Nozzle contraction ratio

10 4 x 2.5

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 at Li free surface

Materials RAF steel or

316SS(back wall)

Back Ground IFMIF ( International Fusion Materials Irradiation Facility ) - Liquid Li Target

Aim of this study Investigation of the flow dynamics - Surface fluctuation of the target - Measurement technique - Engineering issues

Reference from IFMIF Home Pagehttp://insdell.tokai-sc.jaea.go.jp/IFMIFHOME/i_target_en.html

3

Outline of Osaka Univ. Li Loop

Void separation tank

Electro-Magnetic Pump

Free-Surface Test Section

Dump tank Li Ingot

ALIP type EMP < 700 l/minIn a pit

Li inventory : 420 litterIn a pit

1/2.5 scaled model of IFMIF Li target

Main loop : Test section, Void separation tank, EMP and EMF. The total length : 40 m

Daughter loop : Cold Trap, EMP and EMF

4

Outline of Free-Surface Test Section

Viewing ports and Shutter

Nozzle and Flow ChannelNozzle Shima’s model ×2 ( Two convergent sections ) Hight : 10mm, Width : 70mm ( 1/2.5 scale )

made of SS304

Straight Flow Channel Viewing ports

5

Electro-Contact Probe apparatus

Electro-Contact Probe

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)

Detection circuit

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Measured Time Series Signals

at 10 m/sCenter of flow

(c) 10.74mm

(b) 11.04mm

(a) 11.44mm from wall

Probes were moved with 0.1mm step, while recording voltage signals. - Recording time : 20 sec - Sampling freq : 48 kHz ( using PCM recorder)

Higher than the Li free surface

contacts were rare ( almost no contact)

Middle of the surface

contacts made frequently

Lower than the Li free surface

contacts were rare ( almost contact )

No contact

contact

Schematic of contacts

7

Contact frequency :Number of changes between contact and no-contact per unit time

(a) 5m/s (b) 10m/s (c) 15m/s

Contact frequency and contact time rate were defined and calculated statistically from electric signals

Shapes of Li surface waves

Contact time rate :The quotient of total contact period divided by recording time

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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.

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Visual observation of the surface

(a) 2 m/s (b) 3 m/s (c) 5 m/s

(d) 7 m/s (e) 10 m/s (f) 15 m/s

Stroboscopic photography of the Li surface at 175mm downstream from the nozzle exit (second viewing port)

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Boundary layer thickness along the nozzle wall and at the nozzle exit

Nozzle coordinate

Momentum thickness

Transition to turbulent

Momentum thickness along the nozzle was calculated [1] 1. velocity distribution along the nozzle wall ( potential model )

2. Development of laminar boundary layer ( method of Waltz )

3. Transition to turbulent ( Re > 420 )

3. Development of turbulent boundary layer ( method of Buri )

4. Relaminarization ( acceleration parameter K )

Boundary layer thickness at the nozzle exit was estimated from the momentum thickness

22 )664.0/(2

[1] K. Itoh et al., “Free-surface shear layer instabilities on a high-speed liquid jet”, Fusion Technol. 37 (2000) 74-88

D

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Non-dimensional amplitude

Experimental results of the amplitude was summarized to non-dimensional form,

non-dimensional amplitude : A/ against Weber number : We

Weber number was defined as

where T: surface tension, : density, U0 : mean velocity

The non-dimensional amplitude was well predicted by square of We

It is noted that the saturation above We of 5.5 is observed.

T

UWe

20

00495.0443.0278.0/ 2 WeWeA

.

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Summary

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.

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 electro-contact probe apparatus.