- Email: [email protected]
Thermomechanical investigation on divertor supports for fusion experimental reactor: hydraulic experimental results
ELSEVIER
Fusion Engineering and Design 28 (1995) 103-112
Fusion Engineering and Design
Thermomechanical investigation on divertor supports for fusion experimental reactor: hydraulic experimental results T. Arai a, R. Hino a, y . Muto a, M. Nakahira b, M. Shibui b, K. Furuya b, E. Tada b, M. Seki b a Tokai Research Establishment, JAERI, Tokai-mura, Ibaraki 319-11, Japan b Naka Research Establishment, JAERI, Naka-machi, Ibaraki 311-01, Japan
Abstract
The Japan Atomic Energy Research Institute has been conducting technology development aimed at the construction of a fusion experimental reactor to follow JT-60 in Japan. The divertor plate facing the plasma is one of the components of the reactor core assembly, since it has to be operated under severe heat and particle loads and high electromagnetic forces. Thus the divertor supports should be designed so as to provide both flexibility for thermal expansion along the divertor cooling tube and mechanical stiffness for sustaining the electromagnetic force during plasma disruption as well as easy replacement in the case of failure. In order to meet these requirements, we have developed a new divertor support system based on a sliding mechanism for flexibility and a hydraulic cotter for replacement. The basic feasibility of this concept has been demonstrated through critical element development. Based on the feasibility study, a l:l-scale model of the divertor cooling tube test section with sliding mechanism has been fabricated for thermomechanical experiments to characterize the fluid mechanics, flow-induced vibration and flexibility for thermal expansion at various temperature profiles during normal and baking operations. Preliminary experiments on the fluid mechanical characteristics have been conducted as a function of the water velocity and the following results are obtained. (1) The total pressure drop along the whole test section reaches about 0.7 MPa at the rated water velocity of 10 m s - i at 20 °C, which is mostly dominated by swirl tape inserts and several bend sections, as expected by design estimation. (2) Flow-induced vibrations are observed at the two overhang bends with smaller curvatures and become significant at a higher water velocity of more than 10 m s -1.
1. Introduction
Plasma-facing components such as the divertor plate in a fusion experimental reactor are subjected to intense heat loads and high energy particles under normal
operating conditions as well as large electromagnetic forces during plasma disruptions. The divertor plate and the supports should be designed to meet these design conditions and require advanced technologies for cooling high heat fluxes, protecting high energy
0920-3796/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSD! 0920-3796(94) 00095-6
104
T. Arai et al. / Fusion Engineering and Design 28 (1995) 103 112
!or
SU SI
(a) SchematicViewof wholeassembly Vacuum Vessel ;q~--~
Divertor Plate ~/Divertor
Support Frame
(b) Divertor support concept
Fig. 1. Overall structural view of divertor plate and supports. particles and assuring structural integrity under thermal and mechanical loading conditions as well as remote maintainability. Design efforts have been made to develop a structural concept of the divertor plate according to the design requirements. As a result, a divertor structure with a new supporting system composed of a sliding mechanism and a hydraulic cotter has been devised [1] as shown schematically in Fig. 1. In this concept the divertor plate is composed of a number of cooling tubes connected to inlet and outlet manifolds and a divertor frame to assemble the cooling tubes as a unit plate structure. The divertor plate is fixed with a support shield structure by a conical cotter driven by a hydraulic jack system, which can be replaced for mainte-
nance purposes. The cooling tube, made of Cu alloy, is formed into a U-shaped geometry with several bends and an armour tile is brazed on the tube surface facing the plasma. The U-shaped tube is supported together with and fixed to the divertor frame through the sliding mechanism to allow thermal expansion due to their different operating temperatures. The cooling tube has a circular geometry with an inner diameter of 15 mm and a twisted tape (swirl tape) is partially inserted into the tube near plasma-striking points where a high heat flux is applied. With regard to technology development, the cooling capability of this concept has been extensively investigated [2] and it is found that the maximum heat flux should be around 15 MW m -2. In addition, the feasibility of hydraulic jacks has been demonstrated [3] and a total performance test using remote handling equipment is being conducted. The remaining critical issues to be qualified are the thermohydraulic behaviour of the cooling tube with swirl tape inserts and bend sections and the supports under normal and baking conditions. In particular, the following characteristics are to be examined: (1) the hydrodynamics of flow resistance and flowinduced vibration of the cooling tube with swirl tape inserts and bend sections at the rated water velocity of 10ms-l; (2) the structural support layout and the restraint conditions to accommodate non-uniform thermal expansion so as to avoid thermal deformation of the cooling tube under thermal and mechanical loads expected in normal, baking and disruption conditions. For this purpose a l:l-scale test section composed of a U-shaped cooling tube with swirl tape inserts and structural supports including a sliding mechanism has been fabricated and preliminary experiments on the hydraulic characteristics and flow-induced vibration have been conducted as a function of the water velocity and the restraint conditions of the divertor supports. This paper describes the design concept of a l:l-scale test section and the test results on hydrodynamic characteristics.
2. The 1/1-scale divertor test section
Fig. 2 shows the whole assembly of the l:l-scale divertor test section fabricated. The configuration is derived exactly from the actual design concept developed for the fusion experimental reactor. The divertor supports for varying the restraint conditions of the cooling tube are also shown in Fig. 2. The test section
105
T. Arai el al./ Fusion Engineering and Design 28 (1995) 103-112
G) Coolingtub~ Tube restraint @ Slide plnte
E
G(g~
( ~ Thermal insulation @ Support plnte (~) Support cooling tube
,oo
,
' ®
(a) Gravity support
(b) Supporting jigs
@ Cooling tube @ Pressure tap( [] ~ [] ) @ Swirl-tapedtube @ Test stand @ Gravitysupport @ Supportingjigs (overhang region) (~ Inletmanifold @ Supportingjig @ Outletmanifold Q , @ @
1~@ __
[]
[] @. . . ~ --Y~-Iil
(c) Overall structure Fig. 2. Assembly set-up of l:l-scale divertor test section.
is composed of a Cu cooling tube with swirl tape inserts, inlet and outlet manifolds made of stainless steel (SS 304), supporting jigs to adjust the restraint conditions between tubes and gravity supports connected to the test stand through dovetail grooves to allow axial movement of the tubes for thermal expansion. In the high heat flux region (No. 2 in Fig. 2) a twisted tape 0.8 mm thick with a swirl ratio of 3 and
340 mm long is inserted and fitted by mechanical pressing. The major hydraulic parameters and testing conditions of the test section are summarized in Table 1, together with the design parameters of the actual design of divertor plate. Four gravity supports (no. 3 in Fig. 2) for fastening the upper and lower tubes are located in the straight region of the test section and the location can be varied
106
T. Arai et al. / Fusion Engineering and Design 28 (1995) 103-112
Table 1 Hydraulic parameters and testing conditions of l:l-scale test section compared with design parameters of actual divertor Parameter
Actual divertor
Test section
Cooling tube Material Inner/outer diameter (ram) Total length (ram) Swirl taper inserts Thickness (mm) Swirl ratio Tape length (mm)
DS-Cu 15/18 6500
Cu 15/18 7046
0.8 3 500 x 2
0.8 3 340 x 2
Coolant conditions Pressure (MPa) Temperature (°C) Velocity (m s -1) Pressure drop (MPa)
3.5 50 10 0.92
1.5 20-50 1-13
for investigating the optimum layout to minimize thermal deformation. In addition, the axial movement can be restrained by key insertion into the dovetail groove so as to ensure the effect of fixing position on thermal deformation. The supporting jigs are divided into 18 remountable blocks along the test section so as to investigate the thermal deformation and flow-induced vibration under various restraint conditions of the upper and lower tubes. The whole test section can be heated to 400 °C for simulating the thermomechanical behaviour under the baking condition and thermal insulation blocks with electrical heaters are attached to the outer surface of the test section so as to reduce heat loss and keep the
background temperature constant. A cooling tube is installed on the test stand to provide a proper temperature difference between the tubes and test stand. A number of temperature sensors are attached to the tube surface, supporting jigs, gravity supports and test stand for the monitoring temperature gradient during heating experiments. In addition, 10 pressure taps (SS 304 tube of diameter 0.25 in) are installed to measure pressure drops in individual subsections along the cooling tube. The pressure tap layout and hydraulic parameters of each subsection are presented in Fig. 2 and Table 2 respectively.
3. Test facility and measurements An existing facility composed of water loop, nitrogen gas loop and data acquisition system has been modified for thermomechanical experiments on the l:l-'scale divertor test section. This facility is located in the Helium Engineering Demonstration Loop ( H E N D E L ) at the Japan Atomic Energy Research Institute (JAERI) Tokai Research Establishment and is capable of supplying either water at 50 1 s -1 at 1.5 MPa and temperatures below 50 °C or nitrogen gas at 33 1 s -1 below 400 °C. Fig. 3 shows a flow diagram of the water loop for hydrodynamic experiments on the divertor test section. During the experiments the water velocity supplied to the test section is controlled at specified values ranging from 2 to 12. 5 m s -1 by adjusting the rotor speed of the water pump. The pressure at the inlet manifold is normally maintained at 1 MPa by adjusting the outlet valve of the test section and the nitrogen gas pressure in the pressurizing water tank. The temperature of the
Table 2 i Geometrical parameters of subdivisions of l:l-scale test section Pressure tap
Subdivision
Geometrical parameters a
1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10
Inlet manifold Bend part no. 1 Bend part no. 2 Swirl tape insert no. 1 Straight part Bend part no. 3 Swirl tape insert no. 2 Bend part no 4 Bend part no. 5 Lower tube (return line) Outlet manifold
50 mm outer diameter L 169mm, R 80 x 180 mm, L 348 mm, R"519 x 40mm, L 410 mm, '\ L 706 mm, L 196mm, R 581 x 28mm, L 400 mm, L 131 mm, R 408 x 69mm, R 60 x 222mm,
a L, straight length; R, bend radius x angle; T, total length.
50 mm outer diameter
T T T T T T T T T
420mm 710mm 410 mm 706 mm 480mm 400 mm 622mm 300mm 2998 mm
107
T. Arai et al./ Fusion Engineering and Design 28 (1995) 103-I12
Test Flow meter Pump N2 Loop
N2 gas Preheater Cooler
® ®
Thermocouple
v , Water
Pressure gauge
Pressurized water tank
Fig. 3. Flow diagram of water loop for hydrodynamic experiments. water is normally kept at room temperature or raised to 50 °C by a preheater. Metal foil gauge-type pressure transducers are utilized for pressure drop measurements in each subsection. The inlet and outlet pressures of the test section
are monitored by transient pressure transducers with fast time response so as to enable flow oscillation measurements. In the test section two overhang bends with small bend radius are located at the inlet section (bend no. 1) and the front end section (bend no. 5) as
Bend No. 1
Bend No.5
=~ AT • Acceleration transducer DM : Displacement meter •" SG : Strain gauge
Bend No.2
Unit in mm
Bend No.4 Fig. 4. Schematic layout of sensors for flow-induced vibration experiments.
108
T. Arai et al. / Fusion Engineering and Design 28 (1995) 103-112
shown in Fig. 4. In order to measure the flow-induced vibration in such abrupt bend sections, acceleration detectors, eddy-current-type displacement sensors and strain gauges are attached to the tube surface. All measured data from the test section and the water loop are acquired and possessed by a personal computer (PC) system. In addition, transient behaviour such as vibration measurements is stored in a videotape recorder and reproduced on a high speed recorder.
Swirl tape part no. l, which corresponds to the swirl tape section in the upstream region, shows a larger pressure drop than the swirl tape part no. 2 in the downstream region. This discrepancy may be caused by different flow patterns in the two sections due to the tube configuration with several bends, but further quantitative evaluation is necessary. Comparing the flow length of the straight and swirl tape sections, it is concluded that the swirl tape section shows about two or three times the pressure drop per unit length of the straight section. In addition, the straight section indicates a higher friction factor (by approximately 25%) in the Reynolds number range from 4 x 10 4 to 2 x 10s than that predicted by the Blasius correlation, as shown in Fig. 7. This may be caused by residual enhanced turbulence due to upstream swirl flow or a roughened surface of the tube inner wall. The pressure drop characteristics measured in several bend regions of the test section are plotted in Fig. 8 as a function of the water velocity. Bend parts nos. 1-5 correspond to the bends between pressure tabs 1 and 2, 2 and 3, 5 and 6, 7 and 8, and 8 and 9 in Fig. 2 respectively. Bend part no. 1 shows an extremely large pressure drop compared with the other bend regions and the pressure drop reaches 0.14 MPa at 10 m s -1 in Fig. 8. The acceptable data of bend part no. 4 are only the first five plots because of trouble with the pressure transducer.
4. Test results 4.1. Pressuredrop
Fig. 5 shows the measured pressure drop characteristics of the first-half length (upper tube) and full length (upper and lower tubes) of the test section as a function of the water velocity. The pressure drop of the first half is roughly 80% of the total pressure drop because of the high flow resistance due to swirl tape inserts and small bend curvatures. At the rated velocity of 10 m s -1 the total pressure drop of the whole test section reaches 0.67 MPa at 20 °C, which is comparable with the design estimation. The pressure drop characteristics of the straight section and two swirl tape sections are plotted in Fig. 6.
1.2 Temperature Length 1.0 --
13-
:~
20°C 50°C
full full
/0 /.e
0.8
v
Q. 0
"~0
0.6
0 ¢n
if}
0.4
0
13-
0.2 - ~.-~=~"~,
0
,
,
I
5
,
,
,
I
,
,
10
Water velocity (m/s) Fig. 5. Overall pressure drop characteristics of l:l-scale test section.
/Fusion
T. Arai et al.
Engineering and Design 28 (1995) 103
0.2
I
i
•
109
112
L
Straightpart I Swir[tapepart No.1 Swirl tape part No.2
13_
I
OO - ~ 0.1
O-
i
w
~
i i
i
o
i
i
i
r
5
~
i
i
10
Water velocity (m/s) Fig. 6. Pressure drop characteristics of straight and swirl tape regmns.
5
!
4 ......
O O
!
Blaslus
•
I i
I i
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ro
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.......•i ........................ i.............................
.g ~6
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1 10 4
2
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4
6
i 8
10 5
2
4
Reynolds number Fig. 7. Friction factor of straight tube compared with Blasius correlation.
4.2. F l o w - i n d u c e d
vibration
T h e f l o w - i n d u c e d v i b r a t i o n due to t h e h i g h c o o l a n t velocity is o n e o f t h e issues to be clarified for the d i v e r t o r t u b e c o n f i g u r a t i o n w i t h o v e r h a n g b e n d sec-
tions, In o r d e r to qualify the d y n a m i c r e s p o n s e o f the o v e r h a n g b e n d section, the t o p o f t h e o v e r h a n g b e n d section ( b e n d no. 5 in Fig. 4) is hit w i t h a w o o d e n h a m m e r u n d e r " s o f t s u p p o r t " a n d " h a r d s u p p o r t " res t r a i n t c o n d i t i o n s . Soft s u p p o r t m e a n s t h a t t h e r e are n o
T. Arai et al. /Fusion Engineering and Design 28 (1995) 103 112
110
03I
I
Bend ,~ Bend Bend .L Bend ---o--- Bend
(3-
part part part part part
I
No.1 No,2 No.3 No.4 No.5
0.2
v
o
"O
o3 09
0.1
13_
5
10
Water
15
velocity (m/s)
Fig. 8. Pressure drop characteristics of bend sections.
" Hard support / restraint"
"Soft support / restraint" 2
!
8 E E iX3
0
~0
8 -2
0
.
3
~ v
i -2 0.4 0 ]30 3
0.4
40
¢,0
-3
~
0
-10
t t)'s"
0.4
-3 0
tx
I
t(s)
0.4
Fig. 9. Dynamic response of overhang bend tube under soft and hard support constraints (61, displacement of bend no. 5; 62 displacement of bend no. 4; c~, circumferential acceleration of bend no. 5; e, axial surface strain of bend no. 5).
T. Arai et al. /Fusion Engineering and Design 28 (1995) 103-112
1-1
P
~
111
~ 1 . 2 ,
(~
i a"
g
o.
5m/s
7m/s
t
0
t(s)
1Ovals
I
0.2 0
r
0.2 0
12.5m/s .
0.2 0
I
.
0
0.2
Fig. 10. Dependence of dynamic response of overhang bend tube on water velocity (P, coolant pressure; c~, acceleration of bend no. 5; 6, displacement of bend no. 5). supporting jigs between the upper and lower tubes in the overhang bend section, resulting in no constraint of the tubes. In contrast, hard support gives a rigid constraint between tubes by fixing the supporting jigs. Fig. 9 shows the measured displacement, acceleration and axial strain of the tube in these hitting experiments; 6~ and 62 are the displacements of bends nos. 5 and 4 in Fig. 4 respectively and c~ and e are the circumferential acceleration and axial surface strain of bend no. 5 respectively. It is found from Fig. 9 that the soft support restraint shows a slow acceleration response compared with the hard support restraint and the characteristic frequency of the overhang bend is around 15 Hz. The displacement and strain responses are essentially the same in both constraint conditions. The flow-induced vibration characteristics of the overhang bend section (bend no. 5 in Fig. 4) are measured under various water velocity and support restraint conditions. Fig. 10 shows typical flow-induced vibration characteristics obtained under the hard support constraint at water velocities of 5, 7, 10 and 12.5 m s -~, where P, c~ and 6 correspond to the coolant pressure, acceleration and displacement respectively. The coolant pressure is maintained at 1.2 MPa except in the case of 5 m s i flow velocity. It can be seen that the acceleration amplitude is increased with increasing water velocity and, in particular, the flow-induced vibration is highly enhanced at a water velocity of 12.5 m s-L In addition, it is found that a lower coolant pressure gives a higher displacement compared with a higher coolant pressure,
which may be due to a combination of coolant pressure and hydrodynamic forces.
5.
Conclusions
A l:l-scale model of the divertor cooling tube with support-restraint mechanisms has been fabricated for conducting a series of thermomechanical experiments in order to investigate the hydrodynamics and thermal deformation behaviour under operational conditions expected in the fusion experimental reactor. Preliminary experiments on pressure drop and flow-induced vibration have been conducted under various water velocities and several combinations of tube support and restraint conditions. The results obtained are as follows. (1) The total pressure drop of the whole test section reaches about 0.7 MPa at the related flow velocity of 10 m s l and most of the flow resistance is caused by swirl tape inserts and bend sections. The pressure drop characteristics obtained are comparable with those estimated in the design analysis. (2) The characteristic frequency of the overhang bend section with the smallest bend radius is around 15 Hz. Flow-induced vibrations of the overhang bend section become significant in a water velocity of 1012.5 m s -~ . JAERI is developing further evaluation of the results of flow-induced vibration and preparation for thermal experiments.
112
7". Arai et al./ Fusion Engineering and Design 28 (1995) 103-112
Acknowledgments
References
The authors would like to express their sincere appreciation to Drs. N. Wakayama and S. Shimamoto for their continuous encouragement in this work and to K. Tachibana and T. Ootsu for their assistance in the experimental work. They are also grateful to the staff of Nuclear Energy Development of Toshiba Co. for fabrication of the test section.
[1] T. Kuroda et al., ITER plasma facing components, ITER Doc. Ser. 30, 1991 (IAEA, Vienna). [2] M. Araki et al., Thermal cycling tests of plasma facing components for fusion experimental reactors at JAERI, Proc. 14th Symp. on Fusion Engineering, San Diego, CA, September 1991. [3] E. Tada et al., Divertor plate supporting system for fusion experimental reactor, Proc. 17th Syrup. on Fusion Technology, Rome, September 1992.
Fusion Engineering and Design 28 (1995) 103-112
Fusion Engineering and Design
Thermomechanical investigation on divertor supports for fusion experimental reactor: hydraulic experimental results T. Arai a, R. Hino a, y . Muto a, M. Nakahira b, M. Shibui b, K. Furuya b, E. Tada b, M. Seki b a Tokai Research Establishment, JAERI, Tokai-mura, Ibaraki 319-11, Japan b Naka Research Establishment, JAERI, Naka-machi, Ibaraki 311-01, Japan
Abstract
The Japan Atomic Energy Research Institute has been conducting technology development aimed at the construction of a fusion experimental reactor to follow JT-60 in Japan. The divertor plate facing the plasma is one of the components of the reactor core assembly, since it has to be operated under severe heat and particle loads and high electromagnetic forces. Thus the divertor supports should be designed so as to provide both flexibility for thermal expansion along the divertor cooling tube and mechanical stiffness for sustaining the electromagnetic force during plasma disruption as well as easy replacement in the case of failure. In order to meet these requirements, we have developed a new divertor support system based on a sliding mechanism for flexibility and a hydraulic cotter for replacement. The basic feasibility of this concept has been demonstrated through critical element development. Based on the feasibility study, a l:l-scale model of the divertor cooling tube test section with sliding mechanism has been fabricated for thermomechanical experiments to characterize the fluid mechanics, flow-induced vibration and flexibility for thermal expansion at various temperature profiles during normal and baking operations. Preliminary experiments on the fluid mechanical characteristics have been conducted as a function of the water velocity and the following results are obtained. (1) The total pressure drop along the whole test section reaches about 0.7 MPa at the rated water velocity of 10 m s - i at 20 °C, which is mostly dominated by swirl tape inserts and several bend sections, as expected by design estimation. (2) Flow-induced vibrations are observed at the two overhang bends with smaller curvatures and become significant at a higher water velocity of more than 10 m s -1.
1. Introduction
Plasma-facing components such as the divertor plate in a fusion experimental reactor are subjected to intense heat loads and high energy particles under normal
operating conditions as well as large electromagnetic forces during plasma disruptions. The divertor plate and the supports should be designed to meet these design conditions and require advanced technologies for cooling high heat fluxes, protecting high energy
0920-3796/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSD! 0920-3796(94) 00095-6
104
T. Arai et al. / Fusion Engineering and Design 28 (1995) 103 112
!or
SU SI
(a) SchematicViewof wholeassembly Vacuum Vessel ;q~--~
Divertor Plate ~/Divertor
Support Frame
(b) Divertor support concept
Fig. 1. Overall structural view of divertor plate and supports. particles and assuring structural integrity under thermal and mechanical loading conditions as well as remote maintainability. Design efforts have been made to develop a structural concept of the divertor plate according to the design requirements. As a result, a divertor structure with a new supporting system composed of a sliding mechanism and a hydraulic cotter has been devised [1] as shown schematically in Fig. 1. In this concept the divertor plate is composed of a number of cooling tubes connected to inlet and outlet manifolds and a divertor frame to assemble the cooling tubes as a unit plate structure. The divertor plate is fixed with a support shield structure by a conical cotter driven by a hydraulic jack system, which can be replaced for mainte-
nance purposes. The cooling tube, made of Cu alloy, is formed into a U-shaped geometry with several bends and an armour tile is brazed on the tube surface facing the plasma. The U-shaped tube is supported together with and fixed to the divertor frame through the sliding mechanism to allow thermal expansion due to their different operating temperatures. The cooling tube has a circular geometry with an inner diameter of 15 mm and a twisted tape (swirl tape) is partially inserted into the tube near plasma-striking points where a high heat flux is applied. With regard to technology development, the cooling capability of this concept has been extensively investigated [2] and it is found that the maximum heat flux should be around 15 MW m -2. In addition, the feasibility of hydraulic jacks has been demonstrated [3] and a total performance test using remote handling equipment is being conducted. The remaining critical issues to be qualified are the thermohydraulic behaviour of the cooling tube with swirl tape inserts and bend sections and the supports under normal and baking conditions. In particular, the following characteristics are to be examined: (1) the hydrodynamics of flow resistance and flowinduced vibration of the cooling tube with swirl tape inserts and bend sections at the rated water velocity of 10ms-l; (2) the structural support layout and the restraint conditions to accommodate non-uniform thermal expansion so as to avoid thermal deformation of the cooling tube under thermal and mechanical loads expected in normal, baking and disruption conditions. For this purpose a l:l-scale test section composed of a U-shaped cooling tube with swirl tape inserts and structural supports including a sliding mechanism has been fabricated and preliminary experiments on the hydraulic characteristics and flow-induced vibration have been conducted as a function of the water velocity and the restraint conditions of the divertor supports. This paper describes the design concept of a l:l-scale test section and the test results on hydrodynamic characteristics.
2. The 1/1-scale divertor test section
Fig. 2 shows the whole assembly of the l:l-scale divertor test section fabricated. The configuration is derived exactly from the actual design concept developed for the fusion experimental reactor. The divertor supports for varying the restraint conditions of the cooling tube are also shown in Fig. 2. The test section
105
T. Arai el al./ Fusion Engineering and Design 28 (1995) 103-112
G) Coolingtub~ Tube restraint @ Slide plnte
E
G(g~
( ~ Thermal insulation @ Support plnte (~) Support cooling tube
,oo
,
' ®
(a) Gravity support
(b) Supporting jigs
@ Cooling tube @ Pressure tap( [] ~ [] ) @ Swirl-tapedtube @ Test stand @ Gravitysupport @ Supportingjigs (overhang region) (~ Inletmanifold @ Supportingjig @ Outletmanifold Q , @ @
1~@ __
[]
[] @. . . ~ --Y~-Iil
(c) Overall structure Fig. 2. Assembly set-up of l:l-scale divertor test section.
is composed of a Cu cooling tube with swirl tape inserts, inlet and outlet manifolds made of stainless steel (SS 304), supporting jigs to adjust the restraint conditions between tubes and gravity supports connected to the test stand through dovetail grooves to allow axial movement of the tubes for thermal expansion. In the high heat flux region (No. 2 in Fig. 2) a twisted tape 0.8 mm thick with a swirl ratio of 3 and
340 mm long is inserted and fitted by mechanical pressing. The major hydraulic parameters and testing conditions of the test section are summarized in Table 1, together with the design parameters of the actual design of divertor plate. Four gravity supports (no. 3 in Fig. 2) for fastening the upper and lower tubes are located in the straight region of the test section and the location can be varied
106
T. Arai et al. / Fusion Engineering and Design 28 (1995) 103-112
Table 1 Hydraulic parameters and testing conditions of l:l-scale test section compared with design parameters of actual divertor Parameter
Actual divertor
Test section
Cooling tube Material Inner/outer diameter (ram) Total length (ram) Swirl taper inserts Thickness (mm) Swirl ratio Tape length (mm)
DS-Cu 15/18 6500
Cu 15/18 7046
0.8 3 500 x 2
0.8 3 340 x 2
Coolant conditions Pressure (MPa) Temperature (°C) Velocity (m s -1) Pressure drop (MPa)
3.5 50 10 0.92
1.5 20-50 1-13
for investigating the optimum layout to minimize thermal deformation. In addition, the axial movement can be restrained by key insertion into the dovetail groove so as to ensure the effect of fixing position on thermal deformation. The supporting jigs are divided into 18 remountable blocks along the test section so as to investigate the thermal deformation and flow-induced vibration under various restraint conditions of the upper and lower tubes. The whole test section can be heated to 400 °C for simulating the thermomechanical behaviour under the baking condition and thermal insulation blocks with electrical heaters are attached to the outer surface of the test section so as to reduce heat loss and keep the
background temperature constant. A cooling tube is installed on the test stand to provide a proper temperature difference between the tubes and test stand. A number of temperature sensors are attached to the tube surface, supporting jigs, gravity supports and test stand for the monitoring temperature gradient during heating experiments. In addition, 10 pressure taps (SS 304 tube of diameter 0.25 in) are installed to measure pressure drops in individual subsections along the cooling tube. The pressure tap layout and hydraulic parameters of each subsection are presented in Fig. 2 and Table 2 respectively.
3. Test facility and measurements An existing facility composed of water loop, nitrogen gas loop and data acquisition system has been modified for thermomechanical experiments on the l:l-'scale divertor test section. This facility is located in the Helium Engineering Demonstration Loop ( H E N D E L ) at the Japan Atomic Energy Research Institute (JAERI) Tokai Research Establishment and is capable of supplying either water at 50 1 s -1 at 1.5 MPa and temperatures below 50 °C or nitrogen gas at 33 1 s -1 below 400 °C. Fig. 3 shows a flow diagram of the water loop for hydrodynamic experiments on the divertor test section. During the experiments the water velocity supplied to the test section is controlled at specified values ranging from 2 to 12. 5 m s -1 by adjusting the rotor speed of the water pump. The pressure at the inlet manifold is normally maintained at 1 MPa by adjusting the outlet valve of the test section and the nitrogen gas pressure in the pressurizing water tank. The temperature of the
Table 2 i Geometrical parameters of subdivisions of l:l-scale test section Pressure tap
Subdivision
Geometrical parameters a
1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10
Inlet manifold Bend part no. 1 Bend part no. 2 Swirl tape insert no. 1 Straight part Bend part no. 3 Swirl tape insert no. 2 Bend part no 4 Bend part no. 5 Lower tube (return line) Outlet manifold
50 mm outer diameter L 169mm, R 80 x 180 mm, L 348 mm, R"519 x 40mm, L 410 mm, '\ L 706 mm, L 196mm, R 581 x 28mm, L 400 mm, L 131 mm, R 408 x 69mm, R 60 x 222mm,
a L, straight length; R, bend radius x angle; T, total length.
50 mm outer diameter
T T T T T T T T T
420mm 710mm 410 mm 706 mm 480mm 400 mm 622mm 300mm 2998 mm
107
T. Arai et al./ Fusion Engineering and Design 28 (1995) 103-I12
Test Flow meter Pump N2 Loop
N2 gas Preheater Cooler
® ®
Thermocouple
v , Water
Pressure gauge
Pressurized water tank
Fig. 3. Flow diagram of water loop for hydrodynamic experiments. water is normally kept at room temperature or raised to 50 °C by a preheater. Metal foil gauge-type pressure transducers are utilized for pressure drop measurements in each subsection. The inlet and outlet pressures of the test section
are monitored by transient pressure transducers with fast time response so as to enable flow oscillation measurements. In the test section two overhang bends with small bend radius are located at the inlet section (bend no. 1) and the front end section (bend no. 5) as
Bend No. 1
Bend No.5
=~ AT • Acceleration transducer DM : Displacement meter •" SG : Strain gauge
Bend No.2
Unit in mm
Bend No.4 Fig. 4. Schematic layout of sensors for flow-induced vibration experiments.
108
T. Arai et al. / Fusion Engineering and Design 28 (1995) 103-112
shown in Fig. 4. In order to measure the flow-induced vibration in such abrupt bend sections, acceleration detectors, eddy-current-type displacement sensors and strain gauges are attached to the tube surface. All measured data from the test section and the water loop are acquired and possessed by a personal computer (PC) system. In addition, transient behaviour such as vibration measurements is stored in a videotape recorder and reproduced on a high speed recorder.
Swirl tape part no. l, which corresponds to the swirl tape section in the upstream region, shows a larger pressure drop than the swirl tape part no. 2 in the downstream region. This discrepancy may be caused by different flow patterns in the two sections due to the tube configuration with several bends, but further quantitative evaluation is necessary. Comparing the flow length of the straight and swirl tape sections, it is concluded that the swirl tape section shows about two or three times the pressure drop per unit length of the straight section. In addition, the straight section indicates a higher friction factor (by approximately 25%) in the Reynolds number range from 4 x 10 4 to 2 x 10s than that predicted by the Blasius correlation, as shown in Fig. 7. This may be caused by residual enhanced turbulence due to upstream swirl flow or a roughened surface of the tube inner wall. The pressure drop characteristics measured in several bend regions of the test section are plotted in Fig. 8 as a function of the water velocity. Bend parts nos. 1-5 correspond to the bends between pressure tabs 1 and 2, 2 and 3, 5 and 6, 7 and 8, and 8 and 9 in Fig. 2 respectively. Bend part no. 1 shows an extremely large pressure drop compared with the other bend regions and the pressure drop reaches 0.14 MPa at 10 m s -1 in Fig. 8. The acceptable data of bend part no. 4 are only the first five plots because of trouble with the pressure transducer.
4. Test results 4.1. Pressuredrop
Fig. 5 shows the measured pressure drop characteristics of the first-half length (upper tube) and full length (upper and lower tubes) of the test section as a function of the water velocity. The pressure drop of the first half is roughly 80% of the total pressure drop because of the high flow resistance due to swirl tape inserts and small bend curvatures. At the rated velocity of 10 m s -1 the total pressure drop of the whole test section reaches 0.67 MPa at 20 °C, which is comparable with the design estimation. The pressure drop characteristics of the straight section and two swirl tape sections are plotted in Fig. 6.
1.2 Temperature Length 1.0 --
13-
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20°C 50°C
full full
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,
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,
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Water velocity (m/s) Fig. 5. Overall pressure drop characteristics of l:l-scale test section.
/Fusion
T. Arai et al.
Engineering and Design 28 (1995) 103
0.2
I
i
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109
112
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Straightpart I Swir[tapepart No.1 Swirl tape part No.2
13_
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o
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i
r
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Water velocity (m/s) Fig. 6. Pressure drop characteristics of straight and swirl tape regmns.
5
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Reynolds number Fig. 7. Friction factor of straight tube compared with Blasius correlation.
4.2. F l o w - i n d u c e d
vibration
T h e f l o w - i n d u c e d v i b r a t i o n due to t h e h i g h c o o l a n t velocity is o n e o f t h e issues to be clarified for the d i v e r t o r t u b e c o n f i g u r a t i o n w i t h o v e r h a n g b e n d sec-
tions, In o r d e r to qualify the d y n a m i c r e s p o n s e o f the o v e r h a n g b e n d section, the t o p o f t h e o v e r h a n g b e n d section ( b e n d no. 5 in Fig. 4) is hit w i t h a w o o d e n h a m m e r u n d e r " s o f t s u p p o r t " a n d " h a r d s u p p o r t " res t r a i n t c o n d i t i o n s . Soft s u p p o r t m e a n s t h a t t h e r e are n o
T. Arai et al. /Fusion Engineering and Design 28 (1995) 103 112
110
03I
I
Bend ,~ Bend Bend .L Bend ---o--- Bend
(3-
part part part part part
I
No.1 No,2 No.3 No.4 No.5
0.2
v
o
"O
o3 09
0.1
13_
5
10
Water
15
velocity (m/s)
Fig. 8. Pressure drop characteristics of bend sections.
" Hard support / restraint"
"Soft support / restraint" 2
!
8 E E iX3
0
~0
8 -2
0
.
3
~ v
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0.4
40
¢,0
-3
~
0
-10
t t)'s"
0.4
-3 0
tx
I
t(s)
0.4
Fig. 9. Dynamic response of overhang bend tube under soft and hard support constraints (61, displacement of bend no. 5; 62 displacement of bend no. 4; c~, circumferential acceleration of bend no. 5; e, axial surface strain of bend no. 5).
T. Arai et al. /Fusion Engineering and Design 28 (1995) 103-112
1-1
P
~
111
~ 1 . 2 ,
(~
i a"
g
o.
5m/s
7m/s
t
0
t(s)
1Ovals
I
0.2 0
r
0.2 0
12.5m/s .
0.2 0
I
.
0
0.2
Fig. 10. Dependence of dynamic response of overhang bend tube on water velocity (P, coolant pressure; c~, acceleration of bend no. 5; 6, displacement of bend no. 5). supporting jigs between the upper and lower tubes in the overhang bend section, resulting in no constraint of the tubes. In contrast, hard support gives a rigid constraint between tubes by fixing the supporting jigs. Fig. 9 shows the measured displacement, acceleration and axial strain of the tube in these hitting experiments; 6~ and 62 are the displacements of bends nos. 5 and 4 in Fig. 4 respectively and c~ and e are the circumferential acceleration and axial surface strain of bend no. 5 respectively. It is found from Fig. 9 that the soft support restraint shows a slow acceleration response compared with the hard support restraint and the characteristic frequency of the overhang bend is around 15 Hz. The displacement and strain responses are essentially the same in both constraint conditions. The flow-induced vibration characteristics of the overhang bend section (bend no. 5 in Fig. 4) are measured under various water velocity and support restraint conditions. Fig. 10 shows typical flow-induced vibration characteristics obtained under the hard support constraint at water velocities of 5, 7, 10 and 12.5 m s -~, where P, c~ and 6 correspond to the coolant pressure, acceleration and displacement respectively. The coolant pressure is maintained at 1.2 MPa except in the case of 5 m s i flow velocity. It can be seen that the acceleration amplitude is increased with increasing water velocity and, in particular, the flow-induced vibration is highly enhanced at a water velocity of 12.5 m s-L In addition, it is found that a lower coolant pressure gives a higher displacement compared with a higher coolant pressure,
which may be due to a combination of coolant pressure and hydrodynamic forces.
5.
Conclusions
A l:l-scale model of the divertor cooling tube with support-restraint mechanisms has been fabricated for conducting a series of thermomechanical experiments in order to investigate the hydrodynamics and thermal deformation behaviour under operational conditions expected in the fusion experimental reactor. Preliminary experiments on pressure drop and flow-induced vibration have been conducted under various water velocities and several combinations of tube support and restraint conditions. The results obtained are as follows. (1) The total pressure drop of the whole test section reaches about 0.7 MPa at the related flow velocity of 10 m s l and most of the flow resistance is caused by swirl tape inserts and bend sections. The pressure drop characteristics obtained are comparable with those estimated in the design analysis. (2) The characteristic frequency of the overhang bend section with the smallest bend radius is around 15 Hz. Flow-induced vibrations of the overhang bend section become significant in a water velocity of 1012.5 m s -~ . JAERI is developing further evaluation of the results of flow-induced vibration and preparation for thermal experiments.
112
7". Arai et al./ Fusion Engineering and Design 28 (1995) 103-112
Acknowledgments
References
The authors would like to express their sincere appreciation to Drs. N. Wakayama and S. Shimamoto for their continuous encouragement in this work and to K. Tachibana and T. Ootsu for their assistance in the experimental work. They are also grateful to the staff of Nuclear Energy Development of Toshiba Co. for fabrication of the test section.
[1] T. Kuroda et al., ITER plasma facing components, ITER Doc. Ser. 30, 1991 (IAEA, Vienna). [2] M. Araki et al., Thermal cycling tests of plasma facing components for fusion experimental reactors at JAERI, Proc. 14th Symp. on Fusion Engineering, San Diego, CA, September 1991. [3] E. Tada et al., Divertor plate supporting system for fusion experimental reactor, Proc. 17th Syrup. on Fusion Technology, Rome, September 1992.