- Email: [email protected]
Design and Construction of Long Cryogenic Piping Lines
Design and Construction of Long Cryogenic Piping Lines
Katsumi Kawano, Kazuya Hamada, Takashi Kato, Tadaaki Honda, Kazuhiko Nishida, Kunihiro Matsui, Yadao Hiyama, Kiichi Ohtsu, Shuuichi Sekiguchi, Hiroshi Tsuji, Mamoru Ando*, Tetsuo Hiyama* and Kaoru. Ichige* Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, 801-1, Muko-yama, Nakamachi, Naka-gun, Ibaraki, 311-01, Japan, *Hitachi Oxygen, Co., LTD., 3-1-17, Kokubun-cho, Hitachi-shi, Ibaraki, 316, Japan
An unique heat-leak measurement method has been developed, being useful to determine the heat leak for a long-length cryogenic piping line. The method is only to measure the outer surface temperature of the cryogenic piping line when liquid helium flowing. The method has been verified that the measurement result by the method had a good agreement with the other measurement method such as a liquid helium transfer efficiency measuring method and a enthalpy mass flow rate measurement method. The method provides a simple verification method for cryogenic piping line performance.
INTRODUCTION It is generally complicate and delicate to determine a heat leak of a cryogenic piping line such as liquid helium transfer line and a cold helium transfer line. The heat leak is ordinary evaluated to measure liquid helium transfer coefficient, or mass flow rate and enthalpy difference through the piping line. However, it will be almost impossible to determine the heat leak in the case that there aren't any sensors to measure the inlet and the outlet condition of transferring helium. Japan Atomic Energy Research Institute (JAERI) is the Japanese representative research institute of International Thermonuclear Experimental Reactor (ITER) and has the charge of fabrication of ITER Central Solenoid (CS) model coil[1 ], construction of CS model coil common test facility (CSTF)[2], and implementation of the CS model coil testing. The CSTF has been constructed, involving the development of a large cryogenic system[3]. The construction of the large cryogenic system required some of a new long-length cryogenic piping line to transfer cold helium from the new cryogenic system to the existing cryogenic system which is the test facility for the ITER full size superconducting conductor and its joint. The longest cryogenic line is nearly 90 m and the others are around 50 to 60 m, respectively. Low heat leak is specified to be around 1 W/m including all the heat leak from the joint and support parts of the cryogenic piping line. One line, however, is not available to measure the liquid helium transfer coefficient or the enthalpy difference. Therefore, we has tried to develop a new measurement method that can determined the heat leak of the piping without any sensors at the inlet and the outlet of the piping. The new measurement method is presented in the paper.
DEVELOPED MEASUREMENT METHOD Recent cryogenic piping has a relatively small outer tube diameter due to use of high performance thermal insulator. For instance, around 60-mm diameter outer tube is used for a 20-mm inner tube diameter that is applied for a typical liquid helium transfer piping line. To consider the heat leak from the air to the surface of the outer tube, the heat leak (q) is easily calculated as the following equation, assuming free convection heat transfer coefficient (h); 493
494
ICEC16/ICMC Proceedings Flow Meter
),)
ATM
LN 2
~C-" / 2400
w
O :Measurement Point
gC
\
\1
Figure 1 Heat transfer coefficient measurement in factory
q = h AT S L
(1)
Where A T is the temperature difference between the outer tube surface and the ambient atmosphere, S and L are the outer tube area with unit length and the length of the outer tube, respectively. The free convection heat transfer coefficient is generally in the range of 5- 25 W/m2.K. It will be around 5-6 W/m2"K at static indoor condition. The heat leak is tried to calculate by substituting the 60mm outer-diameter tube and the free convection heat transfer coefficient of 5 W/m2"K. In the case that the heat leak of unit length is assumed to be 1 W/m, the A T is determined to be around 1 K. If the accuracy of the temperature difference measurement is less than 1 K, it can measure the heat leak of around 1 W/m for the cryogenic piping. When the h is evaluated in advance, the heat leak of the piping can be easily determined by measuring the temperature difference between the surface of the outer tube and the ambient atmosphere. Determination of free convection heat transfer coefficient To determine the free convection heat transfer coefficient in advance, an experiment was performed in indoor condition by using the practical cryogenic piping as shown in Fig. 1. Liquid nitrogen was stored in the inner tube of the piping and boil-off rate was measured after cooling the piping down completely. The heat leak was calculated from the obtained boil-off rate. Simultaneously, the surface temperature and the ambient atmosphere temperature were measured at each point of the piping as indicated in the figure. Combining both measurement results, the free convection heat transfer coefficient was determined to be 5.5 W/mZ'K. This value was used to calculate the heat leak of the newly constructed long-length cryogenic piping lines. NEW CRYOGENIC PIPE LINES Three long-length cryogenic piping lines have been constructed and installed to communicate cold helium between the CSTF cryogenic system and the ITER full size conductor test facility as shown in Fig. 2 Their specification is summarized in Table 1. Each piping line was designed and fabricated to achieve the overall heat leak of less than 1 W/K including all the inner tube support and the bayonet joints.
ICEC16/ICMC Proceedings
495
IC~
' Ef Co,d He,ium etum L,no , ~
J,!:
/1
~
I
~l~e~,',
0 34.0 X tl.65 60m
]
ress~
]
'
~
i
'F---l--
LN2 '~
Cold Helium Supply Line 0 21.7 •
90m [Cold-Box
Liquid Helium Supply Line ~521.7 • t 1.65 52m
ZX
-----W-_ -
20,000L LIQUID HELIUM TANK
ITER Full Size Conductor Test Facility
Figure 2
Table 1
Cryogenic piping between cold box and existing test facility
Specification of new piping line Cold helium supply line
Length (m) Inner Diameter (mm) Outer Diameter Number of Joint Target value(W/m)
86 21.7 60.5 12 0.735
Liquid Helium Supply line 52 21.7 60.5 7 0.97
Cold helium return line 60 34 9 1.03
HEAT LEAK MEASUREMENT RESULTS On the liquid helium supply line, the heat leak was estimated by using two kinds of method such as the liquid helium transfer method and the developed surface temperature measuring method. This line is connected with the 58-m existing line of which heat leak of 3.42 W/m was already determined. When liquid helium was transferred, the liquid helium storage rate of 332 liter/h and the liquid helium withdraw rate of 676 liter/h were measured, respectively. The heat leak was calculated to be 0.98 W/m, considering the heat leak from the existing line. The surface temperature measurement method was performed. The 51 points were measured as shown in Fig. 3, according to one point every meter. The measurement results are shown in Fig. 3. Some of peek are observed in the figure such as the measuring point numbers of 12, 16, 25, 36, and 42, which corresponds to the location of piping joints and flexible tubes. The average temperature difference is calculated to be 0.82 K except the data for the joints and the flexible tubes. On the contrary, the average temperature difference for the joints and the tubes are 1.3 K. The total averaged heat leak is finally determined to be 0.97 W/m that has almost the same as the result of the liquid helium transfer method. Therefore, the developed heat leak measurement method has been verified to be useful to estimate the heat leak. On the cold helium supply line, the surface temperature measurement and the enthalpy deference measurement through the line with mass flow rate measurement were performed. As a result, the heat leak of 0.53 W/m is estimated by the surface temperature measurement method and the heat leak of 0.59 W/m is measured by the enthalpy measurement.
496
ICEC16/ICMC Proceedings
The cold helium return line didn't have any sensor to measure the helium inlet and the outlet condition. Accordingly, only the surface temperature measurement method was available. The measured results was 1.026 W/m. All measurement results are listed in Table 2. It is verified that our developed surface temperature measurement method is significantly useful. Table 2
Summary of heat leak measurement
Design (W/m) Surface temperature measurement (W/m) Liquid helium transfer (W/m) Enthalpy method
~-
High pressure cold helium gas line 0.735 0.527
Liquid helium line 0.97 0.98 0.98 -
-
0.59
Low pressure Recovery line 1.2 1.03 -
302
14.0
300
12.0
298
10.0 "~" ti
L_
~ a.
296
!
i
:
~
,
,
I
~ ~ ! i i : i ] ' ' ! ! ; i ~' i ,
294
' ~I i ~ i : ~ [ ,
} [
i ri i i , : ; i ! i
~ ,._.,~_] ~:__L_i_.ll_i__!_ii_~_] [ : i --~-SurfaceTemperature(K) i i 'i " A m b i e n t T e m p e r a t u r e ( K )
8.0
~
6.0
.4--,
a
=
E ~-" 2 9 2
4.0
290
2.0
E
(D I--
0.0
288 1
3
5
7
9
11 13 15 17 19 21 2 3 2 5 2 7 2 9 31 3 3 3 5 3 7 3 9 41 4 3 4 5 4 7 4 9 51
Measurement Position (longitudinal)
Figure 3
Temperature profile of the surface temperature measurement
CONCLUSION Heat leak measurement for the long-length cryogenic piping line has been successfully carried out and the performance of cryogenic piping line is satisfied with the design requirement. Using free convection heat transfer coefficient, heat leak can be estimated from the surface temperature of the piping line. The results has good agreements with the both of liquid helium transfer efficiency measurement and enthalpy massflow measurement. New and useful heat leak measurement method for the cryogenic piping line has been developed and established. ACKNOWLEDGMENT The authors would like to thank Drs. M. Ohta, T. Nagashima and S. Matsuda for their continuous encouragement and support on this work. The fabrication work from JECC Corporation, is well acknowledged. REFERENCE
1 2 3
Thome. R., Design & Development of the ITER Magnet System,. Cryogenics (1994) Vol. 34 ICEC Supplement 39-45 Shimamoto, S. and Hamada, K. et al., Construction of ITER Common Test Facility for CS model coil, Proceeding of 14th International Conference of Magnet Technology 1995 Kato, T. et al., Cryogenic system for ITER CS model coil, to be published in Advanced in Cryogenic Engineering (1994) 41
Katsumi Kawano, Kazuya Hamada, Takashi Kato, Tadaaki Honda, Kazuhiko Nishida, Kunihiro Matsui, Yadao Hiyama, Kiichi Ohtsu, Shuuichi Sekiguchi, Hiroshi Tsuji, Mamoru Ando*, Tetsuo Hiyama* and Kaoru. Ichige* Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, 801-1, Muko-yama, Nakamachi, Naka-gun, Ibaraki, 311-01, Japan, *Hitachi Oxygen, Co., LTD., 3-1-17, Kokubun-cho, Hitachi-shi, Ibaraki, 316, Japan
An unique heat-leak measurement method has been developed, being useful to determine the heat leak for a long-length cryogenic piping line. The method is only to measure the outer surface temperature of the cryogenic piping line when liquid helium flowing. The method has been verified that the measurement result by the method had a good agreement with the other measurement method such as a liquid helium transfer efficiency measuring method and a enthalpy mass flow rate measurement method. The method provides a simple verification method for cryogenic piping line performance.
INTRODUCTION It is generally complicate and delicate to determine a heat leak of a cryogenic piping line such as liquid helium transfer line and a cold helium transfer line. The heat leak is ordinary evaluated to measure liquid helium transfer coefficient, or mass flow rate and enthalpy difference through the piping line. However, it will be almost impossible to determine the heat leak in the case that there aren't any sensors to measure the inlet and the outlet condition of transferring helium. Japan Atomic Energy Research Institute (JAERI) is the Japanese representative research institute of International Thermonuclear Experimental Reactor (ITER) and has the charge of fabrication of ITER Central Solenoid (CS) model coil[1 ], construction of CS model coil common test facility (CSTF)[2], and implementation of the CS model coil testing. The CSTF has been constructed, involving the development of a large cryogenic system[3]. The construction of the large cryogenic system required some of a new long-length cryogenic piping line to transfer cold helium from the new cryogenic system to the existing cryogenic system which is the test facility for the ITER full size superconducting conductor and its joint. The longest cryogenic line is nearly 90 m and the others are around 50 to 60 m, respectively. Low heat leak is specified to be around 1 W/m including all the heat leak from the joint and support parts of the cryogenic piping line. One line, however, is not available to measure the liquid helium transfer coefficient or the enthalpy difference. Therefore, we has tried to develop a new measurement method that can determined the heat leak of the piping without any sensors at the inlet and the outlet of the piping. The new measurement method is presented in the paper.
DEVELOPED MEASUREMENT METHOD Recent cryogenic piping has a relatively small outer tube diameter due to use of high performance thermal insulator. For instance, around 60-mm diameter outer tube is used for a 20-mm inner tube diameter that is applied for a typical liquid helium transfer piping line. To consider the heat leak from the air to the surface of the outer tube, the heat leak (q) is easily calculated as the following equation, assuming free convection heat transfer coefficient (h); 493
494
ICEC16/ICMC Proceedings Flow Meter
),)
ATM
LN 2
~C-" / 2400
w
O :Measurement Point
gC
\
\1
Figure 1 Heat transfer coefficient measurement in factory
q = h AT S L
(1)
Where A T is the temperature difference between the outer tube surface and the ambient atmosphere, S and L are the outer tube area with unit length and the length of the outer tube, respectively. The free convection heat transfer coefficient is generally in the range of 5- 25 W/m2.K. It will be around 5-6 W/m2"K at static indoor condition. The heat leak is tried to calculate by substituting the 60mm outer-diameter tube and the free convection heat transfer coefficient of 5 W/m2"K. In the case that the heat leak of unit length is assumed to be 1 W/m, the A T is determined to be around 1 K. If the accuracy of the temperature difference measurement is less than 1 K, it can measure the heat leak of around 1 W/m for the cryogenic piping. When the h is evaluated in advance, the heat leak of the piping can be easily determined by measuring the temperature difference between the surface of the outer tube and the ambient atmosphere. Determination of free convection heat transfer coefficient To determine the free convection heat transfer coefficient in advance, an experiment was performed in indoor condition by using the practical cryogenic piping as shown in Fig. 1. Liquid nitrogen was stored in the inner tube of the piping and boil-off rate was measured after cooling the piping down completely. The heat leak was calculated from the obtained boil-off rate. Simultaneously, the surface temperature and the ambient atmosphere temperature were measured at each point of the piping as indicated in the figure. Combining both measurement results, the free convection heat transfer coefficient was determined to be 5.5 W/mZ'K. This value was used to calculate the heat leak of the newly constructed long-length cryogenic piping lines. NEW CRYOGENIC PIPE LINES Three long-length cryogenic piping lines have been constructed and installed to communicate cold helium between the CSTF cryogenic system and the ITER full size conductor test facility as shown in Fig. 2 Their specification is summarized in Table 1. Each piping line was designed and fabricated to achieve the overall heat leak of less than 1 W/K including all the inner tube support and the bayonet joints.
ICEC16/ICMC Proceedings
495
IC~
' Ef Co,d He,ium etum L,no , ~
J,!:
/1
~
I
~l~e~,',
0 34.0 X tl.65 60m
]
ress~
]
'
~
i
'F---l--
LN2 '~
Cold Helium Supply Line 0 21.7 •
90m [Cold-Box
Liquid Helium Supply Line ~521.7 • t 1.65 52m
ZX
-----W-_ -
20,000L LIQUID HELIUM TANK
ITER Full Size Conductor Test Facility
Figure 2
Table 1
Cryogenic piping between cold box and existing test facility
Specification of new piping line Cold helium supply line
Length (m) Inner Diameter (mm) Outer Diameter Number of Joint Target value(W/m)
86 21.7 60.5 12 0.735
Liquid Helium Supply line 52 21.7 60.5 7 0.97
Cold helium return line 60 34 9 1.03
HEAT LEAK MEASUREMENT RESULTS On the liquid helium supply line, the heat leak was estimated by using two kinds of method such as the liquid helium transfer method and the developed surface temperature measuring method. This line is connected with the 58-m existing line of which heat leak of 3.42 W/m was already determined. When liquid helium was transferred, the liquid helium storage rate of 332 liter/h and the liquid helium withdraw rate of 676 liter/h were measured, respectively. The heat leak was calculated to be 0.98 W/m, considering the heat leak from the existing line. The surface temperature measurement method was performed. The 51 points were measured as shown in Fig. 3, according to one point every meter. The measurement results are shown in Fig. 3. Some of peek are observed in the figure such as the measuring point numbers of 12, 16, 25, 36, and 42, which corresponds to the location of piping joints and flexible tubes. The average temperature difference is calculated to be 0.82 K except the data for the joints and the flexible tubes. On the contrary, the average temperature difference for the joints and the tubes are 1.3 K. The total averaged heat leak is finally determined to be 0.97 W/m that has almost the same as the result of the liquid helium transfer method. Therefore, the developed heat leak measurement method has been verified to be useful to estimate the heat leak. On the cold helium supply line, the surface temperature measurement and the enthalpy deference measurement through the line with mass flow rate measurement were performed. As a result, the heat leak of 0.53 W/m is estimated by the surface temperature measurement method and the heat leak of 0.59 W/m is measured by the enthalpy measurement.
496
ICEC16/ICMC Proceedings
The cold helium return line didn't have any sensor to measure the helium inlet and the outlet condition. Accordingly, only the surface temperature measurement method was available. The measured results was 1.026 W/m. All measurement results are listed in Table 2. It is verified that our developed surface temperature measurement method is significantly useful. Table 2
Summary of heat leak measurement
Design (W/m) Surface temperature measurement (W/m) Liquid helium transfer (W/m) Enthalpy method
~-
High pressure cold helium gas line 0.735 0.527
Liquid helium line 0.97 0.98 0.98 -
-
0.59
Low pressure Recovery line 1.2 1.03 -
302
14.0
300
12.0
298
10.0 "~" ti
L_
~ a.
296
!
i
:
~
,
,
I
~ ~ ! i i : i ] ' ' ! ! ; i ~' i ,
294
' ~I i ~ i : ~ [ ,
} [
i ri i i , : ; i ! i
~ ,._.,~_] ~:__L_i_.ll_i__!_ii_~_] [ : i --~-SurfaceTemperature(K) i i 'i " A m b i e n t T e m p e r a t u r e ( K )
8.0
~
6.0
.4--,
a
=
E ~-" 2 9 2
4.0
290
2.0
E
(D I--
0.0
288 1
3
5
7
9
11 13 15 17 19 21 2 3 2 5 2 7 2 9 31 3 3 3 5 3 7 3 9 41 4 3 4 5 4 7 4 9 51
Measurement Position (longitudinal)
Figure 3
Temperature profile of the surface temperature measurement
CONCLUSION Heat leak measurement for the long-length cryogenic piping line has been successfully carried out and the performance of cryogenic piping line is satisfied with the design requirement. Using free convection heat transfer coefficient, heat leak can be estimated from the surface temperature of the piping line. The results has good agreements with the both of liquid helium transfer efficiency measurement and enthalpy massflow measurement. New and useful heat leak measurement method for the cryogenic piping line has been developed and established. ACKNOWLEDGMENT The authors would like to thank Drs. M. Ohta, T. Nagashima and S. Matsuda for their continuous encouragement and support on this work. The fabrication work from JECC Corporation, is well acknowledged. REFERENCE
1 2 3
Thome. R., Design & Development of the ITER Magnet System,. Cryogenics (1994) Vol. 34 ICEC Supplement 39-45 Shimamoto, S. and Hamada, K. et al., Construction of ITER Common Test Facility for CS model coil, Proceeding of 14th International Conference of Magnet Technology 1995 Kato, T. et al., Cryogenic system for ITER CS model coil, to be published in Advanced in Cryogenic Engineering (1994) 41