- Email: [email protected]
Installation and commissioning of a cryogen distribution system for the TPS project
Accepted Manuscript Installation and Commissioning of a Cryogen Distribution System for the TPS Project H.H. Tsai, F.Z. Hsiao, H.C. Li, M.C. Lin, C. Wang, W.R. Liao, T.F. Lin, W.S. Chiou, S.H. Chang, P.S.D. Chuang PII: DOI: Reference:
S0011-2275(15)30056-4 http://dx.doi.org/10.1016/j.cryogenics.2016.04.014 JCRY 2571
To appear in:
Cryogenics
Received Date: Accepted Date:
18 December 2015 27 April 2016
Please cite this article as: Tsai, H.H., Hsiao, F.Z., Li, H.C., Lin, M.C., Wang, C., Liao, W.R., Lin, T.F., Chiou, W.S., Chang, S.H., Chuang, P.S.D., Installation and Commissioning of a Cryogen Distribution System for the TPS Project, Cryogenics (2016), doi: http://dx.doi.org/10.1016/j.cryogenics.2016.04.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Installation and Commissioning of a Cryogen Distribution System for the TPS Project
Tsai H. H.1, Hsiao F. Z., Li H. C., Lin M. C., Wang C., Liao W. R., Lin T. F., Chiou W. S., Chang S. H., and Chuang P. S. D. 1
National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan, R.O.C
ABSTRACT A cryogen distribution system was installed and commissioned to transfer liquid nitrogen (LN2) and liquid helium (LHe) from storage dewars to superconducting radio-frequency (SRF) cavities for the 3-GeV Taiwan Photon Source (TPS) project. The cryogen distribution system comprises one distribution valve box (DVB), four control valve boxes (CVB) and seven sections of multichannel transfer line (MCL). The DVB distributes the LHe and LN2 to the CVB, and then to the SRF cavities through independent vacuum-jacketed transfer lines. The vaporized GHe and GN2 from the cryomodules are collected via the MCL. The cryogen distribution system was installed and commissioned from October 2014 to the end of March 2015. This paper presents the installation, pre-commissioning and commissioning of the cryogen distribution system, and describes the heat load test. Thermal Acoustic Oscillation (TAO) was found in the GHe process line; this phenomenon and its solution are also presented and discussed. KEY WORDS Multichannel transfer line, TPS, thermal acoustic oscillation
INTRODUCTION The Taiwan Photon Source (TPS) project entailing an electron accelerator with beam current 500 mA at 3 GeV and low emittance 2 nm rad is in progress at NSRRC. The circumferences of the storage ring and the booster ring are 518.4 m and the 496.8 m, respectively. The superconductive RF (SRF) modules are installed in short straight sections and maintain the energy level of the beam. A new helium cryogenic system is required to produce sufficient LHe for the SRF modules. The cryogenic distribution system is required to feed the LHe and LN2 to the SRF modules individually and to recover the vaporized GHe to the cryogenic system. The cryogenic system has maximum cooling capacity 890 W at 4.5 K with associated compressors, an oil-removal system (ORS), four helium buffer tanks, one 7000-L Dewar, gaseous helium piping at room temperature, transfer lines to distribute helium, and a transfer system for liquid nitrogen. The helium cryogenic system was installed and commissioned in year 2014 [1].
Figure 1 shows the layout of the cryogenic distribution system, which comprises one DVB, four CVB and seven sections of multichannel transfer line. Four SRF cavities are located, two upstream and two downstream of the DVB. A total heat load 100 W is expected for the acceptance test of the cryogenic distribution system. The features of the TPS cryogenic distribution system were simple, programmable control for the fluid flow, a small heat load and pressure drop, and recovery of the vaporized GN2 and GHe from the SRF modules and process line [2] . The system was installed and commissioned in 2014 and 2015, respectively. The measured heat load fulfilled the operational requirement of the SRF cavities. This paper presents the installation and commissioning of the cryogenic distribution system and discusses the results of the heat-load measurements. The safety valves and their exhaust pipeline were installed on every process line between the control valves inside the DVB, TL2 and TL4, as figure 2 shows. The exhaust pipeline of safety valves penetrates the outer case of the DVB and then connects to the process line. The cold fluid is isolated from the warm helium gas, as the safety valves are closed under normal operational conditions. The interface and the ventilation line outside the DVB remain warm during the operation. We found freezing phenomena at the interface and on the ventilation line for the GHe process line, which was due to thermal acoustic oscillation (TAO); this phenomenon and its treatment are also presented and discussed in this paper.
Figure 1 Overview of the layout of the cryogenic distribution system
Figure 2 Process diagram of the DVB
INSTALLATION AND PRE-COMMISSIONING OF THE CRYOGENIC DISTRIBUTION SYSTEM Installation challenge The cryogenic distribution system is located at the inner ring. The DVB, CVB and MCL had to be transported over the tunnel from the outer ring to the inner ring using a crane. The challenge in this installation was due mostly to the positioning of the MCL because of the confined space of the piping duct. The MCL was located between the cable tray and the air duct, which had a gap only 500 mm. The MCL piping duct was also blocked by the control and instrument area (CIA); the positioning of the MCL could thus be performed only from both ends. The installation not only had to hang over the tunnel but also to roll into the piping duct. The movement of the MCL had to be slow to avoid a collision with the cable tray and the wind duct. A roller was installed on the piping support to slide the MCL from the end of the piping duct into its position. Figure 3 shows the method of installation of the MCL using both a crane and a mobile scissor lift.
Figure 3 Installation of the MCL Pre-commissioning Impurities in the helium gas are a critical issue for a helium cryogenic system due to the operating temperatures 80 K to 4.6 K from the first heat exchanger to the J-T valve. A large concentration of moisture was trapped not only inside the valve seat but also in the first heat exchanger of the cold box, which introduced a pressure drop and decreased the cooling power of the system. The impurity gases (i. e., nitrogen) can become concentrated, so as to solidify, to impact and to break a turbo expander wheel or bearing as well. The helium cryogenic system must thus be clean, dry and leak-tight to avoid damage to the turbo expanders. The LHe/GHe and LN2/GN2 process lines were filled with helium gas at 2 barg and 5 barg to perform leakage tests after the MCL, CVB and DVB were completely connected. The measured rate of helium leakage was less than 1.0x10-9 mbar L s-1 in the evacuation mode with 1.0x10-3 mbar vacuum level for every process line on all vacuum jackets, which fulfilled the leak tight and low heat loss requirement of the cryogenic system operation. The clean and dry nitrogen gas was then connected to the pumping port (i. e., P1 in figure 2) of DVB to purge the entire process line. The measurement of the dew point was less than -70 oC and the particles were reached class 100 after purging for two weeks. The vacuum jacket was pumped to 1.0x10-5 mbar to restrain the convective heat transfer. Both helium and nitrogen process lines were filled with liquid nitrogen, which was called the cold-shock test. The objective was to test the effect of thermal stress on the fitting and weld bead. Every fitting and weld bead was helium leak-tested under 80 K and after warming to 200 K. The above process was repeated twice. The measured rate of leakage was less than 1.0x10-9 mbar L s-1. The final step was to purge with N50 pure helium gas, to retain for 30 min and then to pump to 1.0x10-2 mbar. This process was repeated three times to ensure the helium purity of the cryogenic distribution system. The gaseous helium was circulated through the analyzer of the cryogenic system, and N2, H2O and CxHy were analyzed. The cooling procedure was initiated after the concentrations were observed to be below 2 ppm.
MEASUREMENT OF THE HEAT LOAD Configuration of the Heat-load Measurement Figure 4 shows a flow chart of the heat-load measurement. Loop A comprised the heat load of half of the DVB, TL2, CVB2, TL3, CVB1 and TL6 for liquid helium and the gaseous helium process line. Loop B comprised the heat load of half of the DVB, TL4, CVB3, TL5 and TL7 for the liquid helium and gaseous helium process line also. The heat load of the SRF cavities was excluded; the liquid helium was thus circulated from the bypass loop of the end of TL6 and TL7. A test dewar (1000 L) was installed at the end of the circulation loop to ensure that the transfer line filled with liquid helium. The heat loads of loops A and B were measured individually.
Figure 4
Flow chart of the heat-load measurement
Measurement of the Heat Load The pure saturated liquid helium was delivered from a 7000-L dewar and flowed through the cryogenic distribution system in Loops A and B. The static heat load along the entire path qTL vaporized the liquid and thus delivered mixed liquid and gas to the 1000-L dewar at the end of the system. The total mass flow rate, mT, measured after warming the cold gas through a passive heater. mT included not only the vaporized liquid helium from the static heat load but also the transport flow rate from the 7000-L dewar to the test dewar through the transfer line, as the liquid helium was delivered continually during the measurement. The calculation of the heat load was based on the following equation,
(1)
mT × h fg = qTL + qTD + qTD − H + q MD −TL
where qTD represents the static heat load which was determined from the static boil-off rate of the test dewar, qTD-H represents the dynamic heat load, which was applied using the built-in heater in the test dewar, and qMD-TL represents the static heat load to liquid in the transfer line flowing from the 7000-L main dewar to the DVB. The net heat load of cryogenic distribution system, qTL, is: (2)
qTL = mT × h fg − qTD − qTD − H − q MD −TL
The mass flow rates of loops A and B were measured individually, denoted by mT-A and mT-B, respectively. The heat loads of loops A and B were calculated based on equation (2), denoted by qTL-A and q TL-B, respectively. The flash loss, x, was considered, which was due to a pressure difference between the supply pressure and the end pressure inside the test dewar during the transport [3]. The calculation was based on the law of conservation of energy, which leads to
hl −MD = hl −TD × (1 − x) + hg −TD × x
(3)
in which hl-MD and hl-TD represent the enthalpy of the supplied liquid from the main dewar and the test dewar respectively; hg-TD represents the enthalpy of the gas at the test dewar; x represents the flash loss. The heat load was excluded from equation (3). The calculated flash loss was 5.68 %. Commercial software (HEPAK [4]) was used to determine the helium properties for the calculation. The total flow rate was measured using a mass flow meter (OMEGA, uncertainty 1 %). RESULTS AND DISCUSSION Heat Load of the Transfer Line The flow was measured until the mass flow rate was observed to be stabilized on the flow meter. The mass flow rate was measured under three heating powers of the test dewar, as shown in figure 5.
1600
mT-A 1560
mT-B
1520
mT (SLPM)
1480 1440 1400 1360 1320 1280 1240 1200 0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
qTD-H (W) Figure 5 Variation of total mass flow rate with heating power of the test dewar
The vaporized mass flow rate includes q TD, q TD-H, qMD-TL and the flash loss, as summarized in Table 1. The measured heat load qTD was based on the static vaporization rate test, which was equal to 0.8 W. The measurement of qMD-TL was based on the difference of the combined heat load tests of loop A and a loop to subtract one of these two loops. The average heat load of the combination of loop A and loop B was 110.55 W without the flash loss. The heat load qMD-TL was 20.16 W after subtraction of the single-loop heat load from the heat load of the combined loops. The large heat load might be due to the lack of liquid-nitrogen shielding on the multichannel adaptor. The net heat load of the transfer line was calculated based on equations (2) and (3), as figure 6 shows. Table 1 Summary of mass flow rate, heat load and flash loss Transfer line loop A
mT-A (SLPM) 1376 1456 1591 1317 1395 1554
loop B
qTD /W
qTD-H /W 5.3 12.3 18.8 5.3 12.3 18.8
0.8
qMD-TL /W
x /%
20.16
5.68
Figure 6 shows the variation of the net heat load with heating power of the test dewar. The average heat loads of loops A and B were 44.57 W and 42.47 W, respectively, after subtracting the q TD, qTD-H, qMD-TL and 5.68% flash loss. The results show also that the test could be duplicated within 6 % deviation for varied transfer rates from the main dewar.
50
qTL-A
49
qTL-B
48 47
qTL (W)
46 45 44 43 42 41 40 0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
qTD-H (W)
Figure 6 Net heat load of the transfer line for varied heating power of the test dewar
Thermal Acoustic Oscillation of DVB
P (bara)
Figure 7 shows the pressure fluctuation of the GHe pipeline during operation, known as thermal acoustic oscillation (TAO). The cold helium gas was pushed to the warm part through a pulsation effect. The TAO not only introduced an additional heat load but also affected the operational stability of the SRF cavities. The pressure fluctuations for TL1, TL2 and TL4 were about +/-50 mbar, +/-65 mbar and +/-40 mbar, respectively. The frequency was about 17 Hz, which was measured using a FFT scope from the pressure fluctuation signal. This condition might be due to the combined effect of the aspect ratio of the diameter of GHe to the ventilation pipeline and the cross section to the length of ventilation line, which were 4 and 200, respectively. The TAO did not appear on the other process lines, as the aspect ratio of the diameter was small for the process line to the ventilation line. The buffers (diameter 100 mm and length 150 mm), as shown in figure 8, were installed on pumping ports P4, P5 and P6 of the ventilation pipeline of the GHe safety valves. The isolation valve of the buffers was kept at 40 % opening to break the pulsation structure of the flow, which was the key point of damping the pulsation. The buffer would have introduced a larger pulsation effect if the isolation valve were fully open. These buffers successfully suppressed the pressure fluctuation without modifying the ventilation line for the safety valves. The pressure fluctuation was decreased to +/-10 mbar, +/-5 mbar, and +/- 10 mbar for TL1, TL2 and TL4, respectively. The freezing phenomena did not appear on the ventilation pipeline and the pressure stability also satisfied the operational requirement for the SRF cavities. 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12 1.10 1.08
pres sure variation wi thout buffer pres sure variation wi th buffer
P (bara)
0
2
3
4
5
6
7
8
9
10
t (minute)
1.32 1.29 1.26 1.23 1.20 1.17 1.14 1.11 1.08
pressure variation with out buffer pressure variation with buffer
0
P (bara)
1
(a) press ure variation of TL1
1
2
3
4
5
6
t (minute) press ure variation wit hout buffer press ure variation wit h buffer
1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12 1.10 1.08 0
1
2
3
4
5
(b) pressure vari ati on of TL2
7
8
9
10
(c) pressure vari ati on of TL4
6
7
8
9
10
t (minute) Figure 7 Variation of pressure of the transfer line with and without buffers installed at the pumping port
Exhaust pipeline for safety valve Pumping port of DVB TAO suppression buffer Pumping port of buffer Figure 8 The TAO suppression buffer of the DVB
CONCLUSION The cryogenic distribution system was installed and commissioned in 2014 and 2015, respectively. We overcame the space constraint to install the multichannel transfer line. The average heat loads of loops A and B were 44.57 W and 42.47 W, respectively, after subtracting the qTD, qTD-H, qMD-TL and 5.68% flash loss. The results show also that the test could be duplicated within 6 % deviation for varied transfer rates from the main dewar. The proposed method and technique of heat load measurement was feasible and successful, which can serve to improve the heat load for other cryogenic distribution systems in the future. TAO phenomena were observed, and a suppression method was proposed. The opening of the isolation valve was tested, which proved that opening 40 % was an effective way to break the pulsation flow structure; the TAO was then suppressed. The benefit of the buffer installation was to avoid modifying the pipeline, which provides a quick way to solve the problem.
ACKNOWLEDGEMENT Ministry of Science and Technology, R.O.C., supported this work.
REFERENCES [1] Tsai H. H., Hsiao F. Z., Li H. C., Chang S. H., Lin T. F., Chiou W. S., Liu C. P., “Commissioning of the Helium Cryogenic System and LN2 Transfer System in the TPS Ring”, Physics Procedia, 2015, Vol. 67:183-188. [2] Tsai H. H., Hsiao F. Z., Wang C., Lin M. C., Liu C. P., Chang M. H., Li H. C., Lin T. F., Chiou W. S., and Chang S. H. “Design of A Liquid-helium Transfer System for the TPS Project”, Proceedings of Particle Accelerator Conference, New York, USA, 2011:1220-1222. [3] Lin M. C., Wang C., Chang M. H., Chung F. T., Yeh M. S., Lin Y. H., Chen L. J., Tsai M. H., Yang T. T., Lo C. H., Yu T. C., Chang L. H., Hsiao F. Z., Tsai H. H., Chiou W. S., Li H. C., Lin T. F., “Operational Characteristics of the 200-m Flexible Cryogenic Transfer System”, Journal of Superconductivity and Novel Magnetism, 2013, Vol. 26: 1479-1483. [4] HEPAK: A commercial computer program (CRYODATA, Inc., Louisville, Colorado, USA).
Highlight
We overcame the space constraint to install the multichannel transfer line.
The proposed method and technique of heat load measurement was feasible and successful, which can serve to improve the heat load for other cryogenic distribution systems in the future.
The average heat loads of loops A and B were 44.57 W and 42.47 W, respectively, after subtracting the qTD, qTD-H, qMD-TL and 5.68% flash loss
The results show also that the test could be duplicated within 6 % deviation for varied transfer rates from the main dewar
TAO phenomena were observed, and a suppression method was proposed.
S0011-2275(15)30056-4 http://dx.doi.org/10.1016/j.cryogenics.2016.04.014 JCRY 2571
To appear in:
Cryogenics
Received Date: Accepted Date:
18 December 2015 27 April 2016
Please cite this article as: Tsai, H.H., Hsiao, F.Z., Li, H.C., Lin, M.C., Wang, C., Liao, W.R., Lin, T.F., Chiou, W.S., Chang, S.H., Chuang, P.S.D., Installation and Commissioning of a Cryogen Distribution System for the TPS Project, Cryogenics (2016), doi: http://dx.doi.org/10.1016/j.cryogenics.2016.04.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Installation and Commissioning of a Cryogen Distribution System for the TPS Project
Tsai H. H.1, Hsiao F. Z., Li H. C., Lin M. C., Wang C., Liao W. R., Lin T. F., Chiou W. S., Chang S. H., and Chuang P. S. D. 1
National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan, R.O.C
ABSTRACT A cryogen distribution system was installed and commissioned to transfer liquid nitrogen (LN2) and liquid helium (LHe) from storage dewars to superconducting radio-frequency (SRF) cavities for the 3-GeV Taiwan Photon Source (TPS) project. The cryogen distribution system comprises one distribution valve box (DVB), four control valve boxes (CVB) and seven sections of multichannel transfer line (MCL). The DVB distributes the LHe and LN2 to the CVB, and then to the SRF cavities through independent vacuum-jacketed transfer lines. The vaporized GHe and GN2 from the cryomodules are collected via the MCL. The cryogen distribution system was installed and commissioned from October 2014 to the end of March 2015. This paper presents the installation, pre-commissioning and commissioning of the cryogen distribution system, and describes the heat load test. Thermal Acoustic Oscillation (TAO) was found in the GHe process line; this phenomenon and its solution are also presented and discussed. KEY WORDS Multichannel transfer line, TPS, thermal acoustic oscillation
INTRODUCTION The Taiwan Photon Source (TPS) project entailing an electron accelerator with beam current 500 mA at 3 GeV and low emittance 2 nm rad is in progress at NSRRC. The circumferences of the storage ring and the booster ring are 518.4 m and the 496.8 m, respectively. The superconductive RF (SRF) modules are installed in short straight sections and maintain the energy level of the beam. A new helium cryogenic system is required to produce sufficient LHe for the SRF modules. The cryogenic distribution system is required to feed the LHe and LN2 to the SRF modules individually and to recover the vaporized GHe to the cryogenic system. The cryogenic system has maximum cooling capacity 890 W at 4.5 K with associated compressors, an oil-removal system (ORS), four helium buffer tanks, one 7000-L Dewar, gaseous helium piping at room temperature, transfer lines to distribute helium, and a transfer system for liquid nitrogen. The helium cryogenic system was installed and commissioned in year 2014 [1].
Figure 1 shows the layout of the cryogenic distribution system, which comprises one DVB, four CVB and seven sections of multichannel transfer line. Four SRF cavities are located, two upstream and two downstream of the DVB. A total heat load 100 W is expected for the acceptance test of the cryogenic distribution system. The features of the TPS cryogenic distribution system were simple, programmable control for the fluid flow, a small heat load and pressure drop, and recovery of the vaporized GN2 and GHe from the SRF modules and process line [2] . The system was installed and commissioned in 2014 and 2015, respectively. The measured heat load fulfilled the operational requirement of the SRF cavities. This paper presents the installation and commissioning of the cryogenic distribution system and discusses the results of the heat-load measurements. The safety valves and their exhaust pipeline were installed on every process line between the control valves inside the DVB, TL2 and TL4, as figure 2 shows. The exhaust pipeline of safety valves penetrates the outer case of the DVB and then connects to the process line. The cold fluid is isolated from the warm helium gas, as the safety valves are closed under normal operational conditions. The interface and the ventilation line outside the DVB remain warm during the operation. We found freezing phenomena at the interface and on the ventilation line for the GHe process line, which was due to thermal acoustic oscillation (TAO); this phenomenon and its treatment are also presented and discussed in this paper.
Figure 1 Overview of the layout of the cryogenic distribution system
Figure 2 Process diagram of the DVB
INSTALLATION AND PRE-COMMISSIONING OF THE CRYOGENIC DISTRIBUTION SYSTEM Installation challenge The cryogenic distribution system is located at the inner ring. The DVB, CVB and MCL had to be transported over the tunnel from the outer ring to the inner ring using a crane. The challenge in this installation was due mostly to the positioning of the MCL because of the confined space of the piping duct. The MCL was located between the cable tray and the air duct, which had a gap only 500 mm. The MCL piping duct was also blocked by the control and instrument area (CIA); the positioning of the MCL could thus be performed only from both ends. The installation not only had to hang over the tunnel but also to roll into the piping duct. The movement of the MCL had to be slow to avoid a collision with the cable tray and the wind duct. A roller was installed on the piping support to slide the MCL from the end of the piping duct into its position. Figure 3 shows the method of installation of the MCL using both a crane and a mobile scissor lift.
Figure 3 Installation of the MCL Pre-commissioning Impurities in the helium gas are a critical issue for a helium cryogenic system due to the operating temperatures 80 K to 4.6 K from the first heat exchanger to the J-T valve. A large concentration of moisture was trapped not only inside the valve seat but also in the first heat exchanger of the cold box, which introduced a pressure drop and decreased the cooling power of the system. The impurity gases (i. e., nitrogen) can become concentrated, so as to solidify, to impact and to break a turbo expander wheel or bearing as well. The helium cryogenic system must thus be clean, dry and leak-tight to avoid damage to the turbo expanders. The LHe/GHe and LN2/GN2 process lines were filled with helium gas at 2 barg and 5 barg to perform leakage tests after the MCL, CVB and DVB were completely connected. The measured rate of helium leakage was less than 1.0x10-9 mbar L s-1 in the evacuation mode with 1.0x10-3 mbar vacuum level for every process line on all vacuum jackets, which fulfilled the leak tight and low heat loss requirement of the cryogenic system operation. The clean and dry nitrogen gas was then connected to the pumping port (i. e., P1 in figure 2) of DVB to purge the entire process line. The measurement of the dew point was less than -70 oC and the particles were reached class 100 after purging for two weeks. The vacuum jacket was pumped to 1.0x10-5 mbar to restrain the convective heat transfer. Both helium and nitrogen process lines were filled with liquid nitrogen, which was called the cold-shock test. The objective was to test the effect of thermal stress on the fitting and weld bead. Every fitting and weld bead was helium leak-tested under 80 K and after warming to 200 K. The above process was repeated twice. The measured rate of leakage was less than 1.0x10-9 mbar L s-1. The final step was to purge with N50 pure helium gas, to retain for 30 min and then to pump to 1.0x10-2 mbar. This process was repeated three times to ensure the helium purity of the cryogenic distribution system. The gaseous helium was circulated through the analyzer of the cryogenic system, and N2, H2O and CxHy were analyzed. The cooling procedure was initiated after the concentrations were observed to be below 2 ppm.
MEASUREMENT OF THE HEAT LOAD Configuration of the Heat-load Measurement Figure 4 shows a flow chart of the heat-load measurement. Loop A comprised the heat load of half of the DVB, TL2, CVB2, TL3, CVB1 and TL6 for liquid helium and the gaseous helium process line. Loop B comprised the heat load of half of the DVB, TL4, CVB3, TL5 and TL7 for the liquid helium and gaseous helium process line also. The heat load of the SRF cavities was excluded; the liquid helium was thus circulated from the bypass loop of the end of TL6 and TL7. A test dewar (1000 L) was installed at the end of the circulation loop to ensure that the transfer line filled with liquid helium. The heat loads of loops A and B were measured individually.
Figure 4
Flow chart of the heat-load measurement
Measurement of the Heat Load The pure saturated liquid helium was delivered from a 7000-L dewar and flowed through the cryogenic distribution system in Loops A and B. The static heat load along the entire path qTL vaporized the liquid and thus delivered mixed liquid and gas to the 1000-L dewar at the end of the system. The total mass flow rate, mT, measured after warming the cold gas through a passive heater. mT included not only the vaporized liquid helium from the static heat load but also the transport flow rate from the 7000-L dewar to the test dewar through the transfer line, as the liquid helium was delivered continually during the measurement. The calculation of the heat load was based on the following equation,
(1)
mT × h fg = qTL + qTD + qTD − H + q MD −TL
where qTD represents the static heat load which was determined from the static boil-off rate of the test dewar, qTD-H represents the dynamic heat load, which was applied using the built-in heater in the test dewar, and qMD-TL represents the static heat load to liquid in the transfer line flowing from the 7000-L main dewar to the DVB. The net heat load of cryogenic distribution system, qTL, is: (2)
qTL = mT × h fg − qTD − qTD − H − q MD −TL
The mass flow rates of loops A and B were measured individually, denoted by mT-A and mT-B, respectively. The heat loads of loops A and B were calculated based on equation (2), denoted by qTL-A and q TL-B, respectively. The flash loss, x, was considered, which was due to a pressure difference between the supply pressure and the end pressure inside the test dewar during the transport [3]. The calculation was based on the law of conservation of energy, which leads to
hl −MD = hl −TD × (1 − x) + hg −TD × x
(3)
in which hl-MD and hl-TD represent the enthalpy of the supplied liquid from the main dewar and the test dewar respectively; hg-TD represents the enthalpy of the gas at the test dewar; x represents the flash loss. The heat load was excluded from equation (3). The calculated flash loss was 5.68 %. Commercial software (HEPAK [4]) was used to determine the helium properties for the calculation. The total flow rate was measured using a mass flow meter (OMEGA, uncertainty 1 %). RESULTS AND DISCUSSION Heat Load of the Transfer Line The flow was measured until the mass flow rate was observed to be stabilized on the flow meter. The mass flow rate was measured under three heating powers of the test dewar, as shown in figure 5.
1600
mT-A 1560
mT-B
1520
mT (SLPM)
1480 1440 1400 1360 1320 1280 1240 1200 0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
qTD-H (W) Figure 5 Variation of total mass flow rate with heating power of the test dewar
The vaporized mass flow rate includes q TD, q TD-H, qMD-TL and the flash loss, as summarized in Table 1. The measured heat load qTD was based on the static vaporization rate test, which was equal to 0.8 W. The measurement of qMD-TL was based on the difference of the combined heat load tests of loop A and a loop to subtract one of these two loops. The average heat load of the combination of loop A and loop B was 110.55 W without the flash loss. The heat load qMD-TL was 20.16 W after subtraction of the single-loop heat load from the heat load of the combined loops. The large heat load might be due to the lack of liquid-nitrogen shielding on the multichannel adaptor. The net heat load of the transfer line was calculated based on equations (2) and (3), as figure 6 shows. Table 1 Summary of mass flow rate, heat load and flash loss Transfer line loop A
mT-A (SLPM) 1376 1456 1591 1317 1395 1554
loop B
qTD /W
qTD-H /W 5.3 12.3 18.8 5.3 12.3 18.8
0.8
qMD-TL /W
x /%
20.16
5.68
Figure 6 shows the variation of the net heat load with heating power of the test dewar. The average heat loads of loops A and B were 44.57 W and 42.47 W, respectively, after subtracting the q TD, qTD-H, qMD-TL and 5.68% flash loss. The results show also that the test could be duplicated within 6 % deviation for varied transfer rates from the main dewar.
50
qTL-A
49
qTL-B
48 47
qTL (W)
46 45 44 43 42 41 40 0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
qTD-H (W)
Figure 6 Net heat load of the transfer line for varied heating power of the test dewar
Thermal Acoustic Oscillation of DVB
P (bara)
Figure 7 shows the pressure fluctuation of the GHe pipeline during operation, known as thermal acoustic oscillation (TAO). The cold helium gas was pushed to the warm part through a pulsation effect. The TAO not only introduced an additional heat load but also affected the operational stability of the SRF cavities. The pressure fluctuations for TL1, TL2 and TL4 were about +/-50 mbar, +/-65 mbar and +/-40 mbar, respectively. The frequency was about 17 Hz, which was measured using a FFT scope from the pressure fluctuation signal. This condition might be due to the combined effect of the aspect ratio of the diameter of GHe to the ventilation pipeline and the cross section to the length of ventilation line, which were 4 and 200, respectively. The TAO did not appear on the other process lines, as the aspect ratio of the diameter was small for the process line to the ventilation line. The buffers (diameter 100 mm and length 150 mm), as shown in figure 8, were installed on pumping ports P4, P5 and P6 of the ventilation pipeline of the GHe safety valves. The isolation valve of the buffers was kept at 40 % opening to break the pulsation structure of the flow, which was the key point of damping the pulsation. The buffer would have introduced a larger pulsation effect if the isolation valve were fully open. These buffers successfully suppressed the pressure fluctuation without modifying the ventilation line for the safety valves. The pressure fluctuation was decreased to +/-10 mbar, +/-5 mbar, and +/- 10 mbar for TL1, TL2 and TL4, respectively. The freezing phenomena did not appear on the ventilation pipeline and the pressure stability also satisfied the operational requirement for the SRF cavities. 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12 1.10 1.08
pres sure variation wi thout buffer pres sure variation wi th buffer
P (bara)
0
2
3
4
5
6
7
8
9
10
t (minute)
1.32 1.29 1.26 1.23 1.20 1.17 1.14 1.11 1.08
pressure variation with out buffer pressure variation with buffer
0
P (bara)
1
(a) press ure variation of TL1
1
2
3
4
5
6
t (minute) press ure variation wit hout buffer press ure variation wit h buffer
1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12 1.10 1.08 0
1
2
3
4
5
(b) pressure vari ati on of TL2
7
8
9
10
(c) pressure vari ati on of TL4
6
7
8
9
10
t (minute) Figure 7 Variation of pressure of the transfer line with and without buffers installed at the pumping port
Exhaust pipeline for safety valve Pumping port of DVB TAO suppression buffer Pumping port of buffer Figure 8 The TAO suppression buffer of the DVB
CONCLUSION The cryogenic distribution system was installed and commissioned in 2014 and 2015, respectively. We overcame the space constraint to install the multichannel transfer line. The average heat loads of loops A and B were 44.57 W and 42.47 W, respectively, after subtracting the qTD, qTD-H, qMD-TL and 5.68% flash loss. The results show also that the test could be duplicated within 6 % deviation for varied transfer rates from the main dewar. The proposed method and technique of heat load measurement was feasible and successful, which can serve to improve the heat load for other cryogenic distribution systems in the future. TAO phenomena were observed, and a suppression method was proposed. The opening of the isolation valve was tested, which proved that opening 40 % was an effective way to break the pulsation flow structure; the TAO was then suppressed. The benefit of the buffer installation was to avoid modifying the pipeline, which provides a quick way to solve the problem.
ACKNOWLEDGEMENT Ministry of Science and Technology, R.O.C., supported this work.
REFERENCES [1] Tsai H. H., Hsiao F. Z., Li H. C., Chang S. H., Lin T. F., Chiou W. S., Liu C. P., “Commissioning of the Helium Cryogenic System and LN2 Transfer System in the TPS Ring”, Physics Procedia, 2015, Vol. 67:183-188. [2] Tsai H. H., Hsiao F. Z., Wang C., Lin M. C., Liu C. P., Chang M. H., Li H. C., Lin T. F., Chiou W. S., and Chang S. H. “Design of A Liquid-helium Transfer System for the TPS Project”, Proceedings of Particle Accelerator Conference, New York, USA, 2011:1220-1222. [3] Lin M. C., Wang C., Chang M. H., Chung F. T., Yeh M. S., Lin Y. H., Chen L. J., Tsai M. H., Yang T. T., Lo C. H., Yu T. C., Chang L. H., Hsiao F. Z., Tsai H. H., Chiou W. S., Li H. C., Lin T. F., “Operational Characteristics of the 200-m Flexible Cryogenic Transfer System”, Journal of Superconductivity and Novel Magnetism, 2013, Vol. 26: 1479-1483. [4] HEPAK: A commercial computer program (CRYODATA, Inc., Louisville, Colorado, USA).
Highlight
We overcame the space constraint to install the multichannel transfer line.
The proposed method and technique of heat load measurement was feasible and successful, which can serve to improve the heat load for other cryogenic distribution systems in the future.
The average heat loads of loops A and B were 44.57 W and 42.47 W, respectively, after subtracting the qTD, qTD-H, qMD-TL and 5.68% flash loss
The results show also that the test could be duplicated within 6 % deviation for varied transfer rates from the main dewar
TAO phenomena were observed, and a suppression method was proposed.