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Hydrogen liquefiers with efficient heat exchangers
HYDROGEN LIQUEFIERS WITH EFFICIENT HEAT EXCHANGERS E. S. B O R O V I K ,
I. F. M I K H A i L O V ,
and N. A. KOSIK
Physico-Technical Institute, Academy of Sciences, U.S.S.R. Received 9 March 1964 t
T HE use of liquid hydrogen has recently greatly increased. Liquid hydrogen is used in high vacuum condensation pumps, 1,2 to obtain high magnetic fields by means of coils cooled by liquid hydrogen, 3-5 in hydrogen bubble chambers, 6 etc. Simple and reliable liquefiers with sufficiently high output are required for satisfying liquid hydrogen requirements. In the end the problem of providing large economical liquefiers may only be solved by using turbo-expander devices. As an intermediate step, however, it is desirable to build large output machines working on the Joule-Thomson effect which are relatively simple. One should use all means for reducing the energy consumption of such machines, and also their size and weight. The most successful way of reducing the size is to use heat exchangers formed of different diameter tubes soldered to one another for heat contact, 7,s first used in a liquid hydrogen condensation pump. z This article describes liquefiers with these heat exchangers.
and 12 mm diameter, 1 mm wall thickness for the hydrogen outflow) bent into coils and soldered together. The hydrogen entering is fully cooled by the cold of the low pressure hydrogen flowing out. Exchanger 3 is 6 m long. The compressed hydrogen expands in valve 5 and partially liquefies. The liquid hydrogen enters collector 6, and the unliquefied hydrogen and that evaporating from the collector return to the compressor, giving up cold to the incoming hydrogen in heat exchangers 3 and I. All the heat exchangers of the VO-10 liquefier are made of seamless tubing. In the high pressure line there is, therefore, only one vacuum joint--where the high pressure tubing and the throttling valve are soldered together. Liquid hydrogen is siphoned off through the vacuum insulated tube 8, which passes through the
The VO-lO hydrogen liquefier As in the majority of small output liquefiers, a single stage cooling of the hydrogen by nitrogen boiling under reduced pressure is used in the VO-10 hydrogen liquefier. The design of the liquefier is shown in Figure 1. High pressure hydrogen enters heat exchanger 1, made in the form of a coil of three tubes soldered together in thermal contact: 6 mm diameter, 1 mm wall thickness for the high pressure hydrogen; 12 mm diameter, 1 mm wall thickness for the low pressure hydrogen; and 20 mm diameter, 1 mm wall thickness for pumping the nitrogen. In the heat exchanger the compressed hydrogen is cooled from room temperature by the cold of the low pressure hydrogen and pumped nitrogen. The mean length of the tubes of heat exchanger 1 is about 7.5 m. The nitrogen can 4 is placed inside the upper heat exchanger spirals, without touching them. The high pressure hydrogen tube, 2 m in length, is wound round and soldered to the lower part of the nitrogen tank. After being cooled in heat exchanger 2 of the nitrogen can, the high pressure hydrogen enters exchanger 3, ~vhich consists of two tubes (the tubes are 6 mm diameter, 1 mm wall thickness for compressed hydrogen
I : Upper heat exchanger 2: Nitrogen heat exchanger 3: Lower heat exchanger 4: Nitrogen can 5 : Expansion valve 6: Liquid hydrogen collector 7 and 9: Shields 8: Transfer tube
Figure 1. Construction of VO-IO liquefier
J" Received by PTI~ Editor 4 May 1962: Pribory i Tekhnika l~ksperimenta No. 3, p. 165 (1963)
358
CRYOGENICS,
DECEMBER 1964
central 30 mm diameter german silver tube to which the liquid collector is fastened. The rod of expansion valve 5 also passes through this tube. To reduce loss from radiation, the upper exchanger 1 is covered by the aluminium foil shield ~7, and the lower exchanger 2 and collector 6 by the polished copper shield 9. Shield 9 is soldered to the nitrogen vessel 4. The nitrogen can is suspended from the upper flange of the liquefier by two german silver tubes: one tube is used for filling in liquid nitrogen and the other for measuring the liquid level in the can. The heat exchangers are in a vacuum produced by an external charcoal adsorption pump. The whole liquefier is mounted on the upper flange so that it can easily be taken out of its case, giving access to any part. The heat exchangers weigh 11 kg and the case is made of 20 cm diameter tubing, 80 cm long. The construction of the VO-50 liquefier In liquefiers of large output the power consumption in pumping the evaporating nitrogen is high in absolute magnitude, and, besides, the necessity of pumping a large amount of nitrogen leads to an increase in the dimensions of the nitrogen side of the upper heat exchanger. For this reason two-stage cooling of the
1 : U p p e r heat exchanger 2: First nitrogen heat exchanger 3: Intermediate heat exchanger 4: P u m p e d nitrogen bath heat exchanger 5: Lower heat exchanger 6: Expansion valve 7 : Collector 8 a n d 9: Nitrogen tanks 10: Valve for regulating nitrogen flow into tank 9 I I : Nitrogen shield 12: Case 13 : Transfer tube 14: Charcoal 15: Nitrogen p u m p i n g
Figure 2. Section through VO-50 liquefier
CRYOGENICS.
D E C E M B E R 1964
hydrogen by liquid nitrogen is used in the VO-50 liquefier. This considerably reduces the size and noticeably lowers the power consumption for pumping nitrogen. This arrangement has also been used successfully in the past. 8,9 The liquefier is shown in section in Figure 2. High pressure hydrogen from the compressor enters heat exchanger !, in which it is cooled from room temperature TI to T., ~ 112° K by the returning low pressure hydrogen and nitrogen. Heat exchanger 1 is in the form of a coil wound from three tubes of different diameter soldered together in thermal contact: the high pressure hydrogen enters through a 6 mm diameter tube of 1 mm wall thickness, the unliquefied hydrogen returns through an 18 mm diameter tube of 1 mm wall thickness, and the gaseous nitrogen from tank 8 passes through a 16 mm diameter tube of I mm wall thickness. The heat exchanger is about 20 m long. The hydrogen entering heat exchanger 2 is cooled to T3 ~ 81 ~ K by the cold from nitrogen boiling at a slightly elevated pressure. Tile high pressure hydrogen tube in this heat exchanger is wound round tank 8 on its lower part and soldered to it; its length is about 5 m. The compressed hydrogen passes through the intermediate heat exchanger 3 made in a coil of two tubes soldered" together: 6 mm diameter, 1 mm wall thickness for the hydrogen entering, and 16 mm diameter, l mm wall thickness for the returning hydrogen; the coil is 2.8 m long. The intermediate heat exchanger reduces further the consumption of nitrogen boiling under reduced pressure by a factor of 2. As a result it is not essential to make full use of the cold contained in the pumped nitrogen vapour. The cold of this vapour is partially used in heat exchanger 1, since pumping of can 9 takes place through the straight german silver tubes 15 soldered to the coils of this heat exchanger. Heat exchanger 4 is about 15 m long and is inside the nitrogen tank. In exchanger 5 the compressed hydrogen is only cooled by the returning low pressure hydrogen. It is made up of the same tubing as the intermediate heat exchanger and is 17 m long. After cooling in the heat exchangers the high pressure hydrogen reaches the expansion valve 6. The gas is partially liquefied on expansion and flows into the liquid collector 7, while the unliquefied portion and that evaporating from the collector returns to the compressor inlet, giving up its cold to incoming hydrogen in exchangers 5, 3, and 1. The total weight of the heat exchangers is about 37 kg. The nitrogen vessels 8 and 9 and the liquid collector 7 are pressed out of pure copper sheet and soldered with tin solder. Tube 13, with two outlets for convenience in pouring, is used to siphon liquid hydrogen from the collector. The upper heat exchanger 1 is covered by an aluminium foil shield to reduce losses by radiation. Heat exchangers 3 and 5 and the liquid collector 7 are surrounded by the copper shield 11. Nitrogen flows from tank 8 to tank 9 through valve 10. 359
Compressor output (mS/hr) Liquid H2 output (l./hr) Liquefaction yield (per cent) Hydrogen pressure (atm) Pressure after expansion valve (atm) Nitrogen pressure in pumped N~ bath
(torrs) Start-up time (rain)
VO-IO
VO-50
Liquefier 200
63,6
143
36
65
45 "5
10
18
27
27
145
130
0"4 110 12-20
0-3 110 12-20
23 "5 130 0'17 100 12-20
23 -5 130 0.35 10(O120 12-20
Note. For VO-50 the nitrogen consumption is 1-2 I. per litre of liquid hydrogen
heat exchanger is greater than 95 per cent. The regeneration loss in the upper heat exchanger at its upper end is 11° at the hydrogen side and 11° at the nitrogen side; the upper exchanger thus also works with an efficiency of more than 95 per cent. With compressor outputs of 45 and 180 m3/hr the VO-10 and VO-50 liquefiers have outputs of 12.5 and 57 l./hr. They work better than liquefiers of equivalent outputs described by Zel'dovich and Pilipenko 9 and by Fradkov, t° and are on a level with the best hydrogen liquefiers with nitrogen cooling 11 in their performance figures. In addition, the liquefiers are simple in construction and economical in weight. Their weight, apart from the outer casing, is 2-3 times less than that of liquefiers previously described, s-~° The authors thank P. V. Saratovskii for his help in assembling and adjusting the liquefiers. REFERENCES
The whole liquefier is mounted on the upper flange. The case is made of 31 cm diameter tubing and is 140 cm long. The bottom of the case is pressed out of 2 mm copper and is soldered on with tin solder. The vacuum in the case of the VO-50 liquefier is produced by an external charcoal adsorption pump. The charcoal pump 14, placed on the liquid hydrogen collector 7, pumps the hydrogen in case of a small leak. Test results The main results of testing the liquefiers are shown in Table 1. In the VO-50 liquefier there is a thermometer soldered to the 6 mm diameter outlet tube from the lower nitrogen tank 9, so that the temperature difference between the liquid and the high pressure hydrogen can be determined. The hydrogen temperature after exchanger 4 is 65-66 ° K, which corresponds to a theoretical liquefaction yield of 27 per cent. The measured yield agrees with the calculated within the experimental accuracy, showing that the efficiency of the lower
360
1. LAZAREV, B. G., BOROVIK, E. S., FEDOROVA, M. F., and TSIN, N. i . Ukr. Phys. J. 11, 175 (1951) 2. BOROVIK, E. S., LAZAREV, B. G., and MIKHA1LOV, I. F. Atomn. Energ. 7, 117 (1959) 3. LAQUER, H. K., and HAMMEL, E. F. Rev. sci. Instrum. 28, 875 (1957) 4. BOROVlK, E. S., and LIMAR', A. G. J. tech. Phys., Moscow 31,939 (1961) 5. BOROVIK, E. S., BUSOL, F. I., and GRISHIN, S. F. J. tech. Phys., Moscow 31,459 (1961) 6. BAGG, D. Bull. Acad. Sci. U.R.S.S. 74, 675 (1961) 7. BOROVIK,E. S., and MIKHAILOV,]. F. Automation News No. 138258 (Section 17]')203 (1960) 8. DAUNT, J. G. The Physics of Low Temperatures (Russian version, 1959) 9. ZEL'DOVlCH, A. G., and PILIPENKO, YO. K. Prib. i. Tekh. l~ksper. No. 2, 185, (1961) 10. FRADKOV,A. B. Oxygen 5, 3 (1958) 1 t. Scoyr, R. B. Cryogenic Engineering (Van Nostrand, Princeton, N. J., 1959) This paper has been especiallytranslated for CRYOGENICSand is included by permission of the Editors of Pribory i Tekhnika l~ksperimenta. We are also indebted to the Instrument Society of America and Consultants Bureau Enterprises Inc., who publish their own cover-to.covertranslation of PT# by arrangement with the Russian publisher.
CRYOGENICS.
DECEMBER
1964
I. F. M I K H A i L O V ,
and N. A. KOSIK
Physico-Technical Institute, Academy of Sciences, U.S.S.R. Received 9 March 1964 t
T HE use of liquid hydrogen has recently greatly increased. Liquid hydrogen is used in high vacuum condensation pumps, 1,2 to obtain high magnetic fields by means of coils cooled by liquid hydrogen, 3-5 in hydrogen bubble chambers, 6 etc. Simple and reliable liquefiers with sufficiently high output are required for satisfying liquid hydrogen requirements. In the end the problem of providing large economical liquefiers may only be solved by using turbo-expander devices. As an intermediate step, however, it is desirable to build large output machines working on the Joule-Thomson effect which are relatively simple. One should use all means for reducing the energy consumption of such machines, and also their size and weight. The most successful way of reducing the size is to use heat exchangers formed of different diameter tubes soldered to one another for heat contact, 7,s first used in a liquid hydrogen condensation pump. z This article describes liquefiers with these heat exchangers.
and 12 mm diameter, 1 mm wall thickness for the hydrogen outflow) bent into coils and soldered together. The hydrogen entering is fully cooled by the cold of the low pressure hydrogen flowing out. Exchanger 3 is 6 m long. The compressed hydrogen expands in valve 5 and partially liquefies. The liquid hydrogen enters collector 6, and the unliquefied hydrogen and that evaporating from the collector return to the compressor, giving up cold to the incoming hydrogen in heat exchangers 3 and I. All the heat exchangers of the VO-10 liquefier are made of seamless tubing. In the high pressure line there is, therefore, only one vacuum joint--where the high pressure tubing and the throttling valve are soldered together. Liquid hydrogen is siphoned off through the vacuum insulated tube 8, which passes through the
The VO-lO hydrogen liquefier As in the majority of small output liquefiers, a single stage cooling of the hydrogen by nitrogen boiling under reduced pressure is used in the VO-10 hydrogen liquefier. The design of the liquefier is shown in Figure 1. High pressure hydrogen enters heat exchanger 1, made in the form of a coil of three tubes soldered together in thermal contact: 6 mm diameter, 1 mm wall thickness for the high pressure hydrogen; 12 mm diameter, 1 mm wall thickness for the low pressure hydrogen; and 20 mm diameter, 1 mm wall thickness for pumping the nitrogen. In the heat exchanger the compressed hydrogen is cooled from room temperature by the cold of the low pressure hydrogen and pumped nitrogen. The mean length of the tubes of heat exchanger 1 is about 7.5 m. The nitrogen can 4 is placed inside the upper heat exchanger spirals, without touching them. The high pressure hydrogen tube, 2 m in length, is wound round and soldered to the lower part of the nitrogen tank. After being cooled in heat exchanger 2 of the nitrogen can, the high pressure hydrogen enters exchanger 3, ~vhich consists of two tubes (the tubes are 6 mm diameter, 1 mm wall thickness for compressed hydrogen
I : Upper heat exchanger 2: Nitrogen heat exchanger 3: Lower heat exchanger 4: Nitrogen can 5 : Expansion valve 6: Liquid hydrogen collector 7 and 9: Shields 8: Transfer tube
Figure 1. Construction of VO-IO liquefier
J" Received by PTI~ Editor 4 May 1962: Pribory i Tekhnika l~ksperimenta No. 3, p. 165 (1963)
358
CRYOGENICS,
DECEMBER 1964
central 30 mm diameter german silver tube to which the liquid collector is fastened. The rod of expansion valve 5 also passes through this tube. To reduce loss from radiation, the upper exchanger 1 is covered by the aluminium foil shield ~7, and the lower exchanger 2 and collector 6 by the polished copper shield 9. Shield 9 is soldered to the nitrogen vessel 4. The nitrogen can is suspended from the upper flange of the liquefier by two german silver tubes: one tube is used for filling in liquid nitrogen and the other for measuring the liquid level in the can. The heat exchangers are in a vacuum produced by an external charcoal adsorption pump. The whole liquefier is mounted on the upper flange so that it can easily be taken out of its case, giving access to any part. The heat exchangers weigh 11 kg and the case is made of 20 cm diameter tubing, 80 cm long. The construction of the VO-50 liquefier In liquefiers of large output the power consumption in pumping the evaporating nitrogen is high in absolute magnitude, and, besides, the necessity of pumping a large amount of nitrogen leads to an increase in the dimensions of the nitrogen side of the upper heat exchanger. For this reason two-stage cooling of the
1 : U p p e r heat exchanger 2: First nitrogen heat exchanger 3: Intermediate heat exchanger 4: P u m p e d nitrogen bath heat exchanger 5: Lower heat exchanger 6: Expansion valve 7 : Collector 8 a n d 9: Nitrogen tanks 10: Valve for regulating nitrogen flow into tank 9 I I : Nitrogen shield 12: Case 13 : Transfer tube 14: Charcoal 15: Nitrogen p u m p i n g
Figure 2. Section through VO-50 liquefier
CRYOGENICS.
D E C E M B E R 1964
hydrogen by liquid nitrogen is used in the VO-50 liquefier. This considerably reduces the size and noticeably lowers the power consumption for pumping nitrogen. This arrangement has also been used successfully in the past. 8,9 The liquefier is shown in section in Figure 2. High pressure hydrogen from the compressor enters heat exchanger !, in which it is cooled from room temperature TI to T., ~ 112° K by the returning low pressure hydrogen and nitrogen. Heat exchanger 1 is in the form of a coil wound from three tubes of different diameter soldered together in thermal contact: the high pressure hydrogen enters through a 6 mm diameter tube of 1 mm wall thickness, the unliquefied hydrogen returns through an 18 mm diameter tube of 1 mm wall thickness, and the gaseous nitrogen from tank 8 passes through a 16 mm diameter tube of I mm wall thickness. The heat exchanger is about 20 m long. The hydrogen entering heat exchanger 2 is cooled to T3 ~ 81 ~ K by the cold from nitrogen boiling at a slightly elevated pressure. Tile high pressure hydrogen tube in this heat exchanger is wound round tank 8 on its lower part and soldered to it; its length is about 5 m. The compressed hydrogen passes through the intermediate heat exchanger 3 made in a coil of two tubes soldered" together: 6 mm diameter, 1 mm wall thickness for the hydrogen entering, and 16 mm diameter, l mm wall thickness for the returning hydrogen; the coil is 2.8 m long. The intermediate heat exchanger reduces further the consumption of nitrogen boiling under reduced pressure by a factor of 2. As a result it is not essential to make full use of the cold contained in the pumped nitrogen vapour. The cold of this vapour is partially used in heat exchanger 1, since pumping of can 9 takes place through the straight german silver tubes 15 soldered to the coils of this heat exchanger. Heat exchanger 4 is about 15 m long and is inside the nitrogen tank. In exchanger 5 the compressed hydrogen is only cooled by the returning low pressure hydrogen. It is made up of the same tubing as the intermediate heat exchanger and is 17 m long. After cooling in the heat exchangers the high pressure hydrogen reaches the expansion valve 6. The gas is partially liquefied on expansion and flows into the liquid collector 7, while the unliquefied portion and that evaporating from the collector returns to the compressor inlet, giving up its cold to incoming hydrogen in exchangers 5, 3, and 1. The total weight of the heat exchangers is about 37 kg. The nitrogen vessels 8 and 9 and the liquid collector 7 are pressed out of pure copper sheet and soldered with tin solder. Tube 13, with two outlets for convenience in pouring, is used to siphon liquid hydrogen from the collector. The upper heat exchanger 1 is covered by an aluminium foil shield to reduce losses by radiation. Heat exchangers 3 and 5 and the liquid collector 7 are surrounded by the copper shield 11. Nitrogen flows from tank 8 to tank 9 through valve 10. 359
Compressor output (mS/hr) Liquid H2 output (l./hr) Liquefaction yield (per cent) Hydrogen pressure (atm) Pressure after expansion valve (atm) Nitrogen pressure in pumped N~ bath
(torrs) Start-up time (rain)
VO-IO
VO-50
Liquefier 200
63,6
143
36
65
45 "5
10
18
27
27
145
130
0"4 110 12-20
0-3 110 12-20
23 "5 130 0'17 100 12-20
23 -5 130 0.35 10(O120 12-20
Note. For VO-50 the nitrogen consumption is 1-2 I. per litre of liquid hydrogen
heat exchanger is greater than 95 per cent. The regeneration loss in the upper heat exchanger at its upper end is 11° at the hydrogen side and 11° at the nitrogen side; the upper exchanger thus also works with an efficiency of more than 95 per cent. With compressor outputs of 45 and 180 m3/hr the VO-10 and VO-50 liquefiers have outputs of 12.5 and 57 l./hr. They work better than liquefiers of equivalent outputs described by Zel'dovich and Pilipenko 9 and by Fradkov, t° and are on a level with the best hydrogen liquefiers with nitrogen cooling 11 in their performance figures. In addition, the liquefiers are simple in construction and economical in weight. Their weight, apart from the outer casing, is 2-3 times less than that of liquefiers previously described, s-~° The authors thank P. V. Saratovskii for his help in assembling and adjusting the liquefiers. REFERENCES
The whole liquefier is mounted on the upper flange. The case is made of 31 cm diameter tubing and is 140 cm long. The bottom of the case is pressed out of 2 mm copper and is soldered on with tin solder. The vacuum in the case of the VO-50 liquefier is produced by an external charcoal adsorption pump. The charcoal pump 14, placed on the liquid hydrogen collector 7, pumps the hydrogen in case of a small leak. Test results The main results of testing the liquefiers are shown in Table 1. In the VO-50 liquefier there is a thermometer soldered to the 6 mm diameter outlet tube from the lower nitrogen tank 9, so that the temperature difference between the liquid and the high pressure hydrogen can be determined. The hydrogen temperature after exchanger 4 is 65-66 ° K, which corresponds to a theoretical liquefaction yield of 27 per cent. The measured yield agrees with the calculated within the experimental accuracy, showing that the efficiency of the lower
360
1. LAZAREV, B. G., BOROVIK, E. S., FEDOROVA, M. F., and TSIN, N. i . Ukr. Phys. J. 11, 175 (1951) 2. BOROVIK, E. S., LAZAREV, B. G., and MIKHA1LOV, I. F. Atomn. Energ. 7, 117 (1959) 3. LAQUER, H. K., and HAMMEL, E. F. Rev. sci. Instrum. 28, 875 (1957) 4. BOROVlK, E. S., and LIMAR', A. G. J. tech. Phys., Moscow 31,939 (1961) 5. BOROVIK, E. S., BUSOL, F. I., and GRISHIN, S. F. J. tech. Phys., Moscow 31,459 (1961) 6. BAGG, D. Bull. Acad. Sci. U.R.S.S. 74, 675 (1961) 7. BOROVIK,E. S., and MIKHAILOV,]. F. Automation News No. 138258 (Section 17]')203 (1960) 8. DAUNT, J. G. The Physics of Low Temperatures (Russian version, 1959) 9. ZEL'DOVlCH, A. G., and PILIPENKO, YO. K. Prib. i. Tekh. l~ksper. No. 2, 185, (1961) 10. FRADKOV,A. B. Oxygen 5, 3 (1958) 1 t. Scoyr, R. B. Cryogenic Engineering (Van Nostrand, Princeton, N. J., 1959) This paper has been especiallytranslated for CRYOGENICSand is included by permission of the Editors of Pribory i Tekhnika l~ksperimenta. We are also indebted to the Instrument Society of America and Consultants Bureau Enterprises Inc., who publish their own cover-to.covertranslation of PT# by arrangement with the Russian publisher.
CRYOGENICS.
DECEMBER
1964