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Cryogenics news
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Research news NASA's advanced cooling system NASA engineers are developing a refrigeration system for space operations that could also lead to commercial development of pumps, motors, compressors and other mechanical devices which would operate virtually without wear.
The development could increase system operation lifetime of astronomical and Earth-watching instruments in space by as much as six times, from the present six to ten months up to three to five years, according to the Goddard Space Flight Centre engineers.
and displacer chambers, continually adjusting the magnetic fields via an electronic controller. The electronic controller assures that the linear motors drive the piston in the compression stage and the displacer in the expansion section with the proper phase relationship.
The engineers have been working on the project for about two years and expect to deliver the first model for testing in April. The new system, a Stirling cycle cooler, uses helium gas to develop refrigeration, features two linear motors, one for compression and one for expansion, and two sets of magnetic bearings. The bearings employ four electromagnets surrounding the piston
Previously, most spacecraft intruments did not require significant cooling systems. As those instruments, such as gamma and infrared types, have become more sophisticated, improved cooling systems have become necessary. The new system will provide a much higher capacity for cooling, according to the engineers. (NASA, Washington DC 20546, USA)
Observation in this way avoids undesirable processes such as evaporation, sublimation or chemical treatment (eg fixation and dehydration), any of which can remove or obscure a structure. Biological tissue therefore closely resembles its natural state at the moment of freezing. Inner structures can be observed after fracturing a sample with the specimen fracturing knife.
lier attempts to produce cryo specimens. Images may be viewed and recorded in the conventional way with an SEM and the information presented is, for biological specimens at least, obtained from surfaces in the completely hydrated state. This new feature will increase the scope of the SEM scientist in many disciplines. (JEOL (UK) Ltd., JEOL House, Grove Park, London NW9 0JN, UK).
The new development eliminates the friction and, therefore, the wear associated with moving parts. The piston and displacer in the NASA cooling system are suspended in a magnetic field, permitting the parts to move without touching the sides of their housing and so no friction is incurred.
Industrial news Cryo stage for scanning electron microscopes With the JEOL Cryoscan system, tissue and specimens which are sensitive to electron beams or temperature can be very rapidly frozen in liquid nitrogen to preserve their natural structure. This is followed with a simple procedure for fracturing and locating them in the eucentric tilt stage of the scanning electron microscope (SEM). Temperature is guaranteed by JEOL to be lower than -185°C throughout examination. The whole system is designed to enable direct observations of surface structures of biological or material specimens in the frozen state.
CRYOGENICS. JUNE 1981
Cryoscan is especially useful in the fields of medicine and biology, where much dehydration occurs in most conventional preparations and in the observation of heat sensitive specimens such as plastics and waxes, say JEOL. This new system is a significant refinement over ear-
Auxiliary cooling system An auxiliary cooling system which offers temperature control for a wide variety of refrigeration applications has been introduced by CryoService Ltd. This Nitrochill
377
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e--WSl will be produced. (CryoService Ltd., Roebuck Hill, Jump, Barnsley, South Yorkshire $74 OJP, UK)
Industrial process laboratory
Nitrochill TCE-196 system from CryoService Ltd
An industrial process laboratory has been opened by BOC in Leeds, UK. It is designed to study industrial problems such as process reliability, safety, fuel and capital expenditure
saving. It will initially concentrate on the development of liquid nitrogen as an inert gas for heat treatment of metals and as a source of 'cold' for cryogenic reclamation and grinding. All the facilities will be available to BOC customers to test their processes to an industrial specification. The different uses to which liquid nitrogen can be put in reclaiming scrap materials is being investigated at
TCE-196 system can be installed as the sole means of temperature control or as an emergency back-up for existing refrigeration equipment. It provides the facility for almostimmediate temperature settings from ambient t o - 1 9 6 ° C Applications may range from sub zero laboratory testing to the preservation of foodstuffs and biological products during storage or transportation. Liquid nitrogen is used as the refrigeration medium with this cooling system which consists basically of a control box, a temperature sensor, and, when required, a fan unit. The control box incorporates a thermostat control which can be set at any temperature between ambient and -196°C. This control operates a liquid nitrogen solenoid valve to maintain the temperature within the refrigeration zone to an accuracy of _+1°C. The Nitrochill TCE-196 is designed for operation on a 12 volt supply. There is an automatic cut-off switch to the liquid nitrogen supply which operates when the door or lid of the cold chamber is opened, and this switch is also linked with the system fan. If, for any reason, the cold chamber cools down to more than 10°C below the controlled setting, a visual and audible warning signal
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Ladies' shoe heels about to be treated with liquid nitrogen prior to grinding
CRYOGENICS. JUNE 1981
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cooled with liquid nitrogen before the molten metal is poured in, waste due to oxidation contamination will be greatly reduced. (BOC Limited, Industrial Processes Dept, 15/17 Northgate, Baildon, Shipley, West Yorkshire BD17 6JZ, UK)
Continuous flow cryostat The CF500 from Oxford Instruments is a cooling unit intended mainly for variable temperature Mossbauer absorber studies in the horizontal plane. It provides sample temperatures in the range 4-300 K using the absolute minimum of liquid helium, and 77-300 K using liquid nitrogen. It may also be readily employed for neutron, X-ray and other long term experiments where low operating costs are of paramount importance.
Cooling a mould for metal castingwith liquid nitrogento reducethe oxidationcontamination Leeds. One novel idea on reclamation is the polycarbonate from ladies' shoe heels. These have a steel pin running through them, making it impossible to reclaim the polycarbonate by conventional means. However, after placing the heels in liquid nitrogen and grinding them, the steel pins are found loose in amongst the ground polycarbonate. The pins are then easily removed with a magnet, and the polycarbonate can be recycled.
cess will cause them to melt. Similarly, liquid nitrogen can be used to freeze-grind rubber. Worn car tyres can be recycled by cooling the rubber with liquid nitrogen, which allows the rubber to be mechanically separated from other components. The rubber component can then be ground to a crumb of the required size.
Liquid nitrogen can be used to counteract the heat generated when grinding materials to fine, or even coarse, powders. Plastics, in particular, cannot be ground without cooling. The heat generated in the grinding pro-
Another potential use of liquid nitrogen which is being developed at Leeds is in the c~=sting of metal. Waste from these processes can be high due to oxidation contamination of the metal. However, if the solid mould is
CRYOGENICS . JUNE 1981
Grinding of spices in liquid nitrogen is being developed. The flavour, often due to volatile oils, is preserved by grinding at cryogenic temperatures.
Oxford say that the simplicity of operation and compatibility with all proprietory storage dewars makes the CF500 an easy unit to use. The sample holder, electrical connector, evacuation valve, and exchange gas admittance valve are all mounted to the top flange to facilitate easy and rapid sample changes. The unit is equipped with an integral supply tube which is fitted into the neck of the dewar. The type of dewar used governs the length of tube supplied. An adapter is provided at the base of the unit which seals into the top of the storage/transport dewar. As the unit mounts directly to the dewar, losses inherent with normal transfer tubes are eliminated. The adapter is fitted with a valved connection to the gas recovery system and a pressure relief valve. To ensure that the required flow of liquid cryogen is maintained with
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and gamma ray detector, the aluminised 'Mylar' windows are located 100 mm above the mounting clamp. The standard window material employed on the outer vacuum case are aluminised Mylar film, approximately 0.17 mm thick, and 0.07 mm thick aluminium foil on the radiation shield. (Oxford Instruments, Osney Mead, Oxford OX2 0DX, UK)
LNG heat exchanger for Malaysia The first of three liquefied natural gas (LNG) heat exchangers has been completed by Air Products for Malaysian LNG, Sarawak, Malaysia. The Air Products' LNG heat exchanger cools natural gas to -260°F (-162°C) at which temperature it becomes a liquid. Since LNG occupies about 1/600th the volume of natural gas in a gaseous state, it is easier and more economical to store and transport. The LNG from the Sarawak plant will be shipped in special LNG tankers to customers overseas.
CF500 cooling unit from Oxford Instruments
good long term stability a flow pump is provided, the flow rate being regulated by a gas control unit. Variable operating temperatures are achieved by controlling the electrical power to the built-in heater using a three-term temperature controller. To avoid interference with the horizontally aligned Mossbauer drive
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TCF 20 system is between 8 and 40 I h -1 liquid helium (8 to 30 I h -1 without the precooling by liquid nitrogen) and between 35 and 130 W refrigeration at 4.5 K (-269°C). The liquefier version includes a fully automatic helium-cooled purifier which also facilititates operation with contaminated helium gas. Like the larger capcity systems TCF 100 and TCF 200, the TCF 20 features two cryogenic turbo expanders connected in series and dynamic gas bearings. Here, the fully automatic operation eliminates the need for manual interventions and plant supervision, even during cooling down and warming up phases. The TCF 20 unit is arranged on two skid-mounted and works-tested modules - - the cold box and the compressor group - - and can be installed in any desirable location
The heat exchanger measures 176 ft (53.65 m) in length, 14 ft (4.27 m) in diameter and weighs approximately 520 000 Ib (236 080 kg). Two additional units will be completed and shipped later this year. (Air Products and Chemicals, Inc., Allentown, Pennsylvania 18105, USA) Fully automatic small helium
liquefier A new standard small helium liquefier/refrigerator system under the name Turbocryofridge TCF 20 has been developed by Sulzer. Depending on the selected mode of operation, the capacity range of the
The high-vacuum insulated cold box of the TCF 20 helium liquefier/refrigerator system, from Sulzer
CRYOGENICS . JUNE 1981
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Inewsj without foundations. The singlestage compressor has been specially developed for this application and is characterized by its smooth running behaviour and low noise level. Servicing and maintenance, in principle, only apply to the compressor, because the turbo expanders operate completely free of mechanical content and wear. (Sulzer, Aktiengesellschaft, CH-8401 Winterthur, Switzerland)
4.5 K refrigerator Stable cold temperatures down to 4.5 K with loads up to 3 W can be produced with the LTS-1020-4.5 K System. This is suited for applications which require a stable, longterm, low maintenance cold source, which does not consume or expend cryogens. Typical applications include cooling of x-band masers, infrared and other detectors, Josephson junction mixers, superconducting computers and memories, as well as cryopumping. The Model LTS-1020-4.5-3 is a three stage, closed cycle, continuous duty cryogenic refrigerator providing up to 3 W of refrigeration at 4.5 K. The operating principals of the refrigerator are based on the combination of a highly reliable, well proven, mechanically driven Gifford-McMahon expansion engine with a high capacity JouleThompson, expansion-evaporator circuit providing the very low temperature operation. The refrigerant employed is high purity helium gas supplied by a completely selfcontained and pre+charged compressor unit. The pressures and flow rates for both the Gifford-McMahon and Joule-Thompson circuits are pre-set and no adjustments are required
CRYOGENICS. JUNE 1981
LTS-1020-4.5 K cold heads from Lake Shore
during normal operation of the refrigerator. The LTS-1020-4.5-3 refrigerator is designed with a modular building block concept to maximize application flexibility. A custom design service is available for interfacing the Model LTS-1020-4.5-3 with applications not readily accommodated by the standard accessory options. (Lake Shore Cryotronics, Inc., 64 E Walnut Street, Westerville, Ohio 43081, USA)
Low temperature system for Oak Ridge A continuously-operating helium-3 refrigerator has been installed by Oxford Instruments at the Oak Ridge National Laboratory in Tennessee, USA for their high-flux isotope reactor. The refrigerator will be used for neutron diffraction experiments at temperatures down to 0.4 K.
During installation, it was possible to accumulate neutron diffraction data on a sample at 0.4 K. The system was supplied by Oxford complete with all necessary pumps and pipework and can therefore be easily moved to perform experiments on spectrometers at different locations. The design will, at a later date, allow the addition of a dilution unit to convert the helium-3 cryostat to a complete dilution refrigerator. In a separate project, Oxford have also recently delivered a 100 microwatt (measured at 0.1 K) dilution refrigerator to the National Physical Laboratory at Teddington in the UK, where it will be used for lowtemperature thermometry research and for calibration. During testing at Oxford, the specified base temperature of 7 mK was surpassed and 6 mK was achieved in the continuous mode.
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The model 100 is one of a range of dilution refrigerators available from Oxford with cooling power up to 1000 microwatts and base temperature specified at 6 mK. A feature of all models is the ability to top-load samples without interrupting the refrigeration cycle. (Oxford Istruments, Osney Mead, Oxford Oxford OX2 0DX, UK)
Biological freezer for large tissue/blood banks An extra-large capacity freezing chamber, the TRA-7, which is specifically designed for the automatic, routine freezing of blood, lymphocytes, bone marrow, platelets and spermatoza has been introduced. It is ideal for use by blood banks and major medical research centres in hospitals and the pharmaceutical industry. It is equally valuable for materials testing for resistance to thermal shock. Twice the capacity of their established TRA-5 freezing chamber, Cryotech's new TRA-7 is capable of freezing 44.5 I of tissue or other material over a temperature range of 30°C to -180°C. The material to be frozen can be packed, if required, in ampoules, straws, bottles or plastic bags. The freezing programme is controlled by a solenoid valve, actuated by a temperature controller, and by two platinum resistor sensors and two copper/constantan thermocouples mounted in the freezing chamber. The solenoid controls the flow of the cooling agent, liquid nitrogen, into the freezing chamber. As soon as the liquid encounters a centrifugal blower, it is evaporated and the cold gas is distributed homogeneously
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around the preparations to be frozen. A ducting design keeps the temperature gradient in the stainless steel chamber under control and ensures even distribution of the coolant, and maximum economy. The system is fully protected by safety devices and is equipped with a heater which brings the chamber back to room temperature within a few minutes for recycling. As soon as the cover of the TRA-7 is opened, the nitrogen supply is closed and the blower stops. This prevents formation of ice in the chamber. Finally, a pressure relief valve, set at 3 kg cm -2 protects the liquid nitrogen piping system. (Cryotech Ltd., 2 Frogmore Lane, Stanford-in-the-Vale, Faringdon, Oxon, UK)
Taiwan hydrogen recovery A hydrogen purification unit for an oil refinery in Taiwan is to be supplied by Petrocarbon. The contract was awarded by the Chinese Petroleum Corporation (CPC) via the Central Trust of China and the plant will be situated at the Lin Yuan Refinery, Kaohsiung, Taiwan. The ability of the process to recover liquefied petroleum gases was an important factor in awarding the contract to Petrocarbon. The increasingly valuable LPG fraction in the hydrogen-rich feedgas will be recovered and transferred to the refinery's existing LPG recovery facility. LPG recovery is only possible with cryogenic hydrogen purification processes. The hydrogen purification unit for CPC, which is due to come onstream in 1982, is Petrocarbon's first in Taiwan. The capacity will be
12 000 Nm 3 h "1 of feedgas and 95% purity hydrogen will be recovered together with the LPG. Manchesterbased Petrocarbon will be responsible for the design and supply of the plant and for erection and commissioning advice. (Petrocarbon Developments Ltd, Petrocarbon House, Sharston Road, Manchester M22 4TB, UK)
The Cryex system for liquefaction of natural gas As an alternative to pretreating a natural gas stream before liquefaction, the Cryex (cryogenic extraction) freeze-separation system removes potential contaminants such as carbon dioxide via crystallization and clarification under controlled conditions and without damage to the heat exchangers, valves or pumps. The Cryex system has been successfully installed and demonstrated at two commercial peakshaving facilities. It tolerates an appreciable increase in the gas feed stream's carbon dioxide content with much less effect on the liquefaction capacity than in other systems. Most existing LNG facilities can be retrofitted with only a minor capacity reduction and with little or no modification to the primary refrigeration system. An energy-saving variation of the Cryex system recovers a significant amount of the refrigeration used to freeze the carbon dioxide and reuses it for reliquefying the storage-tank boiloff, while a second variation handles lowpressure, high carbon dioxidecontent gas streams. (The Cryex system for liquefaction of natural gas with removal of carbon dioxide by freeze separation. Y.A. Selcukoglu, T.A. Gallagher, R.J. Dortwegt. American Gas Association, Oper Sect Proc, T236-40 (1980) 5 pp)
CRYOGENICS. JUNE 1981
news International news Short courses in cryogenics The Institute of Cryogenics is organising two courses. 'Cryogenic Technology' will take place between 6 and 10 July 1981 inclusive. It is designed to meet the needs of laboratory and cryogenic-plant technicians and engineers. The course is residential with lectures in the mornings and laboratory work in the afternoons. A residential intensive short course on 'Cryogenics above 70 K' for graduates in science of engineering, or people with equivalent qualifications, will be held between 7 and 19 September 1981 inclusive. This course will consist of lectures given by University staff and industrialists. (The Secretary, Institute of Cryogenics, The University, Southampton SO9 5NH, UK)
Temperature control symposium The 6th Symposium on Temperature Control and Measurement will include cryogenic thermometry. The symposium will be held from March 14-18th 1982 in Washington DC, USA. Amongst topics to be covered are temperature scales and control, electronic bnd cryogenic thermometry. The deadline for abstract (not more than 500 words) of papers is June 15th 1981. There will also be exhibits of instruments and sensors for temperature measurement and control. (Program Chairman, 6th Tempera-
CRYOGENICS. JUNE 1981
ture Symposium, Room B128, Physics, National Bureau of Standards, Washington DC 20234, USA)
can Society for Testing and Materials. (Conference Steering Committee, c/o I.S. Jacobs, General Electric Corp., PO Box 8, Schenectady, NY 12301, USA)
Magnetism conference The 27th Annual Conference on Magnetism and Magnetic Materials will be held at the Sheraton-Atlanta Hotel, Atlanta, Georgia, USA from 10-13 November 1981. The Conference brings together scientists and engineers interested in recent developments in all branches of fundamental and applied magnetism. Emphasis is traditionally placed on experimental and theoretical research in magnetism, the properties and synthesis of new magnetic materials and advances in magnetic technology. The programme will consist of both invited and contributed papers. Selection of contributed papers is based on abstracts which must be received by 20 July 1981. A programme booklet listing titles and authors of all papers selected for presentation at the Conference will be distributed prior to the Conference. An abstract booklet will be available in advance of the Conference, but those registering will receive this booklet at the Conference. This conference is sponsored jointly by the American Institute of Physics and the Magnetics Society of the IEEE in co-operation with the American Physical Society, the Office of Naval Research, the Metallurgical Society of the AIME and the Ameri-
Cryosurgery-cryotherapy conference A meeting dealing with all aspects of cryosurgery and cryotherapy, and sponsored jointly by the Society for Low Temperature Biology and International manufacturers of associated equipment is to be held in Oxford, UK, from September 19-22, 1981. The conference will be concerned with the latest techniques and equipment, together with the current experimental work and data which may extablish cryosurgery on a more scientific base. Experimental clinicians will present their result in treating certain conditions as definite, well documented series of cases with long-term follow-up, comparing their results with alternative methods. Apart from inviting speakers of international repute in this field, it is proposed to organise poster sessions, practical demonstrations and exhibitions of equipment, and leave sessions free for short communications from anybody willing to talk about their personal experiences in cryosurgical practice. Panel discussions will be held at the end of each half-day session. (The Conference Secretary, Trevor Hudson, BOC Medical Cryogenics, 24 Deer Park Road, Morden, Surrey SW19 3UF, UK)
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Research news NASA's advanced cooling system NASA engineers are developing a refrigeration system for space operations that could also lead to commercial development of pumps, motors, compressors and other mechanical devices which would operate virtually without wear.
The development could increase system operation lifetime of astronomical and Earth-watching instruments in space by as much as six times, from the present six to ten months up to three to five years, according to the Goddard Space Flight Centre engineers.
and displacer chambers, continually adjusting the magnetic fields via an electronic controller. The electronic controller assures that the linear motors drive the piston in the compression stage and the displacer in the expansion section with the proper phase relationship.
The engineers have been working on the project for about two years and expect to deliver the first model for testing in April. The new system, a Stirling cycle cooler, uses helium gas to develop refrigeration, features two linear motors, one for compression and one for expansion, and two sets of magnetic bearings. The bearings employ four electromagnets surrounding the piston
Previously, most spacecraft intruments did not require significant cooling systems. As those instruments, such as gamma and infrared types, have become more sophisticated, improved cooling systems have become necessary. The new system will provide a much higher capacity for cooling, according to the engineers. (NASA, Washington DC 20546, USA)
Observation in this way avoids undesirable processes such as evaporation, sublimation or chemical treatment (eg fixation and dehydration), any of which can remove or obscure a structure. Biological tissue therefore closely resembles its natural state at the moment of freezing. Inner structures can be observed after fracturing a sample with the specimen fracturing knife.
lier attempts to produce cryo specimens. Images may be viewed and recorded in the conventional way with an SEM and the information presented is, for biological specimens at least, obtained from surfaces in the completely hydrated state. This new feature will increase the scope of the SEM scientist in many disciplines. (JEOL (UK) Ltd., JEOL House, Grove Park, London NW9 0JN, UK).
The new development eliminates the friction and, therefore, the wear associated with moving parts. The piston and displacer in the NASA cooling system are suspended in a magnetic field, permitting the parts to move without touching the sides of their housing and so no friction is incurred.
Industrial news Cryo stage for scanning electron microscopes With the JEOL Cryoscan system, tissue and specimens which are sensitive to electron beams or temperature can be very rapidly frozen in liquid nitrogen to preserve their natural structure. This is followed with a simple procedure for fracturing and locating them in the eucentric tilt stage of the scanning electron microscope (SEM). Temperature is guaranteed by JEOL to be lower than -185°C throughout examination. The whole system is designed to enable direct observations of surface structures of biological or material specimens in the frozen state.
CRYOGENICS. JUNE 1981
Cryoscan is especially useful in the fields of medicine and biology, where much dehydration occurs in most conventional preparations and in the observation of heat sensitive specimens such as plastics and waxes, say JEOL. This new system is a significant refinement over ear-
Auxiliary cooling system An auxiliary cooling system which offers temperature control for a wide variety of refrigeration applications has been introduced by CryoService Ltd. This Nitrochill
377
RVO:Emt
e--WSl will be produced. (CryoService Ltd., Roebuck Hill, Jump, Barnsley, South Yorkshire $74 OJP, UK)
Industrial process laboratory
Nitrochill TCE-196 system from CryoService Ltd
An industrial process laboratory has been opened by BOC in Leeds, UK. It is designed to study industrial problems such as process reliability, safety, fuel and capital expenditure
saving. It will initially concentrate on the development of liquid nitrogen as an inert gas for heat treatment of metals and as a source of 'cold' for cryogenic reclamation and grinding. All the facilities will be available to BOC customers to test their processes to an industrial specification. The different uses to which liquid nitrogen can be put in reclaiming scrap materials is being investigated at
TCE-196 system can be installed as the sole means of temperature control or as an emergency back-up for existing refrigeration equipment. It provides the facility for almostimmediate temperature settings from ambient t o - 1 9 6 ° C Applications may range from sub zero laboratory testing to the preservation of foodstuffs and biological products during storage or transportation. Liquid nitrogen is used as the refrigeration medium with this cooling system which consists basically of a control box, a temperature sensor, and, when required, a fan unit. The control box incorporates a thermostat control which can be set at any temperature between ambient and -196°C. This control operates a liquid nitrogen solenoid valve to maintain the temperature within the refrigeration zone to an accuracy of _+1°C. The Nitrochill TCE-196 is designed for operation on a 12 volt supply. There is an automatic cut-off switch to the liquid nitrogen supply which operates when the door or lid of the cold chamber is opened, and this switch is also linked with the system fan. If, for any reason, the cold chamber cools down to more than 10°C below the controlled setting, a visual and audible warning signal
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Ladies' shoe heels about to be treated with liquid nitrogen prior to grinding
CRYOGENICS. JUNE 1981
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cooled with liquid nitrogen before the molten metal is poured in, waste due to oxidation contamination will be greatly reduced. (BOC Limited, Industrial Processes Dept, 15/17 Northgate, Baildon, Shipley, West Yorkshire BD17 6JZ, UK)
Continuous flow cryostat The CF500 from Oxford Instruments is a cooling unit intended mainly for variable temperature Mossbauer absorber studies in the horizontal plane. It provides sample temperatures in the range 4-300 K using the absolute minimum of liquid helium, and 77-300 K using liquid nitrogen. It may also be readily employed for neutron, X-ray and other long term experiments where low operating costs are of paramount importance.
Cooling a mould for metal castingwith liquid nitrogento reducethe oxidationcontamination Leeds. One novel idea on reclamation is the polycarbonate from ladies' shoe heels. These have a steel pin running through them, making it impossible to reclaim the polycarbonate by conventional means. However, after placing the heels in liquid nitrogen and grinding them, the steel pins are found loose in amongst the ground polycarbonate. The pins are then easily removed with a magnet, and the polycarbonate can be recycled.
cess will cause them to melt. Similarly, liquid nitrogen can be used to freeze-grind rubber. Worn car tyres can be recycled by cooling the rubber with liquid nitrogen, which allows the rubber to be mechanically separated from other components. The rubber component can then be ground to a crumb of the required size.
Liquid nitrogen can be used to counteract the heat generated when grinding materials to fine, or even coarse, powders. Plastics, in particular, cannot be ground without cooling. The heat generated in the grinding pro-
Another potential use of liquid nitrogen which is being developed at Leeds is in the c~=sting of metal. Waste from these processes can be high due to oxidation contamination of the metal. However, if the solid mould is
CRYOGENICS . JUNE 1981
Grinding of spices in liquid nitrogen is being developed. The flavour, often due to volatile oils, is preserved by grinding at cryogenic temperatures.
Oxford say that the simplicity of operation and compatibility with all proprietory storage dewars makes the CF500 an easy unit to use. The sample holder, electrical connector, evacuation valve, and exchange gas admittance valve are all mounted to the top flange to facilitate easy and rapid sample changes. The unit is equipped with an integral supply tube which is fitted into the neck of the dewar. The type of dewar used governs the length of tube supplied. An adapter is provided at the base of the unit which seals into the top of the storage/transport dewar. As the unit mounts directly to the dewar, losses inherent with normal transfer tubes are eliminated. The adapter is fitted with a valved connection to the gas recovery system and a pressure relief valve. To ensure that the required flow of liquid cryogen is maintained with
379
and gamma ray detector, the aluminised 'Mylar' windows are located 100 mm above the mounting clamp. The standard window material employed on the outer vacuum case are aluminised Mylar film, approximately 0.17 mm thick, and 0.07 mm thick aluminium foil on the radiation shield. (Oxford Instruments, Osney Mead, Oxford OX2 0DX, UK)
LNG heat exchanger for Malaysia The first of three liquefied natural gas (LNG) heat exchangers has been completed by Air Products for Malaysian LNG, Sarawak, Malaysia. The Air Products' LNG heat exchanger cools natural gas to -260°F (-162°C) at which temperature it becomes a liquid. Since LNG occupies about 1/600th the volume of natural gas in a gaseous state, it is easier and more economical to store and transport. The LNG from the Sarawak plant will be shipped in special LNG tankers to customers overseas.
CF500 cooling unit from Oxford Instruments
good long term stability a flow pump is provided, the flow rate being regulated by a gas control unit. Variable operating temperatures are achieved by controlling the electrical power to the built-in heater using a three-term temperature controller. To avoid interference with the horizontally aligned Mossbauer drive
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TCF 20 system is between 8 and 40 I h -1 liquid helium (8 to 30 I h -1 without the precooling by liquid nitrogen) and between 35 and 130 W refrigeration at 4.5 K (-269°C). The liquefier version includes a fully automatic helium-cooled purifier which also facilititates operation with contaminated helium gas. Like the larger capcity systems TCF 100 and TCF 200, the TCF 20 features two cryogenic turbo expanders connected in series and dynamic gas bearings. Here, the fully automatic operation eliminates the need for manual interventions and plant supervision, even during cooling down and warming up phases. The TCF 20 unit is arranged on two skid-mounted and works-tested modules - - the cold box and the compressor group - - and can be installed in any desirable location
The heat exchanger measures 176 ft (53.65 m) in length, 14 ft (4.27 m) in diameter and weighs approximately 520 000 Ib (236 080 kg). Two additional units will be completed and shipped later this year. (Air Products and Chemicals, Inc., Allentown, Pennsylvania 18105, USA) Fully automatic small helium
liquefier A new standard small helium liquefier/refrigerator system under the name Turbocryofridge TCF 20 has been developed by Sulzer. Depending on the selected mode of operation, the capacity range of the
The high-vacuum insulated cold box of the TCF 20 helium liquefier/refrigerator system, from Sulzer
CRYOGENICS . JUNE 1981
clc--,m,+,Icl
Inewsj without foundations. The singlestage compressor has been specially developed for this application and is characterized by its smooth running behaviour and low noise level. Servicing and maintenance, in principle, only apply to the compressor, because the turbo expanders operate completely free of mechanical content and wear. (Sulzer, Aktiengesellschaft, CH-8401 Winterthur, Switzerland)
4.5 K refrigerator Stable cold temperatures down to 4.5 K with loads up to 3 W can be produced with the LTS-1020-4.5 K System. This is suited for applications which require a stable, longterm, low maintenance cold source, which does not consume or expend cryogens. Typical applications include cooling of x-band masers, infrared and other detectors, Josephson junction mixers, superconducting computers and memories, as well as cryopumping. The Model LTS-1020-4.5-3 is a three stage, closed cycle, continuous duty cryogenic refrigerator providing up to 3 W of refrigeration at 4.5 K. The operating principals of the refrigerator are based on the combination of a highly reliable, well proven, mechanically driven Gifford-McMahon expansion engine with a high capacity JouleThompson, expansion-evaporator circuit providing the very low temperature operation. The refrigerant employed is high purity helium gas supplied by a completely selfcontained and pre+charged compressor unit. The pressures and flow rates for both the Gifford-McMahon and Joule-Thompson circuits are pre-set and no adjustments are required
CRYOGENICS. JUNE 1981
LTS-1020-4.5 K cold heads from Lake Shore
during normal operation of the refrigerator. The LTS-1020-4.5-3 refrigerator is designed with a modular building block concept to maximize application flexibility. A custom design service is available for interfacing the Model LTS-1020-4.5-3 with applications not readily accommodated by the standard accessory options. (Lake Shore Cryotronics, Inc., 64 E Walnut Street, Westerville, Ohio 43081, USA)
Low temperature system for Oak Ridge A continuously-operating helium-3 refrigerator has been installed by Oxford Instruments at the Oak Ridge National Laboratory in Tennessee, USA for their high-flux isotope reactor. The refrigerator will be used for neutron diffraction experiments at temperatures down to 0.4 K.
During installation, it was possible to accumulate neutron diffraction data on a sample at 0.4 K. The system was supplied by Oxford complete with all necessary pumps and pipework and can therefore be easily moved to perform experiments on spectrometers at different locations. The design will, at a later date, allow the addition of a dilution unit to convert the helium-3 cryostat to a complete dilution refrigerator. In a separate project, Oxford have also recently delivered a 100 microwatt (measured at 0.1 K) dilution refrigerator to the National Physical Laboratory at Teddington in the UK, where it will be used for lowtemperature thermometry research and for calibration. During testing at Oxford, the specified base temperature of 7 mK was surpassed and 6 mK was achieved in the continuous mode.
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The model 100 is one of a range of dilution refrigerators available from Oxford with cooling power up to 1000 microwatts and base temperature specified at 6 mK. A feature of all models is the ability to top-load samples without interrupting the refrigeration cycle. (Oxford Istruments, Osney Mead, Oxford Oxford OX2 0DX, UK)
Biological freezer for large tissue/blood banks An extra-large capacity freezing chamber, the TRA-7, which is specifically designed for the automatic, routine freezing of blood, lymphocytes, bone marrow, platelets and spermatoza has been introduced. It is ideal for use by blood banks and major medical research centres in hospitals and the pharmaceutical industry. It is equally valuable for materials testing for resistance to thermal shock. Twice the capacity of their established TRA-5 freezing chamber, Cryotech's new TRA-7 is capable of freezing 44.5 I of tissue or other material over a temperature range of 30°C to -180°C. The material to be frozen can be packed, if required, in ampoules, straws, bottles or plastic bags. The freezing programme is controlled by a solenoid valve, actuated by a temperature controller, and by two platinum resistor sensors and two copper/constantan thermocouples mounted in the freezing chamber. The solenoid controls the flow of the cooling agent, liquid nitrogen, into the freezing chamber. As soon as the liquid encounters a centrifugal blower, it is evaporated and the cold gas is distributed homogeneously
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around the preparations to be frozen. A ducting design keeps the temperature gradient in the stainless steel chamber under control and ensures even distribution of the coolant, and maximum economy. The system is fully protected by safety devices and is equipped with a heater which brings the chamber back to room temperature within a few minutes for recycling. As soon as the cover of the TRA-7 is opened, the nitrogen supply is closed and the blower stops. This prevents formation of ice in the chamber. Finally, a pressure relief valve, set at 3 kg cm -2 protects the liquid nitrogen piping system. (Cryotech Ltd., 2 Frogmore Lane, Stanford-in-the-Vale, Faringdon, Oxon, UK)
Taiwan hydrogen recovery A hydrogen purification unit for an oil refinery in Taiwan is to be supplied by Petrocarbon. The contract was awarded by the Chinese Petroleum Corporation (CPC) via the Central Trust of China and the plant will be situated at the Lin Yuan Refinery, Kaohsiung, Taiwan. The ability of the process to recover liquefied petroleum gases was an important factor in awarding the contract to Petrocarbon. The increasingly valuable LPG fraction in the hydrogen-rich feedgas will be recovered and transferred to the refinery's existing LPG recovery facility. LPG recovery is only possible with cryogenic hydrogen purification processes. The hydrogen purification unit for CPC, which is due to come onstream in 1982, is Petrocarbon's first in Taiwan. The capacity will be
12 000 Nm 3 h "1 of feedgas and 95% purity hydrogen will be recovered together with the LPG. Manchesterbased Petrocarbon will be responsible for the design and supply of the plant and for erection and commissioning advice. (Petrocarbon Developments Ltd, Petrocarbon House, Sharston Road, Manchester M22 4TB, UK)
The Cryex system for liquefaction of natural gas As an alternative to pretreating a natural gas stream before liquefaction, the Cryex (cryogenic extraction) freeze-separation system removes potential contaminants such as carbon dioxide via crystallization and clarification under controlled conditions and without damage to the heat exchangers, valves or pumps. The Cryex system has been successfully installed and demonstrated at two commercial peakshaving facilities. It tolerates an appreciable increase in the gas feed stream's carbon dioxide content with much less effect on the liquefaction capacity than in other systems. Most existing LNG facilities can be retrofitted with only a minor capacity reduction and with little or no modification to the primary refrigeration system. An energy-saving variation of the Cryex system recovers a significant amount of the refrigeration used to freeze the carbon dioxide and reuses it for reliquefying the storage-tank boiloff, while a second variation handles lowpressure, high carbon dioxidecontent gas streams. (The Cryex system for liquefaction of natural gas with removal of carbon dioxide by freeze separation. Y.A. Selcukoglu, T.A. Gallagher, R.J. Dortwegt. American Gas Association, Oper Sect Proc, T236-40 (1980) 5 pp)
CRYOGENICS. JUNE 1981
news International news Short courses in cryogenics The Institute of Cryogenics is organising two courses. 'Cryogenic Technology' will take place between 6 and 10 July 1981 inclusive. It is designed to meet the needs of laboratory and cryogenic-plant technicians and engineers. The course is residential with lectures in the mornings and laboratory work in the afternoons. A residential intensive short course on 'Cryogenics above 70 K' for graduates in science of engineering, or people with equivalent qualifications, will be held between 7 and 19 September 1981 inclusive. This course will consist of lectures given by University staff and industrialists. (The Secretary, Institute of Cryogenics, The University, Southampton SO9 5NH, UK)
Temperature control symposium The 6th Symposium on Temperature Control and Measurement will include cryogenic thermometry. The symposium will be held from March 14-18th 1982 in Washington DC, USA. Amongst topics to be covered are temperature scales and control, electronic bnd cryogenic thermometry. The deadline for abstract (not more than 500 words) of papers is June 15th 1981. There will also be exhibits of instruments and sensors for temperature measurement and control. (Program Chairman, 6th Tempera-
CRYOGENICS. JUNE 1981
ture Symposium, Room B128, Physics, National Bureau of Standards, Washington DC 20234, USA)
can Society for Testing and Materials. (Conference Steering Committee, c/o I.S. Jacobs, General Electric Corp., PO Box 8, Schenectady, NY 12301, USA)
Magnetism conference The 27th Annual Conference on Magnetism and Magnetic Materials will be held at the Sheraton-Atlanta Hotel, Atlanta, Georgia, USA from 10-13 November 1981. The Conference brings together scientists and engineers interested in recent developments in all branches of fundamental and applied magnetism. Emphasis is traditionally placed on experimental and theoretical research in magnetism, the properties and synthesis of new magnetic materials and advances in magnetic technology. The programme will consist of both invited and contributed papers. Selection of contributed papers is based on abstracts which must be received by 20 July 1981. A programme booklet listing titles and authors of all papers selected for presentation at the Conference will be distributed prior to the Conference. An abstract booklet will be available in advance of the Conference, but those registering will receive this booklet at the Conference. This conference is sponsored jointly by the American Institute of Physics and the Magnetics Society of the IEEE in co-operation with the American Physical Society, the Office of Naval Research, the Metallurgical Society of the AIME and the Ameri-
Cryosurgery-cryotherapy conference A meeting dealing with all aspects of cryosurgery and cryotherapy, and sponsored jointly by the Society for Low Temperature Biology and International manufacturers of associated equipment is to be held in Oxford, UK, from September 19-22, 1981. The conference will be concerned with the latest techniques and equipment, together with the current experimental work and data which may extablish cryosurgery on a more scientific base. Experimental clinicians will present their result in treating certain conditions as definite, well documented series of cases with long-term follow-up, comparing their results with alternative methods. Apart from inviting speakers of international repute in this field, it is proposed to organise poster sessions, practical demonstrations and exhibitions of equipment, and leave sessions free for short communications from anybody willing to talk about their personal experiences in cryosurgical practice. Panel discussions will be held at the end of each half-day session. (The Conference Secretary, Trevor Hudson, BOC Medical Cryogenics, 24 Deer Park Road, Morden, Surrey SW19 3UF, UK)
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