INTRODUCTION TO CRYOGENIC SYSTEMS

INTRODUCTION TO CRYOGENIC SYSTEMS

1.1. Introduction

The word cryogenics means, literally, the production of icy cold; how­ever, the term is used today as a synonym for low temperatures. The point on the temperature scale at which refrigeration in the ordinary sense of the term ends and cryogenics begins is not sharply defined. The workers at the National Bureau of Standards at Boulder, Colorado, have chosen to consider the field of cryogenics as that involving temperatures below -150°C (123 K) or - 240°F (220⁰R). This is a logical dividing line, because the normal boiling points of the so-called permanent gases, such as helium, hydrogen, neon, nitrogen, oxygen, and air, lie below - 150°C, while the Freon refrigerants, hydrogen sulfide, ammonia, and other con­ventional refrigerants all boil at temperatures above -150°C. The posi­tion and range of the field of cryogenics are illustrated on a logarithmic thermometer scale in Fig. 1.1.

In the field of cryogenic engineering, one is concerned with developing and improving low-temperature techniques, processes, and equipment. As contrasted to low-temperature physics, cryogenic engineering primar­ily involves the practical utilization of low-temperature phenomena, rather than basic research, although the dividing line between the two fields is not always clear-cut. The engineer should be familiar with physical phenomena in order to know How to utilize them effectively; the physicist should be familiar with engineering principles in order to design experiments and apparatus.

A system may be defined as a collection of components united by def­inite interactions or interdependencies to perform a definite function. Examples of common engineering systems include the automobile, a petroleum refinery, and an electric generating power plant. In many cases the distinction between a system and a component depends upon one's point of view. For example, consider the transportation system of a coun­try. An automobile is a system also; however, it would be only one part or subsystem of the entire transportation system. Going even further, one could speak of the power system, braking system, steering system, etc., of the automobile. In general, we shall use the term cryogenic system to refer to an interacting group of components involving low temperatures. Air­ liquefaction plants, helium refrigerators, and storage vessels with the associated controls are some examples of cryogenic systems.

1.2. Historical background

In 1726 Jonathan Swift wrote in Gulliver's account of his trip to the mythical Academy of Lagado:

He (the universal artist) told us he had been thirty years employing his thoughts for the improvement of human life. He had two large rooms full of wonderful curiosities, and fifty men at work. Some were condensing air into a dry tangible substance, by extracting the nitre, and letting the aqueous or fluid particles percolate.

At the time Gulliver's Travels was written, air was considered to be a "permanent gas." Thus Swift envisioned the liquefaction of air some 150 years before the feat was actually accomplished.

In the 1840s, in an attempt- to relieve the suffering of malaria patients, Dr. John Gorrie, a Florida physician, developed an expansion engine for the production of ice. Although Dr. Gorrie’s engine was used only to cool air for air conditioning of sickrooms and was not part of a cryogenic sys­tem, most large-scale air liquefaction systems today use the same princi­ple of expanding air through a work-producing device, such as an expan­sion engine or expansion turbine, in order to extract energy from the air so that the air can be liquefied.

It was not until the end of 1877 that a so-called permanent gas was first liquefied. In this year Louis Paul Cailletet, a French mining engineer, pro­duced a fog of liquid-oxygen droplets by precooling a container filled with oxygen gas at approximately 300 atm and allowing the gas to expand sud­denly by opening a valve on the apparatus. About the same time Raoul Pictet, a Swiss physicist, succeeded in producing liquid oxygen by a cas­cade process.

In the early 1880s one of the first low-temperature physics laboratories, the Cracow University Laboratory in Poland, was established by Szyg­munt von Wroblewski and K. Olszewski. They obtained liquid oxygen "boiling quietly in a test tube" in sufficient quantity to study properties in April 1883. A few days later, they also liquefied nitrogen. Having suc­ceeded in obtaining oxygen and nitrogen as true liquids (not just a fog of liquid droplets), Wroblewski and Olszewski, now working separately at Cracow, attempted to liquefy hydrogen by Cailletet's expansion tech­nique. By first cooling hydrogen in a capillary tube to liquid-oxygen tem­peratures and expanding suddenly from 100 atm to I atm, Wroblewski obtained a fog of liquid-hydrogen droplets in 1884, but he was not able to obtain hydrogen in the completely liquid form.

The Polish scientists at the Cracow University Laboratory were pri­marily interested in determining the physical properties of liquefied gases. The ever-present problem of heat transfer from ambient plagued these early investigators because the cryogenic fluids could be retained only for a short time before the liquids boiled away. To improve this situation, an ingenious experimental technique was developed at Cracow. The experimental test tube containing a cryogenic fluid was surrounded by a series of concentric tubes, closed at one end. The cold vapor arising from the liquid flowed through the annular spaces between the tubes and intercepted some of the heat traveling toward the cold test tube. This con­cept of vapor shielding is used today in conjunction with high-perfor­mance insulations for the long-term storage of liquid helium in bulk quantities.

A giant step forward in preserving cryogenic liquids was made in 1892 when James Dewar, a chemistry professor at the Royal Institution in London, developed the vacuum-jacketed vessel for cryogenic-fluid stor­age. Dewar found that using a double-walled glass vessel having the inner surfaces silvered (similar to present-day thermos bottles) resulted in a reduction of the evaporation rate of the stored fluid by a factor of 30 over that of an uninsulated container. This simple container played a signifi­cant role in the liquefaction of hydrogen and helium in bulk quantities. In May 1898 Dewar produced 20 cm) of liquid hydrogen boiling quietly in a vacuum-insulated tube, instead of a mist.

In 1895 two significant events in cryogenic technology occurred. Carl von Linde, who had established the Linde Eismaschinen AG in 1879, was granted a basic patent on air liquefaction in Germany. Although Linde was not the first to liquefy air, he was one of the first to recognize the industrial implications of gas liquefaction and to put these ideas into practice. Today the Linde Company is one of the leaders in cryogenic engineering.

After more than 10 years of low-temperature study, Heike Kamerlingh Onnes established the Physical Laboratory at the University of Lei den in Holland in 1895. Onnes' first liquefaction of helium in 1908 was a tribute both to his experimental skill and to his careful planning. He had only 360 liters of gaseous helium obtained by heating monazite sand from India. More than 60 cm³ of liquid helium was produced by Onnes in his first attempt. Onnes was able to attain a temperature of 1.04 K in an unsuccessful attempt to solidify helium by lowering the pressure above a container of liquid helium in 1910.

The physicists at the Leiden laboratory were interested in investigating the properties of materials at low temperatures and in checking natural principles known to be valid at ambient temperatures, at cryogenic tem­peratures. It was in 1911, while he was checking the various theories of electrical resistance of solids at liquid-helium temperatures, that Onnes discovered that the electrical resistance of the mercury wire on which he was experimenting suddenly decreased to zero. This event marked the first observation of the phenomenon of superconductivity-the basis for many novel devices used today.

In 1902 Georges Claude, a French engineer, developed a practical sys­tem for air liquefaction in which a large portion of the cooling effect of the system was obtained through the use of an expansion engine. Claude's first engines were reciprocating engines using leather seals (actually, the engines were simply modified steam engines). During the same year, Claude established l'Air Liquide to develop and produce his systems.

Although cryogenic engineering is considered a relatively new field in the U.S., it must be remembered that the use of liquefied gases in U.S. industry began in the early 1900s. Linde installed the first air-liquefaction plant in the United States in 1907, and the first American-made air-liq­uefaction plant was completed in 1912. The first commercial argon-pro­duction was put into operation in 1916 by the Linde company in Cleve­land, Ohio. In 1917 three experimental plants were built by the Bureau of Mines, with the cooperation of the Linde Company, Air Reduction Company, and the Jefferies-Norton Corporation, to extract helium from natural gas of Clay County,' Texas. The helium was intended for use in airships for World War I. Commercial production of neon began in the United States in 1922, although Claude had produced neon in quantity in France since 1907.

On 16 March 1926, Dr. Robert H. Goddard conducted the world's first successful flight of a rocket powered by liquid-oxygen-gasoline propellant on a farm near Auhurn, Massachusetts. This first flight lasted only 2½ seconds, and the rocket reached a maximum speed of only 22 m/s (50 mph). Dr. Goddard continued his work during the 1930s and by 1941 he had brought his cryogenic rockets to a fairly high degree of perfection. In fact, many of the devices used in Dr. Goddard's rocket systems were used later in the German V-2 weapons system.

During that same year (1926), William Francis Giauque and Peter Debye independently suggested the adiabatic demagnetization method for obtaining ultralow temperatures (less than 0.1 K). It was not until 1933 that Giauque and MacDougall at Berkeley and De Haas, Wiersma, and Kramers at Leiden made use of the technique to reach temperatures from 0.3 K (Giauque and MacDougall) to 0.09 K (De Haas et al.).

As early as 1898 Sir James Dewar made measurements on heat transfer through evacuated powders. In 1910 Smoluchowski demonstrated the significant improvement in insulating quality that could be achieved by using evacuated powders in comparison with unevacuated insulations. In 1937 evacuated-powder insulations were first used in the United States in bulk storage of cryogenic liquids. Two years later, the first vacuum ­powder-insulated railway tank car was built for the transport of liquid oxygen.

The world became aware of some of the military implications of cry­ogenic technology in 1942 when the German V -2 weapon system was suc­cessfully test-fired at Peenemunde under the direction of Dr. Walter Dornberger. The V-2 weapon system was the first large, practical liquid­ propellant rocket. This vehicle was powered by liquid oxygen and a mix­ture of 75 percent ethyl alcohol and 25 percent water.

Around 1947 Dr. Samuel C. Collins of the department of mechanical engineering at Massachusetts Institute of Technology developed an effi­cient liquid-helium laboratory facility. This event marked the beginning of the period in which liquid-helium temperatures became feasible and fairly economical. The Collins helium cryostat, marketed by Arthur D. Little, Inc., was a complete system for the safe, economical liquefaction of helium and could be used also to maintain temperatures at any level between ambient temperature and approximately 2 K.

The first buildings for the National Bureau of Standards Cryogenic Engineering Laboratory were completed in 1952. This laboratory was established to provide engineering data on materials of construction, to produce large quantities of liquid hydrogen for the Atomic Energy Com­mission, and to develop improved processes and equipment for the fast­ growing cryogenic field. Annual conferences in cryogenic engineering have been sponsored by the National Bureau of Standards (sometimes sponsored jointly with various universities) from 1954 (with the excep­tion of 1955) to 1973. At the 1972 conference at Georgia Tech in Atlanta, the Conference Board voted to change to a biennial schedule alternating with the Applied Superconductivity Conference. This schedule has been followed with meetings in Kingston, Ontario in 1975, Boulder in 1977, Madison, Wisconsin in 1979, San Diego, California in 1981, and Colo­rado Springs in 1983.

Early in 1956 work with liquid hydrogen was greatly accelerated when Pratt and Whitney Aircraft was awarded a contract to develop a liquid­ hydrogen-fueled rocket engine for the United States space program. The following year the Atlas ICBM was successfully test-fired. The Atlas was powered by a liquid-oxygen-RP-l propellant combination and had a sea ­level thrust of I. 7 MN (380,000 Ib_f). At the Cape Kennedy Space Center on 27 October 1961, the first flight test of the Saturn launch vehicle was conducted. The Saturn V was the first space vehicle to use the liquid ­hydrogen-liquid-oxygen propellant combination.

In 1966, Hall, Ford, and Thompson at Manchester, and Neganov, Bor­isov, and Liburg at Moscow independently succeeded in achieving con­tinuous refrigeration below 0.1 K using a He³-He⁴ dilution refrigerator. This new refrigeration technique had been proposed in 1951 by H. Lon­don. The dilution refrigerator had certain advantages over the magnetic refrigerator, which relied on the adiabatic demagnetization principle to achieve temperatures in the 0.01 K to 0.10 K range. Thus considerable research effort has been devoted to the study and improvement of the dilution refrigerator. .

In 1969 a 3250-hp, 20D-rpm superconducting motor (Fawley motor) was constructed by the International Research and Development Co., Ltd., in England. In 1972 IRD installed a superconducting motor in a ship to drive the electrical propulsion system.

This chronology of cryogenic technology is summarized in Table 1.1.

We see that cryogenics has grown from an interesting curiosity in the times of Linde and Claude to a diversified, vital field of engineering.

1.3. Present areas involving cryogenic engineering

Present-day applications of cryogenic technology are widely varied, both in scope and in magnitude. Some of the areas involving cryogenic engi­neering include:

1.       Rocket propulsion systems. All the large United States launch vehicles use liquid oxygen as the oxidizer. The Space Shuttle propulsion system uses both cryogenic fluids, liquid oxygen, and liquid hydrogen.

2.       Studies in high-energy physics. The hydrogen bubble chamber uses liq­uid hydrogen in the detection and study of high-energy particles pro­duced in large particle accelerators.

3.       Electronics. Sensitive microwave amplifiers, called masers, are cooled to liquid-nitrogen or liquid-helium· temperatures so that thermal vibrations of the atoms of the amplifier element do not seriously interfere with absorption and emission of microwave energy. CryogenicaIly cooled masers have been used in missile detectors, in radio astronomy to listen to faraway galaxies, and in space communication systems.

Table 1.1. Chronology of cryogenic technology

Year	Event
1877	Cailletet and Pictet liquefied oxygen (Pictet 1892).
1879	Linde founded the Linde Eismaschinen AG.
1883	Wroblewski and Olszewski completely liquefied nitrogen and oxygen at the Cracow University Laboratory (Olszewski 1895).
1884	Wroblewski produced a mist of liquid hydrogen.
1892	Dewar developed a vacuum-insulated vessel for cryogenic-fluid storage (Dewar 1927).
1895	Onnes established the Leiden Laboratory. Linde was granted a basic patent on air liquefaction in Germany.
1898	Dewar produced liquid hydrogen in bulk at the Royal Institute of London.
1902	Claude established l'Air Liquide and developed an air-liquefaction system using an expansion engine.
1907	Linde installed the first air-liquefaction plant in America. Claude produced neon as a by-product of an air plant.
1908	Onnes liquefied helium (Onnes 1908).
1910	Linde developed the double-column air-separation system.
1911	Onnes discovered superconductivity (Onnes 1913).
1912	First American-made air-liquefaction plant completed.
1916	First commercial production of argon in the United States.
1917	First natural-gas liquefaction plant to produce helium.
1922	First commercial production of neon in the United States.
1926	Goddard test-fired the first cryogenically propelled rocket. Cooling by adiabatic demagnetization independently suggested by Giauque and Debye.
1933	Magnetic cooling used to attain temperatures below I K.
1934	Kapitza designed and built the first expansion engine for helium. Evacuated-powder insulation first used on a commercial scale in cryogenic-fluid storage vessels.
1939	First vacuum-insulated railway tank car built for transport of liquid oxygen.
1942	The V-2 weapon system was test-fired (Dornberger 1954). The Collins cryostat developed.
1948	First 140 ton/day oxygen system built in America.
1949	First 300 ton/day on-site oxygen plant for chemical industry completed.
1952	National Bureau of Standards Cryogenic Engineering Laboratory established (Brickwedde 1960).
1957	LOX-RP-I propelled Atlas ICBM test-fired. Fundamental theory (BCS theory) of superconductivity presented.
1958	High-efficiency multilayer cryogenic insulation developed (Black 1960).
1959	Large NASA liquid-hydrogen plant at Torrance, California, completed.
1960	Large-scale liquid-hydrogen plant completed at West Palm Beach, Rorida.
1961	Saturn launch vehicle test-fired.
1963	60 ton/day liquid-hydrogen plant completed by Linde Co. at Sacramento, California.
1964	Two liquid-methane tanker ships designed by Conch Methane Services. Ltd., entered service.
1966	Dilution refrigerator using HeJ-He' mixtures developed (Hall 1966; Neganov 1966).
1969	3250-hp de superconducting motor constructed (Appleton 1971).
1970	Liquid oxygen plants with capacities between 60,000 mJ/h and 70,000 mJ/h developed.
1975	Record high superconducting transition temperature (23 K) achieved.

Tiny superconducting electronic elements, called SQUIDs (super­conducting quantum interference devices) have been used as extremely sensitive digital magnetometers and voltmeters. These devices are based on a superconducting phenomenon, called the Josephson effect, which involves quantum mechanical tunneling of electrons from one superconductor to another through an insulating barrier.

In addition to SQUIDs, other electronic devices that utilize super­conductivity in their operation include superconducting amplifiers, rectifiers, transformers, and magnets. Superconducting magnets have been used to produce the high magnetic fields required in MHD sys­tems, linear accelerators, and tokamaks. Superconducting magnets have been used to levitate high-speed trains at speeds up to 500 km/h.

4.       Mechanical design. By utilizing the Meissner effect associated with superconductivity, practically zero-friction bearings have been con­structed that use a magnetic field as the lubricant instead of oil or air. Superconducting motors have been constructed with practically zero electrical losses for such applications as ship propulsion systems. Superconducting gyroscopes with extremely small drift have been developed.

5.       Space simulation and high-vacuum technology. To produce a vacuum that approaches that of outer space (from 10-¹² torr to 10-¹⁴ torr), one of the more effective methods involves low temperatures. Cryopump­ing or freezing out the residual gases, is used to provide the ultrahigh vacuum required in space simulation chambers and in test chambers for space propulsion systems. The cold of free space is simulated by cooling a shroud within the environmental chamber by means of liquid nitrogen. Dense gaseous helium at less than 20 K or liquid helium is used to cool the cryopanels that freeze out the residual gases.

6.       Biological and medical applications. The use of cryogenics in biology, or cryobiology, has aroused much interest. Liquid-nitrogen-cooled containers are used to preserve whole blood, tissue, bone marrow, and animal semen for long periods of time. Cryogenic surgery (cryosur­gery) has been used for the treatment of Parkinson's disease, eye sur­gery, and treatment of various lesions. This surgical procedure has many advantages over conventional surgery in several applications.

7.       Food processing. Freezing as a means of preserving food was used as far back as 1840. Today frozen foods are prepared by placing cartons on a conveyor belt and moving the belt through a liquid-nitrogen bath or gaseous-nitrogen-cooled tunnel. Initial contact with liquid nitrogen freezes all exposed surfaces and seals in flavor and aroma. The cry­ogenic process requires about 7 minutes compared with 30 to 48 min­utes required by conventional methods. Liquid nitrogen has also been used as the refrigerant in frozen-food transport trucks and railway cars.

8.       Manufacturing processes. Oxygen is used to perform several important functions in the steel manufacturing process. Cryogenic systems are used in making ammonia. Pressure vessels have been formed by plac­ing a preformed cylinder in a die cooled to liquid-nitrogen tempera­tures. High-pressure nitrogen gas is admitted into the vessel until the container stretches about 15 percent, and the vessel is removed from the die and allowed to warm to room temperature. Through the use of this method, the yield strength of the material has been increased 400 to 500 percent.

9.       Recycling of materials. One of the more difficult items to recycle is the automobile or truck tire. By freezing the tire in liquid nitrogen, tire rubber is made brittle and can be crushed into small particles. The tire cord and metal components in the original tire can be separated easily from the rubber, and the rubber particles can be used again for other items. At present the cryogenic technique is the only effective one to recover the rubber from steel radial tires.

These are a few of the areas involving cryogenic engineering-a field in which new developments are continually being made.

References

1. Cryogenic Systems               -             Barron R. F
2. Cryogenic Engineering           -           Scot R. W.
3. Cryogenic Engineering           -           Bell J.H.