Cryogenics

1. LOW TEMPERATURES IN SCIENCE AND TECHNOLOGY.

Cryogenics is defined as that branch of physics which deals with the production of very low temperatures and their effect on matter [1], a formulation which addresses both aspects of attaining low temperatures which do not naturally occur on Earth, and of using them for the study of nature or the human industry. In a more operational way [2], it is also defined as the science and technology of temperatures below 120 K. The reason for this latter definition can be understood by examining characteristic temperatures of cryogenic fluids (Table 1): the limit temperature of 120 K comprehensively includes the normal boiling points of the main atmospheric gases, as well as of methane which constitutes the principal component of natural gas. Today, liquid natural gas (LNG) represents one of the largest – and fast-growing – industrial domains of application of cryogenics (Figure 1), together with the liquefaction and separation of air gases (Figure 2). The densification by condensation, and separation by distillation of gases was historically – and remains today - the main driving force for the cryogenic industry, exemplified not only by liquid oxygen and nitrogen used in chemical and metallurgical processes, but also by the cryogenic liquid propellants of rocket engines (Figure 3) and the proposed use of hydrogen as a ―clean‖ energy vector in transportation (Figure 4). Table 1 Characteristic temperatures of cryogenic fluids [K] Cryogen

Triple point

Normal

boiling Critical point

point Methane

90.7

111.6

190.5

Oxygen

54.4

90.2

154.5

Argon

8338

87.3

150.9

Nitrogen

63.1

77.3

126.2

Neon

24.6

27.1

44.4

Hydrogen

13.8

20.4

33.2

Helium

2.2*

4.2

5.2

1

Figure 1 130 000 m3 LNG carrier heat

Figure 2 Cryogenic air separation plant with

exchanger and distillation column towers(source Air Products)

a) Ariane 5

b) Space Shuttle

(25 t liquid hydrogen, 130 t liquid oxygen)

(100 t liquid hydrogen, 600 t liquid

Figure 3 Rockets using cryogenic liquid propellants

Figure 4 Automotive liquid hydrogen fuel tank 2

The quest for low temperatures however finds its origin in early thermodynamics, with Amontons’s gas pressure thermometer (1703) opening the way for the concept of absolute zero inferred a century later by Charles and Gay-Lussac, and eventually formulated by Kelvin. It is however with the advent of Boltzmann’s statistical thermodynamics in the late nineteenth century that temperature – until then a phenomenological quantity - could be explained in terms of microscopic structure and dynamics. Consider a thermodynamic system in a macrostate which can be obtained by a multiplicity W of microstates. The entropy S of the system was postulated by Boltzmann as S = kB ln W (1) with kB ≃ 1.38 10-23 J/K. This formula, which founded statistical thermodynamics, is displayed on Boltzmann’s grave in Vienna (Figure 5).

Figure 5 L. Boltzmann’s grave in the Zentralfriedhof, Vienna, bearing the entropy formula Adding reversibly heat dQ to the system produces a change of its entropy dS, with a proportionality factor T which is precisely temperature T = (dQ / dS) Thus a low-temperature system can be defined as one to which a minute addition of heat produces a large change in entropy, i.e. a large change in its range of possible microscopic configurations. Boltzmann also found that the average thermal energy of a particle in a system in equilibrium at temperature T is E ~ kB T (3) Consequently, a temperature of 1 K is equivalent to a thermal energy of 10-4 eV or 10-23 J per particle. A temperature is therefore low for a given physical process when kB T is small compared to the characteristic energy of the process considered. Cryogenic 3

temperatures thus reveal phenomena with low characteristic energy (Table 2), and enable their application when significantly lower than the characteristic energy of the phenomenon of interest. From Tables 1 and 2, it is clear that ―low temperature‖ superconductivity requires helium cryogenics: several examples of helium-cooled superconducting devices are shown in Figure 6. Considering vapour pressures of gases at low temperature (Figure 7), it is also clear that helium must be the working cryogen for achieving ―clean‖vacuum with cryopumps. Table 2 Characteristic temperatures of low-energy phenomena Phenomenon

Temperature [K]

Debye temperature of metals

few 100

High-temperature superconductors

~ 100

Low-temperature superconductors

~ 10

Intrinsic transport properties of metals

< 10

Cryo pumping

Few

Cosmic microwave background

2.7

Super fluid helium 4

2.2

Bolometers for cosmic radiation

<1

Low-density

atomic

Bose-Einstein

~ 10-6

condensates

2. CRYOGENIC FLUIDS 2.1 Thermo Physical Properties The simplest way of cooling equipment with a cryogenic fluid is to make use of its latent heat of vaporization, e.g. by immersion in a bath of boiling liquid. As a consequence, the useful temperature range of cryogenic fluids is that in which there exists latent heat of vaporization, i.e. between the triple point and the critical point, with a particular interest in the normal boiling point, i.e. the saturation Temperature at atmospheric pressure. This data is given in Table 1. In this introduction to cryogenics, we will concentrate on two cryogens: helium which is the only liquid at very low 4

temperature, and nitrogen for its wide availability and ease of use for pre-cooling equipment and for thermal shielding.

d)

Figure 6 Helium-cooled superconducting devices a) Large Hadron Collider at CERN, b) ) 5 MW HTS ship propulsion motor (AMS), c) c) ITER experimental fusion reactor, d) d) whole-body MRI system (Bruker)

5

Figure 7 Vapour pressures of common gases at cryogenic temperature To develop a feeling about properties of these cryogenic fluids, it is instructive to compare them with those of water (Table 3). In both cases, but particularly with helium, applications operate much closer to the critical point, i.e. in a domain where the difference between the liquid and vapour phases is much less marked: the ratio of liquid to vapour densities and the latent heat associated with the change of phase are much smaller. Due to the low values of its critical pressure and temperature, helium can be used as a cryogenic coolant beyond the critical point, in the supercritical state. It is also interesting to note that, while liquid nitrogen resembles water as concerns density and viscosity, liquid helium is much lighter and less viscous. This latter property makes it a medium of choice for permeating small channels inside superconducting magnet windings and thus stabilizing the superconductor.

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Table 3 Properties of helium and nitrogen compared to water

2.2 Liquid boil-off The factor of ten in latent heat of vaporization between helium and nitrogen, combined with the lower density of the former, induces a large difference in vaporization rates under the same applied heat load (Table 4). This illustrates the need for implementing much better insulation techniques in liquid helium vessels to achieve comparable holding times. Table 4 Vaporization of liquid helium and liquid nitrogen at normal boiling point under 1 W applied heat load

Boil-off measurements constitute a practical method for measuring the heat load of a cryostat holding a saturated cryogen bath. In steady conditions, i.e. provided the liquid level in the bath is maintained constant, the boil-off m vap precisely equals the vapor flow m out escaping the cryostat, which can be warmed up to room temperature and measured in a conventional gas flow-meter. At decreasing liquid level though, part of the vapor will take the volume in the cryostat previously occupied by the liquid which has vaporized,

7

and the escaping flow will be lower than the boil-off. More precisely, if the boil-off vapor is taken at saturation in equilibrium with the liquid

2.3 Cryogen usage for equipment cooldown For both fluids, the sensible heat of the vapour over the temperature range from liquid saturation to ambient is comparable to or larger than the latent heat of vaporization. This provides a valuable cooling potential at intermediate temperature, which can be used for thermal shielding or for precooling of equipment from room temperature. The heat balance equation for cooling a mass of, say iron mFe of specific heat CFe(T) at temperature T by vaporizing a mass dm of cryogenic liquid at saturation temperature Tv, latent heat of vaporization Lv and vapour specific heat C (taken as constant), is assuming perfect heat exchange with the liquid and the vapour mFe CFe(T) dT = [Lv + C (T - Tv)] dm Hence the specific liquid cryogen requirement for cool-down from temperature T0 The term C (T - Tv) adding to Lv in the denominator brings a strong attenuation to the specific liquid requirement, provided there is good heat exchange between the solid and the escaping vapor. Calculated values of specific liquid cryogen requirements for iron are given in Table 5, clearly demonstrating the interest of recovering the sensible heat of helium vapor, as well as

that of pre cooling Equipment with liquid nitrogen.

The term C (T - Tv) adding to Lv in the denominator brings a strong attenuation to the specific liquid requirement, provided there is good heat exchange between the solid and the escaping vapor. Calculated values of specific liquid cryogen requirements for iron are 8

given in Table 5, clearly demonstrating the interest of recovering the sensible heat of helium vapor, as well as that of pre-cooling equipment with liquid nitrogen. Table 5 Volume [l] of liquid cryogens required to cool down 1 kg of iron Using

Latent heat only

Latent heat and enthalpy of vapor

Liquid helium from 290 K 29.5

0.75

to 4.2 K Liquid helium from 77 K to 1.46

0.12

4.2 K Liquid nitrogen from 290 K 0.45

0.29

to 77 K

2.4 Phase domains Typical operating domains with cryogenic helium are shown in Figure 8, superimposed on the – peculiar – phase diagram of the substance: the solid phase only exists under pressure and the normal liquid He I undergoes below 2.2 K a transition to another liquid phase, He II instead of solidifying. There is no latent heat associated with this phase transition, but a peak in the specific heat, the shape of which gave the name ―-line‖ to the phase boundary. He II exhibits super fluidity, a macroscopic quantum behavior entailing very high thermal conductivity and very low viscosity. While operating in saturated He I provides fixed (saturation) temperature and high boiling heat transfer at moderate heat flux, it may develop instabilities in two-phase flow and is prone to boiling crisis above the peak nucleate boiling flux (about 1 W/cm2). The use of mono-phase supercritical helium in forced-flow systems avoids the problems of two-phase flow. However, the strongly varying properties of the fluid in the vicinity of the critical point may create other issues, such as density wave oscillations. More fundamentally, supercritical helium exhibits no latent heat, so that applied heat loads result in temperature increases which must be contained by high flow-rate or periodic re-cooling in extended systems. At lower temperature, He II demonstrates excellent transport properties which make it a coolant of choice for advanced superconducting devices [3]. Besides the thermodynamic penalty of 8 lower temperatures, the use of He II imposes that at least part 9

of the cryogenic circuits operate at sub atmospheric pressure, thus requiring efficient compression of low-pressure vapor and creating risks of a dielectric breakdown and contamination by air in-leaks. Thermo-physical properties of cryogenic fluids are available from tables, graphs and software running on personal computers, a selection of which is listed in the bibliography.

Figure 8 Phase diagram of helium, showing typical operating domains.

3. REAL CYCLE AND REFERIGARATION EQUIPMENT So far we have only addressed cryogenic refrigeration and liquefaction through thermodynamics, i.e. through the exchanges of mass, heat and work at the boundaries of machines seen as ―black boxes‖. We will now consider cycles, cooling methods and equipment of real refrigerators. In order to minimize the specific mechanical work requirement (and hence the size and power consumption), an efficient refrigerator should try and approximate the Carnot cycle, which is represented by a rectangle on the temperature-entropy diagram: the two isotherms are horizontal lines, while the two isentropic transforms are vertical lines. To liquefy helium, the base of the rectangle 10

should intercept the liquid-vapor dome (Figure 14). However, superimposing this cycle on the temperature-entropy diagram of helium shows that one should operate at a high pressure of about 613 kbar (!), with a first isentropic compression from 1.3 bar to 82 kbar (!), followed by an isothermal compression. This is clearly impractical, and real helium cycles are elongated along isobar (or isochoric) lines, thus involving transforms which require heat exchange between the high- and low-pressure streams. This heat exchange can be performed in recuperative or regenerative heat exchangers, respectively for continuous or alternating flows. In the following, we focus on the continuous-flow cycles using recuperative heat exchangers which constitute the operating principles of largecapacity helium refrigerators and liquefiers.

Figure 14 A hypothetical Carnot cycle for helium liquefaction

Practical elementary cooling processes are shown on the temperature-entropy diagram in Figure 15. The gas stream can first undergo quasi-isobar cooling in a counterflow heat exchanger (segment AB1): modern refrigerators make use of brazed aluminum plate heat exchangers. Refrigeration can be produced by adiabatic (quasi-isentropic) expansion with extraction of mechanical work (segment AB’2): the expansion engine is a gas turbine, with the extracted power transmitted to a compressor wheel sharing a common shaft and later dissipated in a brake circuit. A third process is isenthalpic JouleThomson expansion, i.e. without extraction of mechanical work, in a valve or restriction (segment AB3).

Unfortunately, this latter process does not does work for ideal

gases, the enthalpy of which is a sole function of temperature. For real gases, however, enthalpy depends both on temperature and pressure, so that isenthalpic expansion can 11

produce warming or cooling, depending upon the slope of the isenthalps on the diagram. In order to cool the gas stream, Joule-Thomson expansion must start below a limit called the inversion temperature. The values of inversion temperature for cryogenic fluids (Table 10) show that while air can be cooled from room temperature by Joule-Thomson expansion (the risk of freezing the pressure reducer on the air bottle is well known to scuba divers), helium must first be pre-cooled down to below its inversion temperature of 43 K. The moderate downward slope of isenthalps on the temperature-entropy diagram indicates that in any case, Joule- Thomson expansion generates substantial entropy. Its relative inefficiency with respect to adiabatic expansion is however accepted in view of the simplicity of its implementation, particularly when it results in partial condensation of the stream entailing two-phase flow conditions which would be difficult to handle in an expansion turbine. Cryogen

Maximum inversion temperature [K]

Helium

43

Hydrogen 202

202

Neon 260

260

Air 603

603

Nitrogen 623

623

Oxygen 761

761

12

These elementary cooling processes are combined in practical cycles, a common example for helium refrigeration is provided by the Claude cycle and its refinements. A schematic two-pressure, two-stage Claude cycle is shown in Figure 15: gaseous helium, compressed to HP in a lubricated screw compressor, is re-cooled to room temperature in water-coolers, dried and purified from oil aerosols down to the ppm level, before being sent to the HP side of the heat exchange line where it is refrigerated by heat exchange with the counter-flow of cold gas returning on the LP side. Part of the flow is tapped from the HP line and expanded in the turbines before escaping to the LP line. At the bottom of the heat exchange line, the remaining HP flow is expanded in a Joule-Thomson valve and partially liquefied. Large-capacity helium refrigerators and liquefiers operate under this principle, however with many refinements aiming at meeting specific cooling duties and improving efficiency and flexibility of operation, such as three- and sometimes four-pressure cycles, liquid nitrogen pre-cooling of the helium stream, numerous heat exchangers, many turbines in series or parallel arrangements, Joule-Thomson expansion replaced by adiabatic expansion in a ―wet‖ turbine, cold compressors to lower the refrigeration 13

temperature below 4.5 K. A view of such a large plant appears in. The capital cost of these complex machines is high, but scales less than linearly with refrigeration power, which favors large units. Operating costs are dominated by that of electrical energy, typically amounting to about ten percent of the capital cost per year in case of quasi continuous operation. For overall economy, it is therefore very important to seek high efficiency, which is also easier to achieve on large units. For a review of these aspects, see reference [6].

Figure 15 Schematic example of two-pressure, two-stage Claude cycle: T-S diagram (left) and flow scheme (right)

4. DEVELOPMENT IN CRYOGENICS.  Pioneering work in low-temperature Physics by the British chemists Sir Humphrey Davy and Michael Faraday, between 1823 and 1845, prepared the way for the development of cryogenics. Davy and Faraday generated gases by heating an appropriate mixture at one end of a sealed tube shaped like an inverted V. The other end was chilled in a salt-ice mixture. The combination of reduced temperature and increased pressure caused the evolved gas to liquefy. When the tube was opened, the liquid evaporated rapidly and cooled to its normal boiling 14

point. By evaporating solid carbon dioxide mixed with ether, at low pressure, Faraday finally succeeded in reaching a temperature of about 163 K (about 110°C/-166°F).  The temperature of a gas that is allowed to expand can increase or decrease depending on the initial temperature of the gas. The special temperature at which a particular gas will cool down instead of heat up when it expands is called the inversion temperature. If a gas initially at a moderate temperature is expanded through a valve, its temperature increases. But if its initial temperature is below the inversion temperature, the expansion will cause a temperature reduction as the result of what is called the Joule-Thomson effect.  The person considered by most to be the originator of modern experimental science, Francis Bacon, died as a result of a spontaneous experiment he was conducting on the effects of low temperatures. In 1623, while traveling on a cold and snowy day, Bacon decided to .experiment. to see whether snow would delay the purifications of flesh. He stuffed a fowl to know its effects. In ,the process, he caught a sudden chill. Over the years, this turned into acute bronchitis, which contributed to his death in 1626.well.from there it started.  Sir Humphry Davy and Michael Faraday carried out pioneering work in low temperature physics between 1823 and 1845. They used an inverted V-tube, one end of which was chilled in a salt ice mixture and the other end had appropriate mixture for generating required gases. Due to lower temperature and high pressure, the gas liquefies and when released, succeeds giving temperatures as low as 163K(that is .110*C or-166*F)  French physicist Louis Paul Callitet and the Swiss scientist Raoul Pierre Pictet, using the cascading of Joule Thompson effect, were able in 1877 to produce droplets of liquid oxygen; which thereby marked the end of the idea of permanent gases.  Dutch physicist Heike Kamerlingh Onnes set up the first liquid air plant in 1894, using the cascade principle. The British chemist James Dewar liquefied hydrogen in 1898 and Kamerlingh Onnes liquefied Helium, the most difficult of gases to liquefy, in 1908.the work of Soviet physicist Peter Leonidovich Kapitza and American mechanical engineer Samuel Collins has been noteworthy.

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 The next Japanese infrared space telescope SPICA features a large 3.5-m-diameter primary mirror and an optical bench cooled to 4.5 K with advanced mechanical cryocoolers and effective radiant cooling instead of using a massive and shortlived cryogen system. To obtain a sufficient thermal design margin for the cryogenic system, cryocoolers for 20 K, 4 K, and 1 K have been modified for higher reliability and higher cooling power. The latest results show that all mechanical cryocoolers achieve sufficient cooling capacity for the cooling requirement of the telescope and detectors on the optical bench at the beginning of life.[4]

5. CRYOGENIC TECHNOLOGIES The evaporation of liquid helium at reduced pressures produces temperatures as low as 0.7 K (-272.44°C/-458.4°F). Still-lower temperatures can be attained by adiabatic demagnetization. This procedure requires that a magnetic field be established around a paramagnetic substance, that is, a substance made of paramagnetic ions, while the substance is cooled in liquid helium. The field aligns the ionic magnets and later, when the field is removed, the tiny magnets resume their random alignments, reducing the thermal energy of the whole sample in the process. The temperature, therefore, falls to levels as low as 0.002 K (-273.15°C/-459.67°F). Similar alignments of atomic nuclei that have periods of magnetization followed by removal of the magnetic field have produced temperatures close to 0.00001 K. To reach temperatures closer to absolute zero, techniques using magnetic fields, lasers, and radio waves can be used. In one approach, gases of atoms are confined by a magnetic field. Multiple laser beams are used to cool the atoms in the gas by first exciting the electrons, which then emit photons that carry energy away from the atoms. After the gas has been placed in a much stronger magnetic trap, radio waves can then be used to selectively remove the highest-energy atoms, leaving only atoms at the lowest energy state. Another technique is to trap atoms or molecules in a ―box‖ of laser light. Two additional lasers can be used to create an optical wall that confines the atoms or molecules on one side of the laser light box. The space that holds the atoms and

16

molecules can be expanded and contracted with the lasers, lowering the temperature with no addition of heat. Different types of cryogenic refrigeration devices (commonly called cryocoolers) have been developed for use in industry, in military and space technology, and in scientific research. Most of these devices use the expansion of gases or fluids to draw away heat. Among the most widely used cryocoolers are Stirling cryocoolers, which work with the aid of a compressor. However, moving mechanical parts can cause vibrations and wear. Another design called a pulse tube cryocooler eliminates most moving parts that cause friction and wear, and uses acoustic power in an oscillating gas system. Research is under way to develop more efficient and compact pulse tube cryocoolers. For storing liquids at cryogenic temperatures, Dewar flasks have proved useful. Such vessels consist of two flasks, one within the other, separated by an evacuated space. The outside of the inner flask and the inside of the outer flask are both silvered to prevent radiant heat from passing across the vacuum. Substances colder than liquid air cannot be handled in open Dewar flasks because air would condense in the sample or form a solid plug to prevent escape of released vapors; the accumulated vapors would eventually rupture the container. Devices used to maintain substances or objects at cryogenic temperatures are call cryostats. Measurement of temperatures in the cryogenic range presents problems. One procedure is to measure the pressure of a known quantity of hydrogen or helium, but this procedure fails at the lowest temperatures. The vapor pressure of helium-4, that is, helium of atomic mass 4, or of helium-3 (atomic mass 3) supplements the preceding method. Determinations of the electrical resistance of metals or semiconductors and their magnetic measurements extend the range still further. Available devices include cryogenic thermometers that use semiconductor film materials and diode temperature micro sensors.[4]

6. CHANGE IN CRYOGENIC PROPERTIES AT CRYOGENIC TEMPERATURE At cryogenic temperatures many materials behave in ways unfamiliar under ordinary conditions. Mercury solidifies and rubber becomes as brittle as glass. The 17

specific heats of gases and solids decrease in a way that confirms the predictions of quantum theory. The electrical resistance of many, but not all, metals, metalloids, and some metal alloys decreases abruptly to zero at temperatures below 23 K, a property called superconductivity. If an electric current is introduced into a ring of metal that has been cooled to the superconductive state, it will continue to travel around the ring and may be detected hours later. Since the discovery of the first so-called high-temperature superconductor in 1986, researchers have identified a number of ceramic compounds containing copper-oxide that become superconducting at temperatures as high as 125 K. The ability of a superconductive material to retain current has led to experiments for constructing computer memory modules that would operate at these low temperatures. The behavior of helium at low temperatures is remarkable in a number of ways. The two stable isotopes of helium, helium-4 (2 protons + 2 neutrons) and helium-3 (2 protons + 1 neutron), show unusual properties at different temperatures. Both isotopes remain liquid even after the most extreme cooling. To solidify helium-4 it is necessary to subject the liquid to a pressure in excess of 25 atmospheres. Liquid helium-4 changes, furthermore, to a super fluid state at temperatures below 2.18 K (-270.97°C/-455.75°F). In this state its viscosity appears to be nearly zero. It forms thick films on the surface of the containers, and helium flows through the film without resistance. Theory still fails to account fully for this behavior. Helium-3 does not exhibit super fluidity unless its temperature is reduced even further, to less than 0.00093 K (-273.15°C/-459.67°F). One of the most dramatic achievements in cryogenic research has been the creation of Bose-Einstein condensates. When a gas of atoms that are composite bosons (atoms with even numbers of protons and neutrons in the nucleus) is confined in a magnetic field and cooled to extremely low temperatures using lasers and radio waves, some of the atoms in the gas can take on the same quantum state and behave together like a single giant particle. This special state of matter was predicted by the physicists Albert Einstein and S. N. Bose. Researchers have also created a related low-temperature quantum phenomenon call a fermionic condensate. Atoms in a gas that are composite fermions (atoms with an odd number of protons and neutrons in the nucleus) 18

form pairs and behave like bosons. Like the atoms in a Bose-Einstein condensate, the atoms in a fermionic condensate can then ―condense‖ into the same quantum state.[5]

7. APPLICATION IN CRYOGENICS Among the many important industrial applications of cryogenics are the largescale production of oxygen and nitrogen from air. The oxygen can be used in a variety of ways, for example, in rocket engines, for cutting and welding torches, for supporting life in space and deep-sea vehicles, and for blast furnace operations. The nitrogen goes into the making of ammonia for fertilizers, and it is used to prepare frozen foods by cooling them rapidly enough to prevent destruction of cell tissues. It can also serve as a refrigerant and for transporting frozen foods. Cryogenics has also made possible the commercial transportation of liquefied natural gas. Without cryogenics, nuclear research would lack liquid hydrogen and helium for use in particle detectors and for the powerful electromagnets needed in large particle accelerators. Such magnets are also being used in nuclear fusion research. Infrared devices, masers, and lasers can employ cryogenic temperatures, as well. Cryogenic cooling

is

often

used

in

space

telescopes that

observe

objects

in infrared

and microwave wavelengths. More efficient and compact cryocoolers allow cryogenic temperatures to be used in an increasing variety of military, medical, scientific, civilian, and commercial applications, including infrared sensors, superconducting electronics, and magnetic levitation trains. Bose-Einstein condensates and fermionic condensates are useful for scientific research into quantum phenomena such as super fluidity and superconductivity. Such unusual states of matter may also lead to quantum computing and devices such as atomic lasers. Chemical reactions and other properties of molecules can also be studied at cryogenic temperatures. Cryogenic temperatures are also used in cryobiology—the study of life and life processes at very low temperatures. Cryobiology includes cold temperatures used in 19

medicine and surgery, as well as the cryogenic preservation of biological and medical materials. One of the important uses of cryogenics is cryogenic fuels. cryogenic fuels, mainly oxygen and hydrogen, has been used as rocket fuels. For example ,NASA’s Work Horse. space shuttle uses cryogenic oxygen and hydrogen fuels as its primary means of getting into orbit, as did al of the rockets built for the Soviet .s space program by Sergei Korolev.

Rocket fuels or rocket propellants are a mixture of fuel and oxidizer. Basing on the state, propellants are divided into three types: A. Solid propellants: These are the simplest of propellants. They have both fuel and oxidizer in solid form. These have a variety of uses. The Titan, Delta and Space Shuttle launch vehicles use strap-on solid propellant rockets to provide added thrust to rockets. B. Liquid propellants: In such, fuel and oxidizer are stored in separate tanks and fed through a system of pipes, valves and turbo pumps to a combustion chamber where they are combined and burned to produce thrust. These are more complex than solid propellants but can be controlled better. NASA’s I stage Saturn 1-B and Saturn V, Atlas/Centaur launch vehicles and few others have used these propellants. C. Hybrid propellants: These make use of both solid and liquid propellants (generally solid fuel and liquid oxidizer) for combustion. These are very complex and engines supporting these are very rarely built. Industrial Applications: Cryogenic treatment renders stronger and more wear resistant metal. Cryogenic treatment works on reamers (both carbide or HSS), tool bits, tool punches, carbide drills, carbide cutters, milling cutters, files, shaping equipments, scissors, razors, clippers, knives, band saw blades, saw blades, reciprocating blades, Saber saw, form tooling cutting tools and dies. 20

Increase your automobile’s life: How much is the average engine life of an automobile, Say 18 yrs.20.25 years? Would u like to make it to about 90 years? Imagine a racer and crew who would normally tear down their engine after every race or two, suddenly discovering a process that would allow them safely go up to 30 races or more without any major rebuild. Yes, this is verily possible by cryogenic treatment of automotive parts. This can be achieved by deep cryogenic tempering of the engine parts. Super Conductivity: Almost total lack of electrical resistance is observed in certain materials when they are cooled to a temperature near absolute zero. Super conducting materials allow low power dissipation, high speed operation, and high sensitivity. When an electric current is passed in a super conducting metal ring, the current may travel for hours without being detected. These super conductors also have the ability to prevent external magnetic fields from penetrating their interiors and are perfect diamagnetism. This property was first discovered in 1911 by Kamerlingh Onnes in mercury. Since then they have found its application in medical imaging, magnetic energy storage systems, motor generator, transformers, computer components and sensitive magnetic field Measuring devices. Industrial Applications: Cryogenic treatment renders stronger and more wear resistant metal.cryogenic treatment works on reamers (both carbide or HSS), tool bits, tool punches, carbide drills, carbide cutters, milling cutters, files, shaping equipments, scissors, razors, clippers, knives, band saw baldes, saw blades, reciprocating blades, Saber saw, form tooling cutting tools and dies.[6]

8. CASE STUDY DEVELOPMENT OF CRYOGENIC FUEL AIRCRAFT In mid-1970-s of previous century energy strategic dominated in the USSR according to which all atomic energy was supposed to be utilized first while oil and gas should have been considered of minor importance in view of small resources as they erroneously believed at that time. Realization of Hydrogen Energy Program started. Tupolev’s specialists were involved in the Program. As it used to happen many times in the background of our company – Alexey Tupolev took a courageous decision - to build 21

―Hydrogen‖ aircraft. Such aircraft was built and successfully tested without any serious incidents. It was preceded by a long-term Program of bench and ground tests intended for testing functioning of new systems (such systems were more than 30 on the aircraft) and mainly for providing safe operation. Unfortunately mentioned above energy strategy turned to be not very correct.

Atomic energy has not become dominating. It was natural gas that turned to be of paramount importance in the Energetic Program of our country. The content of natural gas exceeds 50% of energy balance. That’s why our flying laboratory having status of experimental TU-155 a/c was modified to use not only liquid hydrogen but also to use Liquefied Natural Gas (LNG). This is how the first in the world Cryogenic Aircraft was built. Remarkable properties of liquid hydrogen as aviation fuel and first of all its high ecological cleanliness, high heat of combustion and high cooling capacity attracted attention of aviation specialists to this type of fuel. Liquid hydrogen allows to improve aircraft performance significantly, to build aircraft operating at speeds of M>6. Therefore our activities on liquid hydrogen served as a scientific and technological work done which will be used in near-term outlook. However extremely high price of liquid hydrogen makes its commercial use impossible for a long time. If to speak about near future tomorrow task is to introduce LNG as aviation fuel which was reflected in

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―Program on development of Russian civil aviation for the period from 2002 to 2010 and for the period till 2015‖.

Oil shortage is growing. During previous 25 years specific weight of oil in worlds energy balance decreased by more than 10% .Currently price of kerosene is 8000 rubles per tone, LNG price is 3000 rubles per ton. Benefit makes 5000 rubles per each tone of replaced kerosene. The benefit is likely to grow constantly according to opinion of many specialists. Recently some special scientific ―explosion‖ happened in the world and especially in Russia that provoked a vision that traditional and non-traditional resources of natural gas can be increased by an order magnitude greater and exceed total amount of traditional fossil fuel on earth. Natural gas is supplied to substantially each airfield via pipelines i.e. transportation issues have been practically solved now. Its high energy capacity, huge cooling capacity makes it possible to build aircraft with significantly high performance in comparison with aircraft using kerosene. Fuel efficiency of flight using LNG can make 10 g/pass, km. When using LNG potential emission of toxic agents will be decreased as follows: carbon monoxide – 1 – 10 times, hydrocarbons – 2.5 – 3 times, nitrogen oxides – 1.5 – 2 times, polycyclic aromatic hydrocarbons including benzapyrene – 10 times Tupolev‖ PSC elaborated Cryogenic Aircraft Manufacturing Program. On the first phase of this Program TU-156 a/c was built. Cargo-passenger TU-156 a/c was 23

designed for optimization of airborne cryogenic fuel system during long-term operation and its certification and also for optimization of ground infra-structure. Cryogenic components of the aircraft will be installed on consequent serial Tupolev’s cryogenic aircraft. The aircraft uses two fuels: aviation kerosene and liquefied natural gas which makes it possible to operate the aircraft from usual airfields and from airfields provided with LNG fueling systems. Use of two fuels improves flight safety level significantly. TU-156 a/c is capable to carry 14 t of payload for distance 2600 km using LNG and for distance of 3300 km using LNG and kerosene. In rear portion of passenger cabin there is a ventilated compartment to receive a main cryogenic tank of 13 t capacity. Nose baggage compartment is provided with ventilated bay wherein trim cryogenic fuel tank is installed composed of two horizontal communicating vessels capable to receive 3.8 tonesof LNG.[7]

9. FUTURE OF CRYOGENICS Though a lot of work and research has been done in the field of cryogenics a lot, more is needed to be done. The inherent disadvantage of cryogenic process is the heavy cost which needs to be incurred in the equipment and the costs of the process itself. Future use of superconductivity system is proposed for high speed rail transport. If research in this field is successful it will be revolutionize the land transport systems. Another field where cryogenics can play a vital role is that of automobile field. With the increasing cost of hydrocarbons and the possibility that their reserves may soon be exhausted hydrogen presence an excellent alternative from all consideration including the fact that it does not produce any pollution on combustion. If hydrogen becomes the fuel of the future it will have to be store in the liquid state thus giving cryogenics an undreamed future. Also the application in medicine and biology will have far reaching effects on the society. The use of artificial insemination in cattle is made possible by cryogenics which is beyond doubt a boon to the villagers in our country helping them become stronger socially and economically. A similar technology to freeze the human sperms and able to thaw it successfully after maintaining it in the frozen condition for many years is possible with cryogenics. 24

10. CONLUSION Cryogenics hence is a branch of science dealing with extremely low temperatures and treatment of materials at such temperatures. Cryogenics can be applied to almost everywhere in every field. It finds its application in military, tooling industry, agricultural industry, aerospace, medical, recycling, household, automobile industry, cryogenics is found to improve the grain structure of everything treated be it metal or plastic or coils or engines or musical instruments or fiber. Cryogenics has helped the field of science by helping produce liquefied hydrogen and helium for various important researches and inventions. it helped the aerospace industry by helping gather numerous helpful data about outer space accurately. Cryogenics has also been helpful to biologists trying to find solutions to storage and treatment of organisms. In spite of all these achievements and advances, Cryogenics promises to be a field with lots of scope of improvement. As the temperature lowers further towards absolute zero, newer discoveries are bound to emerge. This field could be put to many other applications in various fields. Its reaches in the mentioned industries hold a good chance of extension. Hence Cryogenics proves to be very promising for the future in this world of materials.

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11. REFERENCES (1) Oxford English Dictionary, 2nd edition, Oxford University Press (1989). (2) New International Dictionary of Refrigeration, 3rd edition, IIR-IIF Paris (1975). (3) Ph. Lebrun & L. Tavian, The technology of super fluid helium, CERN-2004-008, Geneva (2004) 375. (4) http://encarta.msn.com/encyclopedia_761563758_1/Cryogenics.html (5) http://encarta.msn.com/encyclopedia_761563758_2/Cryogenics.html (6) S. Claudet et al., Economics of large helium cryogenic systems: experience from recent Projects at CERN, Adv. Cryo. Eng. 45B (2000) 1301. (7) http://www.tupolev.ru/English.pdf (8) http://pdf-searchengine.com/ (9) http://pdfcoke.com/engineering/cryogenic.html (10)

http://www.cryogenicsindia.com/

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ACKNOWLEDGMENT

I Avail this opportunity to thank all those people who helped me in making this seminar report a success. I would especially like to extend my grateful thanks to Prof. M.S.Sadare (seminar guide), who helped and enlightened me in every possible way. I am indebted to him for bringing order to this report out of the chaos that was many times presented to him. I would like to express my respect, deep gratitude and regards to Prof A.K.MISHRA (H.O.D. Mechanical Department) for his support.

GODSE MILIND SURESH [TE MECHANICAL]

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