vtu cryogenics notes unit 1 introduction to cryogenic systems

Cryogenics [email protected]

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UNIT - 1

Introduction To Cryogenic Systems

Cryogenics: The branches of physics and engineering that study very

low temperatures (below −150 °C, −238 °F or 123 K) and the

behavior of materials at those temperatures.How to produce them, and

how materials behave at those temperatures. A person who studies

elements that have been subjected to extremely cold temperatures is

called a cryogenicist.

Cryogenic fluids or Cryogens: There are different cryogenic fluids

like liquid nitrogen (LN� ), liquid helium (LHe), liquid hydrogen

(LH�), liquid neon, liquid oxygen (LOX) etc.

Cryogenics is derived from greek word kryo which means very cold;

and genics means to produce (production of icy cold). So, basically

cryogenic means, science and technology associated with generation

of low temperature below 123K (kelvin).


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However, the location on the temperature scale at which refrigeration

generally ends and cryogenics begins has never been well 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 (220°R).

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 (above fig). Cryogenic engineering therefore is

involved with the design and development of low-temperature

systems and components. In such activities the designer must be

familiar with the properties of the fluids used to achieve these low

temperatures as well as the physical properties of the components

used to produce, maintain, and apply such temperatures.

123K is the dividing line between cryogenics and refrigeration. You

can see the gases under the title cryogenics which got their boiling

points below 123 K, and on the right side of these dividing line you

can see refrigerants having boiling points above 123K.

Cryogenics = below 123 K.


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Refrigeration = above 123K below the room temperature.

All the gases in the left side were earlier called as permanent gases. It

was thought that these gases could never be liquefied. Some tried to

liquefy those gases at room temperature by pressurizing these gases.

If you pressurize them at room temperature to a very high pressure of

300 to 400 bar, these gases will not get liquefied, so, you have to use

some different techniques to go below the room temperature and then

liquefy these gases.

Rather than the relative temperature scales

Note:

Relationship between Fahrenheit and Celsius scales of

temperature:

°�� =

°�� or

°� =

°��

°� = � (°� – 32)

°� = � (°� +32)

Kelvin, K = °�+273 or °� = K – 273

Importance of Cryogenics:

• Cryogenics is important because rocket fuel (oxygen and

hydrogen) must be loaded in as liquids at cryogenic

temperatures.

• Cryogenics is also important for attaining super-conduction and

for cryogenic tempering of metals for hardening.

• Cryogenics finds its application in good preservation of body

tissues by cooling and vitrification, future science will be

required to cure presently incurable diseases and to rejuvenate

elderly people to a youthful condition.

• Deep cryogenic processing is different from conventional

cryogenic processing and requires cooling the parts to more than


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300° below zero compared to about 120° for conventional

cryogenic processing. Deep cryogenic processing is a

microprocessor controlled dry process, which includes cooling

the parts at a programmed rate. Soaking the parts for up to 36

hours, and then an additional tempering operation to relieve any

stress that may remain. During heat treating, steel’s micro-

structure transforms from austenite to martensite, which makes

the steel much more wear resistant. However, some small

pockets of austenite may not transform and this does not allow

the knives to perform as well as they can. Deep cryogenic

processing helps change retained austenite to martensite,

completing the transformation process.

• Cryogenic processing: Cryogens, like liquid nitrogen, are further

used for specialty chilling and freezing applications. Some

chemical reactions, like those used to produce the active

ingredients for the popular ststin drugs, must occur at low

temperatures of approximately -100°C (about -148°F). special

cryogenic chemical reactors are used to remove reaction heat

and provide a low temperature environment. The freezing of

foods and biotechnology products, like vaccines, requires

nitrogen in blast freezing or immersion freezing systems.

Certain soft or elastic materials become hard and brittle at very

low temperatures, which make cryogenic milling (cryomilling)

an option for some materials that cannot easily be milled at

higher temperatures.

Chronology of cryogenic technology:

1848 John Gorrie produces first mechanical

refrigeration machine.

1857 Siemens suggests recuperative cooling or

‘‘self-intensification’’.

1866 Vander Waals first explored the critical point,

essential to the work of Dewarand Onnes.

1867 Henry P. Howard of San Antonio Texas uses

Gorrie’s air-chilling system totransport frozen

beef from Indianola TX to cities along the Gulf


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of Mexico.

1869 Malthusian revolution in England, predicting

worldwide starvation.

1872 Carl von Linde liquefies air using Joul-

Thomson Expansion principle and regenerating

cooling.

1873 James Harrison attempts to ship frozen beef

from Australia to the UK aboardthe SS

Norfolk., the project failed.

1875 Thomas Mort tries again to ship frozen meat

from Australia to the UK, this timeaboard the

SS Northam. Another failure. Gorrie’s air

system eventuallyproduce success by Bell and

Coleman 1877.

1877 Coleman and Bell produce commercial version

of Gorrie’s system for freezingbeef. The frozen

meat trade becomes more successful and stems

the Malthusianrevolution.

Paul Cailletet and Raoul Pictet liquefied

oxygen. This was really the beginning of

“cryogenics” as an area separate from

“refrigeration.”

1884 Wroblewski (Kracow University, Poland) first

liquefied hydrogen as a mist.

1892 Sir James Dewar (England) developed the

vacuum-insulated vessel for storage of

cryogenic fluids.

1895 Heike KamerlinghOnnes (Holland) established

the Leiden Cryogenic Lab, and Karl von Linde

(Germany) obtained a basic patent for air

liquefaction.

1898 James Dewar produced liquid hydrogen by

Regenerative cooling technique at the Royal

Institute of London.

1902 Georges Claude developed the first air-


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liquefaction system using an expansion engine.

1905 Linde obtains pure oxygen and nitrogen.

1908 H. KammerlinghOnnes first liquefied helium–

the last of the so-called “permanent gases” to

be liquefied.

1911 H.Kammerlingh. Onnes discovered

superconductivity.

1916 First commercial American-made air

liquefaction plant completed.

1922 First commercial production of neon in the

United States.

1926 Robert Goddard conducted the world’s first

successful flight of a rocket powered by

cryogenic (liquid) oxygen and non-cryogenic

gasoline propellant.

1933 Magnetic cooling used to reach temperatures

below 1K.

1934 Peter Kapitza built the first expansion engine

for a helium liquefier.

1939 First vacuum-insulated railway tank car built

for transport of liquid oxygen.

1947 The Collins cryostat developed for liquefaction

of helium.

1952 National Bureau of Standards Cryogenic

Engineering Laboratory established in Boulder,

Colorado.

1957 Atlas ICBM powered by LOX/RP-1 was test

fired. Fundamental theory (Bardeen-Cooper-

Schrieffer or BCS theory) of superconductivity

presented.

1958 Multilayer insulation (MLI) developed.

1961 Saturn launch vehicle, powered by liquid

oxygen and liquid hydrogen, was test-fired.

1966 He3/He4 dilution refrigerator developed.


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1969 3250-hp dc superconducting motor constructed

for ship drive application.

1970 Liquid oxygen plants with capacities between

60,000 m�/h and 70,000 m�/h developed.

1973 B. D. Josephson, I. Giaever, and L. Esaki

awarded the Nobel prize for discoveryof the

Josephson Junction (tunneling supercurrents).

1978 Peter Kapitzareceive the Nobel for the

characterization of HeII as a superfluid.

1986 Georg Bednorz and Alex Muller discover high-

transition-temperature ceramic superconductor

with a Tc of about 30K.

1987 Paul Chu (Univ. of Houston) and Maw-Kuen

Wu (Univ. of Alabama at Huntsville) develop

the 1-2-3 yttrium based high-Tc superconductor

with a Tc of about 90K.

J. G. Bednorz and K. A. Mueller awarded the

Nobel Prize for discoveringhigh-temperature

superconductorsY–BA–Cu–O ceramic

superconductors found.

1996 D. Lee, D. D. Osheroff, and R. C. Richardson

receive the Nobel prize of thediscovery of

superfluidity in helium-3

1997 S. Chu and Claude Cohen-Tannoudji awarded

the Nobel prize for discovering methodsto cool

and trap atoms with lasers.

1998 R. B. Laughlin, H. L. Stormer, and D. C. Tsui

receive the Nobel prize for discovering anew

form of quantum fluid excitations at extremely

low temperatures.

2001 Eric A. Cornell, Wolfgang Ketterleand Carl E.

Wiemanawarded the Nobel prize for achieving


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theBose–Einstein condensate at near absolute

zero.

2003 Alexei A. Abrikosov, Vitaly L. Ginzburg and

Anthony J. Leggettawarded the Nobel prize"for

pioneering contributions to the theory of

superconductors and superfluids".

Liquid nitrogen, liquid oxygen and liquid helium are by far the most

widely used cryogens andare delivered at door steps. LO2 is used in

steel factories and hospitals. LN2 is widely used inFertilizer Plants

and as a pre-cooling cryogen wherever LH2 and LHe are used. LO2

and LN2are either stored in large vessels and are filled on site. Large

size captive plants are installedwhere the usage is on a large scale.

Cryogenics in India:

Cryogenics became a buzz word with common man in India in 1990s

when ISRO (Indian Space Organization) was denied the supply of

Cryogenic Engine by Russia. It’s history in the country is, however,

quite old. Great scientist and a visionary, Sir K.S. Krishnan, the

Founder Director, National Physical Laboratory acquired a helium

liquefier and established a competent group of physicists to start

studies at low temperature down to 1 Kelvin. This culture of low

temperature studies soon spread to other reputed institutes like TIFR

Bombay, IISc. Bangalore , DAE Centres, IITs and Universities. This

community, under the leadership of Prof. Akshay Bose of Jadavpur

University, formed Indian Cryogenic Council (ICC) in 1975 with its

Head Quarter at Jadavpur University, Kolkata..

During 1980s use of cryogenic grew rather rapidly in application

areas. NMR and MRI were the biggest promoter of the use of liquid

helium. Production and use of liquid nitrogen (LN2) and liquid

oxygen (LO2) saw a phenomenal growth primarily because of large

expansion in fertilizer and hospital industry respectively. Research

institutions chalked out big projects, such as Accelerators at IUAC,

New Delhi and TIFR Bombay, Fusion Reactor (SST-1) at IPR,


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Gandhinagar and Superconducting Cyclotron at VECC, Kolkata.

These projects injected new blood in to the cryogenic activities in the

country. Production of LHe and LN2 grew leaps and bound. Young

scientists and engineers got involved in designing and fabricating

complicated cryostats, large superconducting coils and magnets and

superconducting cavities and so on. These projects are bearing fruits

now.

Chronology of cryogenic technology in India:

Year Development

1924 theory of the Bose–Einstein condensate.

A Bose–Einstein condensate (BEC) is a state of

matter of a dilute gas of bosons cooled to

temperatures very close to absolute zero (that is,

very near 0 K or −273.15 °C). Under such

conditions, a large fraction of bosons occupy the

lowest quantum state, at which point macroscopic

quantum phenomena become apparent.

This state was first predicted, generally, in 1924–

25 by SatyendraNath Bose and Albert Einstein.

The class of particles that obey Bose–Einstein

statistics, bosons, was named after Bose by Paul

Dirac.

1930’s Cryogenics, however, started in India when a

British company installed an Oxygen Plant.

1935 Indian oxygen company (INOX) was started air

separation plants.

1938 IOL(now called BOC India Ltd.) established first

air separation plant (30 ��/hr) at Jamshedpur.

Note: Today Air Separation Plants of capacities of

more than 1000 Tons / per day are being

manufactured by several Indian

and Multinational Companies in the country.

1941 asiatic oxygen in collaboration with Air products


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of USA established Air separation plant at

Howrah.

1952 National Physical laboratory was the first in India

to have acquired a liquid Helium Plant of capacity

4 litres/ hr.

1953 Indian Association for the Cultivation of Sciences

(IACS), Kolkata started low temperature research

in 1953 by Prof. A. Bose.

1960s

1962 Tata Institute of Fundamental

Research (TIFR), Bombay got its helium liquefier

1966 Solid State Physics

Laboratory (SSPL), Delhi and the University of

Delhi got its helium liquefier

1970s Bhabha Atomic Research Centre

(BARC), Bombay, Indira Gandhi Centre for

Atomic Research (IGCAR), Kalpakkam, Indian

association for the Cultivation of Science (IACS)

Kolkata and Indian Institute of Sciences

(IISC), Bangalore, established the liquid helium

facility

1976 A Philips helium liquefier, PL He-210 with a

capacity of 10 l / hr was installed First

Superconducting

NMR unit was installed at IISc. Bangalore

1977 - 78 Indira Gandhi Centre for Atomic Research

(IGCAR), KalpakkamIts Material Science

Division (MSD) started low temperature research

facility in the year 1977-

78 by acquiring a Koch Process helium liquefier

of 10 l /hr capacity (with LN2 pre cooling). The

facility has been used for the characterization of a

variety of materials with respect to their

properties down to 4.2 K. Since around 1990 the

group developed the technology of making Nb

based Josephson junctions which led to the

development of SQUID magnetometer based


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NDT

(Non Destructive Testing) set up.

1980s The use of liquid helium spread during 1980s due

to the popularity of high resolution Nuclear

Magnetic Resonance (NMR) Spectrometers which

invariably use superconducting magnets and

need liquid helium for operation. NMR

Spectrometer is a powerful tool for the study of

the

structures of complex molecules and is widely

used as an analytical tool in Physical, Chemical,

Biological and Pharma Laboratories.

1982 the Department of Science

and Technology (DST) declared Cryogenics as a

Thrust Area Programme and supported

cryogenic activities in the country in a significant

way.

1986 First Superconducting MRI in India was installed

at INMAS, New Delhi

1986 A private industry (Pure Helium) started

importing large quantities of liquid helium in ship

tankers and

selling liquid helium to all these NMR and MRI

units and helium gas to research laboratories to

run their liquefiers. This easy availability of liquid

helium within the country encouraged more

and more hospitals to install MRI units. The

Pharma and Petrochemical Sector too started

buying

high frequency NMR units


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1980 – 1990 s BARC established a full

flagged facility to develop multifilamentary Cu-Ti

wire. BARC also designed 1000 A Nb-Ti

cable for use in Superconducting Cyclotron and

presently engaged in developing Nb3Sn

conductor for being used for fusion reactor. At the

same time NPL developed next generation

multifilamentary superconductors, namely, Nb3Sn

and V3Ga on a laboratory scale. NPL team

made many 7 T and 11 T superconducting

magnets and supplied to other institutions.

BHEL

(Bharat Heavy Electricals Ltd.) Hyderabad in

collaboration with NPL produced India’s first

Superconducting High Gradient Magnetic

separator (SC-HGMS). BHEL also developed a

200

KVA superconducting generator in collaboration

with NPL, IISC etc. Both of these were the first

ever industrial applications of superconductivity

in the country.

Large scale use of cryogenic liquids, namely,

liquid hydrogen and liquid oxygen started in India

by ISRO to boost their geo-synchronous satellite

launch vehicle programme. This Launch vehicle

in its final stage has a cryogenic engine using

hydrogen as fuel and oxygen. as an oxidizer.

Liquid Propulsion Space Centre at Valiamala and

Mahendrogiri is dedicated for

this Cryogenic Engine Development Programme.

Remarkable facilities for the design,

development and testing of Cryogenic Engine

have been established at the Centre. More than


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200 Scientists, Technologists and Technicians are

working at this centre.

1990s The projects initiated were particle accelerators at

Nuclear

Science centre (now IUAC), at New Delhi and at

TIFR at Mumbai both using superconducting

cavities and liquid helium for refrigeration,

Tokomak Fusion Reactor (SST-1) at IPR (Institute

for Plasma Research) Gandhinagar and

Superconducting Cyclotron at VECC (Variable

Energy

Cyclotron Centre) Kolkata. All these projects are

either successfully completed and in operation

or at an advanced stage of completion.

Department of Atomic Energy (DAE) has

embarked

recently on an ambitious programme, namely

Accelerator Driven System (ADS) Reactor. Indian

industry like BHEL, BOC, Vacuum Techniques,

INOX India Ltd. and many other associated

industries actively participated and contributed to

the success of these projects. These projects led to

the commissioning of helium liquefiers of larger

capacities in the range of 300 litres/hr.

2002 The CE-7.5 is a cryogenic rocket engine

developed by ISRO to power the upper stage of its

GSLV Mk-2 launch vehicle in the year 2002. The

engine was developed as a part of the Cryogenic


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Upper Stage Project (CUSP). It replaced the

KVD-1 (RD-56) Russian cryogenic engine that

powered the upper stage of GSLV Mk-1.

2015 The CE-20 is a cryogenic rocket engine being

developed by the Liquid Propulsion Systems

Centre, a subsidiary of Indian Space Research

Organisation in the year 2015. It is being

developed to power the upper stage of the

Geosynchronous Satellite Launch Vehicle III. It is

the first Indian cryogenic engine to feature a gas-

generator cycle.

1.3 Basic Principle of Liquefaction

The basic principle of liquefaction is always a combination of two

processes, namely anisothermal compression followed by an adiabatic

expansion using a series of heat exchangers.Since helium gets

liquefied at very low temperature (4.2 K) we use three steps of

cooling.Compressed gas expands at two different temperature stages

followed by a final expansionthrough a J-T Valve. The expanders can

either be of piston type or a turbo type. Modern largecapacity helium

liquefiers are turbine based machines.

Applications Areas of Cryogenics Engineering:

A major application of cryogenics is the fractional distillation of air to

produce oxygen, nitrogen, and other gases. This process requires

cooling the air to low temperatures to liquefy the gases in it. Natural

gas, oxygen, nitrogen, and other gases are often liquefied for storage

and transport because they occupy much less space in liquid rather

than gaseous form.

1 Basic Research: Temperature, Pressure and Magnetic Field are

three important parameters for studies, which can alter the behaviour

of a material quite drastically. Whenever the temperature was reduced

by a significant step some discovery or the other of fundamental

importance took place. The physics at low temperature is extremely


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interesting and it is the physics of order. Lower the temperature, more

subtle is the nature of this order.

Superfluidity in the two liquids (liquid H.� e and liquid H.� e) and

superconductivity in a large number of elements, alloys and

compounds are two most striking examples of quantum behaviour of

matter at macroscopic scale.

2 Superconductivity: Soon after the liquefaction of helium in 1908

KammerlinghOnnesdiscovered the phenomenon of superconductivity

wherein a number of metallic elements loose their electrical resistivity

when cooled to a few degrees above absolute zero. Later the same

behaviour was found in a vast number of alloys and compounds. The

zero resistivityof these materials made them most attractive material

for electro technical devices whichare based upon a magnetic coil.

The Joule heating in these materials is absent and thus save power.

Superconductors are widely used for building magnets for a variety of

applications.

Superconducting magnets are used in research laboratories, High

Energy Physics, Accelerators, Fusion Reactors, High Gradient

Magnetic Separators, NMR Spectroscopy, Magnetic Resonance

Imaging (MRI), Train Levitation, Superconducting Magnet Energy

Storage (SMES) and many other applications. Materials called High

Temperature Oxide Superconductors have been discovered which turn

superconducting at LN2 (77 K) temperatures. Super conducting

materials are used for power transmission lines that have the potential

in reducing electrical transmission losses due to resistivity. These

losses can be as high as 20% in conventional powerlines. Such

cryogenic lines combined with super conducting magnets for energy

storage are being explored for future use.

3 Space

Cryogenic has two types of application in Space, namely as a Fuel

and to cool the detectors below their operational temperatures.

Hydrogen and oxygen are considered the best rocket propellants for

space application because of their high specific impulse. Liquid

Hydrogen usedas a fuel and oxygen as an oxidizer. They combine

together in the combustion chamber and produce thrust.it has a high

propulsive energy per unit mass.Both the gases being light need large


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volumes and therefore used in the form of liquids to conserve

space.These liquids are stored in insulated vessels and transported to

the combustion chamber through pipes, valves and turbo pumps.Many

of the space missions use infrared, gamma ray, and x-ray detectors

that operate at cryogenic temperatures. Cooling of IR detectors,

Telescopes, Cold probes, etc. are some of the major applications of

cryogenics. The detectors are cooled to increase their sensitivity.

Astronomy missions often use cryogenic telescopes to reduce the

thermal emissions of the telescope, permitting very faint objects to be

seen. Vibration free Mini size cryo coolers are used to cool these

detectors.Space simulations chambers are realistic environment for air

craft. The levels of vacuum required in space simulation chambers are

very high, This is achieved by the use of cryo pumps and turbo

molecular pumps. To produce a vaccum to that of a space (from

10��10�� ton) involving low temperature cryopumping or

freezing out of the residual gases to provide ultra highvaccum

required in space simulation chambers and test chambers for space

propulsion system.The cold space is simulated at cryogenic

temperatures by use of LN2. LHe at 20K is used to cool cryopanels

that freezes residual gases.

Aviation and aerospace industry:

Critical heat treatment routines for jet engine blades, and shrink

fitting’ techniques in the production and re-conditioning of static

storage tanks, and some bearing metal components with fine

tolerances.Proving breathing oxygen to pilots in high altitude in high

performance military aircraft.Gaseous nitrogen for aircraft tire

inflation.Liquid nitrogen is used for food preservation in commercial

aircraft.

4 Fuel

The Liquefied Natural Gas (LNG), which is mostly methane, is

considered to be an efficient and least polluting fuel. It turns in to a

liquid at a temperature of 111 K and the volume is reduced by a factor

of 600. LNG is transported by laying a pipeline. In case it is not

feasible to lay a pipeline or it is too costly, the alternative is to


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transport LNG in special sea vessels. At the receiving terminal it is

again converted in to gas and distributed. Hydrogen could become an

important source of energy in the near future and thus liquid hydrogen

will be widely used in many sectors other than Space.

5 Industrial and technical use:

Magnetic separation technique is used in variety of applications like

enhancing the brightness of kaolin, improving the quality of ultra-

high purity quartz etc.- Superconducting Magnet ensures proper

separation.

. M D Department of Mechanical Engineering, IIT Bomba

Cryogenic recycling - turns the scrap into raw material by subjecting

it to cryogenic temperatures.

• This is mostly used for PVC, rubbers.

Nitrogen, oxygen and argon are produced by fractional distillation of

air.

Liquid nitrogen is cheap and safe source of cold. It is used for

freezing of food (e.g Hamburgers).

1. Pressurization of plastic bottles and aluminium cans containing

drink: a small quantity of LN is injected into the liquid just

before sealing the bottle.

2. The LN vaporizes and produces a pressure slightly above the

atmospheric pressure, which makes the container very strong

and capable of standing piling up (10��of LN in a bottle with

10��over the liquid produces an overpressure of about 0.5

atm).

3. Fixing of pipelines by freezing the liquid on either side of the

leak, without emptying the whole system.

4. ground freezing, to allow excavation and tunnelling operation in

wet unstable soils;

5. deflashing of moulded polymer products: deflashing can be

obtained by a tumblingprocess rather than by treating each piece

individually;.

6. heat treatment of metals, e.g. steel tools to improve the wear

resistance, temper of musical instruments, etc.; The lives of the

tools, die castings & their dies, forgings, jigs & fixtures etc


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increase when subjected to cryogenic heat treatment.The life of

guitar strings increases by 4 to 5 times with no need for tuning.

7. working of solid explosive and bomb disposal: freezing of

explosives makes themtemporarily harmless;

8. cooling of cold traps in vacuum systems;

9. precooling of ��.� dewars and, in astronautics, of fuel tanks

before filling them withliquid oxygen or liquid hydrogen;

10. Cryo-cleaning, which is a blasting process that uses dry

ice. Similar in size to ricecorns, the granules are created by

expanded liquid carbon dioxide. By impact, theyclean and

sublime directly into the gas phase;

11. a magnetic energy storage system to provide power to

industrial electric loads subjectedto short-term voltage

disturbances.

Liquid hydrogen (and deuterium) is used in high-energy physics

experiments as a target for the particles produced by accelerators and

in bubble chambers.

(A) Steel Industry

Oxygen gas is used to enrich air and increase combustion

temperatures in blast and open hearth furnaces. It also raises steel

temperature and enhances recycling of scrap metal in electric arc

furnaces. Oxygen replaces coke as the combustible material in steel

making.Large size air separation plants are built at the steel

manufacturing sites to meet oxygen requirement. The present trend is

to give contract to gas manufacturers to erect the large air separation

plants at the Steel industry site itself and ensure the supply of oxygen

round the year. The manufacturer is allowed to sell the surplus

oxyegen in the open market.

(B) Fertilizers

Compounds of nitrogen such as Ammonium Nitrate (NH4NO3) and

Ammonium Sulphate(NH4)2 SO4 are essential for plant growth for

making proteins. Plants however cannot take nitrogen from plentiful

atmosphere but can absorb nitrogen from the soil water. Synthetic

fertilizers are produced by combining nitrogen and hydrogen in to


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ammonia. Nitrogen needed for the the production of the fertilizers is

again obtained by liquefying atmospheric air and separating nitrogen

and oxygen.

(C) Petrochemicals

Industrial gases through their captive air separation plants are

associated with petrochemical complex and fertilizer industry.

Nitrogen is used for production of ammonia, synthesis of ammonia by

washing with liquid nitrogen. Oxygen is used for production of

Ethylene glycol by oxidation of ethylene. Pure nitrogen is used for

blanketing and purging various equipments in petrochemical

complex.

(D) Mechanical design:

By utilizing the meissner effect associated with superconductivity,

practically zero-friction bearings have been constructed that uses a

magnetic field as the lubricant instead of oil or air. Superconducting

motors for ship propulsion systems have been constructed and also for

gyroscopes with zero electrical loss.

Deep Cryogenic Processing

Certain materials, when subjected to extremely low temperatures,

show signs of increased resistance to wear.Deep cryogenic processing

is a standard technique to improve the Metallurgical and structural

properties of a variety of materials, such as ferrous and non ferrous

metals, metallic alloys, carbides, plastics and ceramics. The process

need computer control, an insulated chamber and liquid nitrogen.

Deep cryogenic process relieves internal stress,improves abrasive

wear life and enhances the useful life of the tools and components.

Added advantage of this process is that the treatment is not confined

to the surface alone but the entire mass of the material. The enhanced

strength of the material stays till theend and without affecting the

hardness of the material. Cryogenic processing has been proved to

improve performance, reliability, durability of racing engines, brake-

transmission and drive lines, suspension springs etc.

Cryogenic treatment of firearms (pistols, guns) has been known for its

ability to increase their accuracy and to reduce wear. Cryogenic

processing of machine tools, machine parts, punching dies and other


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cutting tools is known to respond well, thereby reducing the cost of

production while improving the quality of the products.

(E) Cryo Grinding

Cryo grinding technique is widely used for all types of plastic

products, rubber, pharmaceuticals, cosmetics and spices. The material

becomes very brittle at cryogenic temperatures and can be grinded to

fine size uniform particles. The physical and chemical characteristics

of the material are preserved and there are no thermal damages or loss

of volatile constituents.

6 Medical

Use of cryogenics in Medical Sector is very extensive and it serve the

public at large.Magnetic Resonance Imaging (MRI), based upon the

principles of Nuclear MagneticResonance (NMR) has become a very

vital and useful diagnostic tool with all thehospitals across India. MRI

needs a very stable magnetic field. Such stable field can onlybe

provided by a superconducting magnet. Indeed MRI uses a large size

superconductingmagnet cooled by liquid helium. The magnet runs in

persistent mode, wherein the magnetcurrent flows persistently forever

and without a power supply..

A new area of medical research, namely “Magneto Encephalography‟

has started to mapthe brain functioning.

The device uses an array of SQUIDS (super conducting quantum

interference detector – sensitivity for the detection of small electrical,

magnetic or electromagnetic signals). A SQUID uses a pair

ofJosephson junctions and is operated at liquid helium temperature.

Josephson junctionconsists of a pair of superconductors separated by

a thin insulating barrier. The device iscapable of measuring feeble

magnetic field inside the brain, of the order of a femto Tesla(10��/

T).

Another application is in the area of cryo surgery of malignant tumors

and ophthalmicsurgeries. The device is popularly called “Cryo

Probe”. It instantly freezes the part to beoperated upon and is a blood

less surgery. Doctors use the cryoprobe to freeze and destroy certain

kinds of tissue, including warts, skin tumors, and eye tumors. The

probe either uses a spray of LN2 or the tipof the probe is cooled in

situ by a cooling process such as a J-T or Stirling. Most surgicaltools


21 | P a g e

are expensive and are invariably deep cryogenic processed to have

longer life.

Oxygen gas, produced by the cryogenic process, is one of the most

vital item to bestocked by any hospital. Yet another very important

application of cryogenics is in the Cryo Preservation ofhuman blood,

sperms, semen,bull semen (for breeding purposes), human eggs,

human embryos, bone marrow or any otherorgan. The process usually

involves a cryo protectant to counter the freeze damage andcooling to

LN2 temperature (77 K). It is well established now that human blood

(usuallyred cells) can be preserved for a very long time.

preservation of Stem Cells / cord cells using liquid nitrogen as

refrigerant. A young donor can thus deposit his blood only to be used

by him in old age. The cryo preserved blood is far superior inquality

to the whole blood preserved by old techniques. Unfortunately this

has not pickedup in Indian hospitals.

Electronics:

Sensitive microwave amplifiers called masers are cooled to LN2 or

LHe temperature so that thermal vibrations of the atoms of the

amplifier element donot seriously interfere with absorption and

emission of microwave energy. Cryogenically cooled masers have

been used in missile detectors, in radio astronomy to listen to far away

galaxy and space communication system.

8 Superconducting Magnets and Systems

The maximum use of superconductors have been in building magnets

which are very compact, light in weight, produce intense field and

consume very little power and as mentioned majority of them finds

application in world accelerator programme. Other thanaccelerator

and Tokamakprogramme, SC magnet is also used for the development

of SC generator, Sc motor and SEMS system. Considering the

difficulty on handling liquid helium for this application, demand of

this equipment was restricted. But with the discovery of High

temperature superconductor, fresh efforts are initiated on these

developments by using liquid nitrogen.

9 High Speed Transport


22 | P a g e

Japan National Railways had pursued this programme during 1980s &

1990s and developed trains running at speed greater than 550 km /

hour. Superconducting magnets operate on board and aluminum strips

run along the track in a concrete slab. At a critical speed the eddy

currents produced within the Al strips by the moving magnets is high

enough to produce an opposing field which lifts the train above the

track. The friction between the wheels and the rail disappears, train

picks up high speed. Trains have, however, not been put to

commercial use probably because of economical reason.

10 Cryo Preservation of Food

Most varieties of food items like meat, fruits, vegetables and marine

products areperishable in nature. They deteriorate fast because of

bacteriological, enzymatic, oxidative and other chemical reactions.

Since most chemical reactions die down below - 120°C the self life of

these products can be significantly enhanced by Instant Quick

Freezing (IQF) Technique. The technique enables to preserve the

taste, aroma, texture or the nutrition value of the food product. Shelf

life of the products is increased dramatically. The cryopreservation of

food and marine products for storage and exports has become an ever

growing industry with large market share.

Frozen foods are prepared by placing cartons on a conveyor belt and

moving the belt through a liquid nitrogen bath. It seals in flavor and

aroma. The cryogenic preservation process requires about 7 minutes

compared to 30 – 48 minutes in conventional process. Liquid nitrogen

is used as a refrigerant in frozen-food transport trucks and railway

cars. Cryogenic gases are also used in transportation of large masses

of frozen food, when very large quantities of food must be transported

to regions like war zones, earthquake hit region, etc they must be

stored for a long time so cryogenic food freezing is also helpful for

large scale food processing industries.

In Physics:

The Nobel Prize is the epitome of excellence in scientific

investigation.No less than15 Nobel prizes have been awarded for

research either involving some cryogenic phenomenon itself or where

cryogenics was required to induce the phenomena.


23 | P a g e

Johannes Diderik van der Waals (nobel prize in 1910) "for his work

on the equation of state for gases and liquids",

Heike Kamerlingh-Onnes(nobel prize in 1913) - "for his

investigations on the properties of matter at low temperatures which

led, inter alia, to the production of liquid helium",

John Bardeen, Walter Houser Brattain, William Bradford

Shockley (nobel prize in 1956) - "for their researches on

semiconductors and their discovery of the transistor effect"

Chen Ning Yang, Tsung-Dao (T.D.) Lee–(Nobel Prize in 1957)for

their penetrating investigation of the so-called parity laws which has

led to important discoveries regarding the elementary particles"

Lev Davidovich Landau (nobelprize in 1962) -"for his pioneering

theories for condensed matter, especially liquid helium"

Luis Walter Alvarez (nobel prize in 1968)- "for his decisive

contributions to elementary particle physics, in particular the

discovery of a large number of resonance states, made possible

through his development of the technique of using hydrogen bubble

chamber and data analysis".

John Bardeen, Leon Neil Cooper, John Robert Schrieffer (nobel

prize in 1972) - "for their jointly developed theory of

superconductivity, usually called the BCS-theory"


24 | P a g e

Noble prize in Physics 1973 was divided, one half jointly to Leo

Esaki, Ivar Giaever - "for their experimental discoveries regarding

tunneling phenomena in semiconductors and superconductors,

respectively" and the other half to Brian David Josephson (nobel

prize in 1973 - for his theoretical predictions of the properties of a

supercurrent through a tunnel barrier, in particular those phenomena

which are generally known as the Josephson effects".

PyotrLeonidovich Kapitsa (nobel prize in 1978) -"for his basic

inventions and discoveries in the area of low-temperature physics"

Johannes Georg Bednorz, Karl Alexander Müller, (nobel prize in

1987)- "for their important break-through in the discovery of

superconductivity in ceramic materials"

Douglas D. Osheroff, Robert Coleman Richardson (nobel prize in

1996)- for their discovery of superfluidity in helium-3"

Eric Allin Cornell, Carl Edwin Wieman, Wolfgang Ketterle (noble prize in 2001) - "for the achievement of Bose–Einstein

condensation in dilute gases of alkali atoms, and for early

fundamental studies of the properties of the condensates"

Alexei AlexeyevichAbrikosov, VitalyLazarevichGinzburg,

Anthony James Leggett (noble prize in 2003) - "for pioneering

contributions to the theory of superconductors and superfluids"

are among the many Nobel Laureates who employed cryogenics in

their investigations.

11 Future Outlook

Interesting developments are taking place and at a fast pace. Close

Cycle Refrigerators or popularly known as Cryo Coolers of cooling

power of 1.5 W are commercially available.


25 | P a g e

Various equipments are designed and built to operate using these cryo

coolers thus doing away with the use of LHe no more liquefaction of

helium or recovery of the He-gas for recycling. Cry

freesuperconducting magnets which are operated using cryo coolers

andhigh temperature superconducting (HTSC) current leads have

become very popular with researchers. There are high expectations

from the HTSC materials. These superconductors are operated at LN2

temperature (77 K) and devices and systems based on these materials

will be extremely economical. Power Transmission Line could be one

such applicationwhich can be realized in near future. Once the

problem of drop in critical current with magnetic field is resolved

HTSC materials will replace almost all conventionalsuperconducting

devices and systems. Production of LO2 and LN2 is directly related to

the industrial growth and is bound to go up at all times.

Electric power transmission:

In big cities it is difficult to transmit power by overhead cables in big

cities, so underground cables are used. But underground cables get

heated and the resistance of the wire increases leading to waste of

power. Superconductors could be used to increase power throughput,

although they would require cryogenic liquids such as nitrogen or

helium to cool special alloy-containing cables to increase power

transmission. Several feasibility studies have been performed and the

field is the subject of an agreement within the International Energy

Agency.

Low Temperature Properties of Engineering Materials:

A knowledge of the properties and behavior of materials used in

anycryogenic system is essential for proper design considerations.

Often the choice of materials for the construction of cryogenic

equipment will be dictatedby consideration of mechanical and

thermophysical properties such as thermalconductivity (heat transfer

along a structural member), thermal expansivity(expansion and

contraction during cycling between ambient and low

temperatures),and density (mass of system).


26 | P a g e

MECHANICAL PROPERTIES:

Ultimate and yield strength: The ultimate strength of a material is

defined as the maximum nominal stress that can be attained during a

simple tensile test.

The yield strength is defined as the value of stress at which the strain

begins to increase quite rapidly with an increase in the applied stress.

When the stress – strain behavior is unknown, or it does not exhibit a

sharp change in the behavior, the yield strength is defined as the stress

required for permanently deforming the material by 0.2%. the effect

of temperature variations on ultimate and yield strengths of several

engineering materials are shown in fig (a) and (b) respectively.

Fig (a) Effect of temperature on ultimate strength of engineering

materials: (1) 2024-T4 aluminium, (2) beryllium copper, (3) K Monel,


27 | P a g e

(4) titanium, (5) 304 stainless steel, (6) C1020 carbon steel, (7) 9%

nickel steel, (8) Teflon, (9) Invar-36.

Fig (b) Effect of temperature on yield stress of engineering materials:

(1) 2024-T4 aluminium, (2) beryllium copper, (3) K Monel, (4)

titanium, (5) 304 stainless steel, (6) C1020 carbon steel, (7) 9% nickel

steel, (8) Teflon, (9) Invar-36.

It may be noticed that alloys are stronger than the basic materials,

when the alloying atom is smaller in size. For example, carbon steel

has carbon as the alloying element. At low temperatures, there is less

thermal vibration of the atoms, and a larger stress is required for

dislocations in the neighborhood of alloying atoms. As a result, yield

strength increases with lowering of temperatures. It can be seen that

stainless steel-304 has the highest strength at temperatures above


28 | P a g e

100K whereas the strength of titanium exceeds that of stainless steel

below 100 K.

Fatigue strength:

The stress required for failure after given number of cycles is called

the fatigue strength S� . For some material like (carbon steels and

aluminium-magnesium alloys) the fatigue failure will not occur if the

stress is less than endurance limit (S�) no matter how many cycles are

elapsed. As shown in graph the fatigue strength increases as the

temperature is decreased. Fatigue failure occurs in three stages at

1000 cycles.

1. Micro crack initiation.

2. Slow crack growth until critical crack growth occurred final.

3. Rapid failure either by ductile rupture or by cleavage.


29 | P a g e

The micro crack initiation occurs at the surface of the material due to

shear deformation or for small flaws at the surface. The slow crack

growth leads to failure of the material, due to high stress around the

crack. At low temperatures, a higher stress is required for the growth

of the crack. As a consequence, the fatigue strength increases as the

temperature is lowered. It may be seen that stainless steel-304 has the

highest and aluminium has the lowest fatigue strength at any

cryogenic temperature.

Impact strength:

Materials sometimes fail when subjected to suddenly applied load or

stress, and in order to assess their capacity to stand such sudden

impact, the impact tests are performed.

The charpy and izod impact tests indicate the energy absorbed by the

material when it is fractured by a suddenly applied force. The impact

behavior of a material is usually decided by its lattice structure. There

may be a transition in the impact strength leading to ductile-brittle

transition with lowering of temperature as in the case of carbon steel

(which may be seen from below graph) as a result of severely reduced

impact strength at low temperatures. In the absence of this transition,

(e.g. for stainless steel- 304), the impact strength increases with

lowering of temperature. The metals with the face-centered-cubic

(fcc) lattice structure or hexagonal lattice tend to fail by plastic

deformation and retain their resistance to impact at the lowered

temperature. The metals with the body-centered-cubic (bcc) lattice

structure tend to fracture by cleaving and thereby absorbing less

amount of energy. So these are brittle at low temperatures. Most

plastics and rubber materials (with exceptions to Teflon and Kel-F)

become brittle at very low temperatures.


30 | P a g e

Fig Effect of temperature on impact strength of engineering



nickel steel.

Hardness and ductility:

Ductility is that property of a material which enables it to draw out

into thin wire. The ductility is a measure of the capacity to elongate

by a simple tensile force and is indicated by the percentage elongation

or reduction of cross-sectional area at the limit of its failure. The

materials that elongate by more than 5% before failure are called

ductile and the rest are called brittle (i.e. those who fail at less than

5% elongation). The available data on the variation of ductility of

different materials with temperature is presented in (below graph).

The ductility usually increases with lowering of temperature for

materials (e.g. K Monel) that do not undergo ductile-brittle transition


31 | P a g e

with lowering of temperature. For the materials, which exhibit

ductile-brittle transition at low temperatures, like carbon steel, the

ductility decreases from 25-30% to 2-3% during transition. So these

materials with ductile-brittle transition should not be used at

cryogenic temperatures when ductility needs to be considered.

Fig Effect of temperature on impact strength of engineering



nickel steel.

The hardness of metals is indicated by the indentation made on the

surface of the material by a standard procedure using a hardness

tester, namely, a ball indenter (for the Brinell test), diamond pyramid

indenter (for the vickers test), and ball or diamond indenter with

various loads (for the Rockwell test). In general, these tests are

analogous to tensile test. This is due to the fact that the hardness is


32 | P a g e

directly related to the ultimate stress of the material and accordingly

the hardness increases with lowering of temperature.

Elastic moduli:

There are three commonly used elastic moduli

Young’s modulus (E), The rate of change of tensile stress with respect

to strain at constant temperature in the elastic region.

Shear modulus (G), The rate of change of shear stress with respect to

shear strain at constant temperature in the elastic region; and

Bulk modulus (B), The rate of change of pressure (corresponding to a

uniform three - dimensional stress) with respect to volumetric strain

(change in volume per unit volume) at constant temperature.

For many isotropic polycrystalline engineering materials, E, G and B

are related in terms of the Poisson’s ratio �. The Poisson’s � isdefinedastheratioofstraininonedirectionduetostressappliedperpendiculartothatdirectiontothestrainparalleltothestress

B = /

�(��1) , G =/

�(�31)

Where, 4 = 56789:;<7;<:=9>?@876A6B<8;;@9<=567<55

56789:;878@@<@6A6B<8;;@9<=567<55


33 | P a g e

Fig (b) Effect of temperature on Young’s modulus of engineering



nickel steel.

As the temperature is decreased, interatomic and intermolecular

forces tend to increase because of decrease in the disturbing influence

of atomic and molecular vibrations. Carbon steel has the highest and

aluminium has the lowest values of E.

Thermal properties:

Thermal conductivity K of a material is defined as the heat – transfer

rate per unit area divided by the temperature gradient causing the heat

transfer.


34 | P a g e

To understand the variation of thermal conductivity at low

temperatures, one must be aware of the different mechanisms for

transport of energy through materials.

There are three basic mechanisms responsible for conduction of heat

through materials:

1. Electron motion, as in metallic conductors.

2. Lattice vibrational – energy transport, or phonon motion, as in

all solids; and

3. Molecular motion, as in organic solids and gases.

For heat conduction in solids related other properties

KD = �E (9γ – 5)ρFG4̅I

Where,

ρ = density of material.

γ = specific heat ratio.

FG= specific heat at constant volume.

4̅= average particle velocity.

I= mean free path of particles.

Thermal conductivity decreases with decrease in temperature at

very low temperature region. In pure metal thermal conductivity is

very high as the temperature is lowered.

Phonon will be higher at below N� liquefying temperature (77K).

In liquids – molecular vibrational energy.Translational energy

(monoatomic gases) and translational and rotational for diatomic

gases.

Specific heats of solids:

The specific heat of a substance is defined as the energy required to

change the temperature of the substance by one degree while the

pressure is held constant (F;) or while the volume is held constant

(FG).

Specific heat is a physical property that can be predicted accurately

by mathematical models, through statistical mechanics and

quantum theory.


35 | P a g e

For solids the Debye model gives satisfactory representation of the

variation of specific heat with temperature.

Specific heat of a monoatomic crystalline solid as obtained through

Debye theory is

R = E.�� J

KLMNODPQRST�RUVDPWQPX�SYXZWT�RUVD( [

\]^)

FG = _`ab

cdbe fg<h=f

(<h�)ijk/am = 3R o a

jkp�

D o ajk

p

qr = Debye characteristic temperature and is a property of the

material.

D o ajk

p = is called the Debye function.

Specific heat of copper at 80K = 204.9 J/Kg-K.

Specific heat of aluminium at 20K = 9.708 J/Kg-K.

Coefficient of thermal expansion:

The volumetric coefficient of thermal expansion β is defined as the

fractional change in volume per unit change in temperature while

the pressure on the material remains constant.

For isotropic materials β = 3I6

I6 = linear coefficient of thermal expansion.

β = volumetric coefficient of thermal expansion.

As the molecule acquires more energy (or its temperature is

increased) its mean position relative to its neighbors becomes

larger; that is, the material expands.

β = tuvwx

y

z = density of the material.


36 | P a g e

{ = bulk modulus.

|}= Gruneisen constant

F~= specific heat at constant volume.

Specific heat and coefficients of thermal expansion are associated

with intermolecular energy.

Relation between (B and β) thermal expansion and specific heat

β = tuvwx

y

Electric and Magnetic Properties

Electrical Conductivity:

The electrical conductivity �< of a material is defined as the

electric current per unit cross-sectional is divided by the voltage

gradient in the direction of current flow.

Electrical conductivity increases as the temperature is lowered for

metallic conductors. Electrical resistivity �< is reciprocal of

electrical conductivity. When external electric field is applied to

an electric conductor, free electrons in the conductor are forced to

move in the direction of the applied field. This motion of electrons

opposed by positive ions of the metal lattice and impurity atoms

present in the material.

When temperature is decreased vibrational energy of the ions

decreases and electron flow increases.

Electrical conductivity increases as the temperature is lowered for

metallic conductors.

K< = o�

�p<i��1�

Where, N/V = number of free electrons per unit volume

e = Charge of electron

� = electron mean free path

�< = mass of electron

4̅ = Average speed of electron.


37 | P a g e

Superconductivity:

Certain materials exhibit at low temperature is superconductivity.

The simultaneous disappearance of all electric resistance and the

appearance of perfect diamagnetism.This property was first

discovered in 1911 by KammerlinghOnnes when disappearance of

electrical resistance was observed in mercury at a temperature near

4K. since then the absence of resistance has led to serious research

investigations on the theories of superconductivity as well as on

utilization of superconductivity devices for a variety of

applications. One such application involves superconducting coils

in a powerful electromagnet.

It is well known that many elements, compounds and alloys exhibit

negligible electrical resistance in the environment of zero

magnetic-field at a definite temperature �� , called transition

temperature. However, the resistance reappears on increasing the

magnetic field beyond a fixed value, called critical magnetic field

strength, �> depending on its temperature.

There are two types of superconducting materials.

Type I superconductor the transition from the superconducting

state to the normal state takes place rather abruptly at a single

magnetic field strength.

Type II superconductor, the transition occurs gradually over a span

of magnetic field strength bound by the upper and the lower values.

Meissner effect: When a material is normal, the magnetic flux

lines can penetrate the material. When the material becomes

superconducting, the magnetic field is expelled from with in the

material.

When the normal material changes to superconductivity

i) Specific heat : increases abruptly.


38 | P a g e

ii) Thermoelectric effect :peltier, Thomson seebeck effect

vanishes.

iii) Thermal conductivity : Thermal conductivity of pure metal

decreases in the presence of magnetic field abruptly. When it

becomes superconducting, thermal conductivity increases. In

the absence of a magnetic field, there is no discontinuous

change.

iv) Electrical Resistance: Type 1 Superconductors (Single value

of critical field) decrease of resistance to zero abrupt. Type 2

conductors (lower and upper critical fields) the change is

some times spread over temperature range as large as 1K.

v) Magnetic permeability : Magnetic permeability decreases

suddenly to zero for type 1- superconductors (The Meissner

effect) for type 2 Superconductors – magnetic fields are

greater than lower critical field.

Gas – Liquefaction Systems:

Study of the systems that can produce low temperature required for

liquefaction. It is possible to produce cryogenic fluids with the help of

various systems. We shall be concerned with the performance of the

various systems. The performance of each system is measured by the

performance parameters or payoff functions. In ideal system 100% of

gas compressed and liquefied.

System performance parameters:

W� = Power

m� = mass flow rate

m�� = liquid mass flow rate.

y = liquid yield.

i) Work required per unit mass of gas compressed, - W� /m� . ii) Work required per unit mass of gas liquefied, - W� /m�� .

iii) Fraction of the total flow of gas that is liquefied, y = m�� /m� .

The last two payoff functions are related to the first one by

(- W� /m� ) = (- W� /m�� )y� 1


39 | P a g e

In any liquefaction system, we should want to minimize the work

requirements and maximize the fraction of gas that is liquefied.

Payoff functions are different for different gases.

Figure of merit (FOM) is defined as the theoretical minimum work

requirement divided by the actual work requirement for the system:

FOM = �� =

�� \��

��\��

= ��

��M

Performance parameters applied to the component of real systems:

i) Compressor and expander adiabatic efficiencies.

ii) Compressor and expander mechanical efficiencies.

iii) Heat – exchanger effectiveness.

iv) Pressure drops through piping, heat exchangers, and so on.

v) Heat transfer to the system from ambient surroundings.

First we assume all efficiencies and effectivenesses are 100% and

irreversible pressure drops (losses) and heat inleaks are zero.

Symbols used in liquefaction cycle:

Compressor:


40 | P a g e

A compressor increases the pressure of the gas. It interacts with

the surroundings in the following ways. It gives heat of

compression �� to the surrounding and �� denotes work

required for compression.

Connecting flow lines :

The flow of fluid is assumed to be frictionless and there is no

pressure drop during the flow. The direction of the arrow

indicates the gas flow direction.

Expander:

The schematic for a expander is as shown above. The expansion is

isentropic and during expansion it produces work �� .

Liquid container or liquid reservoir:

Once you liquefy the gas, it is stored in liquid container and it is

assumed that the container is perfectly insulated from the

surroundings.

Thermodynamically ideal system:


41 | P a g e

This system is ideal in thermodynamic sense, but it is not ideal as far

as practical system is concerned. The perfect cycle in

thermodynamics is the carnot cycle. Liquefaction is essentially an

open-system process, therefore for an ideal liquefaction, the first two

processes in the carnot cycle is chosen;

A reversible isothermal compression, followed by reversible

isentropic expansion. The gas to be liquefied is compressed reversibly

and isothermally from ambient conditions 1 to some high pressure

point 2. The high pressure is selected such a way that the gas will

become saturated liquid upon reversible isentropic expansion through

expander (point f). The final condition f is taken as the same pressure

as the initial pressure at point 1.

The pressure attained at the end of isothermal compression is

extremely high in the order of 70GPa to 80 GPa (10�� )for ¡�. It is

highly impractical to attain this pressure in a liquefaction system. It is

not a ideal process for a practical system.


42 | P a g e

1st law of thermodynamics for steady flow

¢:<6� - £:<6� = ∑ m� (ℎ + 1i�§¨

�A?6@<65 + ©ª

©¨) - ∑ m� (ℎ +9:@<65

1i�§¨

+ ©ª©¨

)

¢:<6� = heat transfer to or from the system.

£:<6� =net workdone on or by the system

g> = conversion factor in Newton’s second law

g> = 1.00 kg-m/N-��

g = local acceleration due to gravity, 9.806m/��.

In our system analysis Kinetic energy and potential energy are much

smaller than enthalpy changes, hence these energy terms may be

neglected 1st law for steady flow

¢:<6� − £:<6� = m� m� ℎ − m� ℎ�®:@<65

�A?6@<65

Applying 1st law to the system as show in fig

¢�̀ − £®� = m� ¯h� − h�° = m� ¯h� − h�°

The heat transfer process is reversible and isothermal in the carnot

cycle. Thus, from the 2nd

law of thermodynamics

¢�̀ = m� T�(s� − s�) = −m� T�¯s� − s�°

The process is from point 2 to point f is isentropic, s� = s�, where

s is the entropy of the fluid. Substituting ¢�̀ from eqn (6) into eqn

(5) we may determine work requirement for ideal system:

− £®�m� = T�¯s� − s�° −¯h� − h�° = £®�

m��

In the ideal system, 100% of the gas compressed is liquefied, or m� =

m�� , so that y = 1.


43 | P a g e

Liquefaction system is a work absorbing system – net work

requirement is negative − ²³�Q� is a positive number.

Eqn (7) gives minimum work requirement to liquefy a gas. The ideal

work requirement depends only on the pressure and temperature at

appoint 1 and the type of the gas liquefied.

Production of low temperature:

INVERSION CURVE : Most practical liquefaction system utilizes an

expansion valve or Joule – Thomson valve, to produce low

temperature by applying steady flow to this valve at ideal condition

ℎ� = ℎ� eventhough the flow within the valve is irreversible. In

drawing a series of points by varying inlet and outlet states, the states

lie on the enthalpy curve. For a real gas it is shown there is aregion in

which expansion through the value produces an increase in

temperature, while the other region expansion results decrease in

temperature. The curve that separates these two regions is called

inversion curve. We are interested in a region where temperature

decreases.

The effect of change in temperature for an isenthalpic change in

pressure is represented by the Joule-Thomson effect.

´µa = ¶·�·�¸

B

Definition: The derivative is represented as the isenthalpic line shown

in fig. Joule-Thompson co-efficient is zero along the inversion curve.

For temperature increase during expansion ´µa is negative, for

temperature decrease ´µa is positive.

´µa = (¹a¹;)B = −(¹a

¹;);(¹B¹;)a�(9)


44 | P a g e

dh = = (¹B¹a);º� + (¹B

¹;)aº� = F»º� +¼4 − �(¹1¹a);½�(10)

where� = specific volume of the material. By comparison of the co-

efficients of dT and dp in eqn (10), we see that

F; = (¹B¹a);and(¹B

¹;)a = � - T(¹1¹a);�(11)

Combining eqns (9) and (11) the Joule – Thomson co-efficient may

be expressed in terms of other thermodynamic properties as

´µa = �v¾

¿� o¹1¹ap − 4À = 0�(12)

For an ideal gas, �= Á� �Â , and


45 | P a g e

(¹1¹a); =

`; =

1a

Therefore, from eqn (12), for an ideal gas

´µa = �v¾

¿� o¹1¹ap − 4À = 0for other gases

´µa = �v¾

¿� o1ap − 4À = 0for ideal gas

An ideal gas would not experience a temperature change upon

expansion through an expansion valve. Ie.,´µa is zero

From this the real gases are imperfect

u = internal energy

h = u+p��(13)´µa = − �

v¾Äo¹1

¹ap + ¿¹(;1)¹; À

aÅ�(14)

Internal energy of a gas is a function of temperature alone.

u = u(T) = F~T. This term is zero for ideal gases. This term is negative

for real gases always.

It contributes production of low temperature (+´µa)

This is internal work method. It separates the liquid formed after

expansion from the vapour. The liquid that entrained in the vapour

that can be separated by swirling the mixture in a centrifugal action.

This can be achieved by curving the outlet tube. It operates under

more widely varying inlet gas flows.

Production of low temperatures:

There are essentially three methods of continuous production of cold

or low temperatures, namely,

1. Throttling process or Joule-thomson (J-T) expansion,


46 | P a g e

2. Adiabatic turbine expansion and

3. Isobaric cooling by an external refrigerant.

The first two methods are direct, as the substance to be cooled

undergoes the process, whereas the third method is indirect, as the

substance to be cooled, transfers heat to the refrigerant by means of a

heat exchanger. The refrigerant, which undergoes the phase change, is

cooled by the first method. The direct methods are undoubtedly more

efficient than the indirect one while the indirect method is employed

for cooling because of the ease of operation and/or for a part of the

net cooling required. There are also other methods of producing

extremely low temperatures by bringing about discontinuous changes

in the thermo-physical properties of the working substance for

providing specific cooling requirements.

The Joule-Thomson Effect:

The Joule-Thomson (JT) effect is a thermodynamic process that

occurs when a fluid expands from high pressure to low pressure at

constant enthalpy (an isenthalpic process). Such a process can be

approximated in the real world by expanding a fluid from high

pressure to low pressure across a valve. Under the right conditions,

this can cause cooling of the fluid.

This effect was first observed in an experiment conducted by James

Joule and Thomson in 1852 in which they flowed high pressure air

through a small porous plug causing the pressure to drop. Joule and

Thomson noted that the air was cooled by this procedure (which is a

good approximation of an isenthalpic process).

Building on this work, in 1895, Linde in Germany and Hampson in

England independently developed and patented a refrigerator that

combined the JT effect with heat exchangers and a piston compressor.

This became known as the Linde-Hampson or Joule–Thomson cycle.

Such a refrigerator played an important role in James Dewar’s liquefaction of hydrogen in 1898.


47 | P a g e

The Joule-Thomson effect can be described by means of the Joule-

Thomson coefficient which is simply the partial derivative of the

pressure with respect to temperature at constant enthalpy. If this

coefficient is positive, then the fluid cools upon expansion and if it’s

negative the fluid warms upon expansion. The JT coefficient varies as

a function of pressure and temperature and varies from fluid to fluid.

The curve described by the JT coefficient equaling zero as a function

of pressure and temperature is known as the inversion curve.

Underneath this curve cooling of the fluid occurs upon expansion. It

is also possible to define for a given fluid the maximum inversion

temperature. The fluid must be colder than this temperature to cool

when expanded.

In the case of nitrogen, the maximum inversion temperature is 623K.

It is completely possible to make liquid nitrogen simply by using a

high pressure cylinder of room temperature nitrogen, a JT valve and

appropriate heat exchangers that cool the higher pressure room

temperature gas with gas that has expanded through the JT valve and is thus colder.

Joule-Thomson refrigerators do not have cold moving parts and are

able to work well with fluids that change from single phase to two-

phase as they expand through the JT valve. Such devices may also

have miniaturized cold ends and may be designed to rapidly cool

down to operating temperature from room temperature. Due to these

advantages, Joule-Thomson liquefiers/refrigerators have been used for

a variety of applications in the aerospace, defense and medical fields.

While they have to some extent been replaced by pulse tube

cryocoolers, JT liquefiers and refrigerators remain an important class

of small cryocooler either alone or in combination with other

cryocooler types.

The maximum inversion temperature of helium is 43K, meaning that

helium has to be cooled to this temperature before the JT effect will

cause cooling rather than warming. As a result, there is generally a JT

valve near the lowest temperature portion of helium

refrigerators/liquefiers to provide the final cooling stage. Expansion


48 | P a g e

through a JT valve is also the final step in producing He II (superfluid

helium, T < 2.2K) from liquid helium at 4.2K. It’s worth noting that

the inversion curve for helium between 1.2K and 2.2K is actually

negative, meaning that in most of the He II regime itself, isenthalpic

expansion of the helium causes a slight amount of heating.

Adiabatic expansion:

Adiabatic expansion of the gas through a work producing device can

cause the low temperature to the gas (expansion engine). In ideal case

expansion would be reversible and adiabatic, and therefore isentropic.

External work method

Isentropic expansion coefficient, μÇ = oÈÉÈÊp

Ç�eqn 1 at constant

entropy.

Definition μÇ = isentropic expansion coefficient which expresses

temperature change due to a pressure change at constant entropy.

μÇcan be related to other properties of the gas

μÇ= oÈÉÈÊp

Ç= − oÈÉ

ÈÇpÊ oÈÇÈÊp

É= + É

�ËoÈÌ

ÈÉpÊ�eqn 2

μÇ (Joule – Thomson coefficient)

(liquid water between 0°C and 4°C has negative coefficients of

expansion).

During isentropic process energy removed from the gas due to

external work done.

Expansion valve does not remove energy from the gas but moves the

molecules farther apart under the influence of intermolecular forces.

This method is called the internal work method.


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Questions:

1. What is cryogenics? Explain briefly applications areas of

cryogenic engineering.

2. Explain low temperature properties of engineering materials

i) Mechanical properties

ii) Thermal properties

iii) Electrical properties

3. Explain briefly production of low temperatures.

4. Explain briefly Joule Thompson effect. Explain the function of

J-T valve in cryogenics with sketch.

5. Explain Adiabatic expansion

6. What do you understand by cryogenics? Explain briefly any

four applications areas of cryogenics. (10M) (VTU Jan 2015).

7. Explain working principle of thermodynamically ideal system

with suitable sketches and derive equations for all system

performance parameters. (10M) (VTU Jan 2015)

8. What is cryogenics? Mention the few areas involving cryogenic

engineering (6M) (VTU Jan 2014)

9. Discuss the effects of low temperature on the following

properties of engineering materials: i) Yield strength ii) Thermal

conductivity (6M) (VTU Jan 2014)

10. Explain thermodynamically ideal gas liquefaction system

with sketch and obtain an expression for the work requirement.

(8M) (VTU Jan 2014)

11. Explain the meaning of cryogenics, List the various areas

involving cryogenics. (5M) (VTU June 2010)


50 | P a g e

12. Explain with proper reasoning and graph, the effect of low

temperature on two mechanical and two thermal properties of

engineering materials. . (10M) (VTU June 2010)

13. Discuss Joule – Thomson effect for the production of low

temperature. (5M) (VTU June 2010)

14. List the various areas of applications of cryogenic

engineering. (5M) (VTU Dec 2010)

15. Define the figure of merit of a liquefaction system.

Explain the thermodynamically ideal gas liquefaction system

and obtain an expression for the work requirement for the above

system. (10M) (VTU Dec 2010)

16. Explain with the proper reasoning and graph, the effect of

low temperature on the thermal properties of engineering

materials.(5M) (VTU Dec 2010)