vtu cryogenics notes unit 1 introduction to cryogenic systems
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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
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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
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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.
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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"
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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.
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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).
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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,
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(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
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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.
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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.
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Fig Effect of temperature on impact strength 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.
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
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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
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.
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
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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
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Fig (b) Effect of temperature on Young’s modulus 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.
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.
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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.
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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.
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{ = 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.
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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.
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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
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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:
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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:
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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.
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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.
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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)
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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� � , and
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(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
a�(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,
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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.
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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
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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
�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)
Cryogenics Shashidhar_gs@yahoo.co.in
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)
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