Download CRYOGENICS

CRYOGENICS
PRESENTED BY
RAJKUMAR.G
VASUDAVEN.S
ABSTRACT
• Cryogenic Treatment is a material science and involves the process of
reducing the temperature of components over an extended period of time
to extreme cold levels, usually slightly below -250°C. The use of vapour
compression circuit is to provide pre-cooling emphasis the dependence of
cryogenic cooling technology on refrigeration and the synergy between
the two technologies. It is apparent that gas compression and reduction in
temperature as a result of throttling are common to both systems. The
differences are the thermodynamic properties of the working fluid and the
temperature range of cycle. The significance of critical temperature is also
apparent. In the vapour compression cycle shows all the processes occur
below the critical temperature, as it typical for such cycles, and therefore
condensation of the working fluid is possible simply by rejecting heat to a
sink at a lower temperature. By contrast, in the cryogenic cycle the
temperature of the working fluid only falls below the critical value in the
throttling process. By this method, cryogenic treatment helps to reduce
the temperature very low.
• Keywords
Absolute zero, Linde-Hampson system, Claude system, various
applications.
INTRODUTION
• “Cryogenics” stems from Greek and means "the production of freezing
cold"; however the term is used today as a synonym for the lowtemperature state. It is not well-defined at what point on the temperature
scale refrigeration ends and cryogenics begins. Cryogenics typically
involves a deep-freezing process, usually one that takes object down
below 240 degrees Fahrenheit and changes the molecular alignment of
the material structure. This change creates the new property. Cryogenic
process has been researched and developed by universities and NASA
since the mid-sixties after NASA discovered that deep space exploration
vehicles had improved their structural integrity due to extended exposure
to cryogenic temperature.
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The terms cryogenics, cryobiology are frequently
confused and given below:
• Cryogenics
The branches of physics and engineering that involve the study of very low
temperatures, how to produce them, and how materials behave at those
temperatures.
• Cryobiology
The branch of biology involving the study of the effects of low
temperatures on organisms (most often for the purpose of achieving
cryopreservation).
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TYPES OF CRYOGENIC TREATMENT
SHALLOW CRYOGENICS, made the objects to temperature of approximately 120o F.
FLOODING, takes the component to -120o F, then the chamber is flooded with
liquid nitrogen.
DEEP CRYOGENICS TREATMENT, Subjects the objects to the temperature of
approximately -300o F.
ABSOLUTE ZERO
Absolute zero is a temperature marked by a 0 entropy configuration. It is the coldest
temperature theoretically possible and cannot be reached by artificial or natural
means. Temperature is an entropically defined quantity that effectively determines
the number of thermodynamically accessible states of a system within an energy
range. Absolute zero physically possesses quantum mechanical zero-point energy.
Having a limited temperature has several thermodynamic consequences; for
example, at absolute zero all molecular motion does not cease but does not have
enough energy for transference to other systems, it is therefore correct to say that at
0 Kelvin molecular energy is minimal. In addition, any particle with zero energy
would violate Heisenberg's Uncertainty Principle, which states that the location and
momentum of a particle cannot be known at the same time. A particle at absolute
zero would be at rest, so both its position, and momentum (0), would be known
simultaneously.
• By international agreement, absolute zero is defined as precisely 0 K on the Kelvin
scale, which is a thermodynamic (absolute) temperature scale, and −273.15° on the
Celsius scale.[1] Absolute zero is also precisely equivalent to 0 R on the Rankine
scale (same as Kelvin but measured in Fahrenheit intervals), and −459.67° on the
Fahrenheit scale.
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PRODUCTION OF LOW TEMPERATURE
The following methods are involved to produce the low temperature in
cryogenics:
Heat conduction: It is a relatively simple concept to understand. When two
bodies are in contact, heat flows from the body with the higher temperature to
the body with a lower temperature. Conduction can occur between any and all
forms of matter, whether gas, liquid, or solid. It is essential in the production of
cryogenic temperatures and environments.
Evaporative cooling: Humans are familiar with this process because it is a
mechanism in which our bodies lose heat. Atoms and molecules in the gaseous
state are moving faster than the atoms and molecules in the liquid state. Add heat
energy to the particles in a liquid and it will become gaseous.
The Joule-Thomson effect: It was discovered by the English Physicist James
Prescott Joule, William Thomson and Lord Kelvin, in 1852. They found, for
example, that allowing a gas to expand very rapidly causes its temperature to
drop dramatically. Reducing the pressure on a gas accomplishes the same effect.
The Joule-Thomson effect is an important part of our lives today, even though we
may not be aware of it. Ordinary house hold refrigerators and air conditioners
operate on this principle. First a gas is pressurized and cooled to an intermediate
temperature by contact with a colder gas or liquid. Then the gas is expanded, and
its temperature drops still further. The heat needed to keep this cycle operating
comes from the inside of the refrigerator or the interior of a room, producing the
desired cooling effect.
METHODS OF LIQUIFICATION OF AIR
Linde’s system also known as hampson system.
Claude’s system.
LINDE’S SYSTEM
LINDE’S SYSTEM
• Clean dry air is taken from the atmosphere and is
compressed up to 200 bar.
• The high pressure enters into counter flow air to air heat
exchanger and is then throttled to atm - pressure.
• The J-T cooling up to expansion causes a lowering of
temperature and this cool air is passed through heat
exchanger where it cools the incoming high section.
• Thus the temperature at the valve is progressively
lowered until the liquefaction temperature is reached.
T-S DIAGRAM (Linde’s system)
PROCESS
1-2: Compression
2-3: Pre-cooling of air by pre cooling circuit
3-4: Pre-cooling of air by Heat exchanger
4-5: Throttling process
5’-6: Process in evaporator
CLAUDE’S SYSTEM DIAGRAM
CLAUDE’S SYSTEM
• Claude’s system yields more efficient cycle than
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Linde’s system
The expansion through an expansion valve is an
irreversible process.
In Claude’s system energy is removed from the gas
stream by using an expansion engine or expander.
The expansion process is isentropic and much lower
temp is attained then isenthalpic expansion
In Claude’s system the gas is first compressed to
pressure of the order 4 Mpa.
T-S DIAGRAM (Claude’s system)
How Claude’s system is more efficient than Linde’s system
The advantage of the Claude’s system is, it operates at low compression ratio
compared with linde’s process.
Secondly the temperature of air before coming to the expansion valve in Claude
system is lower than the Linde system.
APPLICATION OF CRYOGENICS
– Aerospace-cryogenic engines
– Medical Field
– Manufacturing field
– Electronics Field
– Fuels research.
CRYOGENIC ENGINES IN AEROSPACE
• The first operational Cryogenic Rocket Engine is the 1961 NASA design the
RL-10 LOX LH2 rocket engine.
• The upgraded cryogenic second-stage Pratt & Whitney RL10B-2 engine is
based on the 30-year heritage of the reliable RL10 engine.
• At Mahendragiri in Tamil Nadu, is the Liquid Propulsion System Centre
[LPSC]. Here work on developing India’s own cryo - engines has been
quietly moving. The system involves materials working at 250 deg below
zero and pumps at speeds of 40,000 rpm. There are also complex metering,
monitoring, integrating technologies involved. The engines are required to
fire for about 700 seconds during the final stage of a launch providing 7
tones of thrust..
• The Engine works on ‘Staged Combustion Cycle’ with an integrated turbo
pump running at around 42,000 rotations per minute (rpm). It is also
equipped with two steering engines developing a thrust of 2 kN each to
enable three-axis control of the launch vehicle during the mission. Another
unique feature of this engine is the closed loop control of both thrust and
mixture ratio, which ensures optimum propellant utilization for the mission.
CRYOGENICS IN MEDICAL FIELD
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CRYOSURGERY
Cryosurgery (also called cryo therapy) is the use of extreme cold produced by
liquid nitrogen (or argon gas) to destroy abnormal tissue.
Cryosurgery is used to treat external tumors, such as those on the skin.
For internal tumors, liquid nitrogen is circulated through a hollow instrument
called a cryoprobe.
Cryosurgery has been used for many years in the treatment of skin cancer
BENEFITS OF CRYOSURGERY
Cryosurgery is very effective and is less expensive than other treatment.
It can be done in your health care provider’s office and an anesthesia is
not necessary.
The treatment can be safely repeated and may be used along with
standard treatments such as surgery, chemotherapy, Harmon therapy and
radiation.
It can be used for patients who are not good candidates for conventional
surgery because of their age or other medical condition.
It is used to treat skin lesions such as freckles (for cosmetic reasons),
hemorrhoids and some skin cancers
CRYOGENICS IN MANUFACTURING
FIELD
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Cryogenic treatment works on Reamers, Tool bits, Tool punches,
Carbide Drills, Carbide Cutters, Milling Cutters, Files, Knives,
Reciprocating Blades, Dies and cutting tools.
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Stress relives ferrous and non ferrous castings and forgings for
enhanced dimensional stability and surface finish upon finish
machining.
CRYOGENICS IN ELECTRONICS FIELD
The super conducting electronic devices like SQUID (Super conducting quantum
interference device) are used in sensitive digital magnetometers and voltmeters.
Zero friction bearings use magnetic field instead of oil or air, derived from the Meissner
effect associated with super conductivity.
Super conducting electric motors are constructed approaching zero electric loses.
CONCLUSION
Refrigeration and cryogenic cooling technology share a
common history and there are many similarities in the
underlying thermodynamics. The significant differences lie in
the temperature range of interest and the properties of the
working fluids.
Whilst it is most unlikely that cryogens can ever replace
more familiar refrigeration technology for ‘high’ temperature
cooling, there may be niche applications where they can offer
an interesting alternative.
REFERENCES
• Cryogenic engines, http://en.wikipedia.org
• Cryogenic engines, www.astronautix.com
• Cook P. & Richatdson R.N., Cryogenic safety
manual, see www.ior.org.uk
• GIST (Previously BOC Transhield), see
www.gistworld.com
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