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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 low-temperature 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. • 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).
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.
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 • 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) PROCESS1-2: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 • Claude’s system yields more efficient cycle than 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.
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 • Cryogenic treatment works on Reamers, Tool bits, Tool punches, Carbide Drills, Carbide Cutters, Milling Cutters, Files, Knives, Reciprocating Blades, Dies and cutting tools. • 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
