Cryogenic engineering is a sub stream of mechanical engineering dealing with cryogenics, and related very low temperature processes such as air liquefaction, cryogenic engines (for rocket propulsion), cryogenic surgery. Generally, temperatures below the boiling point of Nitrogen (77°K) comes under the purview of cryogenic engineering.
In physics, cryogenics is the study of the production of very low temperature (below −150 °C, −238 °F or 123 K) and the behaviour of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit, cryogenicists use the absolute temperature scales. These are Kelvin (SI units) or Rankine scale (English/US units).
Air liquefaction application is that in manufacturing processes the liquid air product is fractionated into its constituent gases in liquid or gaseous form, as the oxygen is especially useful for use in fuel gas welding and cutting, and the argon is useful as an oxygen-excluding shielding gas in some forms of shielded metal arc welding, while Liquid nitrogen is useful in various low-temperature applications, being nonreactive at normal temperatures (unlike the oxygen) and boiling at 77 K (−196 °C; −321 °F).
A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel (liquid hydrogen) or oxidizer (liquid oxygen), that is, its fuel or oxidizer (or both) are gases liquefied and stored at very low temperatures. Notably, these engines were one of the main factors of the ultimate success in reaching the Moon by the Saturn V rocket. Most rocket engines are internal combustion engines.
Cryogenic fuels are fuels that require storage at extremely low temperatures in order to maintain them in a liquid state. Cryogenic fuels most often constitute liquefied gases such as liquid hydrogen. Some rocket engines use regenerative cooling, that circulates their cryogenic fuel around their nozzles before the fuel is pumped into the combustion chamber and ignited. This arrangement was first suggested in 1940s. The Saturn V rocket that sent the first manned missions to the moon used this design element, which is still in use today. Quite often, liquid oxygen is mistakenly called cryogenic "fuel", though it is actually an oxidizer and not a fuel. Russian aircraft manufacturer Tupolev is currently researching a version of its popular Tu-154 design but with a cryogenic fuel system, designated the Tu-155. Using a fuel referred to as liquefied natural gas (LNG), its first flight was in 1989. India developed the technology in 2008 for use in their GSLV rockets.
During World War II, when powerful rocket engines were first considered by the German, American and Soviet engineers independently, all discovered that rocket engines need high mass flow rate of both oxidizer and fuel to generate a sufficient thrust. At that time oxygen and low molecular weight hydrocarbons were used as oxidizer and fuel pair. At room temperature and pressure, both are in gaseous state. Hypothetically, if propellants had been stored as pressurized gases, the size and mass of fuel tanks themselves would severely decrease rocket efficiency. Therefore, to get the required mass flow rate, the only option was to cool the propellants down to cryogenic temperatures (below −150 °C, −238 °F), converting them to liquid form. Hence, all cryogenic rocket engines are also, by definition, either liquid-propellant rocket engines or hybrid rocket engines.
Various cryogenic fuel-oxidizer combinations have been tried, but the combination of liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer is one of the most widely used. Both components are easily and cheaply available, and when burned have one of the highest entropy releases by combustion, producing specific impulse up to 450 s (effective exhaust velocity 4.4 km/s).
The major components of a cryogenic rocket engine are the combustion chamber (thrust chamber), pyrotechnic igniter, fuel injector, fuel cryopumps, oxidizer cryopumps, gas turbine, cryo valves, regulators, the fuel tanks, and rocket engine nozzle. In terms of feeding propellants to combustion chamber, cryogenic rocket engines (or, generally, all liquid-propellant engines) work in either an expander cycle, a gas-generator cycle, a staged combustion cycle, or the simplest pressure-fed cycle. The cryopumps are always turbopumps powered by a flow of fuel through gas turbines. Looking at this aspect, engines can be differentiated into a main flow or a bypass flow configuration. In the main flow design, all the pumped fuel is fed through the gas turbines, and in the end injected to the combustion chamber. In the bypass configuration, the fuel flow is split; the main part goes directly to the combustion chamber to generate thrust, while only a small amount of the fuel goes to the turbine
Currently, five countries have successfully developed and deployed cryogenic rocket engines:
LE-5B
- India is still developing its cryogenic application for rocket launch as of January 31, 2011.
Cryosurgery first advantage is that when the neurosurgeon is can utilize low temperature during neurosurgery. The second is that the advancing front of reduced temperatures tends to cause the removal of blood and the construction of blood vessels in the affected area. This means that little or no bleeding results from cryosurgical procedure. The third is that the equipment employs z freezing apparatus (which is about the size of the large knitting needle) that can be placed in contact with the area to be destroyed with a minimum incision to expose the affected area. The equipment used in cryosurgery utilizes teh same operating priciples as teh controlled rate freezer. The flow of liquid nitrogen is controlled by and electrically operated valve.
Besides the preservation or destruction of life, low temperatures can be employed for teh formulation of drugs to release antibodies or other active agents from their cells.
The industries that use cryogenic engineering are:
· Food and beverages
· Gas industries
· Steel plants and allied industries
· Engineering industries
· Chemical industries
· Hospital, pharmaceutical and fertilizer plants
· Research institutes
Here are Samples of applications
CO2 Tanks are used for Transport and Storage of Liquefied CO2 to breweries, engineering industries, foundries, etc. and vaporises convert the liquid gas to gases form through pumps or auto pressure build up system.
The stored liquid nitrogen is used in hospitals for the preservation of clinical samples of tissue and cells at low temperatures and must be maintained at a temperature of -196˚C. (At room temperature, liquid nitrogen boils expanding like steam to fill a volume 2000 times its liquid state). And also liquid oxygen for patient use and the use of helium for MRI machines.
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