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| Cryogenics |
| Cryogenics means "the production of
icy cold"; 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. The workers at the National Institute of Standards
and Technology at Boulder, Colorado have chosen to consider
the field of cryogenics as that involving temperatures below
–180 °C (93.15 K). This is a logical dividing
line, since the normal boiling points of the so-called permanent
gases (such as helium, hydrogen, neon, nitrogen, oxygen,
and normal air) lie below -180 °C while the Freon refrigerants,
hydrogen sulfide, and other common refrigerants have boiling
points above -180 °C.
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Industrial application
Liquefied
gases, such as liquid nitrogen and liquid helium, are used
in many cryogenic applications. Liquid nitrogen is the most
commonly used element in cryogenics and is legally purchasable
around the world. Liquid helium is also commonly used and
allows for the lowest attainable temperatures to be reached.
These liquids are held in either special containers known
as Dewar flasks, which are generally about six feet tall
(1.8 m) and three feet (91.5 cm) in diameter, or giant tanks
in larger commercial operations. Dewar flasks are named
after their inventor, James Dewar, the man who first liquefied
hydrogen. Museums typically display smaller vacuum flasks
fitted in a protective casing.
Cryogenic transfer pumps are the pumps used on LNG piers
to transfer Liquefied Natural Gas from LNG Carriers to LNG
storage tanks.
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Cryogenic processing
The field of cryogenics advanced during World War II when
scientists found that metals frozen to low temperatures showed
more resistance to wear. Based on this theory of cryogenic
hardening, the commercial cryogenic processing industry was
founded in 1966 by Ed Busch. With a background in the heat
treating industry, Busch founded a company in Detroit called
CryoTech in 1966. Though CryoTech later merged with 300 Below
to create the largest and oldest commercial cryogenics company
in the world, they originally experimented with the possibility
of increasing the life of metal tools to anywhere between
200%-400% of the original life expectancy using cryogenic
tempering instead of heat treating. This evolved in the late
1990s into the treatment of other parts (that did more than
just increase the life of a product) such as musical instruments
or amplifier valves (improved sound quality), brass instruments
(improved tonal characteristics), baseball bats (greater sweet
spot), golf clubs (greater sweet spot), racing engines (greater
performance under stress), firearms (less warping after continuous
shooting), knives, razor blades, brake rotors and even pantyhose.
The theory was based on how heat-treating metal works (the
temperatures are lowered to room temperature from a high degree
causing certain strength increases in the molecular structure
to occur) and supposed that continuing the descent would allow
for further strength increases. Using liquid nitrogen, CryoTech
formulated the first early version of the cryogenic processor.
Unfortunately for the newly-born industry, the results were
unstable, as components sometimes experienced thermal shock
when they were cooled too fast. Some components in early tests
even shattered because of the ultra-low temperatures. In the
late twentieth century, the field improved significantly with
the rise of applied research, which coupled microprocessor
based industrial controls to the cryogenic processor in order
to create more stable results.
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 statin drugs, must occur at low temperatures of
approximately -100 °C. 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 makes cryogenic
milling (grinding) an option for some materials that cannot
easily be milled at higher temperatures.
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Fuels
Another use of cryogenics is cryogenic fuels. Cryogenic fuels,
mainly hydrogen, have been used as rocket fuels. (Oxygen is
used as an oxidizer of hydrogen, but oxygen is not, strictly
speaking, a fuel.) For example, NASA's workhorse space shuttle
uses cryogenic hydrogen fuel as its primary means of getting
into orbit, as did all of the rockets built for the Soviet
space program by Sergei Korolev. (This was a bone of contention
between him and rival engine designer Valentin Glushko, who
felt that cryogenic fuels were impractical for large-scale
rockets such as the ill-fated N-1 rocket spacecraft.)
Russian aircraft manufacturer Tupolev is currently researching
a version of its popular design Tu-154 with a cryogenic
fuel system, known as the Tu-155. The plane uses a fuel
referred to as liquefied natural gas or LNG, and made its
first flight in 1989.
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