Feature
WHEN COLD BECOMES
CRYO-COLD
By Charles Nicolson
The temperature range from the lower limits of general commercial and industrial
refrigeration down to the absolute zero level of minus 273.15°C covers a zone
described as ‘cryogenic’, a relatively old word for an area of technology which
became commercially active only fairly recently.
L
ike many other long-established words, cryogenic is
derived from Greek, specifically cryo meaning cold and
genic which indicates production. The general definition of
cryogenics, therefore, is that it describes the production and
also the behaviour of materials at very low temperatures.
However, there is not yet complete agreement on where the
actual upper temperature boundary of ‘cryogenic’ should be
fixed and defined as such.
HISTORY OF CRYOGENICS
Until about the early 1960s, scientists tended to regard − 150°C
as the transition temperature between ‘refrigerated’ and
‘cryogenic’, even though the US National Institute of Standards
and Technology had chosen −180°C on the basis that normal
boiling points of the gases helium, hydrogen, neon, nitrogen,
oxygen, (which automatically includes normal air) are below
-180°C, whereas manufactured gases such as freon refrigerants,
hydrocarbons, and many other refrigerants have boiling points
above -180°C. In addition, liquefied gases, particularly hydrogen,
nitrogen and oxygen are widely used on a practical basis for
cooling down materials to temperatures where they become
electrically superconducting. However, over the last 50 years or
so as practical methods of working at low temperatures have
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CRYOGENICS REFRIGERATION
Small
pellets and
cylindrical
particles of
dry ice.
become more widely achievable (and affordable), many of
the practical applications which have been developed are now
regarded as cryogenic at temperatures below -50°C although
it can get a bit confusing when specialists working in this field
continue to use terms such as ‘high temperature cryogenic’ for
the range from -50°C down to the boiling point of liquid nitrogen
at -195.79°C.
Prior to the 1940s, earlier experimental work done to achieve
and maintain cryogenic temperatures had been undertaken by
only a few specialised companies mainly to develop methods of
producing hydrogen, nitrogen and oxygen stored in cylinders at
high pressures. Increased availability of these gases along with
backing by governments for technical innovations under wartime
conditions led to more advances across the field of cryogenics
during World War II, in particular when metallurgists determined
that many metals refrigerated down to temperatures between
-80°C and -150°C demonstrated substantial increases in
resistance to wear which was described as ‘cryogenic hardening’.
In 1966, Ed Busch, who had a background in the metals
heat treating industry, started one of the first cryogenic
processing industries when he founded a company in Detroit
called CryoTech for cryogenic hardening on a production
basis. Busch originally experimented with the possibility of
increasing the life of metal machining tools by up to 400%
of the original life expectancy by using cryogenic tempering
instead of lengthy traditional heating and controlled cooling
treatment protocols. After expansions and merging with
another specialist company, 300 Below, in 1995, CryoTech
reportedly became the world's largest as well as the oldest
commercial cryogenic processing company.
RACA Journal I January 2020
Stored gases such as liquid nitrogen, are now used for a large
number of diverse specialty chilling and freezing applications.
Some chemical reactions, like those used to produce the active
ingredients for the widely used although controversial anti-
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