FEATURE
INCORPORATING COLD CHAIN
34
Water-based mixtures and solutions have
come to be known by the generic name
‘brines’. Originally, ‘brine’ meant only sodium
chloride dissolved in water but now includes
many other substances such as the organic
glycols. Sodium chloride brines have been
the most widely used sub -0°C heat transfer
recirculating fluids working down to about
-15°C, which requires a minimum brine
solution strength of 16% by weight. However,
from around 10% brine solution strength,
which has a -9°C freezing point, sodium
chloride brine equates to about 80 000ppm
of dissolved chlorides, which will not cause
fouling problems by precipitating out of
solution but will start to cause high rates of
corrosion on many types of steel surfaces,
including stainless steel. Traditionally, sodium
chloride salt brines have been by far the
cheapest practical option for refrigeration
circuits, where temperatures required are
only a few degrees below zero centigrade
and they are still widely used today.
Mixing water with, for example, glycol
liquids propylene glycol or ethylene
glycol, is easier than making up salt brine
solutions — but costlier. Ethylene glycol
gases in 1876, which made it possible to use
gases in addition to ammonia as refrigerants
such as sulphur dioxide (SO 2 ) and methyl
chloride (CH 3 Cl), which became widely
used until the late 1920s.
At the start of the 20th century, the
change from using ice to installing
on-site refrigeration plants had gained
momentum worldwide, not only on
land but during the preceding 20 years
on ships, particularly those used for
transporting meat and mutton from New
Zealand to the British Isles. Commercial
success of refrigerated shipping led
to broader meat and dairy booms in
Australasia and South America.
Many of the refrigeration plants
installed up until the 20th century
produced only ice, which continued to
be used by existing facilities. By producing
their own ice instead of buying it, users
now had both technical and financial
control of their refrigeration
requirements. However, to
enable separate refrigeration
sections to be connected to
a single central refrigeration
generator resulted in major
investments in developing
refrigerated water-based
circuits capable of maintaining
temperatures of frozen foods
and perishables at levels of
minus 30°C or even lower down
Dunedin, the first commercially successful refrigerated
to minus 40°C.
ship, loading in 1882.
LIQUID PHASE
More than 100 years earlier, Dr William
Cullen had demonstrated the earliest
known artificial refrigeration at the University
of Glasgow in 1748 by allowing ethyl ether
to boil in a partial vacuum. Subsequently,
among many other creative inventors and
chemists, an American, John Gorrie, who
was also a physician, and English chemist
Michael Faraday, were instrumental in
developing circuits in which ammonia
gas was recirculated after compression,
followed by condensation and vaporisation
to achieve practical refrigeration.
The first gas absorption refrigeration
system using ammonia dissolved in water
was developed by Ferdinand Carré of
France and patented in 1860. Carl von
Linde, professor of engineering at the
University of Munich in Germany, began
researching refrigeration in the 1860s in
response to demand from brewers. He
patented an improved method of liquefying
The 1934 oil on canvas painting Filling the Ice House. Ice used to be the primary way of
refrigerating products.
www.coldlinkafrica.co.za
COLD LINK AFRICA • November/December 2018