Refrigeration & Equipment Engineering

Unit 8 - Irradiation

8.4.Cryogenic
The term ‘cryogenic’ is derived from the Greek word Kryos which means cold or frost. It is frequently applied to very low temperature refrigeration applications such as in the liquefaction of gases and in the study of physical phenomenon at temperatures approaching absolute zero.

The first low temperature refrigeration system was primarily developed for the solidification of carbon dioxide and the liquefaction and subsequent factional distillation of gases such as air, oxygen, nitrogen, hydrogen and helium. Oxygen was liquefied in 1877 by Coilletet and Pietet. Hydrogen was liquefied in 1898 by Dewar using Joule-Thomson expansion of gases. The liquid oxygen boils at 9.02K (-182.8^oC) and the liquid hydrogen at 20.4K (-252^oC). The liquefaction helium was accomplished in 1908 by H.Kamerlingh Onnes in the famous cryogenic laboratories of the University of Leiden. Initially, by evaporation of liquid helium under high vacuum, the temperature as low as 1.1K(-271.9^oC) was obtained. But by making improvements in the apparatus, a temperature of 0.7K was reached by the year 1928. In 1933, Giauque and Debye proposed the adiabatic demagnetization of paramagnetic salts for attaining the lower temperature and 0.1K was reached through their methods. Now-a-days, the lowest temperature successfully achieved by this method is 0.001K (i.e. very close to absolute zero).

Note: In refrigeration, the temperatures from -100^oC to -273^oC (or absolute zero) are treated as low temperatures.