Cryogenic Technologies

Abstract

Cryogenics is the science that addresses the production and effects of very low temperatures. The word originates from the Greek words “kryos” meaning “frost” and “genic” meaning “to produce.” Under such a definition, it could be used to include all temperatures below the freezing point of water (0 °C). However, Prof. Kamerlingh Onnes of the University of Leiden in the Netherlands first used the word in 1894 to describe the art and science of producing much lower temperatures. He used the word in reference to the liquefaction of permanent gases such as oxygen, nitrogen, hydrogen, and helium. Oxygen had been liquefied at −183 °C a few years earlier in 1887, and a race was in progress to liquefy the remaining permanent gases at even lower temperatures. The techniques employed in producing such low temperatures were quite different from those used somewhat earlier in the production of artificial ice. In particular, efficient heat exchangers are required to reach very low temperatures. Over the years the term cryogenics has generally been used to refer to temperatures below approximately −150 °C (123.15 K, −238.00 °F).