ABSTRACT
The field of studies, development, and applied use of a cryogen is easily transposed into "cryogenics" and embraces the science that deals with the equipment, processes, and products involving very low-temperature refrigeration. Cryogenic engineers have generally agreed that for temperatures which are lower than -128.89°C (-200°F), the term cryogenics can be applied. Small quantities of cryogens can be produced in laboratories and used for research studies. The most widely accepted method used to produce "tonnage" amounts of cryogens is by the fractional distillation of liquefied air. This economical process is commonly referred to as "air separation". Large plant facilities for tonnage production of air-separation products began to become a reality in the US sometime after the end of World War II. Tonnage air-separation plants are classified as merchant or captive plants.
