ABSTRACT
This chapter provides design information for engineers working perhaps for the first time in cryogenic processing. The range of greatest interest for cryogenic processing is between -101°C (-150°F) and -46°C (-50°F). Both nitrogen and carbon dioxide are widely used cryogens. Carbon dioxide is more difficult to handle because it is a solid at atmospheric pressure. For each pressure, there is a unique boiling temperature. Reducing the pressure below 1 atm in a Dewar that has been at saturation results in the immediate formation of flash vapor. Since the liquid temperature can be either raised or lowered by changing the pressure, it cannot be assumed that the liquid is always delivered at precisely the same temperature. If the pressure falls below the thermodynamic critical pressure for nitrogen, solid-nitrogen or solid-liquid slush will appear and could cause some trouble in the delivery system. Cryogens behave as other fluids with regard to pressure drop in pipes and choking phenomena.
