I-6 RATERMANN Cryogenics T (844) 341-3433 S F (844) 341-3444 S Website: www.rmicryo.com S Email: [email protected] Worcester Control Valves Reference Guide Worcester Control Valves The word cryogenic has its origin in the Greek word meaning cold. Generally, it’s applied to science and engineering applications at very low temperatures. THE CRYOGENS — The range of cryogenic temperatures is commonly restricted to temperatures below -150˚C. (123K or -238˚F). Above this temperature, the normal design procedures used in the refrigeration industry are usually adequate, and most materials behave in a fairly normal manner. But below this temperature, special techniques must often be used. With the definition just given, there are about a dozen common substances having normal boiling points in the cryogenic range. These cryogenic substances, frequently referred to in their liquid state as cryogens, are helium, hydrogen, deuterium, neon, nitrogen, carbon monoxide, fluorine, argon, oxygen, methane, krypton, and nitric oxide. In addition, liquid air is often considered to be a cryogen, although actually it is a mixture of other cryogens. Figure 1 shows these substances arranged on a temperature scale at points corresponding to their normal boiling points. The normal boiling point is the temperature at which a liquid changes into a vapor at atmospheric pressure. Note that helium has the lowest boiling point of any substance, very close to the lowest possible temperature of absolute zero. Table 1 shows some of the important properties of the cryogens listed above. Note that, except for helium, the cryogens all become solid at some temperature in the range above the boiling point of helium. Another important fact is that all of the cryogens have critical temperatures below normal ambient temperatures but critical pressures above normal atmospheric pressure. Cryogenics -150.F -200.F -250.F -300.F -350.F -400.F -450.F Nitric Oxide (-241.0.) Krypton (-244.0.) Methane (-258.6.) Oxygen (-297.3.) Carbon Monoxide (-312.6.) Fluorine (-306.2.) Nitrogen (-320.5.) Neon (-410.7.) Deuterium (-417.3.) Hydrogen (-423.0.) Absolute Zero (-460.) Helium (-452.1.) Argon (-302.6.) HERE'S HOW the normal boiling points of cryogens compare. Figure 1
