I-7 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 Carbon monoxide and nitric oxide, although classed as cryogens by the definition, are not of significant commercial importance in the liquid state to consider further. The inert cryogens: neon, argon, and krypton, are used primarily in the gaseous form in electrical lighting, particularly in advertising signs. They occur in the liquid state during manufacture from air, however, and are thus sometimes called cryogens. They have some use in scientific work where their special properties in the liquid state are needed, but they will not be discussed in detail in this bulletin. The seven remaining cryogens are commercially significant and will be discussed in more detail. HELIUM – Liquid helium is of particular interest to physicists because of its very low boiling point. Temperatures approaching absolute zero to within a fraction of a degree can be obtained by equipment using a special isotope of helium designated He3. Normal helium, designated He4, cannot be cooled to the low temperatures obtainable by the He3 but is a useful cryogen and is particularly of interest because of its behavior below 2.2°F. Normal helium gas is quite useful because of its lightness, inertness, high thermal conductivity, and the fact that it does not normally condense into liquid even at the cryogenic temperatures of liquid hydrogen and other cryogens. HYDROGEN – Liquid hydrogen has become very important in recent years because of its usefulness as a rocket fuel. It is a clean fuel that burns with no smoke or soot. It is commonly used with either liquid oxygen or liquid fluorine as the oxidizer. Liquid hydrogen is also used as an additive in gasoline and in the production of synthetic compounds from hydrocarbons. Hydrogen is normally produced from natural gas or other hydrocarbons and is currently produced at the rate of several tons per day in the United States. DEUTERIUM – Liquid deuterium is liquified heavy hydrogen or an isotope of hydrogen with a neutron in the nucleus of each atom, in addition to the proton contained in atoms of ordinary hydrogen. Deuterium is useful for making heavy water, a moderator in certain types of nuclear reactors. OXYGEN – Liquid oxygen or LOX has become important in recent years not only because of its usefulness in rockets but also because it is a convenient method of storing large quantities of oxygen in a relatively small space. An important application is the storage of oxygen for breathing in high-altitude airplane and space-vehicle flight. Although liquid oxygen is odorless and nontoxic, it is extremely reactive. Its storage creates some hazard. Containers and piping must be very clean. Such reactive materials as most plastics, titanium, and aluminum should be avoided. FLUORINE – Liquid fluorine is primarily of interest because of its potential as an oxidizer with hydrogen and other fuels for rocket propulsion. It is very hazardous to handle and store, however. It produces toxic exhaust gases, and is used much less frequently than oxygen. NITROGEN – Liquid nitrogen is probably the most commonly used of the cryogens because of its inertness and the fact that it is relatively inexpensive. In fact, liquid nitrogen can be purchased for about the same price as gasoline, including taxes. It is used as a pressurant gas and for general-purpose cooling in the cryogenic temperature range. It is quite helpful in flushing out cryogenic systems using oxygen or hydrogen. It is finding increasing use in the freezing and transporting of food and other perishables, in medicine and surgery, in the preservation of biological specimens, and in the operation of chambers which simulate the conditions of outer space. It is odorless, colorless, and nontoxic. Properties of Cryogens Table 1 Normal Normal Liquid Vapor Vapor Enthalpy of boiling point melting point density density density vaporization Critical Critical (at 1 atm) (at 1 atm) (at nbp)† (at nbp) (at 70°F.,1 atm) (at nbp)† temperature pressure Cryogen °F °F lb/ft3 lb/ft3 lb/ft3 Btu/lb °F psia Helium 4 -452.1 -453.5* 7.80 1.06 0.01035 9.9 -450.2 33.2 Hydrogen -423.0 -434.5 4.43 0.0803 0.0522 194.2 -399.8 188 Deuterium -417.3 -426.0 10.7 0.16 0.01041 134 -390.8 239 Neon -410.7 -415.4 74.9 0.593 0.0522 39.4 -379.7 395 Nitrogen -320.5 -345.9 50.4 0.2756 0.0725 85.9 -232.8 492 Carbon monoxide -312.6 -337.1 50.6 0.312 0.0725 92.8 -218.2 509 Fluorine -306.2 -363.2 94.5 0.537 0.0989 77.7 -200 808 Argon -302.6 -308.7 87.4 0.37 0.1033 70.2 -187.6 706 Oxygen -297.3 -361.8 71.2 0.296 0.0828 93.5 -181.8 730 Methane -258.6 -296.4 26.3 0.11 0.0416 219 -116.5 673 Krypton -244.0 -250.9 135.0 0.52 0.2149 46.8 -81.4 720 Nitric Oxide -241.0 -262.6 79.3 0.204 0.0777 199 -137.2 945 *at 1,514 psia. †nbp = normal boiling point
