Copious Cooling

the cooling of substances for the production and practical use of temperatures below 170° K. Copious cooling is achieved using working mediums with critical temperatures below 0° C (273.15° K), such as air, nitrogen, or helium. The copious cooling region is divided into three temperature zones: from 170° K to 120° K, from 120° K to 0.5° K (usually called the cryogenic zone), and extremely low temperatures (below 0.5° K).

Copious cooling is achieved by the cooling of gases while throttling, the expansion of gases or vapors with the performance of external work, and adiabatic demagnetization. The last method is used for the generation of extremely low temperatures. The basic purpose of copious cooling is the liquefaction of gases and the separation of gaseous mixtures. Among the latter, the most important application is the separation of air into its components. Air-separation installations produce industrial oxygen (O₂; 99.2, 99.5, and 99.7 percent), technological oxygen (O₂; 95 percent), and pure nitrogen (N₂; 99.998 percent). There are three types of air-separation installations, which are used for the production of gaseous oxygen at atmospheric pressure, gaseous oxygen at high pressure, and liquid oxygen or liquid nitrogen. At the same time, with the addition of the required devices, these installations may be used for the production of raw argon, primary krypton concentrate, and neon-helium mixture.

Copious cooling is of great importance for the extraction of helium from natural gases, for the separation of coke-oven gas and cracked gases, and pyrolysis of petroleum.

Liquid nitrogen is widely used in medicine and biology for the preservation and prolonged storage (up to several years) of blood, bone marrow, blood vessels, and muscle tissue. It is also used in the storage and shipping of foods in refrigerated trucks and railroad cars, where it replaces ice-salt coolers and installations for light-duty refrigeration. In the 1960’s and early 1970’s, the area of rocket technology became a very large consumer of liquefied gases. The monthly consumption of liquid oxygen for these purposes in the USA exceeds 4,000 tons. The use of liquid hydrogen as the fuel and of liquid oxygen as the oxidizer makes it possible to increase the specific thrust of rocket engines to 450 sec from 280 sec. The possibility of using hydrogen in sludge form, as well as atomic hydrogen, which may be stored in the solid state at 4.2° K, is being developed. Liquid ozone and fluorine are very promising for increasing the specific thrust. Copious cooling is of great importance in atomic technology, in which deuterium, the most important product of nuclear power engineering, is produced by low-temperature distillation. Liquid hydrogen and xenon are used in nuclear engineering for filling bubble chambers. Liquid helium, hydrogen, and neon are being widely used in cryogenic vacuum technology. Microcryogenic cooling apparatus is increasingly being used for copious cooling of various mediums. The devices are used for cooling to 77°-1.7°K—for example, infrared radiation detectors, quantum generators (lasers), sensitive semiconductor instruments, superconducting devices, antennas, and other radio-electronic devices. Microcryogenic devices of the throttling and gas-expansion types are being used. A microcooling machine rests easily in the palm of the hand, weighs about 200-300 g, and has a cooling capacity of several watts. Microcryogenic systems in which the cooling sources are sublimating solidified gases, such as methane, nitrogen, argon, or hydrogen, are being developed.

The use of copious cooling in the field of power engineering is promising. Cooling of the conductors in electrical turbogenerators, electric motors, transformers, magnets, and energy storage devices makes it possible to reduce by a factor of 5-6 the weight of these machines and to increase the unit capacity and sharply decrease the electrical resistance of their windings (by a factor of up to 800).