ABSTRACT
The use of cryogenics and access to low temperatures, once conned to the laboratories searching for the liquefaction of the permanent gases [1], is now almost worldwide. All lowtemperature apparatus must be contained in a cryostat, a word derived from Greek meaning literally frost apparatus. Cryogenic storage and refrigeration are becoming common in our everyday lives. Liquid nitrogen is used for food and living tissue preservation, liquid oxygen for medical patient respiration, and liquid hydrogen for power generation, transportation, and propulsion. Large superconducting magnets are used for magnetic resonance imaging (MRI). All these applications use either vacuum-insulated containers (dewars) or foam-insulated vessels to contain the cryogens. This is because direct exposure to environmental radiation supplies more than enough heat to evaporate the cryogen in a short time. In the future, the use of cryogenic equipment will rapidly increase with new demands, for example, in computers and communication systems (cold and superconducting electronics), medicine (surgery and diagnostics), materials fabrication, transportation (motor vehicles, ships, and magnetically levitated trains), and space travel (propulsion, cooling, and water generation), particularly in the hydrogen economy. This last item is important because large amounts of hydrogen will be used, stored, and transported. There is no better way to store or transport hydrogen than as a liquid cryogen, which is more
CONTENTS
17.1 Introduction ........................................................................................................................ 597 17.2 Storage Vessels, Dewars, and Storage Techniques ........................................................ 598
17.2.1 Non-Vacuum-Insulated Containers .................................................................... 598 17.2.2 Dewars ..................................................................................................................... 599 17.2.3 Zero Boil-Off Storage ............................................................................................. 602
17.3 Small-Scale Refrigeration ..................................................................................................603 17.3.1 4He Evaporation Refrigeration .............................................................................603 17.3.2 3He Evaporation Refrigeration .............................................................................604 17.3.3 3He-4He Dilution Refrigeration ...........................................................................606 17.3.4 Refrigeration above 4.2 K ...................................................................................... 611
Acknowledgments ...................................................................................................................... 613 References ..................................................................................................................................... 613
safe, less expensive, and at higher density than any other form. Scientically, cryogenics are used in virtually every area of research, with the widest uses in propulsion (combustion and fuel cells), condensed matter and particle physics, physical chemistry, geology, biology, and medical sciences.
