Page 170 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: GGY Final Pages
Encyclopedia of Physical Science and Technology EN004D-156 June 8, 2001 15:28

Cryogenic Process Engineering

Klaus D. Timmerhaus
University of Colorado

I. General Applications
II. Low-Temperature Properties
III. Refrigeration and Liquefaction
IV. Separation and Purification of Gases
V. Equipment for Cryogenic Processing
VI. Storage and Transfer Systems
VII. Instrumentation
VIII. Safety

GLOSSARY Helium II Superfluid form of helium-4 liquid existing
below 2.17 K.
Coefficient of performance Criterion used to compare Joule–Thomson expansion Expression representing an
refrigerator performance. isenthalpic throttling process.
Cryobiology The use of cryogens in applications of n-Hydrogen Equilibrium hydrogen existing at ambient
biology. temperatures consisting of 75% orthohydrogen and
Cryocooler Small cryogenic refrigerators and liquefiers. 25% parahydrogen.
Cryogen Any fluid that becomes a liquid below MLI A high-vacuum, multilayered insulation used in
125 K. cryogen storage and transfer.
Cryogenics Term commonly associated with activities Orthohydrogen Higher energy form of hydrogen result-
performed below 125 K. ing from the nuclear spin of the two protons in the same
Cryomedicine The use of cryogens in various medical direction.
and surgical applications. Parahydrogen Lower energy form of hydrogen resulting
Cryopumping Procedure for attaining ultrahigh vacuum from the nuclear spin of the two protons in the opposite
by the freezing of residual gases in a chamber. direction.
Dewar Any cryogenic container shielded by a vacuum- Regenerator Heat exchanger that periodically stores
insulated space. and releases heat from a matrix of high heat
Figure of merit Criterion used to compare liquefier per- capacity.
formance. Superconductivity Simultaneous disappearance of elec-
Helium I Normal form of helium-4 liquid existing above trical resistivity and the appearance of perfect diamag-
2.17 K. netism in a material.

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