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The growth of the cryogenic industry over the past ten years and the accumulated experience in liquefaction, transportation, and storage have resulted in wide applications of cryogenic fluids. Fluids that formerly belonged to the realm of laboratory curiosities such as liquefied methane, oxygen, nitrogen, hydrogen, and helium have become commonplace, not only in the laboratory, but also in large-scale industrial operations. As the uses of these fluids have become widespread, their transportation to the point of use and their storage for extended periods have demanded improved insulation techniques. The doublewall, vacuum-insulated dewar flask which was the most widely used method for storing small quantities of cryogenic fluids has been supplanted by vessels in which thousands of gallons can be stored ready for use in the various industrial applications or as fuel for space missions. The thermal insulations which are required to meet the needs of the cryogenic industry fall into two major categories: (1) insulations which are gas filled and (2) insulations in which the gas has been evacuated to achieve a desired low pressure. The continuing advances being made in the thermal effectiveness of these insulations, particularly of the evacuated type, have brought about the need for an apparatus which not only can operate at cryogenic temperatures, but in addition has the required sensitivity to measure thermal conductivities several orders of magnitude lower than those of insulation materials encountered in industrial practice. Such an apparatus must be capable not only of measuring conventional homogeneous thermal insulations, but also permit the measurement of properties of materials of very high anisotropy as exemplified by multilayer insulations. To carry out meaningful measurements, the effects of variables which control the performance of the insulation such as density, type, and pressure of gas within the insulation, applied compressive loads and radiation interchange with apparatus surfaces have to be closely controlled. A thermal-conductivity measuring apparatus has to be useful in evaluating the thermal performance of different insulation materials and material combinations, as improvements of insulations take place, and to assist in the continuing development of new thermal insulations. To meet these demands, different laboratories either modified existing apparatus or developed new apparatus to carry out measurements. Intercomparison of results obtained by the different laboratories was hampered by the lack of well-characterized standard test material and by the variations in the type of test apparatus used. The continuing expansion of the cryogenic industry is predicated on the availability of thermal insulations with predictable performance characteristics. The standardization of test methods for measuring conductivity will be an important factor in achieving this objective.
Glaser, P. E.
Section headsymposium chairman, Arthur D. Little, Inc., Cambridge, Mass.