LOW TEMPERATURE AND CRYOGENIC INSULATION

RYOLEX® perlite is an inexpensive insulation for low temperature and cryogenic applications. It is widely used because of its low thermal conductivity, cost, ease of handling, non-flammability and low moisture retention. Liquefied gases having boiling points as low as -452°F (-269°C) have created a demand for storage facilities capable of economically reducing evaporation losses. While the storage vessels vary as to configuration, type of supports and accessory equipment, a large majority of the vessels are of double wall construction, and the annulus is filled with expanded perlite. Although other powder insulations have occasionally been used, their greater cost has not warranted their use in most applications. Figure 1 indicates probable values of the apparent thermal conductivity of expanded perlite of from 2 to 12 lbs/ft.³ (32 to 192 kg/m³) at a pressure of one atmosphere and mean temperatures from -300°F to +105°F (-184°C to 41°C).

Figure 1

Atmospheric Service The thermal conductivity of expanded perlite insulation at atmospheric pressure conditions has been shown to correlate directly with density, while perlite gradation has only minor effect on thermal conductivity. Evacuated Service Our RYOLEX® perlite is non-hygroscopic, which adapts it for use under vacuum conditions. If evacuation is to be accomplished in a minimum amount of time, the perlite must be kept dry and the interstitial gas should have a low heat of adsorption. Heat transfer through an evacuated perlite filled annulus is a combination of solid conduction and thermal radiation. Gas conduction is also an important transfer mechanism if the interstitial gas pressure is not reduced to a suitable level. REFERENCES J.L.F. Research, Inc., Reports dated December 24,1962, January 2,1964, July 1,1965. "Thermal Conductivity of Expanded Perlite Cryogenic Fill Insulation," G.R. Kinzer, Jr., ASHRAE Journal, February 1963. "Thermal Conductivity of Perlite at Low Temperatures," L. Adams, Cryogenic Technology, March-April, 1965.

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