Abstract
An apparatus was developed in order to obtain thermal properties of nonmetallic materials for cryogenic storage tanks.
The present apparatus was designed to determine rapidly heat capacity, thermal conductivity and thermal diffusivity on the base of curve-fitting method developed by Harmathy, but the apparatus developed by authors was markedly different as regards the performance characteristics from that reported by him, that is, the new apparatus could be used to measure thermal conductivity in the wide range, approximately 0.01 to 10kcal/m.h. °C, and to measure heat capacity, thermal conductivity and thermal diffusivity in the temperature range of -180 to +50°C.
Firstly, the study was carried out with the polyurethane foam to confirm the performance characteristics of the apparatus conformed ASTM C177-74 and JIS A 1413. Consequently the three conclusions were found:
(1) the measured values of thermal conductivity at approximately -160°C and +30°C agreed respectively with those obtained by using the guarded hot plate apparatus.
(2) maxima of the relative errors in measurements were estimated to be ±16% for the thermal conductivity and to be ±10% for the thermal diffusivity (in case of structural materials, however, those of concretes were ±5% for the thermal conductivity and ±3% for the thermal diffusivity) and
(3) the time required for measuring thermal properties on a condition was less than 8 hours: it was shorter in 70 to 80% than that attained by the guarded hot plate apparatus.
Secondly, in total seven different commercially available materials were evaluated by use of the apparatus.
The materials investigated were such structural materials as concretes, woods, frozen soils and autoclaved lightweight concretes (ALC) as well as such insulating materials as calcium silicates, phenolic foams and polyurethane foams.
The measured results were as follows:
(1) heat capacity of these materials decreased in a monotone with decreasing in temperature, but each experimental curve on heat capacity to temperature of them had a crook at about 0°C in case of the wood containing water of 50% and the soil containing water of 30% respectively. It may be caused by freezing of the free water in the materials.
(2) thermal conductivity of the insulating materials and ALC decreased monotonically as decrease in temperature, while that of the structural materials except for ALC did not show monotonic decrease with decreasing in temperature.
