Abstract
We have designed an apparatus for measuring thermal conductivities of thermal insulations in the temperature range from 100 to 1500℃ under atmospheric pressure and vacuum conditions by applying the cyclic heat method, and have tried to measure the thermal conductivities of alumina silica board and alumina silica blanket under vacuum condition of about 1 Pa at high temperature. The measured values under vacuum condition are shown to be smaller than those obtained by subtracting thermal conductivity of air from those of the specimen under atmospheric pressure. If the whole thermal resistance of the specimen is composed of resistances based on conductions in solid and gas, and radiation, the measured thermal conductivity under the vacuum condition would agree with the above subtracted thermal conductivity. In this study, validity of the thermal resistance model has been investigated by using electrical analog which considers various sizes of porosities in the interior of junction where the adjacent fibers are intersected.
