Abstract
An estimation method of the plane directional thermal conductivity of fibrous heat insulators using both the cyclic heat and transient hot-wire methods is proposed. By assuming that the thermal conductivityλh of anisotropic materials like fibrous heat insulators obtained by the transient hot-wire method is equivalent to that of the isotropic materials which have the same bulk density ρ and specific heat c as the anisotropic materials, the thermal conductivity λh is shown to be equal to √λxλy, that is, a geometrical mean of the thermal conductivities in the direction of the plane and the thicknessλx, λy of the anisotropic materials. ln addition, as for a fibrous heat insulator of alumina silica blanket (ρ=125kg/m3), the thermal conductivity λh and the thermal conductivitiesλx andλy are measured in the temperature range -140°C to 300°C using the transient hot-wire method and the cyclic heat method, respectively. Then, from the comparison of the measured results with estimated values onλx, it is confirmed that the present simple method can estimate the measured values fairly well.
