An estimation method of the plane directional thermal conductivity of fibrous heat insulators using both the cyclic heat and transient hot-wire methods

摘要

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 conductivity λ{sub}h 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 λ{sub}h is shown to be equal to (the square root of (λ{sub}xλ{sub}y)), that is, a geometrical mean of the thermal conductivities in the direction of the plane and the thickness λ{sub}x, λ{sub}y of the anisotropic materials. In addition, as for a fibrous heat insulator of alumina silica blanket (ρ= 125 kg/m{sup}3), the thermal conductivity λ{sub}h and the thermal conductivities λ{sub}x and λ{sub}y 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 on λ{sub}x, it is confirmed that the present simple method can estimate the measured values fairly well.