Effect of “crimped” glass wool structure on effective thermal conductivity
Hussein Humaish, Laurent Marmoret, Christine Pelegris and Hassen Beji
This paper refers to a glass wool insulation material which is produced by crimping process. This process has been developed to improve the mechanical performance of the material by modifying the local orientation of the fibers to obtain a more isotropic texture. The intention of the present investigation is then to evaluate the effect of this process on the effective thermal conductivity of the glass wool material. Several characterizations (specific surface area, density, air permeability, anisotropic factors) have been investigated to determine the morphological properties of the material and to identify relevant parameters. Experimental thermal conductivities have been measured by using the guarded hot plate (steady state technique) and the hot disk (transient plane technique). The results indicate the quasi-isotropic character of the thermal conductivity of the crimped glass wool. Series and parallel models have been used to estimate the total heat transfer and the contribution of the radiation, convection and conduction modes on the effective thermal conductivity. For insulation materials of relatively large density (bulk density equal to 69 kg.m–3), the model has shown that the heat transfer due to radiation is weak and is mainly controlled by the gas conduction. The convection mode cannot be neglected because of the free mean path of the fibrous material (0.226 mm) which is much higher than the mean pore radius (10 μm).
Keywords: Building insulation, glass wool, guarded hot plate, hot disc, effective thermal conductivity, anisotropy