Abstract
The advantage and shortcoming of anisotropic material of thermal conductivity using as building envelope were analyzed in this paper. The thermal performance of anisotropic material of thermal conductivity was presented by rotating the original rectangular axes so as to determine the principal axes and make the cross-derivative terms disappear. The results indicated that the heat flux vector is commonly not perpendicular to the isothermal surface in anisotropic material. Double skin facade has been successfully applied in many building designs. The application of laminated composite with anisotropic thermal conductivity in double skin envelope was proposed to avoid its disadvantage. The interior envelope in double skin system may be made of laminated glaze or other laminated materials. Basing on the combination of anisotropic material and double skin envelope, the indoor cooling and heating load decrease in summer and winter respectively while the anisotropic material was used as interior building envelope. Especially in summer, the effect of energy saving is obvious since the partial magnitude of conductive heat in the interior envelope could be brought out from the cavity by natural ventilation through it.
Highlights
Thermal conductivity of a material k has great influence on its thermal performance
The other is that the magnitude of heat transfer rate of anisotropic material in one direction is relevant to the temperature gradient in this direction, and relevant to the temperature gradient which is normal to the direction [14]
It can be concluded that this combined double skin envelope system, while the interior envelope is made of laminated composite with anisotropic thermal conductivity, will lower indoor cooling load in summer as well as indoor heating load in winter
Summary
Thermal conductivity of a material k has great influence on its thermal performance. It is a measure of how fast heat will flow in that material. A material is normally assumed to be isotropic It has uniform properties in all directions. It is common practice to evaluate the thermal conductivity k at the average temperature and treat it as a constant in calculations [1] This assumption is realistic for most materials, but some materials, such as laminated composite materials and wood, they are anisotropic and exhibit different structural characteristics in different directions. The thermal conductive theory of anisotropic materials plays an important role in many areas of science and technology. Works about it are still limited and relatively few reported. The purpose of this paper is to analyze the thermal conductive characteristics of anisotropic materials, and to discuss the application of anisotropic material of thermal conductivity in double skin envelope system so as to make use of its advantage and avoid its disadvantage
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