Novel prediction of thermal conductivities for nano-aerogel and its composites as vacuum insulation panel core

Abstract

For its advanced adiabatic performance and low effective thermal conductivity (ETC), vacuum insulation panel (VIP), as one of newly developed thermal insulation materials, has already been widely employed in many energy saving fields, especially in buildings industry. Nano-porous aerogel is commonly selected as optimal core materials of VIP. Vacuum is a vital parameter affecting on ETC. A novel theoretical model was proposed and the accuracy was verified by experiments to analyze the ETC. A device was designed and verified in this work to accurately collect the VIP internal pressure. The density, temperature, and vacuum effects on ETC were investigated. The result implied that density had a remarkable effect on ETC. A minimum density of 120 kg/m3 at a temperature 300 K gained the lowest ETC. The increase in temperature caused an increase in the radiative thermal conductivity. At ρa = 100 kg/m3and P > 3 kPa, the gas conduction was predominant part influencing ETC. And at ρa = 200 kg/m3and P > 50 kPa, gas conduction became the major infector. As pure aerogels are fragile, the ETC of aerogel composite core with additive fibers was investigated. It was indicated that the optimal fiber content is about 5% when T < 550 K and about 25% when T > 550 K. At T > 400 K, the total ETC increases significantly versus fiber diameter.