The insulation principle of aerogel materials

Number of visits: Date:2017-11-15

The nano-porous structure of aerogel enables it possesses excellent insulation property, whose thermal conductivity is even lower than air. The thermal conductivity of air at normal atmosphere environment is 0.026W / (m·k). At normal atmosphere environment, the thermal conductivity of aerogel is generally less than 0.015 W / (m·k); in vacuum environment, the thermal conductivity of aerogel can reach as low as 0.004W/(m·k)

The excellent insulation performance of aerogel is associated with its high porosity. There are 3 ways for heat transfer: convection, conduction and radiation. In these 3 ways, the amount of heat transferred through convection is very limited because the thermal conductivity of most gases is very low. The commonly used insulation materials are structurally porous, the reason for that is air would take a part of the volume of the insulation material in order to reduce the overall thermal conductivity of the insulation material. Porosity of aerogel is much higher than traditional insulation materials, in which 95% or above is air, making it as low as air with respect to thermal conductivity. There is a massive amount of pores inside aerogel with a pore size below 70nm, air cannot move freely between the pores, which means convection is refrained, therefore, thermal conductivity of aerogel is reduced. Additionally, the solid framework of aerogel is composed of nano-sized particulates, the contact area between any two of which is extremely small, in such a way that conduction is restricted. What’s more, most of the radiation of aerogel is the infrared radiation with the range of 3-5 m. At normal temperature, infrared radiation is effectively constrained, but as temperatures increases, radiation is getting stronger. For further reduction of radiation at high temperature, such opacifier as carbon black or titanium is added. 

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