Study On The Thermal Conductivity Of Aerogels

The silica aerogel is a material with the porous three-dimensional network-shaped structure, it has a low thermal conductivity, high specific surface area, low density and other characteristics, and thus has a wide application value.This paper take a study on the thermal conductivity of silica aerogels, build a kinetic theory collision model. The collision area is unified as a whole of the area of gas-solid collisions and the collision between gas molecules. Deduce the formula of the free path of gas molecules within the aerogel, and also the thermal conductivity of the aerogel. In-depth analysis of the influence of the aerogel density, the specific surface area, temperature, and pressure on the thermal conductivity and the gas molecules free path. And make a comparison with the free path of the gas in free space and the thermal conductivity. In Constant temperature, the thermal conductivity of the air molecules in free space in a high pressure environment tends to be constant, while the thermal conductivity of the aerogel increases gradually with increasing pressure. The mean free path of air molecules in the aerogel and in the free space curve begins to merge in high pressure. The specific surface area of the aerogel is only associated with the density of the solid material constituting the aerogel mesh structure. The thermal conductivity of the aerogel increases with the reduction ratio of the surface area. Under different pressures, the thermal conductivity of the aerogel changes with the change of temperature. In the high pressure environment, the thermal conductivity of the aerogel increases with increasing temperature.The model of gas molecules Collision is introduced into the solid thermal conductivity Analysis. Build Aerogel solid-phase heat conduction model with a carrier of phonon. Taking into account of the vertical heat flow and lateral heat flow, calculate the free path of the horizontal and vertical phonon using the size of the solid unit of aerogel, at the same time taking into account the phonon scattering and obtain phonon free path formula and thermal conductivity equation. Under the appropriate pressure, the thermal conductivity of the aerogel decreases while the temperature rises. Under the low pressure environment, the thermal conductivity of the aerogel decreases as the temperature rises.Create a simplified structure of the gas-solid silica aerogel cycle model. Using air thermal conductivity and the thermal conductivity of the silica matrix to calculate the thermal conductivity of the aerogel which is related to density of the gel, the calculation result is slightly larger than the experimental results, and the size of the gel pore is the main reason for the difference between the results.