Abstract:

To optimize the aerogel structure and reduce the effective thermal conductivity of the aerogel, the force field, atomic model, heating and cooling calculation modules were added to large-scale atomic/molecular parallel simulator(LAMMPS) to accurately simulate the adsorption of water molecules by silica aerogels and heat transfer processes. The results show that the adsorption capacity of silica aerogels to water molecules increases as the water content increases, showing a significant rise followed by an equilibrium state. With the increase of temperature, the thermal movement of water molecules intensifies, and the adsorption capacity of silica aerogels to water molecules decreases. However, the free water molecular weight increases. As the pressure increases, the collision frequency of water molecules and silica aerogels increases, resulting in an increase in adsorption capacity. When the water content increases and the temperature decreases, the mutual squeezing among water molecules promotes more water molecules to penetrate into the interior of silica aerogels, meanwhile, the thermal motion of water molecules slows down, which is not conducive to their escape from the aerogels pores, resulting in an increase in the number density of the silica aerogels system. Silica aerogels form water films by adsorbing water molecules, and the water films constitute "water bridges". With the increase of water content, the connectivity among "water bridges" is enhanced, and the contact area increases, leading to an increase in effective thermal conductivity of silica aerogels and significant degradation of thermal insulation.

Key words: silica aerogels, adsorption capacity, water molecules, water content, thermal conductivity