Numerical investigation on effective thermal conductivity of fibrous porous medium under vacuum using Lattice-Boltzmann method

Abstract

Up to now, the application of fibrous porous medium (FPM) has gained considerable attention within the field of adiabatic materials, especially in the field of vacuum insulation panels (VIP). In the present study, a holistic numerical approach that combined with a modified 3D fibrous porous structure generation method and a D3Q19-BGK Lattice-Boltzmann method (LBM) is developed to investigate the dependence of effective thermal conductivity (ETC) on the microstructure of FPM under vacuum condition. The modified generation approach can effectively avoid fiber interpenetration. Model is validated with experimental and theoretical data. Influences of different microstructure parameters such as fiber diameter and fiber orientation angle are presented in detail. Results indicated that FPM structure with finer diameter leads to smaller pore size and has a more excellent ability to maintain the lower effective thermal conductivity under higher pressure. Besides, the more the length direction of fiber is inconsistent with the heat transfer direction, the better the insulation performance is. In addition, coupling effect is existed between the fiber diameter and orientation angle under high vacuum. These results are of great significance for the core material optimization of vacuum insulation panels.