THE INFLUENCE OF NATURAL CONVECTION ON EFFECTIVE THERMAL CONDUCTIVITY OF ANISOTROPIC OPEN-CELL FOAM

Abstract

Accurately predicting the effective thermal conductivity (ETC) of anisotropic open-cell foam when natural convection effects are present is a significant challenge. In this work, a comprehensive process was built to predict ETC of anisotropic open-cell foam reconstructed using X-ray computed tomography considering natural convection effects at pore scale. The hybrid thermal lattice Boltzmann method was built to predict the ETC when natural convection was considered. Results show that numerically predicted ETCs fit well with experimental results for both pure conduction and considering natural convection effects, with a relative error of 4.59% and 5.73%. The ETC increases gradually before the flow enters the interacting boundary layer region and then rapidly, and ETC increases 167.8% when local Ra is 3617.15. The anisotropy of the ETC in the orthogonal directions is positively proportional to the aspect ratio of the Feret diameter. The natural convection enhances the anisotropy of ETC under pure conduction conditions when thermal conductivity of the fluid and foam skeleton are the same; when thermal conductivity is not the same, the natural convection weakens the anisotropy of heat transfer under pure conduction conditions. When structure anisotropies are 1.04, 1.38, and 1.44, the anisotropies of ETC decrease by 0.66%, 7.23%, and 8.84% at k_r = 10 and 0.27%, 4.33%, and 4.51% at k_r = 0.1. These findings provide valuable insights for the design of anisotropic open-cell foams for thermal insulation applications.