Impacts of liquid phase distribution on the effective thermal conductivity of closed-cell thermal insulation

This paper proposes a multiscale effective thermal conductivity model combined with liquid phase distribution to explore in detail the influence of the internal structure of closed-cell thermal insulation on the thermal behavior in the presence of moisture. By simulating the liquid phase distribution in the cracks between the insulation cell skeleton and combining it with the representative elementary volume (REV) scale and macroscopic scale thermal conductivity models, the correlations between the structural parameters, saturation, and effective thermal conductivity of phenolic thermal insulation are analyzed. A critical saturation point is proposed for the first time, and the related impact factors are discussed. For the heat and moisture transfer in porous media, the larger the critical saturation, the better the insulation performance. Based on the newly developed improved effective thermal conductivity model, nine groups of phenolic samples with different structural parameters were investigated to compare the impact of porosity, closed-open pore volume ratio, relative deviation ratio, contact angle, and closed-pore diameter on the effective thermal conductivity. Simulation results indicate that the influence of the liquid phase distribution is mainly reflected at low saturation at the REV scale; at the macroscale, the influence of the liquid phase distribution is significantly reduced.