Multi-scale modelling of thermal conductivity of phase change material/recycled cement paste incorporated cement-based composite material

Abstract

Recycled cement paste as a promising shape stabilisation support of phase change material (PCM) has been introduced to prepare cement-based phase change energy storage composite material (PCESCM) due to its advantages regarding building energy conservation and recycling construction waste. In this study, to fully consider the degrees of freedom of material design, a multi-scale framework using lattice Boltzmann method (LBM) is proposed to predict the effective thermal conductivities of hierarchical cement-based PCESCM. The representative volume elements (RVEs) of cement-based PCESCM covering nano-, micro-, and meso-scale are established capturing the complex structural characteristics. Afterwards, an LBM-based thermal conduction model is proposed to simulate the thermal conduction through the reconstructed RVEs. The results indicate that at the nano-scale the thermal conductivity of colloidal C-S-H increases with the packing density of gel particles for both saturated and dried states. At the micro-scale, the thermal conductivities of matrix and PCM composite are highly dependent on the degree of water/PCM saturation. At the meso-scale, the incorporation of PCM composites can lead to a reduction in thermal conductivity. In general, the simulated thermal conductivities of hierarchical cement-based PCESCM using the LBM-based model agree well with the measured values or the estimated results using the analytical model.