A pore-scale physical model for the effective thermal conductivity of porous materials-based phase change composites (PCCs) based on fractal geometry

Abstract

The effective thermal conductivity (ETC) of porous materials-based phase change composites (PCCs) is key for evaluating thermal storage properties; however, it strongly depends on complex microstructures. To address this, fractal geometry is adopted to characterize pore structure and rough surface morphology of PCCs. The solid-liquid thermal contact resistance (TCR) is incorporated to develop a pore-scale physical model for heat conduction through PCCs. The predicted TCR and ETC are in good agreement with experimental data. TCR contributes up to 30.8 % of the ETC when the ratio of solid to liquid thermal conductivity equals 2. The ETC of PCCs increases with the increase of saturation and the decrease of porosity. And it decreases as the fractal dimensions for pores and tortuosity increase. However, the enhancement of the fractal dimension for the rough surface means the increment of the solid-liquid contact density, which reduces the solid-liquid TCR and enhances the ETC accordingly. The proposed pore-scale physical model provides insights into the thermal storage mechanisms of PCCs, and also establishes a theoretical foundation for the applications of PCCs in latent heat storage, smart buildings, microelectronics cooling and spacecraft thermal control systems.