Equivalent thermal conductivity model and performance enhancement method for expanded graphite based composite phase change materials

Low thermal conductivity is one of the main bottlenecks limiting the large-scale applications of phase change materials (PCMs) in thermal energy storage. This work focuses on expanded graphite (EG)based composite PCMs (cPCMs), developing a correlation between microstructural parameters and macroscopic properties via experimental testing and data fitting. A new equivalent thermal conductivity model, based on heterogeneous two-phase approach in equivalent media theory, is introduced for EG-based PCMs. This model not only predicts thermal conductivity with high accuracy but also enables active property control during cPCM preparation. To validate model, three types of EG-based cPCMs with different temperature ranges, EG contents, and molding densities were prepared and tested. The thermal properties closely align well with theoretical predictions, with a maximum error <11 % for EG content under 40 wt%. This validates effectiveness of model in enhancing material performance and provides insights into the micro-mechanisms. The proposed approach serves as a blueprint for developing similar models for other heterogeneous two-phase cPCMs.