Low cost and eco-friendly form stable phase change material based on fly ash-expanded graphite binary supporting materials for large-scale application

The high cost and relatively complex packaging technology constrain the use of phase change materials (PCMs) in the field of thermal energy storage. Hence, in this study, the form-stable phase change materials (FSPCMs) of lauric acid (LA)/raw fly ash (RFA)-expanded graphite (EG) with a low cost were prepared via simple direct impregnation method by impregnating LA into RFA and EG, which was used to further enhancing heat transfer and package efficiency. Thus, the binary supporting materials-based eco-friendly FSPCMs were synthesized by using cheaper supporting materials RFA-EG for large-scale preparation of PCM. Subsequently, the fabricated FSPCMs have been characterized by analysis techniques such as SEM (scanning electron microscope) and BET (Brunauer-Emmet-Teller), FT-IR (Fourier transform infrared spectroscopy), DSC (different scanning calorimetry), and TGA (thermogravimetry analysis) to determine the microstructure, chemical compatibility, thermal properties, and thermal stability. The results show that the maximum mass fraction of LA absorbed into RFA without leakage was up to 50 wt%. The SEM analysis showed that LA could cover the surface of RFA particles and the EG was dispersed in the space among RFA particles. And, the heat storage and release efficiency of LA/RFA-EG exhibited higher heat transfer efficiency than that of LA and LA/RFA. The phase change temperature and latent heat of LA/RFA-EG FSPCM were 45.73 °C and 85.34 J/g, respectively. The TGA demonstrated that LA/RFA-EG FSPCM presented good thermal stability. Compared to pure LA, the thermal conductivity of LA/RFA-EG (10 wt%) was up to 0.933 W/m·k, which increased by 478.46 % due to the introduction of 10 wt% EG and RFA. The heat-storing or releasing time of LA/RFA-EG was decreased by 60 % for the melting process and 76.92 % for the freezing process than that of LA, respectively. Using solid waste as the supporting material, the eco-friendly LA/RFA-EG with high absorption capacity and high latent heat was a promising candidate for the large-scale application of FSPCMs in thermal energy storage.