Kaolinite stabilized paraffin composite phase change materials for thermal energy storage

Abstract Three kinds of kaolinites (platelet, PKaol; layered, LKaol; and rod, RKaol) were used to stabilize paraffin to prepare PKaol/paraffin, LKaol/paraffin, and RKaol/paraffin composites. The effects of kaolinite microstructure on the thermal storage properties of the composites were investigated in detail. It was found that the crystallinity of the paraffin in the composites increased when the proportion of kaolinite pores that are smaller than 5 nm decreased; the pore size also affected the transfer of the heat within the paraffin in the region near the kaolinite. The paraffin in LKaol/paraffin composite showed higher crystallinity ( F c , 98.4%) and greater effective energy storage per unit mass ( E ef , 215.6 J·g − 1 ) than that in the two other composites, indicating that most of the paraffin can contribute to energy storage. This is probably because the LKaol pore structure is more suitable for supporting phase change materials (PCM). This also led to less phonon scattering and therefore a larger phonon mean free path for paraffin in this composite, and a higher thermal conductivity (0.78 W·m − 1 ·K − 1 ). Furthermore, the effect of nanopore confinement within the composites was elucidated at the atomic level. The as-prepared PCM have potential for application in solar thermal energy storage and solar heating.