Thermally enhanced nanocomposite phase change material slurry for solar-thermal energy storage

Abstract

This paper investigates the photothermal conversion performance of an innovative heat transfer fluid containing nano-encapsulated phase change material (PCM) with metallic shell materials in a solar thermal energy storage system. The influences of shell thickness, core size, shell material type, PCM mass and shell volume concentrations on the thermal performance of the heat storage medium are investigated and compared. The results show that the heat transfer rates of water-based Ag, Au, Cu and Al nanofluids are 6.89, 5.86, 7.05 and 6.99 W, respectively, while slurries formed by adding paraffin@Ag, Au, Cu and Al nano capsules to pure water enhance heat transfer by 6.18, 13.38, 10.8 and 11.33 %, respectively. The metallic nanoparticle-based shell materials further augment the temperature and energy storage gains by enhancing the solar radiation capture capability of the heat storage medium. Specifically, depending on the mass concentration of PCM, the storage capacity of paraffin@Cu slurry is augmented by up to 290 %. As the shell thickness of the Ag particles also decreases from 8 to 2 nm, it augments the slurry's storage ability for thermal energy by 7 %. The enhancement in the dimensions of the nano capsules, however, causes the surface area-to-volume ratio (SA:V) to reduce the photothermal conversion of the slurry by clustering. Therefore, the thermal energy storage behaviour of the Paraffin@Cu slurry is diminished by 5 % as the core size enhances from 10 to 40 nm. Further, the augmentation in the volume concentration of Al particles in the shell surprisingly reduces the thermal energy storage by 5 %. Finally, paraffin-based solid PCM is also experimentally tested for validation of the specific heat capacity model at various wind speeds and solar radiation.