Energy Reports (Nov 2021)
Heat transfer enhancement of microencapsulated phase change material by addition of nanoparticles for a latent heat thermal energy storage system
Abstract
In the present study, nanoparticles of MgO, TiO2, and Graphite with mass ratios of 3, 5, 7, and 10% were added to the structure of the synthesized Lauric acid (LA) microcapsules, and the effect of nanoparticles on the thermal properties of microencapsulated Lauric acid as non-toxic phase change material for energy storage applications was investigated. The microcapsules containing nanoparticles were prepared by emulsion polymerization of Styrene as the shell. The microencapsulation ratio (E.R) of LA increases with the amount of MgO and TiO2. However, the microencapsulation ratio was reduced by increasing the mass ratio of nano graphite. The highest microencapsulation ratio (69.90%) belonged to the microcapsules containing 10% of titanium oxide nanoparticles. Scanning electron microscopy (SEM) images showed that microcapsules obtained containing TiO2 were spherical with a smooth surface and narrow particle size distribution. The thermal stability and thermal conductivity coefficient for the pure LA, microencapsulated LA with/without nanoparticles were examined. The thermal stability improved with the increasing mass ratio of the nanoparticles, no considerably. The microcapsules with 10% of TiO2 nanoparticles had higher thermal stability. The weight loss temperatures in the first and second steps are 287 °C and 435 °C, respectively. The thermal conductivity of the lauric acid was increased by microencapsulation from 0.146 W/m.K to 0.149 W/m.K. The thermal conductivity coefficient of microcapsules increased by adding nanoparticles. Finally, the thermal energy storage performance of the obtained samples was evaluated in a designed experimental setup. The decrement percentage of the onset of the melting process time for lauric acid microcapsules and the microcapsules containing graphite nanoparticles, titanium oxide, and magnesium oxide were 1.2, 4.7, 8.5, and 16.7%, respectively.
