Solidification characteristics of biomass-activated aloe vera PCM in a spherical enclosure for efficient cool thermal energy storage

The present work aims to examine the potential of aloe vera liquid (AVL) and activated carbon (AC) as a phase-change material (PCM) for energy efficient cool thermal energy storage (CTES) applications. The low-viscosity and supercooling behavior of deionized water (DIW) limits its usage in the CTES system. Three variants of NEPCMs containing activated-carbon (AC) at concentrations of 1.5 wt%, 1.0 wt%, and 0.5 wt% were analyzed (AVL, DIW, and AVL + DIW). Zeta-potential distribution analysis shows that all the AVL-NEPCMs (−44 mV) are stable, with the particles exhibiting strong mutual repulsion. A maximum thermal-conductivity (TC) enhancement of 24 % and 34 % was noted for the AVL-NEPCMs in the liquid and solid phases, respectively. The AVL has a latent heat of 332 J/g during melting and 305 J/g during freezing, which is nearly equal to that of DIW. In addition, a slight reduction in latent-heat of 8 %, was observed owing to the non-active participation of AC. The freezing characteristics of NEPCMs were studied with spherical enclosure by maintaining a chiller temperature of −8 °C. A 22 % reduction in total solidification time was observed for the AVL-based NEPCM with 1.5 wt% AC, due to the faster nucleation and the elimination of the supercooling process.