Performance analysis of hybrid expanded graphite-NiFe2O4 nanoparticles-enhanced eutectic PCM for thermal energy storage

This current experimental study aims to resolve the demerits of pure PCM by introducing the hybrid nanomaterial-induced composite PCM (HNIPCM) with practical feasibility on solar water heater performance using an indigenously developed setup. To settle out these performance characteristics, expanded graphite (EG) and nickel ferrite nanoparticles (NiFe2O4) with different weight concentrations (ɸ = 1–5 %) were used for the first time as a thermophysical property-enhancing filler material inside a eutectic organic-organic PCM (polyethylene glycol 6000/paraffin wax) by two-step method. A detailed study on the physical and chemical stability, surface morphology, and thermal feasibility of the HNIPCM was conducted to provide the optimized characteristics for the target applications. The energy storage capacity, melting and crystallization temperature, thermal stability, thermal reliability, thermal behaviour, and thermal conductivity were also examined by DSC, TGA, thermal cycling, and charging-discharging, respectively. The HNIPCM with 3 wt% filler concentration revealed comparatively well-balanced thermophysical properties among the prepared samples. The results also showed that the melting point, crystallization point, melting enthalpy, and crystallization enthalpy were changed to 54.55 °C, 48.83 °C, 128.52 J/g, and 129.02 J/g, respectively, for HNIPCM with 3 wt% of filler material in comparison with eutectic PCM of 59.14 °C, 41.23 °C, 154.37 J/g, and 155.21 J/g. An increase in thermal conductivity up to 253.72 %, enhancement in the charging and discharging rate, and good stability up to 500 working cycles with a 12.19 °C decrease in the supercooling were also observed with no physical and chemical alteration. The real-time performance of the prepared HNIPCM was also investigated using a novel indigenously developed solar water heater at different inclination angles (40°, 45°, and 50°), flow rates (1.2 LPM, 2.2 LPM, and 5.2 LPM), and charging periods (90mins, 120mins, and 180mins). Comparatively higher performance at a 45° inclination angle, 2.2LPM water low rate with 68.99 % efficiency (day) and 50.45 % (night) was observed. The enhanced thermophysical properties of the HNIPCM made it suitable for a viable candidate for solar thermal energy, air conditioners, TES, and electronic cooling units.