Comparative experimental investigation of hybrid ceramic/carbon nanoparticle enhanced green eutectic phase change material for solar drying

Enhancing the thermal and structural performance of phase change material (PCM) has become a critical research focus in order to help increase their applicability in thermal energy storage (TES) technologies. In this study, a green eutectic fatty acid ester based PCM, tetradecyl oxalate (DTO), was enhanced with hybrid nanoparticle additives. Its performance was then evaluated through material characterization and in a double pass solar air heater (DPSAH) based drying system. Two hybrid nanocomposites were prepared using hBN + Si 3 N 4 (DBS) and GNP + Si 3 N 4 (DGS), each at a total additive ratio of 1 wt%. Structural, thermal and thermophysical properties were investigated by SEM, XRD, FT-IR, DSC, TGA, thermal conductivity and thermal diffusivity analyses. Among the hybrid nanocomposites, DGS showed the best material performance. Its thermal conductivity reached 0.373 W/mK, corresponding to a 908.1% increase compared with pure DTO. It also preserved phase change enthalpy more effectively than DBS and exhibited better thermal stability. The hybrid nanocomposites were then integrated into a DPSAH and tested under three air velocities of 3, 6 and 9 m/s. The best system performance was obtained with DGS-6 (air velocity 6 m/s). It achieved a useful heat gain of 332.5 W and a thermal efficiency of 82%. Drying experiments showed that the lowest moisture content and water activity values were obtained in the DGS collector. Thermal cycling tests conducted in real outdoor conditions with 300 cycles reveal that the developed hybrid PCMs perform very well in terms of long term reliability. Overall, the results demonstrate that the GNP + Si₃N₄ hybrid structure significantly improved the thermal response of DTO and enhanced drying performance. It also showed strong potential for solar drying and low/medium temperature TES applications.