Experimental evaluation of nano-PCM based thermal energy storage for solar drying applications: Drying kinetics, heat transfer, Differential Scanning Calorimetry (DSC), and quality characteristics

This study presents a novel controlled experimental comparison of paraffin wax phase change material (PCM) and zinc oxide nanoparticle-enhanced paraffin wax (ZnO-PCM) integrated into a solar drying system for potato chips under identical meteorological conditions. Unlike previous studies that investigated PCM and Nano-PCM systems independently, this work systematically quantifies their relative effects on drying kinetics, heat and mass transfer, thermodynamic performance, and product quality. Experiments were conducted in three operating modes: Category-I (without PCM), Category-II (PCM), and Category-III (ZnO-PCM). The initial moisture content (80-88%) decreased to final values of 11-12%, 9-10%, and 6-8% for Category-I, Category-II, and Category-III, respectively, after 21 h of drying. The moisture ratio reduced from 1.0 to 0.10-0.12, 0.08-0.10, and 0.05-0.08, respectively. The maximum drying efficiency increased from 34% in Category-I to 39% and 42% in Category-II and Category-III, respectively. The effective moisture diffusivity ranged from 4.5 × 10 −10 to 6.8 × 10 −10 m 2 /s in Category-I and increased up to 8.5 × 10 −10 m 2 /s in Category-III. The mass transfer coefficient varied between 1.2 × 10 −7 and 4.2 × 10 −7 m/s, while the heat transfer coefficient increased from 8 to 18 W/m 2 K in Category-I to 12-28 W/m 2 K in Category-III. The activation energy was found to be 21.5-30.5 kJ/mol, and water activity decreased from 0.98 to 0.32-0.45. The total color difference (ΔE) was lowest for Category-III (23.50), compared with Category-II (25.20) and Category-I (29.20), indicating superior color retention. Scanning Electron Microscopy (SEM) observations further suggested better preservation of the microstructure in ZnO-PCM-dried samples. Overall, the incorporation of ZnO-PCM significantly enhanced thermal energy storage, heat and mass transfer, drying kinetics, and product quality. These findings demonstrate the potential of Nano-PCM-assisted thermal energy storage as an efficient and sustainable solution for improving solar drying performance and preserving the quality of agricultural products.