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

Abstract

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.

The authors' abstract, as published at the source. Solar Energy Materials and Solar Cells, 2026 · DOI ↗