Performance enhancement of indirect solar dryer using hybrid thermal energy storage: kinetics, energy, and quality analysis of chili

This study presents the development and investigational evaluation of an Indirect Solar Dryer (ISD) integrated with a hybrid Thermal Storage Material (TSM) consisting of glass pieces and paraffin wax for drying red chili (Capsicum annuum). Three ISD configurations were investigated: (i) hybrid TSM with glass pieces and paraffin wax, (ii) glass pieces alone, and (iii) without TSM, along with Open Sun Drying (OSD) as a reference. The hybrid TSM configuration demonstrated the best performance, reducing the moisture content of chili from 83.8% to 8.3% (wet basis) in 26 hours, compared to 42 hours for glass pieces alone and 51 hours without TSM. The maximum solar collector efficiency and ISD efficiency achieved were 60.1% and 69% respectively under the hybrid TSM configuration. Among twelve thin-layer drying models evaluated, the logarithmic model provided the best fit with R² = 0.9782, χ² = 0.0009843, and RMSE = 0.02235. Color analysis revealed that the hybrid TSM configuration achieved the highest luminance (L = 43.45), redness (R= 23.35), indicating superior color retention compared to other configurations and OSD. FTIR spectroscopy confirmed that the ISD-dried samples preserved key chemical compounds, with characteristic C-H stretching bands at 2955 cm⁻¹ and carbonyl absorption at 1766 cm⁻¹, which were absent or diminished in OSD-dried samples, indicating better chemical integrity. These findings establish that the hybrid TSM-assisted ISD is a highly effective and sustainable method for drying and preserving the quality of chili compared to conventional drying methods.