Experimental investigation and drying kinetics of mixed type solar dryer with thermal energy storage material for drying of apple slices

The current study covers drying of 500 g of apple slices of uniform thickness by forced convection mixed solar drying unit integrated with paraffin wax and natural sand as energy storage (thermal) material. The experimental setup consists of solar collector (for heating inlet air) and drying chamber in which heated air removes moisture content of apple slices from 80 to 21.7% (wet basis) in 3.5 h during April 2021. The average moisture diffusivity for lower tray was 1.018 × 10⁻⁸ m²/s which was 16.3% and 28.6% greater than upper tray and open sun drying, respectively. The average drying rate for lower tray (0.5318 kg water/kg dried product/h) was higher than upper tray and open sun drying. At the same drying time of 3.5 h, the final moisture content in lower tray, upper tray and open sun drying were obtained as 21.7%, 22.64% and 25.61%, respectively, which indicates that present solar drying is better than open sun drying. The average drying exergy efficiency was obtained as 48.14% with maximum value as 74%. The maximum (& average) drying efficiency and collector efficiency were 13% (& 5.56%) and 83.3% (& 66.39%), respectively. Wang and Singh model was found the best suitable among 14 thin layer drying models.