Development of phase change material assisted evacuated tube solar dryer: Investigation of thermal profile, drying characteristics, and functional properties of pumpkin slices

Abstract

The present work aimed to develop a phase change material-assisted evacuated tube solar dryer (PCM-ETSD) and experiments were performed with and without PCM for drying pumpkin slices. Thermal performance, drying characteristics, and quality attributes were analyzed with and without PCM at different airflow rates: 34.64 kg/h, 51.96 kg/h, and 69.28 kg/h. The average temperature elevation between the ambient and drying chamber was achieved at 29.62 °C to 36.33 °C and 25.64 °C to 28.93 °C without and with PCM-assisted drying respectively. PCM-ETSD extended the drying period by 2 h and maintained the temperature ranges from 50.78 °C to 61.29 °C after sunshine hours. The PCM-ETSD reduced the moisture content of pumpkin slices by 4–5% and 8% more as compared to without PCM and sun drying respectively. Drying rate and effective moisture diffusivity are enhanced with the increase of airflow rate in the drying process and higher without PCM-assisted drying followed by PCM and sun drying. The total phenolic content and total flavonoid content are higher in PCM-assisted drying and continuously decreased with the increases in airflow rate in both drying processes. Antioxidant activity and total carotenoid content are higher in PCM-assisted drying. FTIR analysis confirmed the presence of active functional groups and phenols in dried pumpkin. The inferior color changes were observed in PCM-assisted drying of pumpkin slices. The developed PCM-ETSD could be capable of drying other food commodities on a pilot scale after sunshine with retention of quality attributes.