Performance assessment of an evacuated tube solar-electric hybrid dryer for lotus seeds drying: Moisture removal behavior, GHG emission and thermodynamic analysis

A novel evacuated tube solar-electric hybrid dryer (ETSED) was developed and evaluated to contribute to global food security from the perspective of optimized processing while reducing energy consumption and greenhouse gas (GHG) emissions. The performance of the ETSED was assessed compared with solar heating drying (SHD), and mixed heating drying (MHD) at temperatures of 55, 65 and 75 degrees C by studying the drying behavior of the samples as well as the thermodynamic analysis and GHG emissions of the system. Results revealed that under all studied experimental conditions, the evacuated tube solar collector provided more than 60% of the thermal supply in the drying process, and significantly improved the fluid exergy. Moreover, the roller shutter mechanism and the heating tube were used together to achieve precise control of the drying temperature. In terms of thermodynamic analysis, the heating tube further enhanced the ETSED performance by providing high quality energy in combination with solar energy in MHD mode. Furthermore, compared with SHD, MHD-65 and 75 degrees C shortened the drying time by 10.4 and 28.2%, improved the drying efficiency by 0.7% and 6.29%, and increased the drying chamber's exergy by 14.99 and 19.36%, respectively. Remarkably, the lowest emissions of CO2 (872.06 g/kg removed water), SO2 (0.13 g/kg removed water) and NOx (0.19 g/kg removed water) were seen in the case of SHD. Based on the obtained results, the increased drying temperature in the MHD led to higher CO2, SO2 and NOX emission levels. Interestingly, when the lotus seeds were dehydrated, the accumulated electric energy generated by the photovoltaic cells almost met the electric consumption of mechanical energy. The results of this study identified the potential of ETSED equipment for food industrial production.