Drying characteristic, sustainability, and 4E (energy, exergy, and enviro-economic) analysis of dried date fruits using indirect solar-electric dryer: An experimental investigation

An indirect solar-electric dryer (ISED) was constructed to valorize the date surplus under drying temperatures of T = 50–65 °C. The effective moisture diffusivity (Deff) values of dates were 4.59 × 10−7, 5.58 × 10−7, 7.29 × 10−7, and 1.04 × 10−6 m2 s−1, respectively, for 50, 55, 60, and 65 °C with convective mass transfer coefficient ranging between 9.18 × 10−7 and 2.08 × 10−6 m s−1. The drying behavior of date fruits using ISED was described by Wang and Singh's model with 99.98% alignment with experimental data. The lowest specific energy consumption (SEC) was 3.71 kWh.kg−1 resulting in T = 65 °C. The highest solar energy fraction (63.2%) and the lowest electric energy fraction (36.8%) were obtained under 60 °C drying temperature. The highest exergy efficiency (ηEx = 73%) was attained at 50 °C. The highest waste exergy ratio and the lowest sustainability index 0.39 and 2.54, respectively were obtained for T = 65 °C. The improvement potential factor increased with the decrease in ηEx and varied between 17.1 and 64.7. Low CO2 emissions amount of 17.23 kg/year was reached, and impressive payback period values of 0.26, 0.25, 0.12, and 0.08 years were estimated, respectively, for T = 50, 55, 60, and 65 °C. The ISED under 65 °C drying temperature is recommended for date fruits.