Utilization of A mixed Mode Solar Dryer Assisted with An Auxiliary Electric Heater for Drying Sweet Potato Slices
Reducing post-harvest losses of perishable fresh products is a key strategic approach to increasing income, national security, and nutrition in the world. A hybrid solar dryer equipped with an auxiliary electric heater was developed and used to dry sweet potato slices, maximizing the use of available solar energy for food drying and producing a high-quality dried product. During the experiments, two different sweet potato cultivars (Abis and Balady) were dried at three different drying air temperatures (50, 60, and 70°C) and a constant slice thickness of 3±0.5mm after pre-treatment with sodium metabisulfite and citric acid. Eleven mathematical models were evaluated to determine the most accurate description of the drying behavior of potato slices. The effective moisture diffusivity, activation energy, and solar dryer efficiency were also calculated. Results indicated that the dryer reached the required temperature and maintained it throughout the experiment. The drying of sweet potato slices occurred during the falling rate period. The logistics model best describes the drying behavior of sweet potato slices from both varieties under the study conditions, followed by the Page model. The effective moisture diffusivity values were in the ranges of (1.8329×10-10 to 2.2888×10-10) and (1.8055×10-10 to 2.2341×10-10) m2/s for the Abis and Balady varieties, respectively. The activation energies were 10.274 and 9.772 kJ/mol for the Abis and Balady varieties, respectively. The overall thermal efficiency of the solar collector ranged from 65.1% to 70.4%. The overall thermal efficiency of the dryer ranged from 11.1245 to 12.5004%.