Drying of apples in an indirect solar dryer with enhanced heated-air turbulence

The paper focuses on an experimental evaluation of apple dehydration in an indirect solar drying unit that relies on natural airflow and a high-performance air-heating mechanism. The duration of drying apples in a drying cabinet with 724 W/m2 of solar radiation in the collector was about 6 days, and the relative moisture content decreased from 80.06% to 14.09% on average. At the same time, the weight of the apples decreased from 1 kg to 146 grams. The duration of drying apples in a drying cabinet with 933 W/m2 of solar radiation on the collector was less than 5 days, and the relative humidity of apples decreased by an average of 80.06% to 13.26%. At the same time, the weight of the apples decreased from 1 kg to 140 grams. Calculations showed that the Grasgoff number of the drying process falls within the interval: Gr≈6.3·109÷1.08·1010. At different levels of solar radiation, ΔT≈11−23 °C, the temperature difference between the cabinet’s average temperature and the outside remains constant. Analysis of the experimental data confirms that turbulence may arise in certain areas of the drying chamber, while the drying performance of apples remains high.

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