Performance evaluation of indirect solar dryer assisted with forced convection for dehydration of sliced tomato at variable solar radiations

A forced convection-assisted indirect solar dryer (ISD) was designed and evaluated for dehydrating sliced tomatoes intended for tomato powder production. Experimental tests were conducted across five months (December to April), representing a range from the coldest to hottest periods of the year. During each test, 10 kg of fresh tomato slices were loaded into the dryer and dried daily from 9:00 a.m. to 6:00 p.m. until the target moisture content of approximately 6% (wet basis) was achieved. During experimental tests, direct normal irradiation (DNI) from the sun varied from 200 W/m2 to 850 W/m2. The drying time was reduced to 19 hours for the test conducted in April in comparison to 35.5 hours in December to reach the desired moisture content, indicating a 46.47% reduction in the drying time. The dryer exhibited an average thermal efficiency of 20.95% for the test conducted in December, which increased to 27.43% for the test conducted in April. With a rise in DNI values from December to April, the dryer exhibited a higher rate of drying, viz., 10.91 × 10−5 kg/s for April in comparison to 7.27 × 10−5 kg/s for December. The Page model best described drying kinetics under varying solar radiation, yielding R2 values of 0.9634–0.9849.