Abstract
A hybrid solar dryer was designed and constructed using direct solar energy and a heat exchanger. The dryer consists of solar collector, reflector, heat exchanger cum heat storage unit and drying chamber The drying chamber was located under the collector. The dryer was operated during normal sunny days as a solar dryer, and during cloudy day as a hybrid solar dryer Drying was also carried out at night with stored heat energy in water which was collected during the time of sun-shine and with electric heaters located at water tank. The efficiency of the solar dryer was raised by recycling about 65% of the drying air in the solar dryer and exhausting a small amount of it outside the dryer. Under Mid-European summer conditions it can raise up the air temperature from 30 to 40 degrees C above the ambient temperature The solar dryer was tested for drying of ripe banana slices The capacity of the dryer was to dry about 30 kg of banana slices in 8 h in sunny day from an initial moisture content of 82% to the final moisture content of 18% (wb). In the same time it reduced to only 62% (wb) moisture content in open Sun drying method. The colour, aroma and texture of the solar dried products were better than the sun drying products (C) 2009 Elsevier Ltd All rights reserved