Drying Performance of Beans Using Natural Convective Step Type Solar Dryer

Development of appropriate technologies for conversion of solar radiation to thermal energy is essential for fruit and vegetable preservation. A natural convective step type solar dryer with 10 trays was used. The drying parameters such as drying temperature, drying rate and dryer efficiency were studied on bright sunny days from top to bottom of the dryer using unblanched and blanched beans. The maximum and minimum temperatures observed were 84ºC and 50ºC at no load, 59ºC and 75ºC using unblanched beans and 51 and 75ºC using blanched beans. While drying on a sunny day, the moisture content removed was from 72 to 14% for unblanched beans and 76 to 7.32% for blanched beans. On quality evaluation, the high rehydration coefficient was found in blanched beans (0.76) than in unblanched beans (0.52). The collection efficiency was found to be 40.92% and drying efficiency was found to be 15.85% using unblanched beans and 18.75% using blanched beans.