Drying of agricultural produce in a greenhouse type solar dryer

A study was conducted to characterize the drying process in a greenhouse type solar dryer using either natural or forced ventilation. A 4 m high circular black polyethylene stack attached to the dryer produced an air flow rate of 0.1 m3/s in the experimental dryer. A three-tier drying rack (1 m × 1 m × 2.5 m) was installed in the greenhouse type solar dryer for multi-tiered drying of agricultural produce. Rewetted mustard was dried, both in the solar dryer and in the open sun. Drying of mustard under natural ventilation and forced ventilation was faster than that in the open sun by about 20 and 45% respectively. The drying data were well represented by Page's drying equation (r2 = 0.6 to 0.93). The drying coefficients 'k' and 'n' in the equation could not be correlated well with drying environmental parameters in this field study. The capacity of the greenhouse type solar dryer varied between 391 (natural ventilation) to 4861 kg/day (forced ventilation).