Mitraniketan has developed a performance enhanced natural convection solar dryer for value addition based micro enterprises. We aimed for a low cost dryer with more drying efficiency. The focus of technology development is the performance improvement of solar dryer in natural convection. The problems behind developing the improved solar dryer is the high humidity found in the existing dryers in Kerala and its high cost.
The dryer works based on increasing air temperature and thereby increasing its moisture holding capacity and also based on its improved air flow. We have incorporated two features in the existing tunnel design: (1) Pre-heater: Pre-heater plates are flat plate solar collectors with darkened substrate and transparent top to harvest maximum amount of heat. Increasing inlet air temperature causes drop in relative humidity. Heating will be carried out in both pre heater and in the drying chamber. (2) Solar chimney: to improve airflow in and out of the drier unit, a chimney is introduced at one side of the tunnel which creates a draft. The air intake holes in the pre-heater collect fresh air in the main drying chamber.
Dryer is fabricated with mild steel square tubular sections of 20x0x1.4mm. The transparent panels of the pre-heater, drying chamber and chimney are made from transparent poly carbonate sheets. Two batches of chopped tapioca (12 kg each) were kept inside the drying as well as in the open sun for trial. Tested the dryer using chopped tapioca weighing 12 kg and is dried in 24 hours (from 3 sunny days) with no moisture. Its weight comedown to 5.5 kg and the quality was high in terms of color and cleanliness than open sun drying.