Study on Forced Convection type Solar Tunnel Dryer for Industrial Applications
A semi-cylindrical forced convection type solar tunnel dryer (STD) was designed and commissioned at M/s Miraj Products Pvt. Ltd., Nathdwara for drying processed tobacco. Essentially it is based on mixed mode having direct and indirect type of heating mechanism i.e. the heated air from different solar flat plate collectors is passed through drying cabinet, and at the same time, the drying cabinet absorbs solar energy directly through the transparent walls and roof. It consists of 16 x 3.75 sq. m. area, tunnel equipped with 12 solar flat plate collectors of 2 sq. m. each propelled with 2 exhaust fan of 1 kw capacity placed on both ends of tunnel. This paper presents the design, development and performance evaluation of this forced convection type STD for drying processed tobacco at users place. The dryer was tested at no load and full load condition. During no load natural convection mode, temperatures inside the dryer were about 18-20 0C higher than the ambient temperature during summer day-light, where as in no-load forced convection mode, it was about 30 0C higher than ambient temperature. A batch of processed tobacco of 500 kg having an initial moisture content 58 % w.b. were successfully dried in full load condition to have final moisture content of about 8 % w.b in one solar day. It has been observed that STD has many other advantages i.e. get rid of toxicant gases to labours during open drying due to lime presence in material, avoidance of product expose to fly contamination & dust concentrations etc.