In this paper, the modelling and thermal performance results of the collector of a semi-cylindrical solar tunnel dryer (STD) have been presented. The performance has been estimated under natural
circulation as well as under forced circulation mode. The volume flow rate and the rise in the inlet air temperature have been optimized for natural circulation mode with respect to the design parameters,
viz., length and radius of the collector. The performance of the collector has also been calculated for different tilt of the STD. All calculations have been made for Delhi climate (28.58 N Latitude). The
development of the natural circulation type STD is very significant because it has certain advantages over the existing forced circulation type STD.