Design and development of energy efficient solar tunnel dryer for industrial drying

A natural convection poly house walk-in type solar tunnel dryer was designed and used for drying surgical cotton on industrial scale. This article deals with the basic design criterion used for development of solar tunnel dryer and result of drying of surgical cotton in actual use. A batch of surgical cotton of 600 kg by mass, having an initial moisture content of 40% wet basis from which 210 kg of water is required to be removed to get a desired moisture content of about 5% wet basis, is used as the drying load in designing the dryer. A drying time of 7-8 h is assumed for the anticipated test location (Udaipur, 27A degrees 42' N, 75A degrees 33' E) with an expected average solar irradiance of 5.5 kW m(-2). Average cost of drying one batch of surgical cotton in a solar tunnel dryer has been worked out to be approximately 4.63 USD as compared to 30.00 USD in the existing diesel fired dryer.