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Journal of Solar Energy
Volume 2017 (2017), Article ID 4525141, 10 pages
Research Article

Design and Testing of a Natural Convection Solar Tunnel Dryer for Mango

Department of Agricultural Engineering, University of Zambia, P.O. Box 32379, Lusaka, Zambia

Correspondence should be addressed to Sam Cherotich; moc.liamg@orehcmas

Received 5 June 2017; Revised 7 August 2017; Accepted 11 September 2017; Published 16 October 2017

Academic Editor: Koray Ulgen

Copyright © 2017 Isaac Nyambe Simate and Sam Cherotich. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A natural convection solar tunnel dryer comprising three major units, a solar collector unit, a drying unit, and a vertical bare flat-plate chimney, was constructed. No-load tests with a horizontal configuration of air entry into the collector resulted in a bidirectional air flow in the dryer. To correct this undesirable situation, an air guide at the collector was incorporated to ensure that air entered in a vertical direction. To investigate its performance, drying experiments with mango were carried out at the University of Zambia, Department of Agricultural Engineering. Uncertainties in the parameters measured in the experiment were analysed and quantified. The results showed that, under solar radiation between 568.4 and 999.5 W/m2, air temperature of up to 65.8°C was attained at the collector unit. The average relative humidity values were 30.8%, 6.4%, and 8.4% for the ambient, collector, and drying unit, respectively. Under these conditions, mango with an initial moisture content of 85.5% (wet basis) was dried to 13.0% (wet basis) in 9.5 hours. The collector, drying, and pick-up efficiencies were found to be 24.7%, 12.8%, and 35.0%, respectively. The average temperature difference between the chimney air and ambient air was 12.1°C, and this was sufficient in driving the flow of air through the dryer.