Design, Construction and Evaluation of a Fan Speed Controller in a Forced Convection Solar Dryer to Optimize the Overall Energy Efficiency

Authors
N. Bagheri
A. Keyhani
S. Mohtasebi
A. R. Alimardani
Sh. Rafee
G. H. Mansoori
Department of Agricultural Machinery, University of Tehran, Karaj, P. O. Box: 4111, Islamic Republic of Iran.
Abstract
To increase agricultural crops’ quality and to minimize losses in the final product and
used energy during the drying process, major drying system parameters should be
continuously controlled. Precise control of such parameters is attained by using automatic
control systems. To optimize the overall dryer efficiency in a forced convective solar
dryer, a controller was designed, constructed and evaluated. The dryer fan speed was
chosen to be the controlled variable. Based upon the mathematical relations and a
monitoring of the air inlet temperature to the collector, the air outlet temperature from
the collector and the air outlet temperature from the drying chamber, the dryer efficiency
was determined. Using the dryer control program the current and the optimized dryer
efficiencies were calculated, compared and the fan speed changed accordingly to maintain
the optimized efficiency. Experiments were carried out in three replications (in three
days) with the results showing that the system was capable of controlling the fan speed to
obtain the optimum efficiency. The dryer equipped with the designed control system
worked with its highest efficiency throughout the day. Statistical analysis showed that the
control system highly improved the dryer efficiency throughout its operation at a 1%
probability level.
Keywords
Automatic control system
Fan speed
Forced-convection
Optimum efficiency
Solar dryer
Journal of Agricultural Science and Technology
Volume 13, Issue 4
July and August 2011
Pages 503-515