Performance Evaluation of a Forced Convection Mixed-Mode Solar Grain Dryer with a Preheater
Johannes P. Angula1, Freddie Inambao2

1Johannes P. Angula*, Department of Mechanical Engineering, University of KwaZulu-Natal, Durban, South Africa.
2Freddie Inambao, Department of Mechanical Engineering, University of KwaZulu-Natal, Durban, South Africa. 

Manuscript received on November 26, 2020. | Revised Manuscript received on January 25, 2021. | Manuscript published on February 28, 2021. | PP: 41-51 | Volume-10 Issue-4, February 2021 | Retrieval Number: 100.1/ijitee.B82831210220| DOI: 10.35940/ijitee.B8283.0210421
Open Access | Ethics and Policies | Cite | Mendeley
© The Authors. Blue Eyes Intelligence Engineering and Sciences Publication (BEIESP). This is an open access article under the CC BY-NC-ND license (

Abstract: In this study the performance of a forced convection mixed-mode solar grain dryer integrated with a preheater was evaluated. The type of grains used in the experiment were 72 freshly harvested maize cobs with a total mass of 17 kg. The experiment was conducted at various airflow speeds and preheater temperatures ranging from 0.5 m/s to 2 m/s and 30 ℃ to 40 ℃, respectively. The aim of the study was to improve the performance of an existing indirect solar dryer which was converted to a mixed-mode solar dryer. The initial thermal efficiency of the indirect solar dryer before modification was 36 %. The results from the experiment indicated a maximum thermal efficiency of 58.8 % with a corresponding drying rate of 0.0438 kg/hr. The minimum thermal efficiency for the mixed-mode solar grain dryer system was 47.7 %, with a corresponding drying rate of 0.0356 kg/hr. The fastest drying time of maize cobs was achieved in 4 hours and 34 minutes from an initial moisture content of 24.7 % wb to 12.5 % wb. The findings show a significant improvement in the dryer system’s performance. This is a clear indication that operating a solar dryer system in mixed-mode operation with forced convection and the assistance of a preheater or backup heater can significantly improve drying processes and increase food preservation. 
Keywords: Mixed-mode operation, Solar drying, Maize cobs, Thermal efficiency, Preheater, Forced convection.