Performance Evaluation of a Forced Convection Mixed-Mode Solar Grain Dryer with a Preheater

Abstract

In this study the performance of a forced convection\nmixed-mode solar grain dryer integrated with a preheater was\nevaluated. The type of grains used in the experiment were 72\nfreshly harvested maize cobs with a total mass of 17 kg. The\nexperiment was conducted at various airflow speeds and preheater\ntemperatures ranging from 0.5 m/s to 2 m/s and 30 ℃ to 40 ℃,\nrespectively. The aim of the study was to improve the performance\nof an existing indirect solar dryer which was converted to a\nmixed-mode solar dryer. The initial thermal efficiency of the\nindirect solar dryer before modification was 36 %. The results\nfrom the experiment indicated a maximum thermal efficiency of\n58.8 % with a corresponding drying rate of 0.0438 kg/hr. The\nminimum thermal efficiency for the mixed-mode solar grain dryer\nsystem was 47.7 %, with a corresponding drying rate of 0.0356\nkg/hr. The fastest drying time of maize cobs was achieved in 4\nhours and 34 minutes from an initial moisture content of 24.7 %\nwb to 12.5 % wb. The findings show a significant improvement in\nthe dryer system s performance. This is a clear indication that\noperating a solar dryer system in mixed-mode operation with\nforced convection and the assistance of a preheater or backup\nheater can significantly improve drying processes and increase\nfood preservation.