DESIGN AND SIMULATION STUDIES OF A COCOA BEAN DRYER

Abstract

A simple cocoa bean drying system with a stirring device was designed, fabricated and evaluated. The dryer consists of a drying chamber (bean basket) the plenum, an axial fan and the heating element. It is designed to handle 3.5 kg of wet fermented cocoa beans per operation and is driven by 1.1 kW electric motor at 1420 rpm. The electric heater has a power rating of2 kW. It was used to measure the drying characteristics of wet fermented cocoa beans. The thin layer experiments were carried out at 47, 58 and noc air temperature and 1.19,2.39 and 3.74 m/s air flow velocity and initial beans moisture content of82.5% (dry basis). The deep layer ex.periments were carried out in beans bed depth of 500 mm, air temperature of 47, 58 and noc, air flow velocity of2.39 m/s and moisture content of about 57% (dry basis) The results of the drying tests show that the drying rate before cocoa beans is dried to about 42% moisture content (dry basis) level is mainly dependent on the combine effect of air temperature and flow velocity, while drying after this level of moisture content depends mainly on the air temperature. The temperature had the most significant effect, while the air flow velocity had very little effect on the drying constant of wet fermented cocoa beans. Logarithmic model was used to simulate the drying. A comparison between the simulated values and the experimental values show that the model can be used to predict the average time history and moisture content with reasonable accuracy. The dryer has an overall thermal efficiency of 75.8%.