Experimental performance analysis of a mixed forced convection solar dryer: Application to cocoa bean drying

Abstract

The influence of a mixed forced convection solar dryer with thermal storage, on the quality of cocoa beans is studied. This study has as reference the quality level recommended by the international standard ISO 2451. A collection of experimental data with the realized dryer was made for six days on a sample of 10 kg of cocoa coming from the cocoa zone of Kekem in Cameroon. This sample consisted of more than 300 cocoa beans as recommended by the standard for testing. The dryer, is mainly made of wood for the frame and polystyrene for the isolating part, it has an operation based on a combination of the direct and indirect model. A control and measuring device for airflow, temperature and humidity has been installed in the drying chamber. The dryer's direct solar component can be used to accelerate the drying process, especially during the first drying phase. This experimental system was able to dehydrate cocoa beans in 2 days with a water content that went from 53.4 % to 4.6 %. From the beginning to the end of the drying process, the temperature and the relative humidity were respectively between 18 and 55 °C and between 28 and 80 %. Placing the same amount of beans in the acceleration chamber, the drying chamber and in the open air, for an amount of water to be removed of about 5.07 kg, the water removal rates were respectively about 0.32 kg/h, 0.21 kg/h and 0.10 kg/h for an effective daily average of 8 h. The drying performances of the acceleration chamber and the drying chamber are respectively 68 % and 52 %, more than the open-air drying.