Design, Fabrication and Performance Assessment of a Mixed Solar Dryer for Cocoa Beans

This work studies the influence of a mixed solar dryer with forced convection on the quality of cocoa beans. Data collection have been carried out during 6 days on a 10 kg sample. The dryer is based on a combination of direct and indirect models with forced convection for each. Its frame and its insulating part are made of wood and polystyrene respectively. The inner surface is covered with a thin layer of aluminum foil. A control and measuring device for air flow, temperature and humidity has been placed in the drying room. The direct solar part of the dryer allows the drying process to be accelerated, especially during the first drying phase. The proposed prototype dehydrated cocoa beans in two days with a moisture content that decreased from 53.4 to 4.6% for the beginning and the end of the drying process respectively, which validates the ISO 2451 standard. The drying process was conducted in an environment where the drying temperature and relative humidity were varying between 18 to 55°C and 28 to 80% respectively. Placing the same quantity of beans in the acceleration room, drying room and in the open air, for a quantity of water to be removed of about 5.07 kg of water, the water removal rates are about 0.32, 0.21 and 0.10 kg/h respectively for an effective daily average of 8 h. The drying efficiencies of the acceleration room and the drying room are 68 and 52% respectively, higher than those of the open air drying.