Heat and mass transfer in coffee fruits drying

This work presents batch drying of coffee cherries on vibrated trays and in a fixed bed drier. The amplitude and the frequency of vibration were: A(x) = 0.211 X 10(-3) and A(y) = 0.945 x 10(-3) m; 60 Hz. The equipment consists of a vertical drying tunnel, in which two aluminum trays with coffee cherries were introduced. The initial moisture content was approximately 66% (wb) and the final moisture content was about 11%. The monitoring of the drying was effected by measuring the weight of the tray of coffee cherries. This data enabled the determination of the drying kinetics and of the heat and mass transfer coefficients, and the effective moisture diffusivity. In all the calculations, the shrinkage of the coffee cherries during the drying was considered. The vibration acted to increase the drying rate and the effective moisture diffusivity and consequently the heat and mass transfer coefficients. The drying time, in the vibrated system at a temperature of 45 degrees C was approximately 11% smaller than in the system without vibration. The effective moisture diffusivity was between 0.1 x 10(-10) and 1 x 10(-10) m(2)/s for a temperature of 45 degrees C and between 0.3 x 10(-10) and 3 x 10(-10) m(2)/s for a temperature of 60 degrees C. (c) 2004 Elsevier Ltd. All rights reserved.