Experimental study of hot air dehydration of Sultana grapes

A laboratory drying unit was designed and constructed at Fluid Mechanics Laboratory, University of Patras, Greece, in order to evaluate the essential drying characteristics of various fruits and vegetables. The paper presents results of experiments done in the case of hot air drying of Sultana grapes. Time evolution of measured parameters is cross analyzed and presented in diagrams. Moisture content, drying rates and relative moisture content are calculated and also presented in diagrams. Thin-layer model and Page’s equation were used for modelling the drying of Sultana grapes up to the water moisture content usually required to attain the shelf stability. The drying constants, effective diffusivity of the bed and product constant were evaluated upon the analytical solution of the thin-layer and Page’s equations. The resulted curves were plotted in diagrams and graphically compared with experimental data. A good agreement was found between measurements and Page’s equation prediction. Another aim of this research was to validate the in-house DrySAC numerical code, developed for effective design and control of industrial drying units. A very good agreement between predictions and measurements was found.