Experimental and mathematical investigations of convective solar drying of four varieties of olive leaves

The aim of this work is to study the drying kinetics of four varieties of Tunisian olive leaves (Chemlali, Chemchali, Zarrazi and Chetoui) by using an indirect forced convective solar dryer consisting of a solar collector, an auxiliary heater, a circulation fan and a drying cabinet used for drying experiments. Experiments are conducted at three temperatures (40, 50 and 60 °C), ambient relative humidity (29–32%) and at a drying air flow rate of 0.0556 m3/s. Three models available in the literature were used to describe experimental kinetics. The experimental drying curves show only the falling rate period. Air temperature has a significant effect on drying kinetics. The statistical parameters (correlation coefficients and standard errors) show that the Page model could be used to determine the curve drying equations from the experimental drying curves. The characteristic drying curves of olive leaves are determined empirically by using the corresponding curve drying equations. Apparent moisture diffusivities of olive leaves were determined from the analytical solution of Fick's equation. Values vary from 2.95 × 10−10 to 3.60 × 10−9 m2/s. They depend on the olive leaves variety and on temperature.