Experimental analysis of solar drying kinetic of Algerian bay leaves (Laurus nobilis L.)

Résumé

In this work, we present an experimental study of thin layer solar drying kinetics of Algerian bay leaves. The experiments were carried out in an indirect solar dryer operating in forced convection fitted with an auxiliary heater with aero controlled conditions. Bay leaves were dried at a relative intervals of relative air humidity, the air temperatures and air velocities ranging from 21 to 40 %, 40 to 60 °C and 0.25 to 0.8 m/s, respectively. 95 % of the water content of the product was reduced for a temperature of 60 °C. The experimental curves obtained show the presence of a decreasing drying rate. This drying rate increases with the increase of air temperature and varies inversely with the drying time. Five empirical mathematical models were used to analyze experimental data of moisture ratio over time. The model of Wang and Singh was the best prediction of drying curves with a correlation coefficient, chi-square, and an average relative error ranging respectively from 0.993 to 0.999, from 0.011 to 0.042 and 2.748 to 16.472 %. The curves obtained for all drying conditions were used for the determination of the drying characteristic curve. This latter has allowed us to empirically determine the equation of bay leaves drying rate which has been interpreted by a three degree polynomial. In addition, the diffusivity of the moisture content of bay leaves was determined from the analytical solution of the Fick’s equation. The values range from 0.9×10^-9 to 6.1×10^-9 m²/s with an activation energy that varies from 47.015 to 64.957 kJ/mole.