KINETICS OF APRICOT THIN LAYER DRYING IN A MIXED AND INDIRECT MODE SOLAR DRYER

This paper presents mathematical modeling of a thin layer solar drying process of apricots. A forced convection mixed and indirect mode cabinet solar dryer (total collector surface area of 4m2 and total tray surface area of 0.7m2) was employed. Each experiment started from 9:00 to18:00 on sunny days in summer. The experiments were conducted at three air flow temperatures of 40, 50 and 60 oC with three air flow rates of 8.7, 6.3 and 3.8 m/s respectively for each indirect and mixed mode dryer types. The solar intensity was measured and recorded from 420 to 1000 W/m2 during the course of experiments. In order to select the most appropriate drying model equation in each mode of drying, 10 different models were examined using the thin layer drying experimental data. The results of curve fitting were validated by comparing the proper statistical coefficients namely: r, χ 2, RMSE using non-linear regression analysis. According to the results, two-term drying model could satisfactorily describes the solar thin layer drying behavior of apricots with correlation coefficient (r) of 0.999 for both types of solar drying with χ2=3.374*10-3, RMSE=4.33*10-2 for the mixed-mode and χ 2=1.243*10-4, RMSE=8.64*10-3 for the indirect mode respectively. The effect of drying operating conditions (air temperature and velocity) on the model constants and coefficients were also investigated using multiple regression analysis.