Mathematical Modelling, Energy and Exergy Analysis of Tomato Slices in a Mixed Mode Natural Convection Solar Dryer

This paper reports the drying kinetics of tomato (Lycopersicon esculentum) with different drying loads in a fabricated mixed mode natural convection solar dryer. The energy utilization ratio (EUR) and exergetic efficiency (ȠEx) was also estimated. Tomato slices were dried to reach the final moisture content of below 8% (w.b) from 93.67% (w.b) in a period of 20 h, 23 h and 30 h for a load of 2 kg/m2, 4 kg/m2 and 6 kg/m2, respectively. Different thin layer mathematical models were selected to fit the experimental data. According to the statistical results, the approximation of Two-term was shown a better fit to the experimental drying for the load of 2 kg/m2 and 4 kg/m2 whereas the Logarithmic model was shown a better fit for a 6 kg/m2. The maximum value of Deff was obtained as 1.14×10-10 m2/s for a loading rate of 2 kg/m2.The EUR was found to be 24.21%, 41.42% and 58.03% for the load of 2 kg/m2, 4 kg/m2 and 6 kg/m2, respectively, and ȠEx was 59%, 54% and 50% for the three load conditions of 2 kg/m2, 4 kg/m2 and 6 kg/m2, respectively. The dryer efficiency increased from 17.33% to 35% with increased in load from 2 kg/m2 to 6 kg/m2.