Performance analyses of mixed mode forced convection solar dryer for drying of stevia leaves

In the present work, experimental investigations carried out on drying of Stevia leaves in a newly developed solar dryer of mixed mode forced convection type (MFSCD) and open sun drying (OSD) are presented. Experiments have been performed under the average solar radiation of 567 W/m(2), ambient temperature of 30 degrees C and drying air flow rate of 0.049 kg/s. The safe (final) moisture content of stevia leaves 0.053 (d.b) has reached in 330 min and 870 min of drying time in MFSCD and OSD, respectively. The overall dryer efficiency and average exergy efficiency of the MFSCD were found as 33.5% and 59.1%, respectively. Quality analyses were carried out for fresh, open sun-dried and solar dried stevia leave samples. It was found that the anti-oxidant and the flavonoids were rich in solar dried samples compared to that of OSD samples. The color preservation is good in solar dried samples compared to OSD. Sensory analysis (flavor, aroma and taste) carried out on stevia leaves indicated that the solar dried stevia leaves provided better score compared to OSD samples. The estimated payback period of the newly developed dryer was found as 0.65 yr.