Solar drying of peppermint leave: Thermal characteristics, drying kinetics, and quality assessment

In the present study, thermal performance of greenhouse solar dryer (GHSD) was analyzed at full load of peppermint leaves for dehydration. The experiments were conducted in both GHSD and sun drying processes to compare drying characteristics, thermal properties, and quality assessment of peppermint leaves. The maximum drying cabin temperature attained during the experimentation was 58.3 degrees C at solar radiation 864W/m2. Initial moisture content of peppermint leaves 81.25% reduced to 11.22% and 22% within 10 h in GHSD and sun drying, respectively. Drying rate was obtained as 0.65 kg water/kg solid.hr and 0.61 kg water/kg solid.hr for GHSD and sun drying process at the end of the experiment. Verma et al. model accurately defined the drying characteristics of peppermint leaves in GHSD and sun drying. Average effective moisture diffusivity (Deff), mass transfer co-efficient (hm) and heat transfer coefficient (h) of peppermint leaves were increased by 12.76%, 17.71%, and 64.23%, correspondingly in GHSD compared to sun drying. Activation energy (Ea) of peppermint leaves was computed as 32.25 kJ/mol in GHSD, while in sun drying method, it was 59.68 kJ/mol. Water activity (Aw) peppermint leaves were 0.850, 0.705, 0.385 and 0.850, 0.765, 0.520 at 8, 14, 19 h in GHSD and sun drying.