MICROWAVE THIN-LAYER DRYING KINETICS, DIFFUSIVITY, AND ENERGY EFFICIENCY OF MEDICINAL OCIMUM GRATISSIMUM AND VERNONIA AMYGDALINA LEAVES
- Authors
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Oladele, Samouel O.
The Federal University of Technology, Akure, Nigeria
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- Keywords:
- Thin-layer, microwave-drying, modeling, activation energy, moisture diffusivity
- Abstract
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Thin-layer microwave drying was applied to highly perishable medicinal herbs, Ocimum gratissimum (scent leaf) and Vernonia amygdalina (bitter leaf), to generate a comprehensive kinetic and energy dataset for these species. Increasing microwave power significantly reduced drying time from 19 minutes to 7 minutes for scent leaf and from 17 minutes to 4 minutes for bitter leaf, thereby avoiding the multi-hour durations required by convective or solar methods. Moisture-ratio curves exhibited only a falling-rate period. Seven thin-layer drying models were evaluated; the Midilli model provided the optimal fit (R² ? 0.990, root mean square error (RMSE) ? 0.030). Effective moisture diffusivity increased by an order of magnitude with applied power, reaching 1.84 × 10?? m² s?¹ for scent leaf and 1.54 × 10?? m² s?¹ for bitter leaf. An Arrhenius-type analysis yielded activation energies of 31.8 W g?¹ and 28.1 W g?¹ for scent leaf and bitter leaf, respectively. Specific energy consumption decreased to 4.09 MJ per kg of water removed (4.09 MJ kg?¹ H?O) at 900 W, while drying efficiency exceeded 97%. These results demonstrate that appropriately selected microwave power levels achieve rapid, energy-efficient dehydration without prolonged thermal exposure, offering a promising preservation approach for nutraceutical herbs in tropical regions. The reported kinetic and diffusivity parameters facilitate scale-up calculations for industrial microwave units targeting bioactive-compound retention.
- Author Biography
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