.

The thin-layer drying characteristics of bitter leaf (Vernonia amygdalina) was investigated over a microwave power
settings range between 90 and 900 W. The effect of microwave power from the experiment affected the samples
drying behaviours. The process of microwave drying of the samples occurred in the falling-rate period. The drying
rate increased as the drying microwave power increased, and the drying process time decreased with the increase in
the microwave power. The total drying time decreased from 3 minutes to 15 seconds with microwave power
increase. Seven mathematical thin-layer drying models were applied to the experimental drying data The Midilli et
al. model was adjudged the best as it adequately gave the best results and showed good consistency with the data
obtained from the experiments over the microwave power range with result values of 0.9930< R2<1, 0.000
×10−2<RMSE<4.80×10−2, 0.000 ×10−2 <SSE <1.03×10−2 and 0.000 ×10−2 <NRMSE <2.57×10−2. The moisture ratio of
the samples during the drying processes decreased with microwave power increase and effective moisture
diffusivity coefficients values of the samples across the microwave output power using Fick's second law of
diffusion varied from 2.30138× 10−8 m2/s to 9.69307 × 10−8 m2/s. The activation energy obtained from the Arrhenius