Numerical Simulation of Newton Model for Solar-Drying Characteristics of Telfairia occidentalis (Pumpkin) and Vernonia amygdalina (Bitter-leaf) using Nigerian Stored Products Research Institute Parabolic Shaped Solar Dryer

Green leafy vegetables (GLVs) are nutrient-rich but highly perishable, making postharvest preservation a major challenge. This study investigated the drying behavior of Telfairia occidentalis and Vernonia amygdalina in the Parabolic Shaped Solar dryer (PSSD) developed by the Nigerian Stored Products Research Institute. Sliced and unsliced samples were dried under monitored meteorological conditions, and drying rate was experimentally determined. A key novelty of this work is the transformation of the Newton drying model using Taylor's series expansion to enhance the accuracy of numerical prediction. The model's performance was also compared with the Levenberg-Marquardt iteration method. The average drying rates of Telfairia occidentalis (sliced and unsliced) dried in the PSSD were 0.0162 ± 0.00025 and 0.0158 ± 0.0004 kg/h; while that of the Vernonia amygdalina was 0.0145 ± 0.00006 and 0.0147 ± 0.00006 kg/h, respectively. The model showed excellent fitting performance with R2 values greater than 0.9, and RMSE values tended toward zero at all conditions. These results demonstrate the potential of the Taylor's series-based numerical transformation to improve thin-layer drying modeling and simulation, and confirm the PSSD as an efficient and hygienic technology for drying GLVs under tropical conditions.