Experimental and numerical study on heat and mass transfer of Zanthoxylum bungeanum microwave drying

Microwave-assisted dehydration has gained many applications in agricultural processing, yet its application to Zanthoxylum bungeanum remains underexplored. Besides, the heat and mass transfer process of the Zanthoxylum bungeanum sample during the microwave drying process, remains poorly understood. To fill this research gap, this work investigates the drying characteristics of Zanthoxylum bungeanum in microwave ovens under different conditions through a combined approach of numerical simulation and experimental validation. We first developed a multiphysics coupled numerical model for the microwave drying of Zanthoxylum bungeanum in COMSOL Multiphysics, with the measured dielectric properties of Zanthoxylum bungeanum. Then, the numerical model was validated with experiments. Subsequently, with the aid of the validated numerical model, we investigated the effects of microwave power and sample layer thickness on the drying process. Parametric analysis revealed non-uniform moisture distribution characterized by central accumulation and edge dehydration under microwave drying conditions. Its moisture gradient ranges from 3.32 % to 7.38 %. Meanwhile, both power and thickness significantly affect the moisture variation coefficient, with ranges of 0.31–0.89 and 0.55–0.90, respectively. In addition, the layer thickness optimisation shows that the temperature variation coefficient is less than 0.15 at 9 mm, and the heating efficiency is higher than 80 %. These findings provide valuable insight into the heat and mass transfer process of Zanthoxylum bungeanum during microwave driving and the application of microwave-assisted dehydration in Zanthoxylum bungeanum, but also guide the microwave drying of other food crops.