Modeling and analysis of heat and moisture transfer during <i>Fructus aurantii</i> drying based on CT scanning

Fructus aurantii, a genuine traditional Chinese medicinal material, undergoes drying as a critical step to ensure the quality of its post-harvest processing at the origin. However, a major challenge in this process are the uneven drying rates between the surface and interior, which often leads to quality defects such as dry and wet spots. In severe cases, it can even cause localized mold growth, significantly compromising the processing quality and market value of the product. To address this issue, this study systematically characterized the microstructure of Fructus aurantii using CT scanning technology, developed a more realistic microstructure model, and accurately obtained key physical parameters including pore structure properties. Based on this microstructure characterization, a transient heat and mass transfer model for the drying process of Fructus aurantii was established and solved numerically. Model validation experiments were performed under drying condition at 55 °C, and the results showed that the maximum deviation between the simulated and experimental moisture ratio values was only 9.2%, confirming the model’s reliability. Using this basis, the dynamic evolution of internal temperature distribution, moisture content distribution, and water vapor partial pressure gradient during drying were thoroughly analyzed. It was found that the low-porosity structure of the Fructus aurantii surface significantly hinders moisture diffusion. Moisture accumulates at the interface between the surface and the fiber layer, leading to the formation of wet spots. Conversely, in the non-aggregated regions between the surface and internal fibers, dry spots tend to form due to restricted moisture diffusion combined with a high evaporation rate. This study systematically reveals the core mechanism of internal moisture migration during the drying of Fructus aurantii, providing important theoretical support for the optimal design of mold-prevention and quality-enhancement drying processes, as well as related engineering innovations for this medicinal material.