Heat and mass transfer characteristics and drying process optimization of Camellia oleifera seeds after hot air drying and shelling of the fruits

This study aims to elucidate the dynamics of moisture and temperature alterations in Camellia oleifera seeds during hot air drying and subsequent bursting. A systematic investigation was carried out to optimize the parameters for superior drying. The exceptional energy efficiency was characterized by minimizing energy consumption. The physical attributes of Camellia oleifera seeds were measured to determine their inherent properties, including thermal conductivity and density. The thermodynamic behavior of Camellia oleifera seeds was explored during drying at distinct temperature intervals of 52, 62, and 72 °C. According to Fick's Second Law, the effective moisture diffusion was then obtained corresponding to each temperature regime. An Arrhenius equation model was constructed in the empirically derived data on effective moisture diffusivity using reverse engineering. There was a significant correlation between effective moisture diffusivity, drying temperature, and activation energy. At the same time, a mathematical framework was designed to combine the heat and mass transfer, in order to simulate the drying of Camellia oleifera seeds. The predictions exhibited striking consistency with the experiments, with a maximum error of 8.5%, indicating the remarkable precision and reliability of the model. The results show that the hot-air drying dynamics of Camellia oleifera seeds were fundamentally dominated by internal mass transfer. The higher moisture gradients were observed than those of temperature ones. The fluctuation of drying rates shared a uniform pattern over the varying drying temperatures. The effective moisture diffusivity of Camellia oleifera seeds increased significantly over the temperature spectrum from 52 °C to 72 °C, ranging from 3.299 4×10-10−5.582 6×10-10 m²/s. The energetic transformations were computed as the activation energy of 25.025 kJ/mol during drying. Therefore, the variable temperature drying was performed better for Camellia oleifera seeds. There was the governing impact of three parameters—the initial wind temperature, the moisture conversion threshold, and the concluding wind temperature on specific energy consumption and drying velocity. Response surface optimization was applied to determine the optimal combination of drying parameters: an initial wind temperature of 63.7 °C, a moisture conversion point of 38.5%, and a terminal wind temperature of 74.8 °C. The better performance was achieved under these optimal conditions. Specific energy consumption was reduced to 5.040 kJ/g and a drying rate peaking at 0.048 g/(g·h). Compared with the model, relative errors for specific energy consumption and drying rate were 7.4% and 12.1%, respectively, indicating the pragmatic applicability and accuracy of the optimized parameters. In summary, a robust theoretical groundwork was offered to refine the practical drying parameters for Camellia oleifera fruit hot air drying and bursting, paving the way for industrial implementation and dissemination of Camellia oleifera fruit drying. Thus, considerable academic significance was provided for the promising practical application.