Simulation and Experimental Studies of Heat and Moisture Transfer and Solute Migration during Hot Air Drying of Apple Slices

In order to reveal the underlying mechanism of heat and moisture transfer and solute migration associated with nutrient losses during the drying process of fruits and vegetables and to determine the influence of factors such as the micropore structure characteristics of fruits and vegetables and the capillary force at the pore interface on the drying process, this study employed interdisciplinary knowledge such as pore network modeling and the principle of heat and mass transfer to establish a pore-scale network model for simulating nutrient losses from fruit and vegetable drying. Visual C++ and Matlab were used to design and develop software to simulate and analyze the temperature, moisture, and sugar distribution during the drying process. Hot air drying experiments and model verification were carried out on apple slices as a typical representative of fruits and vegetables. The results showed that the relative error between the simulated values from the drying curve and the experimental values was less than 10%, indicating that the model could effectively simulate the processes of heat and moisture transfer and solute migration in fruit and vegetable drying and reproduce the occurrence of ‘sugar exudation’ in the drying process. The temperature field and the wet field were interlinked with each other, leading to an obvious temperature dividing line at the drying front. Increasing hot air temperature and velocity and decreasing the relative humidity of hot air all accelerated the drying rate and increased the loss of nutrients from the material. The higher the relative humidity of hot air, the faster the material temperature increased in the early stage of drying. The results of this study provide a theoretical basis for the analysis and optimization of the drying quality of fruits and vegetables and for energy saving and efficiency improvement in the drying process.