Numerical and experimental study on drying shrinkage-deformation of apple slices during process of heat-mass transfer

Food materials with high moisture content were prone to occur drying shrinkage-deformation during dying process. In-depth understanding of drying shrinkage-deformation mechanism for food materials was crucial for optimizing drying parameters as well as for obtaining better quality dried foods. Therefore, the main aim of the present work was to investigate the drying shrinkage-deformation mechanism of apple slices during process of heat and mass transfer. Hot air drying experiment of freshed apple slices was conducted and the shrinkage-deformation values of apple slices were obtained by image analysis. Simultaneously, Heat-mass transfer coupled with stress-strain mathematical model were constructed and solved by COMSOL Multiphysics software. Results showed that the mathematical models of heat-mass transfer and stress-strain can be used to simulate the hot-air drying process of apple slices effectively, and the maximum relative errors of simulated value and experimental value were less than 10%. Temperature distribution and moisture distribution of apple slices during hot-air drying process were uniform. The maximum value of thermal stress and moisture stress were occurred at the middle period of the whole drying process; and the moisture stress during the whole drying process of apple slices were higher than thermal stress, which indicated that moisture stress was the main factor causing the drying shrinkage deformation of apple slices.