Understanding forced convective drying of apple tissue: combining neutron radiography and numerical modelling

A multiphysics model for biological materials, coupling nonlinear viscoelastic deformation to water transport, was used to study forced convective drying of apple tissue samples (cv. Maigold). The accuracy of the model was verified with quantitative neutron radiography experiments, by comparing the total water loss, the transient water distribution profiles and the mechanical deformation. Both model simulations and experiments showed that the largest moisture gradients occurred at the air-tissue interface. The corresponding shrinkage behavior was similar. Furthermore, the difference between simulation results from modeling the water exchange with the environment using a constant mass transfer coefficient or a spatially varying transfer coefficient from a flat-plate correlation was not significant, indicating that the drying kinetics were dominated by the water transport in the tissue rather than by the convective flow at air-tissue interface. The simulated results showed a satisfactory agreement with experimental observations. The validated model is clearly appropriate to be employed for optimization of convective drying processes of food.