Moisture transport and stress development in rice during drying, a Hybrid Mixture Theory-based model

Internal fluid flow during rice drying generates a stress gradient inside the material. If the stress gradient becomes too large or certain rice layers undergo glass transition under a significant stress gradient, stress cracks can form. In this study, modeling equations based on the Hybrid Mixture Theory were solved to simulate moisture transport and the viscoelastic stress that occurs during rice drying. The model’s accuracy was evaluated using experimental moisture content data for two rice varieties: Pusa Basmati 1121 (MAEs: 0.0079–0.0162 g/g solids) and California M206 (MAEs: 0.0022–0.0061 g/g solids). Simulations were then conducted under continuous and time-varying drying conditions to determine the best drying strategy for minimizing stress crack formation. The results showed that gradually increasing the inlet air temperature by 5 °C every 5 min after an initial 28.5 min at 40 °C could reduce stress crack formation effectively while drying rice in only 38.5 min.