Modeling of mass transfer and initiation of hygroscopically induced cracks in rice grains in a thermally controlled soaking condition: With dependency of diffusion coefficient to moisture content and temperature - A 3D finite element approach

Rice grains develop cracks and eventually break during soaking. Since published simulation studies on hygroscopic swelling induced cracking were scarce, the present study attempts to model the mass transfer of moisture and hygroscopic swelling of rice grains using principles of finite element analysis performed in three dimensions (3D). Ultimately, to understand the crack formation in response to the existence of tensile and compressive stresses caused by moisture gradient in the grain during soaking. An empirical equation was developed to establish dependency of the diffusion coefficient of rice to both moisture content and temperature. Using a 3D replica of short grain japonica rice, the modeling was carried out using existing laws of diffusion and was validated using experimental data. Results showed that the rate of moisture diffusion and hygroscopic swelling were found to increase with increase in soaking temperature. The internal stress, however, was found to decrease with increase in soaking temperature. The simulated moisture content and increase in volume of rice grain were favorably in agreement with experimental results. Highly stressed sites that are prone to breakage have been clearly identified.