Numerical investigation of flow similarity of rice grains in friction rice mill and establishment of scale-up rule

Paddy usually requires a series of processing techniques to become edible polished rice. Among them, rice milling is a necessary processing connection closely related to the nutrition content and economic value of rice. How to accurately control rice milling on demand has always been a frontier topic. In this work, the milling process of rice grains in friction milling cavity with different parameter configurations was simulated numerically. The feasibility of the established simulation model was verified through experiments. Kinematic and dynamic similarity of rice grains in milling cavity were analyzed. The main contribution mechanism affecting the energy loss of rice grains was explored. The scale-up rule that can predict the milling degree of rice was proposed for the first time. The results showed that when the structural or operating parameters change, the flow structure of the particle bed will change significantly, which directly determines rice force characteristics. Besides, the energy dissipation between rice depends more on the configurational temperature dominated by the compactness of particle bed than on the granular temperature. The fluctuation of displacement field of particles will be more intense with the decrease of local space porosity and the increase of external input energy. Finally, a parameter scale-up rule – Relative compaction volume (RCV) suitable for friction rice mill is established. The average dissipated energy of rice grains can be characterized as a linear function of RCV. The characteristic parameter RCV is determined by the geometric characteristics and operating conditions of the rice mill. The research results can provide analytical ideas and theoretical direction for the design and parameter selection of rice mill and similar equipment.