Effects of rotation speed and rice sieve geometry on turbulent motion of particles in a vertical rice mill

Performance optimization of a rice mill is an issue of great significance in the rice milling industry. By means of Discrete Element Method (DEM), this work examines how the turbulent motion of particles in the vertical rice mill is affected by the cross-section shape of rice sieve and the rotation speed of roller shaft. The random motion of particles is analyzed in terms of velocity field and velocity distribution in different directions. In addition, a kinetic analytic method for evaluating the intensity of turbulent motion of particles via average turbulent kinetic energy during a grinding process was investigated. The results showed that the collision rate and average collision energy in a milling chamber increase linearly with the average turbulent kinetic energy for the same type of rice sieve, which confirm the validity and practicability of the average turbulent kinetic energy. Furthermore, an average rate of clearance change is proposed to characterize the cavity shape variation in the milling chamber. It was found that there exists a strong correlation between the average turbulent kinetic energy and the average rate of clearance change, irrespective of the cross-section shape of regular polygon sieve. This revealed that the cavity shape variation, which is determined by the geometric parameters of rice sieve and rotation speed, has a great influence on the turbulent motions of particles in the milling chamber. Overall, the results are useful for developing a fundamental understanding of the kinematic and dynamic characteristics of particle behavior, which will help design and control practical processes. (C) 2017 Elsevier B.V. All rights reserved.