Effects of rotation speed and outlet opening on particle flow in a vertical rice mill

Abstract

Rice mill is the key equipment to food processing used for milling unpolished rice to milled rice. However, there are few investigations about the flow process on rice particles inside the mill and the role of operation parameters. In addition, the detailed information about particle interaction and mechanisms of milling remains poorly understood. This paper presents a numerical study based on the discrete element method (DEM) to investigate the flow of rice particles in a vertical rice mill. The effects of operation parameters on the hidden flow properties, including particle orientation angle, particle fill level, collision energy and energy efficiency, were analyzed. The results showed that the particle orientations prefer pointing to 0° and 180° and orientation angles fluctuate at U-shaped distributions on a vertical plane. The wear process of particles can be described by the spatial distribution of collision energy. Wear of particles occurs mainly in the upper half of milling chamber, in which is defined as milling area. The effects of outlet opening on flow structure and particle fill level in milling area are more obvious, compared with that of the rotation speed. However, the increase of rotation speed results in higher collision energy, collision number and energy efficiency, which accelerates wear of rice particles. The findings are useful to understand particle flow, wear and milling behavior of the vertical rice mill.