Analysis of rice grain motion characteristics in a rice polisher based on particle image velocimetry

[Objective] By studying the relationship between the operating parameters of the polishing machine, the motion patterns of rice grains, and the generation of broken rice rates, to seek the basis for optimal parameter control of the polishing machine. [Methods] By analyzing the motion process of rice grains in the polishing chamber, conducting full-factorial experiments, and applying Particle Image Velocimetry (PIV) to analyze the trajectory of rice grain movement, clarifiied the relationship between the motion status of rice grains, the rate of broken rice, and the rotational speed of the polishing machine as well as the opening degree of the pressure gate. [Results] When the pressure gate aperture was set to 20 mm, no coherent motion pattern wwas observed within the experimental range of machine speeds, rendering the rice polishing ineffective. In contrast, with a pressure gate aperture of 4 mm and machine speeds ranging from 600 to 1 400 revolutions per minute, the rice grains exhibited an alternating motion pattern characterized by a relatively small spiral angle and the occurrence of regions with varying velocities. Furthermore, under the condition of a pressure gate aperture of 8 mm and a machine speed of 1 400 r/min, the rice grains demonstrated an alternating motion pattern in regions of high and low velocities (with a velocity difference exceeding 3 m/s). In both of these scenarios, excessive friction and pressure leaded to a high rate of broken rice (exceeding 4%). In the remaining experimental conditions, characterized by appropriate pressure gate apertures and machine speeds, the rice grains exhibited a moderately sized spiral angle in alternating regions of high and low velocities (with a velocity difference of 2～3 m/s). This configuration resulted in a broken rice rate ranging from 2% to 4%, indicative of favorable polishing effects. [Conclusion] The motion patterns formed by rice grains and the resulting broken rice rates vary under different operating conditions. Under suitable opening degree of the pressure gate and rotational speed, rice grains exhibit appropriate motion patterns and achieve better polishing effects.