Study on spatial flow field instability in a disturbing rotary centrifugal air classifier based on simulation and experimental methods

Abstract

Efficient particle classification in air classifiers is essential for optimizing industrial processes. However, the instability of the flow field under loading conditions remains a challenge. The gas-solid phase is subject to complex drag forces in the flow field. An imbalance in these forces can result in phenomena such as vortex eccentricity, which adversely affects the separation of target particles. In this paper, a new disturbing rotary centrifugal classifier is designed. Furthermore, numerical simulations and experimental analyses are utilized to investigate how the operating parameters influence regional flow field instability in air classifiers under loading conditions. Following the experiments, the motion of the gas-solid phase cyclone under the influence of a double-vortex structure is explored. The results indicate that the flow field in the toothed blades area exhibits a double-vortex structure with inner quasi-forced vortices and outer quasi-free vortices. The curved impeller area flow field presents a double-vortex structure with outer axial circulation and inner secondary flow. The flow field stability depends on the stability of the double-vortex structure. The impact of double-vortex structure instability on the flow field is mitigated at a critical rotational speed of 950 rpm. Comprehensive signal and experimental analyses reveal that the flow field stabilizes and classification efficiency increases to 94.9 % at a disturbing frequency of 45 Hz (950 rpm), a feed rate of 0.3 kg/s, and an inclination of - 2°. The causes of flow field instability in classifiers are clarified, and alleviation strategies are proposed in this paper, offering valuable insights for large-scale equipment applications.