Influence of nose angle on performance of dense medium cyclones with volute inlet

Dense medium cyclones (DMCs) are widely used in coal mine sorting processes to improve the quality of coal products and reduce pollution. The conventional linear inlet DMCs has the problems of unstable flow field, high turbulence density and low separation efficiency. Based on these concerns, the volute inlet DMCs was proposed, however the nose angle as one of the most critical parameters has not yet been investigated in depth. In this paper, a DMC with volute inlet is investigated, and the effect of nose angle is studied by a computational fluid dynamics model in terms of flow field, particle motion and the forces acting on the particles. The performance of the DMC is evaluated with respect to the inlet nose angle. As the nose angle increases from 0 to 180 deg., the separation efficiency has a tendency to increase and then decrease with the inflection point founding when nose angle is 180 deg. Then the flow field, particle distribution and particle force are analyzed respectively. The results show that the symmetry and stability of the flow field can be significantly improved as nose angle increases from 0 to 180 deg., but they remain almost constant when nose angle is 270°. In addition, a quantification method of the short-circuiting flow is established and it has been found that increasing the nose angle can notably reduce the short-circuiting flow. In terms of particle phase, increasing the nose angle causes heavier particle distribution tends to concentrate. During this period, the variation pattern of forces on particles with different nose angles is also analyzed. The DMC with a nose angle of 180 deg. has a longer acceleration zone at the entrance height and an increased radial force on the particles, which results in better performance. This study provides a theoretical basis and reference for the structure optimization of dense medium cyclones.