Vortex-generator-induced intensification of fine mineral collection in pipe flow

Abstract

Flotation of fine minerals is becoming increasingly challenging. Mineral particles are believed to collide and attach efficiently to air bubbles in highly turbulent circular pipes. In this study, vortex generators (VGs) are adopted to strengthen the turbulence and improve the collection efficiency of fine minerals in pipe flow flotation. Computational fluid dynamics simulations, bubble size measurements, and flotation tests are conducted in a modified pipe unit with VGs and an initial pipe unit without VGs. The simulation results show that the VGs induce streamwise vortices and increase the turbulent dissipation rate in the pipe unit. Bubble size distribution measurements show that the VGs decrease the bubble size slightly at high velocities. Flotation tests prove that vigorous turbulence induced by VGs is beneficial to the recovery of fine particles. In particular, the flotation rate constant of −20 µm particles at a liquid velocity of 0.7 m/s increases by more than 40% in the presence of VG-s5. Nevertheless, the excessive turbulence induced by VG-s5 caused a 20% decrease in the flotation rate of +45–74 μm particles when the liquid velocity increases to 2.0 m/s. This indicates that a relationship exists between turbulence and the particle size recovered. For a specified particle size, turbulence can be adjusted by varying the vortex generator spacing and changing the flow velocity to achieve the optimum flotation performance.