Abstract
The solid particle suspension inside a flotation machine is significantly dependent on the flow field, particularly the flow hydrodynamics characteristics near the bottom of the flotation machine. In this study, a laser Doppler anemometer (LDA) was utilized to investigate the influence of the impeller diameter and the impeller off-bottom clearance of a flotation machine on the flow velocity distribution characteristics near its bottom. The results showed that centripetal, centrifugal, and transitional spiral ascending vortexes were generated for different cases of the impeller variables. The impeller diameter and the off-bottom clearance were found to have a significant and interactive influence on the flow pattern, radial and axial velocities, velocity vector distribution, and axial fluctuating root mean square (RMS) velocity characteristics. When the centripetal flow was generated with a large impeller diameter and a small off-bottom clearance, the vortex stability was improved, the low-velocity distribution area was reduced near the bottom center, and the high axial RMS velocity distribution area was extended and became more consistent. The latter provided an advantageous condition for the momentum transfer between the liquid flow and the solid particles, as well as the airflow. However, the axial RMS velocity in the centrifugal flow formed in other cases of the impeller variables was less than that in the centripetal flow. Although the increase in the impeller off-bottom clearance contributed to increasing the velocity magnitude, this is certainly disadvantageous to the service life of the impeller blades, as expected from the high-velocity area extension. These results may provide a reference for the impeller design and optimization of a KYF (Kuang Yuan Flotation) flotation machine, as well as a basis for further investigation on the behavior of the dispersed phases inside a flow field.
Highlights
Froth flotation is a method that is used to separate useful minerals and gangue by utilizing air bubbles to carry solid particles upward, which provides an effective method for sorting various complex refractory ores [1]
Particle suspension or mixing determines the method of interaction between particles and bubbles and has an important impact on entrainment; it has always been a concern in laboratory and industrial flotation machines
Considering that the adjustment of the impeller speed has no significant effect on the flow pattern in a fully turbulent regime [13,17,32], the impeller speed was uniformly set as 400 r/min to support the particle suspension during the measurement
Summary
Froth flotation is a method that is used to separate useful minerals and gangue by utilizing air bubbles to carry solid particles upward, which provides an effective method for sorting various complex refractory ores [1]. They found that the flow pattern is mainly affected by the impeller off-bottom clearance and the impeller diameter and that an impeller with a larger diameter is more prone to promote the flow pattern transition These studies indicate that the structural parameters of an impeller are critical to the flow pattern of the fluid flow characteristics and that the flow pattern transition has a further impact on the particle suspension and mixing in a stirred tank. Hadane et al investigated the influence of a stator on the flow field characteristics of a flotation machine using computational fluid dynamics (CFD) simulations [20] It was observed from their simulation results that the rotational motion apparently disintegrates near the stator in the tank center and that the center of the vortex formed below the impeller deviates from the axis.
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