Comparative Studies of Experimental and Numerical Investigations of Fluid Flow and Particle Separation of High-Gravity Spiral Concentrators

Particle stratification in spiral concentrators occurs due to the combined action of gravitational and centrifugal forces. Spiral flows have a free surface, shallow depths, and a transition from laminar to turbulent behavior. The current study investigates the comparisons of the flow field and bicomponent particle separation in high-gravity spirals with conventional coal spirals, often termed low-gravity spirals. A sensitive digital flow depth gauge is utilized to measure the fluid depth across the spiral trough. A high-speed motion camera is utilized to measure the free surface velocity via a tracer tracking approach. This flow visualization technique incorporates lycopodium powder as tracer particles to capture the free surface flow field on a dark background. Further, the two-phase flow is modeled for these designs by utilizing the volume of fluid model (VOF), incorporating the Reynolds stress model and RNG k-ϵ turbulence models. Comparisons were made on the flow patterns between high-gravity and low-gravity spirals, which differ in their trough profiles. High-gravity spiral concentrators exhibit greater depths, free surface velocities, secondary circulations, and turbulence intensities toward the outer edges compared to low-gravity spirals. The discrete phase model (DPM) is employed for particle tracking, thereby understanding particle segregation radially along the spiral trough. Performance data on bicomponent particle separation is presented to compare the separation effectiveness of high- and low-gravity spirals. Heavy mineral ore, such as chromite, is computationally tested with high- and low-gravity spirals, and it was found that low-gravity spirals are ineffective in achieving satisfactory particle separation. Also, the results demonstrate that each spiral has its own distinct size range for effectively separating particles. The DPM model predictions were validated against in-house experiments conducted with monocomponent silica material, and a reasonable match was found with the experimental data.