Evaluation of numerical approaches for the simulation of water-flow in gravity-driven helical mineral separators

Advancing the understanding of the fluid behavior in a mineral separation spiral has seen computational fluid dynamic models being validated using various flow properties. In this research article, capturing a focussed line of bubbles, which is commonly encountered in spirals, was utilized as a novel means to evaluate various numerical simulation approaches. To match experimental data, the simulations used a measured wall roughness, wall contact angle, and bubble size, in addition to a fluid domain geometry based on a 3D scan of a full-scale spiral. Through comparison with experimental data, the research investigated the effects of different numerical modeling approaches on the bubble line behavior, calibrated the unknown bubble mass flow rate, and performed a sensitivity analysis on the bubble diameter, wall roughness, and wall contact angle. The effects of changing the drag coefficient, the use of a simplified turbulence model, and the bubble–water interaction were investigated. The only model that allowed the formation of a bubble line was a two-phase Eulerian multi-fluid VOF model with the bubbles being included as a Lagrangian phase, with both drag and virtual mass forces modeled. The use of this model with a full-length domain of the spiral produced the first numerical evidence of a postulated tertiary radial flow in mineral separation spirals.