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

ABSTRACTAdvancing 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.KEYWORDS: Spiral separatorcomputational fluid dynamics (CFD)Eulerian multi-fluid VOF modelbubble linetertiary flow AcknowledgmentsThe researcher would like to thank the University of Technology Sydney (UTS) for the use of their computational resources for this study.Disclosure statementNo potential conflict of interest was reported by the author(s).Statement of noveltyAn understanding of the flow in a gravity-driven, helical mineral separator, commonly referred to as a “spiral,” has been pursued for decades through complex fluid flow simulations. Due to the large number of mathematical models needed in such simulations, it is critical to validate the complete numerical model with experimental data to confirm the appropriate selection and interaction of models. Unfortunately, computational limitations have necessitated modeling constraints in the past. The prescription of a fixed free surface, the application of periodic boundary conditions, the use of a no-slip wall at the top of the fluid domain, and the exclusion of the spiral’s feed box have all been implemented. These approximations for the boundary conditions increase the possibility of incorrectly representing the actual behavior of the flow in spirals and are removed in this work.Moreover, the simulation of spiral flows has often been validated using experimental data gained from scale models or from spiral models that were superseded in the early 90s. As such, the improvements in full-scale, industry-ready spiral designs that occurred during the last 30 years are not reflected in the available validation data. In the present study, validation data were used that were gathered on a full-scale, modern spiral to determine the required size of the simulation domain and appropriate boundary conditions. The spiral’s feed box was also included.The present study is the first to include and use a focussed line of bubbles, or “bubble line,” which is commonly encountered in spirals, to validate the simulation of the flow behavior. Using up-to-date experimental data and the bubble line as a validation tool, the article focusses on the simplest case as a starting point, that of a water-only flow in spirals. The result is the identification of the necessary physical models and numerical settings for simulation of the flow in mineral separation spirals, which can be used by the research community to build upon. The results showed the first numerical evidence of a postulated tertiary radial flow in mineral separation spirals, in addition to the often-described primary and secondary radial flows.Supplemental dataSupplemental data for this article can be accessed online at https://doi.org/10.1080/01496395.2023.2258274Additional informationFundingThe research study described herein is supported by an Australian Government Research Training Program Scholarship and is co-funded by the Department of Industry, Innovation and Science (Innovative Manufacturing CRC Ltd), the University of Technology Sydney (UTS), and Downer, via its subsidiary Mineral Technologies Pty Ltd (IMCRC/MTC/290418). The funding bodies were not involved in the study design; in the collection, analysis, and interpretation of data; in the writing of the paper; or in the decision to submit the article for publication.