Laminar, transitional and turbulent flow of thickened tailings in open channels
Creators: name: Javadi, Sadegh
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401003
subject: Engineering practice
classificationCode: 401210
subject: Microfluidics and nanofluidics
classificationCode: 401299
subject: Fluid mechanics and thermal engineering not elsewhere classified

description: The hydraulic transport of suspensions is frequently encountered in industry. A typical example is mine tailings which is transported from the dewatering plant to the tailings disposal area through an open channel. In recent years, because of water shortages and environmental and economic issues, tailings system facilities are changing, and thickening of mineral processing plant tailings slurry to achieve high solids content at discharge is becoming common. As a consequence, with increasing concentration, tailings material becomes more viscous and non-Newtonian in nature, and its flow behaviour becomes complex and more difficult to predict.<br><br>Thickened tailings transport is of significant importance in the design of tailings disposal management. Having been dewatered, tailings often travel a long distance to the disposal site. As long as the terrain allows gravity flow, one economical alternative to a pipeline is to utilize an open-top flume to convey the tailings material. The flume can be either artificial channel with commonly used cross sections (e.g. trapezoidal, rectangular, and semi-circular) or natural valley. The design of such a flume depends on the rheological characteristics and flow mechanism of thickened slurry. Therefore, understanding of free surface flow behaviour and characterisation of thickened tailings material is highly important to design the tailings management facilities appropriately. This knowledge is currently lacking and doesn’t lead to generally accepted design procedure.<br><br>This study focuses on the analysis of non-settling thickened tailings free surface flow. It was aimed at developing new approaches in artificial channels flow . The study covers laminar, transitional and turbulent regimes of fluid flow. Since the fluid mechanics, in general, is a fundamentally analytical-experimental engineering science, model development is based on the analytical analysis and the observation of non-Newtonian fluid flow through the semi-pilot constructed flume at RMIT University (4.8 meters long 100 mm width).<br><br>In the laminar regime, a new Reynolds number has been developed to predict the flow of non-Newtonian mining thickened tailings slurries in open channels. This model targets to appropriately evaluate the frictions forces caused by material viscosity in the laminar regime. <br><br>For transitional and turbulent flows, two new analytical models have been developed. Unlike the existing models (Haldenwang and Slatter, 2006, Haldenwang et al., 2010, Burger et al., 2010a, Burger et al., 2015), the new models have been analytically derived using the open channel velocity profile measured by Laser Doppler Anemometer (LDA) for a Newtonian fluid. It is believed that, in addition to the viscous sublayer existing in both pipe flow and open channel flows, two distinctive flow regions (1) inner (log law) and (2) outer are observed in an open channel flow, while on the other hand in the pipe flow only the inner region with logarithmic velocity profile is formed.<br><br>Flow transitional from laminar to transition regimes are also studied. A new model is presented based on the assumption that at the limit of the transitional flow, the laminar shear velocity ( approaches the turbulent regime shear velocity ( . However, the transitions from the transition to the turbulent flow was not studied in this thesis.<br><br>A new experimental data set has been compiled for this thesis. The experimental results along with 2 other independently collected sets, of relevant experimental data, i.e Haldenwang (2003) and Burger et. al. (2010), are used to validate the new models and the existing models reported in the literature.<br><br>It was found that the new models, except the transitional loci determination model, provide a considerably better prediction over the existing models. In the laminar regime, it is shown that the newly defined Reynolds number achieves better estimation of the friction at the boundary and average velocity when compared with the experimental data.<br><br>In the transitional and turbulent regimes, the new models give better flow behaviour prediction when compared to that of Haldenwang-Slatter (2010) model - even for the dataset from which the Haldenwang-Slatter model was developed. The same was observed for the Burger et al. (2015) model using the Burger et al. (2014) dataset. The quantitative comparisons of the proposed models with the current models were achieved using the combined error occurred in the channel slope.