Experiments on Sand Jets, Viscoplastic Fluids and Pumping

• Main Author: Cai, Jianan
• Format: Dissertation
• Language: English
• Subjects: engineering, civil; water resource management
• ISBN: 9780494964125; 049496412X

This study aims to improve our understanding of physical processes related to MFT and sand operations in tailings ponds. Laponite, a synthetic silicate that produces a transparent non-Newtonian gel, was used as a laboratory substitute of MFT.
This thesis first discussed the results of an experimental study of circular sand jets in air from nozzles of various sizes. The frontal speeds of the sand jets and the steady sand jet velocity accelerate due to gravity with negligible air resistance. The diameters of sand jets decrease but gradually approach an asymptotic value and the sand concentration in the jet decreases as the distance from the nozzle increases. Waves were observed at the periphery of the sand jet and some preliminary results of wave speed and wavelength were reported.
In second part of this thesis, experiments were carried out by depositing circular sand jets vertically into viscoplastic fluids. The deformation regimes of sand jets in the gel were investigated, including dispersed jetting, confined jetting and dripping. The penetration of sand drops at the gel surface was monitored and a simplified model was proposed to predict the yield stress. The yield-gravity parameter of the deformed sand drop in the gel was also computed.
Another set of experiments were performed to withdraw viscoplastic Laponite gel or water capped gel from a vertical circular pipe by a progressive cavity pump. The gel velocity field was computed from the images taken during the process. Under the assumption of an axisymmetric flow condition, radial velocity was found to vary with the axial angle and maximum horizontal velocity occurs at a level below the intake pipe. For pumping a single layer of gel, an analytical solution was proposed to describe the radial velocity variation induced by pumping and it shows a good agreement with the experimental data when axial angle is less than 150°. For the selective withdrawal of water and gel, the interface deformation was inspected and critical submergence was found to be mainly controlled by the withdraw discharge. Water and gel discharges were discussed in terms of the subcritical and supercritical stages.