Browsing by Author "Lazarus, JH"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Open Access
    An analytical and experimental investigation of three phase flow in airlift pumps used for diamondiferous marine gravel reclamation
    (1991) Berg, R Rainer; Lazarus, JH
    This dissertation covers an investigation on airlift pumps operating in three phase flow. The investigation is specifically geared towards offshore diamond reclamation and the three phases considered are air, water and marine gravels. The purpose of the research was to develop an analytical technique to simulate mathematically an offshore airlift pump being used in the recovery of diamondiferous marine gravels. This analytical technique is incorporated into computer software which can be used to simulate prototype airlift installations in a CAD (computer aided design) environment. Extensive laboratory work has been conducted on both a 90 mm and 40 mm diameter airlift pump test facility. This investigation involved the measurement of specific components required for the theoretical simulation. Also monitored were airlift pump delivered outputs and behaviour under various operating conditions. Using this information, the proposed mathematical model was formulated, evaluated and compared with other mathematical models presented in the literature. The theoretical approach, which is based on a balance of external and internal pressures, proved successful and theoretically predicted solid and liquid output flow rates compared favourably with measured solid and liquid output flow rates. Furthermore, the computer software which was subsequently developed is presently being used in the diamond mining industry to model prototype airlift pumps. A sensitivity analysis was performed to establish the effect of all the variables used in the mathematical model.
  • Thumbnail Image
    Item
    Open Access
    The dense phase hydraulic transport of high concentration cyclone classified tailings in pipelines
    (1991) Cooke, Robert; Lazarus, JH
    Summary in English. Word processed copy. Includes bibliography.
  • Thumbnail Image
    Item
    Open Access
    The hydraulic transport of high concentration stabilized flow full plant mineral tailings
    (1991) Paterson, Angus John Cawood; Lazarus, JH
    This thesis involves an analytical and experimental investigation of the flow behaviour of high concentration stabilized mineral tailings used as backfill material. At high solids concentrations "anomalous" behaviour occurs and is indicated by diameter dependancy on rheogram curves. These curves are not coincident in the laminar flow region. The anomalous behaviour is examined by postulating the following mechanisms : 1. Slip velocity at the pipe wall 2. Wall effects due to particle interaction 3 . Boundary layer effects 4. Plug flow at high concentrations 5. Particle migration away from the wall leaving a sheared annular zone 6. Lateral dispersive stress acting between particle and pipe wall. The mechanism responsible for "anomalous" behaviour is found to be due to the presence of a dispersive stress acting on the pipe wall due to particle-particle and pipe wall contact. This only occurs above a critical solids concentration ratio which is defined in terms of the critical void ratio or freely settled particle concentration. The total wall shear stress is a combination of both the viscous shear stress and the solid shear stress due to the lateral dispersive stress. Measured data was obtained from several test facilities. in pipe diameters ranging from 13,48 mm to 101,5 mm and for solids volumetric concentrations from 25% to 55%. Measurements included mean mixture velocity, pressure gradient, in situ and delivered volumetric concentration, temperature and the solids particle size distribution. Vertical down pipeline pressure gradients were obtained for a 40 mm NB pipeline which was constructed for the research. A tube viscometer was used to obtain rheological parameters. The measured data was compared with several analytical models using the log standard error. Existing models were found to be unsuitable for these slurries. The "anomalous" behaviour of the high concentration stabilized slurries is explained. The flow behaviour of these slurries is analysed in detail. The output is in the form of a user friendly interactive pipeline design computer program.
  • Thumbnail Image
    Item
    Open Access
    Hydro-pneumatic conveying of liquid by means of an airlift pump
    (1988) Berg, Rolf Rainer; Lazarus, JH
    Airlift pumps operating in two-phase gas-liquid flow are investigated with a view to establishing an analytical technique to aid in theoretically modelling air-lift pump behaviour. Extensive work on two test facilities constructed at the University of Cape Town's Hydrotransport Research facility has been done. Various components needed for the analysis are investigated. These include: (i) static dilation; (ii) dynamic void ratios; (iii) two phase weight component; (iv) two phase friction component; (v) two phase acceleration component. Using theoretical models for each component and combining these into the analysis technique, operating characteristics of airlift pumps with the following variables : (i) pipe diameters; (ii) gas injection depths; (iii) static lift heights; (iv) suction pipe lengths; have been successfully predicted.
  • Thumbnail Image
    Item
    Open Access
    The rheology and flow behaviour of high concentration mineral slurries
    (1988) Neill, R I G; Lazarus, JH
    The rheology and flow behaviour of high concentration backfill tailings are investigated using a modified Balance Beam Tube Viscometer. The viscometer is capable of producing reliable data using a computer based data acquisition system and three different tube diameters. The aim of this research is to determine the rheology of backfill tailings in order to predict friction head losses. The backfill tailings were prepared into four different particle size distributions each with a different maximum particle size. Each particle size distribution was tested over a range of high concentrations in the viscometer. The rheology of the lower concentration backfill tailings was successfully characterized using the yield-pseudoplastic model. It has been found that at high concentrations rheological characterization is impossible because the laminar flow region of the pseudo-shear diagram varies with tube diameter. This anomalous behaviour in the form of diameter dependence has been recorded in the literature. The results of high concentration tests on backfill tailings are investigated using the following theories to establish and account for the cause of the anomalous behaviour: Effective slip analysis - corrects the measured data for effective slip. Dense-Phase Model - based on the sliding friction between solid particles and the tube wall. Wall Effect - based on a reduction of in situ concentration due to a wall effect. Boundary-Layer Effect - corrects for the effect of a boundary-layer of liquid at the wall. Modified Friction Factors - takes into account the hydrodynamic lubrication between the solid particles and the tube wall. The existence of a thin layer of liquid at the wall is credible but not yet proven. The anomalous behaviour is linked to this layer. However a suitable method for correcting the measured data has not yet been established.
  • Thumbnail Image
    Item
    Open Access
    The underwater separation of diamantiferous marine gravels
    (1988) Rossouw, T J; Lazarus, JH
    Three underwater separation devices have been designed, constructed, tested and analysed to determine their suitability for the underwater separation of diamantiferous marine gravels. The research facility where the devices were tested was constructed at the University of Cape Town's Hydrotransport Research facility. The first device tested was a converging elutriator which separates the oversize gravel from the smaller diamond-bearing gravel, using their varying particle settling velocities in an upward flowing fluid. The cyclosieve and spirosieve are two other choices that both use rotational flow to create a centrifugal force, which forces the gravel onto a screening surface. The test work carried out investigated the effect of various variable parameters on the separation efficiency of each device.