Browsing by Author "Meyer, Chris"

Now showing 1 - 6 of 6
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    Application of CFD to hydrocyclone flow prediction
    (2004) Dlamini, Mduduzi Felix; Powell, Malcolm; Meyer, Chris
    The mechanical simplicity of the hydrocylone deceptively suggests non-intricate and well-understood device hydrodynamics. On the contrary, improved understanding on the hydrodynamic behaviour and operation of the hydrocyclone are still being sought in order that, its full classification potential may be realised. Current models describing such behaviour are predominantly highly empirical hence the need for continued complementary research via computational techniques such as Computational Fluid Dynamics (CFD). This dissertation presents the outcome of an investigation into the flow characteristics of a hydrocyclone. Assessment of its hydrodynamic behaviour was conducted via interpretation of numerically predicted velocity and pressure field profiles arising from single phase (water-only) and multiphase (water/air) flow fields.
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    Characterisation of the autoignition delay behaviour of n-heptane in the IQT combustion bomb using CFD modelling
    (2007) Metcalf, Owen J; Swarts, André; Yates, Andrew; Meyer, Chris
    When n-heptane was tested in the IQT device over a range of temperatures and pressures, the measured autoignition delay did not correlate with the chemical autoignition delay associated with a stoichiometric, homogenous mixture as predicted by detailed chemical kinetic models. ... This project involved an investigation to study and reconcile this discrepancy, using computational fluid dynamic (CFD) techniques to explore the physical conditions prevailing in the IQT device. Specifically, CFD was used to model fuel injection into the IQT, this allowed a more accurate description of the fuel/air ratio and temperature history of the fuel inside the IQT combustion chamber than an assumption of global values. An empirical description of autoignition delay, developed by Yates et al. (2004), was then coupled to the CFD code: enabling the model to determine the progress of the fuel/air mixture to autoignition.
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    Development of a CFD model for stirred tank applications
    (2006) Engelbrecht, Darnell Francois; Meyer, Chris; Deglon, Dave
    This thesis deals with the development of a multi phase model for stirred tank applications. The general purpose, commercially available CFD code, FLUENT 6.2, is used to model a Rushton turbine-agitated stirred tank with T = 0.14 m.
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    The development of an enhanced autoignition sub-model for use in CFD combustion simulations
    (2006) Cox, Ryan; Yates, Andrew; Meyer, Chris
    With the ever increasing pressure to manufacture more efficient engines that produce lowerexhaust emissions, there is a corresponding need for a greater understanding of the combustion processes within these engines. Specifically, it is the interaction between the fuel and the engine that represents one of the greatest research challenges. As the systemsbecome increasingly sophisticated, the fuel companies are experiencing an increased demand for high specification fuels with tighter tolerances. Now, more than ever, the fueldesign and engine design need to work as one integrated system to meet these expectations. In this project, an attempt was made to produce a computationally efficient mathematical model of the fuel ignition characteristics that could be used in a CFD simulation of an internal combustion engine or any other generic combustion system. The validation of the model provided useful insight into the need for good quality experimental data for the fuels of interest, highlighting the need for pure ignition delay curves without engine effects, which is a limitation of many of the current models. When modelling a single fuel droplet, the importance of the temperature profile in the vicinity of the evaporating particle was clearly illustrated, as well as the variation in the local air/fuel ratio. These effects were shown to playoff against each other - the centre of the droplet being coldest and hence yielding a longer ignition delay while, at the same time, the high equivalence ratio near the centre had the effect of shortening the ignition delay. Using a simple, two dimensional model and using n-Heptane as the fuel, a realistic prediction of the overall ignition delay was obtained. More importantly, the critical zone of the initial auto ignition was identified. These simulations show how this model can be used in an environment that exhibits both gradients of temperature and equivalence ratio. It also shows the importance of including such in-homogeneities when creating engine models that include fuel injection. This approach can easily be extended into any type of combustion simulation involving fuel droplets where local temperature and equivalence ratios have a controlling effect on the ignition. Some recommendations for future work include the modelling of the IQT™ with the possibility of reconciling the ignition delay of the IQT™ and the cetane test.
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    Modeling of flow in impeller stirred tanks using computational fluids dynamics
    (2004) Siwale, Namwawa Alice; Meyer, Chris; Deglon, David
    The efficiency of mixing processes in impeller agitated tanks depends highly on the hydrodynamics. Computational fluids dynamics (CFD) provides a method of predicting the complex flow structures in stirred tanks. As with any approximate numerical method, CFD methods are subject to errors due to assumptions in the underlying mathematical models, as well as errors due to the numerical solution procedures. The aim of this thesis was to present a CFD method that accurately models the hydrodynamic properties of the 110w in stirred tanks. The general purpose CFD software Fluent 6. 1 was used to develop the model of a laboratory scale stirred tank. Numerical experiments were conducted to investigate the effects of the computational grid density, discretization schemes, turbulence models and impeller modelling method on the accuracy of the simulated flow. The results were validated with Laser Doppler Velocimetry data from the literature. It was found that the density of the numerical grid had more influence on the predicted turbulent quantities than on the mean velocity components. For the mean velocity components, reasonable agreement with the experimental data was observed even on relatively coarse grids. The choice of discretization scheme was found to have significant effect on the predicted turbulent kinetic energy and Power numbers. Very good agreement with experimental data was achieved for both these flow variables when higher order discretization schemes were used on fine grids. This is an important finding as it suggests that the generally reported underestimation of turbulence in literature is caused by numerical errors in the CFD simulation as opposed to inadequacies in the turbulence models as suggested by most researchers. Steady-state and time-dependent impeller models were compared and found to have little effect on the mean velocity and turbulent kinetic energy. However impeller Power numbers calculated from the time-dependent simulations were found to be in better agreement with the experimental values. A comparison was also made between the standard k-s and RNG models. It was found that the standard k-s turbulence model gave better predictions of the flow than the RNG- k-s turbulence model.
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    Numerical modelling of an oscillatory baffled column
    (2005) Bakker, Case W; Meyer, Chris; Deglon, D
    The aim of this project was to develop a numerical model to resolve the flow field in a general OBC. This model can then later be modified to be used to model the more complex aBC that is presently being experimentally tested by the Mineral Processing Research Unit at the University of Cape Town. The commercial CFD code FLUENT 6.2.16 was used to create the modeL Numerical simulations were conducted to investigate the effects of di fferent methods of defining the oscillatory flow, using both RANS turbulence models and Large Eddy Simulation (LES) to model turbulence, as well as different grid sizes and different discretization schemes.