### Browsing by Author "Rousseau, Pieter G"

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- ItemOpen AccessDesign and prototyping of a test facility to investigate the transport properties of dilute phase gas-particle flows applicable to coal-fired power plants(2017) Du Sart, Colin F; Rousseau, Pieter GUnderstanding the properties of dilute phase gas-particle transport and the applicability of the different empirical correlations found in literature for these properties are crucial in the study of Pulverized Fuel conveying applicable to South African coal-fired power plants. Having access to a test facility in which empirical data can be generated under controlled operating conditions would enhance this understanding and will allow more informed application of these correlations. The aim of this thesis was to develop a concept design and prototype of a pneumatic conveying test facility that can be used to evaluate these empirical correlations and property relationships. A comprehensive literature review was conducted of the empirical correlations available and a study was conducted to determine the scaling required to achieve similarity. A theoretical process model was also developed together with a methodology to determine the operating envelope of the blower. The model and methodology were subsequently used in the design of a prototype test facility that would demonstrate the critical particle feed and extraction processes, and to derive suitable specifications for the blower. The prototype, including a complete data acquisition and control system, was developed, constructed and commissioned in cooperation with a commercial engineering company. The facility allows for the control, online measurement and recording of the gas and particle mass flow rates. Practical tests were then conducted with Fly Ash, as a substitute for Pulverized Coal, to demonstrate the particle feed and extraction processes and to evaluate the accuracy of control of the gas and particle mass flow rates. Tests were conducted for loadings (particle to gas mass flow ratios) between 0.988 and 6.860 at gas mass flow rates between 0.051 and 0.115kg/s and particle mass flow rates between 0.077 and 0.600kg/s. A methodology to determine the particle mass flow rate and its associated uncertainty from the Loss In Weight and Gain In Weight systems was developed from basic principles and demonstrated. The relative uncertainties calculated for the measured particle mass flow rates are less than ±1% for all tests. The maximum relative uncertainties calculated for the measured gas mass flow rates and loadings are ±6%. The conceptual overall system layout for the final test facility, including the instrumentation design, was then refined based on the experience gained and recommendations are made for consideration in the detail design. The conceptual design allows for the control of the gas and particle mass flow rates as well as the gas temperature and pressure level. The final test facility will be suitable to conduct pressure drop tests, saltation and choking tests, as well as mass balances and visual observations. The process model and methodologies developed here may now be applied in the detail design and operation of such a final test facility.
- ItemOpen AccessDirect numerical simulation of free-surface and interfacial flow using the VOF method: cavitating bubble clouds and phase change(2018) Malan, Leon; Zaleski, Stéphane; Malan, Arnaud G; Rousseau, Pieter GDirect Numerical Simulation of two-phase ow is used extensively for engineering research and fundamental fluid physics studies. This study is based on the Volume-Of-Fluid (VOF) method, originally created by Hirt and Nicols. This method has gained increased popularity, especially when geometric advection techniques are used coupled with a planar reconstruction of the interface. The focus of the first part of this work is to investigate the hydrodynamics of isothermal cavitation in large bubble clouds, which originated from a larger study of micro-spalling, conducted by the French CEA. A method to deal with volume-changing vapour cavities, or pores, was formulated and implemented in an existing code, PARIS. The ow is idealized by assuming an inviscid liquid, negligible thermal effects and vanishing vapour pressure. A novel investigation of bubble cloud interaction in an expanding liquid using Direct or Detailed Numerical Simulation is presented. The simulation results reveal a pore competition, which is characterised by the Weber number in the ow. In the second part of the study the governing equations are extended to describe incompressible ow with phase change. The description of the work commences with the derivation of the governing equations. Following this, a novel, geometric based, VOF solution method is proposed. In this method a novel way of advecting the VOF function is invented, which treats both mass and energy conservation in conservative form. New techniques include the advection of the interface in a discontinuous velocity field. The proposed algorithms are consistent and elegant, requiring minimal modifications to the existing code. Numerical experiments demonstrate accuracy, robustness and generality. This is viewed as a significant fundamental development in the use of VOF methods to model phase change.
- ItemOpen AccessA row-by-row axial turbine process model based on a one-dimensional thermofluid network approach(2016) Pottas, Roelof J H; Rousseau, Pieter GA detailed turbine process model has been developed, based on a stage-by-stage discretisation using 1D flow elements. The complete turbine is represented by these flow elements in which the fundamental mass, energy and momentum conservation equations for compressible flow through 1D "stationary channels" and 1D "rotating channels" were solved. The required closure relations were obtained from the various loss coefficients for turbine stators, rotors and leakage flows which were characterised using correlations available in the literature. Several of the commonly applied loss calculation methods were investigated. A test case of a real turbine obtained in the literature was used to validate the model. Three models with different discretisation schemes were tested. In each of these schemes the stator and rotor flow passages were represented by a different number of elements along the radial direction. A number of hypothetical anomalies that often occur in industrial turbines were applied to the test case to demonstrate how the modelling approach can be applied in practice. The model agrees well with the test data for the nominal case and several of the off-design cases. For the nominal case the maximum deviation in total pressure of <2% occurs after the first stage and there is little variation between the results obtained with the three different models. The total enthalpy values are predicted within an accuracy of <1%, again with similar results obtained by the three different models. All three models predict the efficiency well for a broad range of relative mass flow rates. A slight improvement in the prediction of losses is observed in the models that use more elements to represent each stator and rotor passage.