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This Technology in Industry Fellowship (TIF) funded Masters Project was structured around Computational Fluid Dynamics (CFD) modelling for Lemar Environmental Ltd (Lemar). This study is a component of a larger programme that is being undertaken by Lemar concerning the vitrification process. The modelling has built on an initial model developed by CSIRO for Lemar and has been carried out under the direction of Canterbury University. The modelling involved computer simulations and detailed comparisons of the gas flow for both high and low swirl vanes, in both the steady state and transient modes. The output of this activity; velocity profiles (tangential and axial), vorticity, as well as particle tracking (in steady state mode only) were compared to literature and evaluated for both scenarios. As the study was restricted to the gas flow in transient mode, no recommendations and extrapolated modifications to the burner geometry and plant equipment can be made as they have to be verified by the particle motion within the gas flow. The steady state particle simulations obtained through this project, did not provide sufficient evidence to conclude that particles attach to the outer wall and only demonstrated the influences that the high and low swirl had on the particles. Further investigations of transient particle tracking would provide an overall interpretation as to whether or not the dried sludge particles bounced or stuck to the viscous slag layer and a commentary as to their movement in the chamber. Lemar's strategic vitrification programme is still active and the resulting redesign process is nearing completion and modifications to the plant are expected to be finalised by January 2008. Following extensive testing by Lemar it is understood that they would be looking to seek venture capital in order to progress the project to the market. In order for the final stage of the sewage sludge vitrification plant project to commence, Lemar has been in consultation with subject matter experts in the field, as well as undertaking trials on the plant, computer modelling and research into both the technical and international marketing prospects for the combustion technology. The detailed analysis and research undertaken through the CFD modelling conducted for this Project, recommends that Lemar conducts further CFD modelling to investigate transient particle tracking before any plant or geometry modifications are proposed and undertaken in order to optimise the ash capture which is a key output of the vitrification process.

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Drag reduction in wall-bounded flows can be achieved by the passive flow control technique using riblets and surface grooves aligned in the mean direction of an overlying turbulent flow. They were inspired by the skin of fast sharks covered with small longitudinal ribs on their skin surfaces. Although it was found that the drag reduction depends on the riblets’ geometrical characteristics, their physical mechanisms have not yet been fully understood in the scientific terms. Regarding riblets sizing, it has been critically explained in the literature how riblets with vanishing size interact with the turbulent flow and produce a change in the drag proportional to their size. Their shapes are focused upon because these are most significant from a technological perspective, and also less well understood. Different riblet shapes have been designed, some with complicated geometries, but except for the simple ones, such as U and V grooves, there has not been enough study regarding shape features. Therefore, special effort is undertaken to the design of an innovative type of ribleted surface, e.g. the Serrate-Semi-Circular shape, and its effect on the skin friction and drag reduction. In this work, the possible physical mechanisms of riblets for turbulent drag reduction have been explored. The modelling and experiments concerning the relationship between the riblets features and the turbulent boundary layer structure have also been reviewed. Moreover, numerical simulations on riblets with different shapes and sizes are presented and studied in detail. An accurate treatment based on k-ε turbulence model was adopted to investigate the flow alteration and the consequent drag reduction on ribleted surfaces. The interaction of the overlying turbulent flow with riblets and its impact on their drag reduction properties are further investigated. In addition, the experimental facilities, instrumentation (e.g. hotwires) and measurement techniques (e.g. time-averaged turbulence structure) have been employed to experimentally investigate the boundary layer velocity profiles and skin friction for smooth and micro-structured surfaces (the proposed riblet shape, respectively and the presented new design of riblets with serration inside provides 7% drag reduction. The results do not show significant reduction in momentum transfer near the surface by riblets, in particular, around the outer region of the turbulent boundary layer. Conclusions with respect to the holistic investigation on the drag reduction with Serrate-Semi-Circular riblets have been drawn based on the research objectives as achieved. Recommendations for future work have been put forward particularly for further future research in the research area.

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Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Modern Computational Fluid Dynamics modelling (CFD) are becoming common design and analysis tools in the engineering field. Nowadays, project designs involve the use of CFD techniques along with physical scale modelling to analyse the complex rapidly varied and turbulent flows which would not be easily analysed by physical modelling. In particular, the consideration and/or use of CFD modelling in the Hydraulic Engineering field remains on the increase. Apart from being used for comparison with other design techniques, CFD may in future become a standalone modelling technique in hydraulic structures design. This research aims to use CFD models to validate the simulation of the flow over two ogee dam spillways which are installed in the Hydraulic Laboratory of Stellenbosch University. To achieve this simulation of the flow which involves an interaction between water and air, the flow behaviour has been mapped by the Volume of Fluid (VOF) and the realisable "𝑘−𝜀" turbulence numerical models. The Volume of Fluid (VOF) and the realisable "𝑘−𝜀" models simulate the free surface of two-phase flow and the flow turbulence, respectively. Firstly, the study embarks with details on the actual design approaches of a typical ogee dam spillway. It subsequently presents the geometry and dimensions of the physical models, the testing procedure and the experimental test results achieved from this modelling exercise. For CFD modelling, a commercially available Computational Fluid Dynamics (CFD) package, Ansys-Fluent, was used. To model the physical model, the use of Reynolds-averaged Navier-Stokes equations in combination with the realisable k-ε eddy-viscosity closure model was adopted. The process of CFD model development and the underlying theory of it are discussed in this thesis. Different test scenarios including steady and fully hydrodynamic states simulation for two and three-dimensional geometries were considered in this simulation to achieve the most accurate results. In order to determine the required mesh size, the mesh sensitivity tests were conducted on the 2 dimensional and 3 dimensional models. Finally, the pressure readings and water levels produced by numerical models are discussed through a validation process by comparing the CFD model results with the results obtained from physical models. The outcome proved that CFD models are able to map the behaviour of both flow phases since they exhibited a close correlation to those achieved in the physical models. Even though some slight differences in values were revealed, the graphical trend remains reasonably similar for all test results. / AFRIKAANSE OPSOMMING: Moderne gerekenariseerde vloeidinamika numeriese modelle (CFD) word deesdae dikwels deur ingenieurs gebruik. Projekontwerpe sluit tans die gebruik van CFD tegnieke asook fisiese skaalmodellering in om komplekse, vinnig-veranderede en turbulente vloei te ontleed. Hierdie tipe vloeie is moeilik om met fisiese modellering te ontleed. Die gebruik van CFD numeriese modelle in hidrouliese ingenieurswese is besig om toe te neem, Die bevindinge van CFD modelering word tans vergelyk met die bevindinge van ander ontwerptegnieke, maar in die toekoms mag dit moontlik gebruik word as die enigste modelleringstegniek in hidrouliese struktuurontwerp. Die doel met hierdie navorsing is om CFD modelering te gebruik om die vloei oor twee ogee-vormige afvoergeute wat in die hidrouliese labrotorium van die Universiteit van Stellenbosch ge-installeer is, te ondersoek. Ten einde hierdie vloei, wat die interaksie tussen water en lug insluit, te simuleer, is die vloeigedrag deur ”volume van vloeistof” (VOF) en die "𝑘−𝜀" turbulensie numeriese modules, gemodeleer. Die VOF en "𝑘−𝜀" numeriese modules simuleer onderskeidelik die vry oppervlakte vloei van die twee-fase vloei en turbulente vloei. Die ontwerp van ’n tipiese ”ogee”-tipe dam oorloop word bespreek, gevolg deur die beskrywing van die geometrie van die fisiese modelle, die toetsprosedure en die eksperimentele toetsresultate. Vir die CFD modellering is die CFD pakket, Ansys-Fluent, gebruik. Vir die simulering van die fisiese model is die Reynolds-gemiddeld Navier-Stokes vergelykings tesame met die k-ε eddy-viskositeit geslote module gebruik. Die proses van CFD ontwikkeling en die onderliggende teorie daarvan word bespreek. Verskillende toets-scenario’s wat 2D en 3D simulasies insluit, uitgevoer. Ten einde die toepaslike berekeningsrooster grootte vir die numeriese model te verkry, is sensitiewiteitstoetse uitgevoer op die twee- en drie-dimensionele numeriese modelle. Laastens is die CFD numeries gesimuleerde drukke en die watervlakke met die van die fisiese modelle vergelyk om die akkuraatheid van die CFD resultate te verkry. Die uitkomstes het getoon dat CFD modelle gebruik kan word om die gedrag van albei vloei fases te simuleer aangesien dit goed vergelyk het met die uitkomstes van die fisiese modellering. Daar was wel klein verskille in die druk waardes, maar die tendense in drukverspreiding was ooreenstemmend.

Dust and hybrid mixture explosions continue to occur in industrial processes that handle fine powders and flammable gases. Considerable research is therefore conducted throughout the world with the objective of both preventing the occurrence and mitigating the consequences of such events. In the current work, research has been undertaken to help advance the field of dust explosion prevention and mitigation from an emphasis on hazards to a focus on risk. Employing the principles of quantitative risk assessment (QRA) of dust and hybrid mixture explosions, a methodological framework for the management of these risks has been developed. The Quantitative Risk Management Framework (QRMF) is based on hazard identification via credible accident scenarios for dust explosions, followed by probabilistic Fault Tree Analysis (using Relex – Reliability Excellence – software) and consequence severity analysis, represented by maximum explosion pressure, (using DESC – Dust Explosion Simulation Code – software). Identification of risk reduction measures in the framework is accomplished in a hierarchical manner by considering inherent safety measures, passive and active engineered devices, and procedural measures. Dust explosion tests to determine icing and granulated sugar dust explosibility characteristics have been achieved in a 20-L Siwek chamber, and, accordingly, DESC fuel files were built and DESC has validated. Three industrial case studies are presented to show how the QRMF could has been helpful in reducing dust and hybrid mixture explosion risk at the Imperial Sugar refinery, the Semabla grain storage silo, and a hypothetical 400-m3 polyethylene storage silo. DESC simulations and Probit equation for structural damage provide the destructive percentage of each pressure zone in the simulations, followed by probabilistic FTA that were achieved for the first two case studies, before and after applying the framework. Detailed individual and societal risks calculations were made and F-N curves plotted for the two processes. The polyethylene silo case study is presented to show how inherent safety measures can be helpful in reducing dust and hybrid mixture explosion risk. The framework showed significant risk reduction to the point where the residual risks are acceptable for both processes. Finally, assessment results are compared and improvements measured. / The research main objective is: to manage the risks of any expected dust or hybrid mixture explosion in industrial complexes (large-scale).

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Wastewater treatment plants discharge effluents containing a number of constituents whose concentrations may negatively affect the receiving waters. Current research in mixing and transport between a point source discharge and the ambient environment attempts to reduce these effects through a better understanding of the physical processes involved and development of numerical models to better predict the fate of the effluents under different conditions. This thesis examined the mixing and transport of ammonia discharged from a multiport diffuser of a municipal wastewater treatment plant into the Ottawa River. The river reach was surveyed using an M9 acoustic Doppler current profiler to obtain spatially distributed measurements of depth and velocity. Water samples were collected at and downstream of the diffuser at multiple depths. The samples were analyzed for ammonia concentration and kinetics. The river reach was also simulated in the FLOW-3D model using available turbulence closure schemes. Comparisons were made between measured and modelled results, as well as some empirical and semi-empirical approximations. A combination of measured and modelled results helped describe (quantitatively and qualitatively) the mixing and transport between the discharged effluent and receiving river. Unionized ammonia was tested for regulatory compliance. Both measured and modelled results showed that although the regulatory end-of-pipe discharge concentrations were met, downstream regulations were not met.

7ABSTRACTAs the energy consumption for thermal comfort and space cooling around the world continues to grow due to a steadily increasing demand and climate change; the use of vapor compression technology, has increased significantly. In this technology, condensation is used to condense out the water vapor from air by maintaining the coils at a cooler temperature than required to meet the sensible load. This results in a high energy consumption for dehumidification and lowers the overall efficiency of the system. They also pose environmental threats due to its significant CO2 emissions.<div><br></div><div>The aim of this research is to address the above problems by using a novel membrane configuration called as a membrane heat exchanger that has integrated cooling coils and simultaneously cools and dehumidifies the air stream with the help of a vacuum pump and a vapor selective membrane.</div><div><br></div><div>In this work, the CFD modeling and design of a membrane heat exchanger is presented. The model is developed for a base case to study the heat and mass transfer performance of the system. The model after validation with existing studies is developed further to obtain several contour plots to understand the effects of concentration polarization, membrane permeance, Reynolds number, pressure drop and other design parameters on the performance of the system.<br><div><br></div></div>