The steam generator in a pressurized water reactor power plant acts as a fission product barrier between primary and secondary system. Material failure of the tube bundle barrier could therefore lead to a release of radioactive product into the secondary side. Several repair methods have been used to address tube leakage, with the most popular being tube plugging. The objective of this study was to quantify the effect of tube plugging on the thermal performance of a steam generator. For this purpose, the systems computational fluid dynamics (CFD) software Flownex® was used. First, a Flownex® model of the steam generator was developed and validated via comparison of the results to a validated model from the literature. Following this, a hydro-thermal analysis was performed to determine the effect of the tube plugging on the thermal performance under normal operational conditions (excluding the possibility of a tube rupture). Tube plugging of up to 20% was investigated. The model predicted the following effects: decrease in heat transfer, primary coolant mass flowrate and primary outlet pressure. Further, primary flow velocity, pressure drop and outlet temperature increase with increasing tube plugging. On the secondary side, tube plugging lowers the mixture quality in the boiling region and steam production while the re-circulation ratio was increased. Lastly, the model predicted a plugging ratio limit of 17.3%. Beyond this point, the steam generator does not extract sufficient heat from the reactor at 100% power.

The field of wavelets concerns the analysis and alteration of signals at various resolutions. This is achieved through the use of analysis functions which are referred to as wavelets. A wavelet is a signal defined for some brief period of time that contains oscillatory characteristics. Generally, wavelets are intentionally designed to posses particular qualities relevant to a particular signal processing application. This research project makes use of wavelets to mitigate interference, and documents how wavelets are effective in the suppression of Radio Frequency Interference (RFI) in the context of radio astronomy. This study begins with the design of a library of smooth orthogonal wavelets well suited to interference suppression. This is achieved through the use of a multi-parameter optimization applied to a trigonometric parameterization of wavelet filters used for the implementation of the Discrete Wavelet Transform (DWT). This is followed by the design of a simplified wavelet interference suppression system, from which measures of performance and suitability are considered. It is shown that optimal performance metrics for the suppression system are that of Shannon’s entropy, Root Mean Square Error (RMSE) and normality testing using the Lilliefors test. From the application of these heuristics, the optimal thresholding mechanism was found to be the universal adaptive threshold and entropy based measures were found to be optimal for matching wavelets to interference. This in turn resulted in the implementation of the wavelet suppression system, which consisted of a bank of matched filters used to determine which interference source is present in a sampled time domain vector. From this, the astronomy based application was documented and results were obtained. It is shown that the wavelet based interference suppression system outperforms existing flagging techniques. This is achieved by considering measures of the number of sources within a radio-image of the Messier 83 (M83) galaxy and the power of the main source in the image. It is shown that designed system results in an increase of 27% in the number of sources in the recovered radio image and a 1.9% loss of power of the main source.

This thesis is concerned with the initial development of a multiphase material model using the Theory of Porous Media (TPM) for the penetration of intermediary rust product into reinforced concrete subjected to chloride-induced corrosion. Research has shown that although the majority of time-to-cracking service life models for reinforced concrete structures neglect the permeation of rust into the cement paste adjacent to the reinforcement, it is this mechanism that is responsible for discrepancies between experimental data and model results. The model presented may be used to simulate the transport of water and gas through the capillary pores in concrete and the diffusion of iron III chloride within the pore solution. Iron III chloride is a soluble chloride complex formed as an intermediary product during the oxidation reaction at the anode of the corrosion cell. This solute is transported in the pore solution from low oxygen conditions and is oxidized in oxygen-rich conditions resulting in the precipitation of rust in the concrete pores. The Theory of Porous Media has proven proficient for modelling the material behaviour of porous solid bodies saturated with one or more fluids but has yet to be applied to chloride-induced reinforcement corrosion of reinforced concrete. This work outlines the initial efforts of using TPM to model the rust transport process coupled with the poro-elastic material response of reinforced concrete. The latter accounts for the stress build-up due to rust precipitation and volume expansion. The chloride complex is described by a concentration within the liquid phase and is therefore not assigned a unique volume fraction. Precipitation of the rust is not included here as it will be added at a later stage in the development of a more accurate reinforced concrete chloride induced corrosion model. It is intended that the model thus developed may be adapted for other deterioration mechanisms in concrete.

Activity, selectivity and stability are invariably among the key factors of the performance of a catalyst. In the development of catalysts these properties are often screened for a range of materials and formulations. Interpretation of these key performance indicators are prone to various confounding effects. Here, performance testing of solid, porous catalysts for gas phase reactions in tubular fixed bed reactors is considered. Transport limitations and particularly internal mass transfer limitations are often cited in this case. Many have given general discussions and guides for effective catalyst performance testing, reviewed or put forward theoretical descriptions for transport phenomena and have measured and correlated associated transport coefficients. Some quantitative requirements and the relative importance of different effects have been found to remain unclear. Here, some of these aspects are addressed by the development of 3 catalyst testing criteria. Specifically, an upper limit is derived for the chemical conversion in a firstorder reaction such that differential rate conditions are established, a lower limit on the chemical conversion is applied to limit the loss of precision in conversion measurements, and an expression is derived to limit the effect of pressure drop across a catalyst bed on the observed rate of a first-order reaction. The prevalence and sensitivity of these and other transport limitation criteria were investigated theoretically in the context of the low-temperature (LT) water-gas shift (WGS) reaction over a Cu/ZnO/Al2O3 catalyst in a laboratory scale performance test. Factorial combination of some commonly manipulated experimental parameters (reactant feed rate, temperature, catalyst particle size, catalyst loading, dilution fraction and reactor tube size) was employed in this regard. The upper conversion limit, the internal mass transfer criterion and the radial heat transfer criterion were found to be particularly severe. So too, to a lesser extent, were the axial dispersion and pressure drop criteria, and the lower conversion limit. The sensitivity analysis indicated optima in the varied experimental parameters and yielded insights into effective control of different effects by selection of process conditions. Application of the set of criteria in an experimental performance test was demonstrated using a proprietary medium-temperature (MT), WGS catalyst under reaction at temperatures of 275 °C, 300 °C and 375 °C, 1 atm total pressure, dry feed composition of 10% CO, 10% CO2, 70% H2, 10% N2, steam-to-dry gas ratio of 0.5 and 158 h-1 weight hourly space velocity (WHSV). The catalyst was found to have near total selectivity towards the WGS reaction with activities of 12.2 ± 1.1, 17.1 ± 0.5 and 24.9 ± 1.5 µmol/s.gcat at 275 °C, 300 °C and 375 °C respectively. This corresponds to an activation energy of 39 ± 2 kJ/mol; a value within range of what is reported in literature for similar catalysts. This experiment also served to compare experimental and predicted internal mass transfer limitations by testing catalyst particles of different mean sizes. This catalyst as well as a CuO/ZnO/Al2O3 catalyst precursor was characterised in respect of their pore size distributions (N2 physisorption and mercury intrusion porosimetry (MIP)), particle size distributions (by photo- and microscopic analysis), bulk and particle densities and product gas compositions (by gas chromatography) to enable evaluation of the various criteria employed. Evaluation of the various criteria indicated that, theoretically, the considered confounding effects had a negligible effect on the measured catalytic activities for the catalyst sample with the smallest mean particle size, while the larger particles experienced only internal mass transfer limitations. Different models considered for effective diffusivities all under-predicted values when compared to the effective diffusivities inferred from the reaction-diffusion experiments. Predictions ranged to within factors of 3 – 20 of the experimental values, depending on whether pore size distribution data were derived from MIP or physisorption data. Here, the lack of characterisation of the macro-porosity by N2 physisorption resulted in more severe under-estimations of the effective diffusivities than the equivalent estimations made with MIP data. The best prediction was made by the ‘parallel-path pore’ model by Johnson & Stewart (1965) using MIP data. Predictions of internal mass transfer limitations varied in a similar manner. It is noted that the simplifications of the highly complex porous catalyst by these model combinations introduce large sources of error in the prediction of internal mass transfer limitations.

The myocardium is composed of interconnected cardiac fibres which are responsible for contraction of the heart chambers. There are several challenges related to computational modelling of cardiac muscle tissue. This is due in part to the anisotropic, non-linear and time-dependent behaviour as well as the complex hierarchical material structure of biological tissues. In general, cardiac tissue is treated as a non-linear elastic and incompressible material. Most computational studies employ the theories of classical continuum mechanics to model the passive response of the myocardium and typically assume the myocardium to be either a transversely isotropic material or an orthotropic material. In this study, instead of a classical continuum formulation, we utilise a micromorphic continuum description for cardiac tissue. The use of a micromorphic model is motivated by the complex microstructure and deformations experienced by cardiac fibres during a heartbeat. The micromorphic theory may be viewed as an extension of the classical continuum theory. Within a micromorphic continuum, continuum particles are endowed with extra degrees of freedom by attaching additional vectors, referred to as directors, to the particles. In this study the directors are chosen such that they represent the deformation experienced by the cardiac fibres. In addition to the passive stresses, the myocardium experiences active stresses as a result of the active tension generated by cardiac fibres. The active tension in the heart is taken to be a function of the sarcomere length, intracellular calcium concentration and the time after the onset of contraction. Experimental studies show that the active behaviour of the myocardium is highly dependent on the tissue arrangement in the heart wall. With a classical continuum description, the sarcomere length is usually defined as a function of the stretch in the initial fibre direction. To allow for a more realistic description of the active behaviour, we define the sarcomere orientation, and consequently also the sarcomere stretch, as a function of the director field. Furthermore, we use the director field to describe the direction in which contraction takes place. The intent of this study is to use a micromorphic continuum formulation and an active-stress model to investigate the behaviour of the left ventricular myocardium during a heartbeat. The simulated results presented here correspond well with typical ventricular mechanics observed in clinical experiments. This work demonstrates the potential of a micromorphic formulation for analysing and better understanding ventricular mechanics.

The valuable components of the platinum group element (PGE) bearing ores of the Bushveld complex in South Africa constitute between 1 % and as little as 0.1 % of the total mass. In the processing of these ores by flotation, the naturally hydrophobic talc minerals cause over stable froths. The drainage of liquid and entrained particles is reduced thus the recovery of other gangue minerals by entrainment increases and grade decreases. In the rougher float depressants are added to produce a manageable froth and improve the grade by reducing the overall amount of the naturally floating gangue in the concentrates. Depending on dosage, depressants may also affect the recovery of the valuable minerals in the ore positively by slime cleaning or negatively by depression. Depression of stabilising gangue minerals such as talc decreases the froth stability and may also affect the recovery of valuables. Frothers are added to flotation systems to create stable froths. They increase the water layer around bubbles and the carrying capacity of the froth and thus recovery by entrainment. The drainage of entrained particles from the froth may be further increased by increasing the froth depth. This study investigated the interactive effects of depressant dosage and type, frother dosage and froth depth on the recovery and grade of copper and nickel sulphides, recovery of water, floatable and entrained gangue in the flotation of a Merensky ore. Since it is known that water recovery is closely related to froth stability it was used to infer froth stability in this study. Two types of depressants carboxymethyl cellulose (CMC) and guar gums which are usually used in the flotation of PGE bearing ores were used. The frother was Dow 250. Results showed that increasing either guar or CMC dosages from 50 to 100 g/t enhanced the recovery of copper and nickel sulphides. This was attributed to the slime cleaning action of the depressants and their stabilising effects. A further increase of dosage to 300 g/t decreased the recovery of copper and nickel indicating that depression of sulphides occurs at high depressant dosages. Both the use of guar and CMC depressants reduced the recovery of floatable gangue with increasing dosage as expected. The guar depressant showed greater depression ability at 50 g/t dosage than the CMC depressant while the CMC was more effective at 100 and 300 g/t dosage. Reduction of water recovery by the CMC depressant was greater than that of the guar depressant indicating that the CMC depressant had greater destabilising effects on the froth. It is known that the CMC depressant has a strong negative charge while the guar depressant is only slightly charged. The guar depressant may have caused aggregation of particles which has less destabilising effects than the dispersed particles in the presence of the CMC depressant. The froth recoveries showed that the effects of depressant and frother dosages counteract each other and that the decrease in the recovery of copper and nickel sulphides obtained at higher depressant dosages can be reversed by increasing frother dosage. However although increased frother dosage readily reverses the depressant effects, an increase of water and recovery by entrainment reduces the grade. The effect of depressant dosage increase on the water and froth stability is small in comparison to the effect of increased frother dosage. Thus for the levels tested the benefit of improved grade obtained by depressant addition would be lost. The increase of froth depth to reduce entrainment resulted in a reduction of the recoveries of the valuable minerals but with the desired increase in grade. Smaller increments of frother dosage are required to produce effective reversal of depressant effects on the recovery of valuable minerals to achieve a good overall flotation performance.

Includes bibliographical references. / A low frequency vibrating sample magnetometer has been built to measure the in-situ properties of ferromagnetic catalysts. The instrument allows measurements to be taken during an experimental catalyst test run (in-situ). The vibration is performed by a motor crank arrangement frequency of 2 Hz. The software designed to control the instrument and the reaction was written in Lab View which enabled a rapid prototyping approach. This thesis focuses on the software and electrical systems of the setup. Results of research conducted using this system are published separately however this document shows the relationship between the magnetic saturation and remnance and the mass of ferromagnetic material present in the reference material as well as the effect of temperature on this material.

Today soil erosion is almost universally recognised as a serious threat to man's well-being, if not to his very existence, and this is shown by the fact that most Governments outside Europe give active support to programmes of soil conservation. But it is relevant, before making any assessment of present knowledge of erosion, to consider the development of this science which was almost unknown eighty years ago, and now enjoys world wide attention.

Includes bibliographical references. / Premature deterioration of reinforced concrete (RC) structures has become an issue of global concern. As a result, many upgrades and improvements have recently been made in design standards and specifications, to include requirements that account for durable RC structures. This dissertation examines and compares such durability requirements in design standards and specifications developed in the United States of America, Australia, Canada, Europe, India, and South Africa. It discusses issues relating to exposure conditions, limiting values of material compositions and proportions, and cover depth to the reinforcing steel. Both prescriptive and performance requirements for concrete durability are described. In general terms, this dissertation concludes that most design standards are based on prescriptive requirements with a few having some elements of performance requirements for durability design. The prescriptive approach that outlines requirements for material compositions and proportions, procedures, and test methods, is commonly used in most design standards and specifications for durability purposes. Though such approaches may encompass requirements for, inter alia, minimum compressive strength, maximum water-to-cementitious material (w/cm) ratio and cover depth, the desired concrete performance is not generally described. Material and construction variability are not taken into account, and even if intensive construction supervision is carried out, it is difficult to ensure all specified parameters are achieved. Moreover, requirements such as maximum w/cm and minimum water content are impractical or costly to measure or verify in practice. Generally, it should be acknowledged that this approach has limited applications and often stifles innovations.In an attempt to move away from the prescriptive approach, research has focused on performance approaches, which measure relevant properties of the concrete, in particular transport-related properties that account for durability. Performance approaches impose few or no restrictions on the concrete composition, proportioning, or construction methods, but rather promote innovations. Worldwide there is a consensus that in order to extend the service life of RC structure, performance approaches are imperative. This dissertation gives an overview of the international efforts in the implementation of performance approaches, either in design standards or in project specifications.

Includes bibliography. / Reinforcement corrosion in concrete remains the most serious cause of premature deterioration of concrete structures world-wide, and many methods have been proposed to combat this problem. One method of improving the durability of concrete in aggressive environments is the use of corrosion inhibitors. In this work the effectiveness of an organic penetrating corrosion inhibitor in reducing the rate of corrosion and delaying the onset of corrosion in carbonated concrete is discussed, with reference to corrosion rates.