Bibliography: pages 58-59. / This report describes a computer program which has been developed to simulate accurately the performance of stand alone photovoltaic systems with battery storage on an hourly basis for one simulated year. The program incorporates models of the POA irradiance, the photovoltaic cell · temperature and the battery temperature to simulate the environmental conditions of the system. These require hourly weather data as input. Typical meteorological years, which constitute a suitable form of input weather data, have been generated for those weather stations in Southern Africa which contain sufficient data. The energy flows within the system are simulated using models of the following parameters: photovoltaic module current, regulator efficiency and voltage, battery current and voltage, inverter efficiency, load shed voltage and load current. These models incorporate versatility in the level of modelling complexity (determined typically by the availability of the data used to characterise the components). The various models are encapsulated in modular units to facilitate alteration and updating at a later stage. The program is designed to simulate photovoltaic systems without maximum power point trackers, necessitating the use of interactive curve solving to compute the system operating point at any time. A robust and comprehensive algorithm has been implemented to execute this function. Improved battery modelling has been effected using data and experience acquired from a parallel research project. The program facilitates, with the judicious selection of input weather data, the economical sizing of systems in that it incorporates loss of power probability analysis and offers a high level of modelling precision. The simulation performance of the program compared favourably with that of PVFORM. The system performance estimated by PVFORM was marginally better, which is expected because PVFORM assumes that the system operates with a maximum power point tracker. In the development of the program there has been a focus on creating an effective user interface. This is designed to simplify and speed up program operation, and to present output in a form which is useful and illustrative.

The repair and maintenance of ageing reinforced concrete (RC) structures has become increasingly costly, especially in the Cape Peninsula. Protection and maintenance of these reinforced concrete structures against concrete deterioration and rebar corrosion have become far more important for road authorities and asset managers. City Engineers are responsible for the repair and rehabilitation of RC structures in different exposure conditions, by identifying the type of deterioration and then employing the correct concrete repair solutions or corrosion resistance measures. This dissertation investigates the environmental exposure conditions in the Cape Peninsula that result in chloride-induced and carbonation-induced corrosion of reinforced concrete structures in the region. It includes a literature review on concrete deterioration mechanisms and the role of aggressive elements in rebar corrosion. The literature review also considered alternative corrosion-resistant rebar. There are a number of available alternatives, which include Fiber Reinforced Polymer (FRP), Hot Dip Galvanized (HDG) steel, and Stainless Steel rebar. Each alternative has advantages and disadvantages depending on design applications and durability requirements. The use of corrosion-resistant rebar would increase the structure's longevity, thus providing long-term cost saving for road authorities. In the City of Cape Town, city engineers have standardised the use of HDG rebar for repair solutions and new concrete structures. HDG improves corrosion resistance, thus making it desirable to road authorities. The HDG process has been developed in the construction industry with low production time and cost, proving favourable factors for engineers. In addition, engineers have to improve concrete quality and construction methods to protect the underlying rebar from corrosion. On a technical level, HDG rebar use in RC structures has benefits which outweigh their cost implications. The exclusive use of HDG rebar without sound engineering judgment based on factors such as the location of the structure, distance from the coast, the structural loading conditions, and construction methods and quality standards, might not ensure better concrete durability and structural longevity. Generally, correct structural rebar design and concrete quality can eliminate the need for the use of corrosion protection methods and materials. The use of HDG is a very attractive solution for structures within 5km from the coast; otherwise, normal steel is suited for most applications. Reinforced concrete members such as concrete bollards, bridge handrails and balustrades can be treated as consumables and can be replaced once steel corrosion or concrete deterioration has occurred and becomes unsightly, which would be about 20 years. This approach would be economically advantageous and politically favourable to the road authority as it creates skills and jobs by reducing initial internal and contractual costs. To illustrate the common forms of rebar deterioration in the Cape Peninsula region, this dissertation has included five repair and rehabilitation projects completed by the City of Cape Town's Road Authority. These rehabilitation projects have been identified for concrete repair and rehabilitation works, and some of these structures have recently undergone extensive concrete rehabilitation. City engineers are faced with many challenges that hinder service delivery, engineering processes and effectiveness. Among these are lack of staff with experience in concrete repair and asset management, and the lack of proactive maintenance tools. The lack of an adequate Bridge Management System (BMS) contributes to the inefficient allocation of resources for rehabilitation and repair projects. The Supply Chain Management System also delays the appointment of appropriate contractors due to unwieldy management systems and bureaucracy. These systemic problems are discussed to provide a better understanding of the current selection of concrete repair systems.

This paper considers the opportunities for the South African and Zimbabwean Saw-milling Industry to be self-sufficient in the generation of power for its own industrial electrical energy requirements. The analysis of the wood residue arising from saw-milling operations in the southern African context confirms that there is a substantial amount of fuel available for the main heating requirement of a wet saw-mill. This heat is generally supplied in the form of steam to the timber drying and conditioning kilns that form part of the timber production process. One of the principal arguments put forward for cogeneration is that by passing steam through a condensing or back pressure turbine the entire power demand of a saw-mill can be met as well as the heat for the kilning process. Due to the situation of unbalanced load that persists at nearly all the saw-mills, there is a surplus of power that is often difficult to dispose of economically.

Includes bibliographical references. / The interests in an alternative, sustainable power generation method has greatly increased in the past decade due to increases in greenhouse gases and its impact on global climate change. The use of fuel cells as a form of energy generation is extremely promising as it converts chemical potential energy directly to electrical energy, bypassing the Carnot cycle limitations. Various types of fuel cells have been developed, with the proton exchange membrane fuel cell (PEMFC) being most promising for mobile and small-scale stationary uses under transient conditions. The PEMFC uses hydrogen and oxygen to generate electrical energy. While oxygen can be obtained from air, hydrogen does not exist in its elemental form; hence a process train is required to refine fuels (such as fossil fuels and bio-fuels) into pure hydrogen. This has been successfully achieved by large-scale industrial plants. A typical fuel processing train consists of a steam reforming stage converting the fuel into syngas. This is followed by a water-gas shift (WGS) stage to convert carbon monoxide, which is a poison for the platinum catalysts within fuel cells, into carbon dioxide. If the CO concentration required is extremely low, a methanation or preferential oxidation stage can be used subsequent to the WGS stage. This study focuses on the water-gas shift stage of the fuel processing train. Industrial base metal WGS catalysts are not suitable for a miniaturized fuel processing train due to the catalysts being developed for continuous operations, as miniaturized fuel processing trains are expected to operate at transient conditions. A slow and controlled reduction process is also required prior to operation, as well as the pyrophoricity of industrial catalysts after reduction. These can pose safety issues with non-technical personnel in household applications (e.g. CHP). PGM-based catalysts have shown high activities for the water-gas shift reaction in literature, are not pyrophoric and do not require lengthy and sensitive reduction processes prior to operation. The objective of this study was to investigate and compare two base metal catalysts (high temperature (HT) shift Fe₃O₄/Cr₂O₃ and low temperature (LT) shift CuO/ZnO/Al₂O₃ catalyst) with a PGM based counterpart, as well as to investigate whether the catalysts are able to achieve a required 1 vol% CO via the water-gas shift reaction. For these investigations a synthetic feedstock was used, based on typical exit concentrations of a steam methane reformer.

The Low Temperature Fischer-Tropsch (LTFT) synthesis involves the catalytic hydrogenation of carbon monoxide with the aim to produce long-chained hydrocarbons. Commercial cobalt-based catalysts incorporate oxidic supports that are known to negatively affect the reducibility and hinder formation of the active phase. Consequently, reduction promoters such as Pt are introduced to facilitate the reduction of cobalt during catalyst pretreatment. However, synergistic and adverse effects of the promoter have been reported under reaction conditions including a higher site-time yield and higher selectivity towards hydrogenated products. The perspective on the operation of the Pt promoter is polarised between 'Hydrogen spillover', which is a so-called remote-control effect that could otherwise occur in the absence of Pt-Co contact, and 'ligand/electronic effects' that require direct Pt-Co coordination. The objective of this study was to explicate the operation of Pt and Au as promoters of the Co/Al2O3 catalyst by decoupling hydrogen spillover from effects that require direct promotercobalt coordination. The analysis was subdivided into the reduction process and the Fischer- Tropsch reaction, which are the two arenas in which the actions of these promoters have been claimed. The employment of model 'hybrid' catalysts, which are mechanical mixtures of the monometallic constituents of the promoted catalyst, presents a novel way to investigate the role of spillover hydrogen in the Pt-Co and Au-Co catalyst systems. Thus far, no systematic investigation of the hydrogen spillover phenomenon using these catalyst systems during both reduction and under commercially relevant LTFT conditions has been encountered in the published literature. Furthermore, this study serves to contribute to the limited body of literature on the role of Au as a potential promoter for the commercial cobalt-based catalyst.

Density functional theory (DFT) calculations have been performed to gain insight into the role of defects present on the surface of graphene and TiO₂ based supports on supported metal clusters. The clusters considered are a Pt₃₈ cluster and a bimetallic Pt₃₂Pd₆ alloy. The defects considered on graphene based supports are monovacancy defective graphene, OH and COOH functionalised graphene. The defects considered on TiO₂ based supports are a partially reduced TiO₂(110) surface with a surface oxygen bridge vacancy and hydroxylated TiO₂(110) surface with surface OH groups. The defect free graphene and TiO₂ surfaces were also considered. For both the Pt₃₈ and Pt₃₂Pd₆ cluster, and on both defect containing graphene and TiO₂ (except on hydroxylated TiO₂(110) surface) the binding of the clusters is enhanced relative to binding on the defect free supports. Enhanced binding at the defects imply that the clusters are bound strongly to the support and thus less likely to detach from the support material relative to binding on the defect free supports. Therefore, the defects may improve the durability of the catalyst by limiting particle detachment. The electronic properties of the cluster are modified differently depending on the identity of the defect present on the support. On the graphene based supports, OH functionalisation is expected to result in weaker binding energy of adsorbate molecules, whereas COOH functionalisation is expected to result in stronger binding energy of adsorbates for the supported Pt₃₈ cluster. This is due to different shifts in d-band centre of the facets on the cluster supported on these supports. Therefore, it can be expected that the Pt₃₈ cluster supported on OH functionalised graphene will be more tolerant to poison molecules. This is due to reduced binding strength of adsorbates on OH functionalised graphene compared to adsorption on COOH functionalised graphene. For the Pt₃₂Pd₆ cluster the OH and COOH functional groups do not appreciably modify the d-band centre of the facets available to reactants, and thus is expected not to significantly modify the binding strength of adsorbate molecules relative to binding on the free unsupported Pt₃₂Pd₆ cluster. The binding energy of adsorbate molecules on the Pt₃₈ cluster supported on defect containing TiO₂ is expected to be stronger than on the Pt₃₈ cluster supported on defective graphene based supports, due to higher extent of upward shift of the d-band centre of the exposed facets. The enhanced binding energy of adsorbates on the Pt₃₈ cluster supported on TiO₂ supports may be detrimental to catalyst durability and activity. This can be due to strong binding of poison molecules and reaction intermediates which maybe too strongly bound on the surface such that they cannot participate in further reaction steps. Overall it might turn out that the functionalised graphene based supports are better support materials over the TiO₂ based materials for particular reactions. The Nb-doped partially reduced TiO₂(110) surface attaches the Pt₃₂Pd₆ cluster strongly to the support compared to the functionalised graphene supports. Furthermore, the binding energy of adsorbate molecules is expected to be weaker on the Pt₃₂Pd₆ cluster supported on the Nbdoped partially reduced TiO₂(110) surface compared to the functionalised graphene supports. This might be beneficial as poison molecules may be weakly bound to the cluster resulting in high resistance to poisoning which can also have a positive effect on catalyst activity. In addition to enhancing binding of the cluster to the support and affecting the binding energy of adsorbates on the supported clusters, some of the defects can also alter the ordering pattern of Pd and Pt atoms within the Pt₃₂Pd₆ cluster. OH functionalised graphene and Nbdoped partially reduced TiO₂(110) surface result in segregation of Pd towards the clustersupport interface, thereby exposing more Pt atoms at the surface facets of the cluster. The modified arrangement of Pt and Pd atoms may result in modification of the reactivity of the Pt₃₂Pd₆ cluster. The results of this study indicate that the defects can play a vital role in determining the activity and durability of the catalyst. By having the right combination of defects on the support material, the durability and catalytic activity of the catalyst can be fine-tuned simultaneously. This can lead to better design of catalysts.

In practice, concrete is initially tested for compressive strength by casting a cube/cylinder, which is left to cure in favourable conditions until the date of testing. The results obtained from such tests can give a consultant guidance on the material's properties such as estimated porosity, density and compressive strength. These tests are known as control and conformity tests. Supplementary tests may be needed if the control test fails or further investigation must be done to the concrete. These tests are done by drilling core specimens out of the in-situ concrete and applying the necessary tests. These results are used to verify conformity with specifications set out by the engineer. The outcome of such a test is extremely important as it is often used as the basis to decide the integrity of the structure. Although important, in-situ compressive strength remains as one of the least understood concrete properties due to the difficulty in relating and interpreting the results. Furthermore, there is no reliable universal relationship between compressive strength of cores and; moulded cubes and cylinders. A comprehensive literature and experimental study was attempted to relate standard cube and core compressive strength, as well as, cylinder and core strengths to identify the factors that may affect the analysis and interpretation of results. An experimental program was set out to relate the compressive strength of cubes, cores and cylinders, with a length/diameter ratio of 1.0. All specimens were cast, cured, prepared and tested in the University of Cape Town, New Engineering Building (NEB) laboratory according to South African National Standards. Twelve concrete mixes were designed using two concrete strengths (30 and 50 MPa), three maximum aggregate sizes (9.2, 19.2 and 26.5 mm) and two aggregate types, namely greywacke and quartzitic sandstone. An additional two mixes of high strength concrete were created (60 and 75 MPa) using 19.2mm greywacke aggregate. The compressive tests involved a 100 mm cube, three diameter cylinders (70, 100 and 150 mm) and four core diameter sizes (50, 70, 100 and 150 mm). All core specimens were drilled from beams that were cast. A total of 520 specimens were tested during this study. An analysis of variance (ANOVA) was applied to all the results to identify if the compressive strengths were statistically significantly different. The compressive strength and statistical results indicate that 100 mm cubes and 100 mm diameter cores have statistically similar compressive strengths. The diameter of the core and cylinder influenced the compressive strength. It was found, as the diameter size decreased the strength increased for core specimens and the opposite was found for the cylinder. Both findings were inconsistent with literature. However, as the core and cylinder diameters increased to a size larger than 100 mm, the compressive strengths were statistically similar. With respect to the maximum aggregate size, the strength was influenced in correspondence with the diameter size. As the core diameter decreased and the maximum aggregate size increased, the compressive strength increased. Whereas, the opposite was found with the cylinders. The strength level further determined the influence that the coarse aggregate type had on the compressive strength. At the 30 MPa strength level, the aggregate types produced statistically similar strength. At the 50 MPa strength level, the sandstone produced a statistically higher compressive strength compared to the greywacke aggregate. Finally, as the strength level increased over 50 MPa there was no significant difference between the mean compressive strength of cubes and cores. It was concluded, owing to the controlled environment that the all specimens were cast, cured, prepared and tested; as well as the similarity in the geometric size, statistically comparable compressive strengths were obtained for cubes and cores.

Froth flotation is a separation method used for the beneficiation of a considerable portion of the world's mineral ores. The majority of flotation occurs in mechanical flotation cells, where effective gas dispersion is a primary requirement for particle-bubble contacting. Due to the mineralogical complexity of ores, it is required that particles be ground even finer to liberate valuable minerals. Mining operations tend to run flotation circuits at fairly high solids concentrations in order to maximise residence time, accommodate higher tonnages and limit water consumption. Mineral slurries processed at fine particle sizes and high solids concentrations have been shown to exhibit non-Newtonian rheological behaviour. The effect of slurry rheology on gas dispersion in a 100 litre mechanical flotation cell was investigated by varying the solids concentration. The study was conducted using kaolin, Bindura nickel and Platreef slurries. All three ores displayed typical non- Newtonian rheological behaviour where the slurry yield stress and viscosity increased exponentially with solids concentration. Bubble size varied from 0.55 to 1.10 mm for all the ores tested. At low solids concentration bubble size was found to decrease with impeller speed, a characteristic trend that was expected. At moderate solids concentrations bubble size was found to either increase/remain relatively constant with impeller speed; this trend was also expected. Unexpectedly, at the highest solids concentration, a dramatic decrease in bubble size was observed. This unexpected drop in bubble size was attributed to slurry rheology. It was also observed that there was a slight increase in bubble size at the highest solids concentration with increasing impeller speed. This increase was attributed to a trade-off relationship between the rheology of the slurries and the existing hydrodynamics (as a result of the rotating impeller). Gas hold-up varied from 2 to 15% across all the ores tested. At low solids concentrations gas hold-up increased with impeller speed as expected. At moderate solids concentration gas hold-up was viewed to either increase/remain relatively constant with impeller speed. A significant drop in gas hold-up was observed at the highest solids concentration. The gas hold-up however still increased with impeller speed albeit at a lower rate at the highest solids concentrations. This drop in gas hold- up at the highest solids concentration (along with the decrease in bubble size) was attributed to the effect of slurry rheology. At high solids concentrations, all three slurries (kaolin, Bindura nickel and Platreef) exhibit non-Newtonian behaviour illustrated by means of high viscosities and yield stresses. High viscosities result in turbulence damping in the cell which inhibits bubble break-up, resulting in larger bubbles and correspondingly lower gas hold-up. It was concluded in this study that the yield stress is the dominant rheological property due to the significant changes observed with increasing solids concentration. High yield stresses resulted in the formation of a 'cavern' of slurry around the impeller region. Within this 'cavern', high power intensities exist around the impeller where small bubbles are formed. However due to the formation of the 'cavern', the slurry in the bulk cell remains relatively stagnant. As a result small bubbles formed around the impeller remain localised in the 'cavern' and cannot be dispersed throughout the cell. This localization and poor dispersion of bubbles resulted in low gas hold-ups.

Background: Risk factors for cardiovascular disease (CVD) include obesity, ethnicity and hypertension. High-density lipoprotein (HDL) has traditionally served as a marker for CVD risk. Latest studies, however, propose that the composition and subclass distribution and the anti-atherogenic function of HDL are more accurate predictors of CVD risk. We therefore explored whether obesity, ethnicity, exercise and hypertension may modulate HDL composition, subclass and function in three different sample populations of patients affected with these CVD risk factors. Methods: The first study sample population consisted of black and white obese and normal-weight South African women (n=40). In the second sample population, obese black South African women were randomly assigned to exercise (combined aerobic and resistance exercise 4 times/week) or control (sedentary) conditions for 12-weeks (n=32). The third sample population included Nigerian out-patients, divided into healthy controls, hypertensive patients and hypertensive patients with heart failure (HF) (n=80). HDL composition measurements included apolipoproteins A1 and M (ApoA1 and ApoM), paraoxonase (PON1) and platelet activating factor acetylhydrolase (PAF-AH) expression (using Western blotting) and sphingosine-1-phosphate (S1P) content (using mass spectometry). Levels of large, intermediate and small HDL subclasses were measured using the Lipoprint® system. HDL functionality was assessed by measuring PON1 activity, PAF-AH activity, reverse cholesterol efflux capacity, HDL-mediated activation of endothelial nitric oxide synthase (eNOS) and quantification of the expression of vascular cell adhesion molecule in endothelial cells. Results: In all sample populations, HDL-cholesterol concentration was not different between groups. PON1 activity was lower in white compared to black women (0.49±0.09 U/L vs 0.78±0.10 U/L, p<0.05). Obese black women had lower PAF-AH activity compared to obese white women (9.34±1.15 U/L vs 13.89±1.21 U/L, p<0.05). Compared to normal-weight women, obese women had lower large HDL, greater intermediate and small HDL. Compared to the sedentary control condition, exercise training was associated with a decrease in PON1 activity (-8.7±2.4% vs +1.1±3.0%, p<0.05), PAF-AH serum expression (-22.1±8.0% vs +16.9±9.8, p<0.005) and small HDL subclasses (-10.1±5.4% vs +15.7±6.6%, p<0.005). S1P content in HDL was lower in hypertensive and HF patients compared to controls (165 ± 55 vs 201 ± 73 pmol/mg, p < 0.05). HDL subclass distribution was different in hypertensive and HF patients with lower large HDL (48 ± 15 vs 63 ± 7%, p<0.005), higher intermediate (45 ± 7 vs 34 ± 5%, p<0.005) and small HDL (7 ± 9 vs 2 ± 4%, p<0.05). In contrast to HDL from control patients, HDL from all hypertensive patients failed to activate eNOS. Conclusions: In all three sample populations, there were associations between CVD risk factors and measures of HDL quality. HDL subclass distribution differences were associated with obesity and hypertensive heart failure, both in cross-sectional studies and in an exercise intervention study. In African sample populations, consideration of HDL quality rather than total HDL quantity may be a more sensitive marker to assess CVD risk.

The intramyocardial injection of biomaterials is an emerging therapy for myocardial infarction. Computational methods can help to study the mechanical effect s of biomaterial injectates on the infarcted heart s and can contribute to advance and optimise the concept of this therapy. The distribution of polyethylene glycol hydrogel injectate delivered immediately after the infarct induction was studied using rat infarct model. A micro-structural three-dimensional geometrical model of the entire injectate was reconstructed from histological micro graphs. The model provides a realistic representation of biomaterial injectates in computational models at macroscopic and microscopic level. Biaxial and compression mechanical testing was conducted for healing rat myocardial infarcted tissue at immediate (0 day), 7, 14 and 28 days after infarction onset. Infarcts were found to be mechanically anisotropic with the tissue being stiffer in circumferential direction than in longitudinal direction. The 0, 7, 14 and 28 days infarcts showed 443, 670, 857 and 1218 kPa circumferential tensile moduli. The 28 day infarct group showed a significantly higher compressive modulus compared to the other infarct groups (p= 0.0055, 0.028, and 0.018 for 0, 7 and 14 days groups). The biaxial mechanical data were utilized to establish material constitutive models of rat healing infarcts. Finite element model s and genetic algorithms were employed to identify the parameters of Fung orthotropic hyperelastic strain energy function for the healing infarcts. The provided infarct mechanical data and the identified constitutive parameters offer a platform for investigations of mechanical aspects of myocardial infarction and therapies in the rat, an experimental model extensively used in the development of infarct therapies. Micro-structurally detailed finite element model of a hydrogel injectate in an infarct was developed to provide an insight into the micromechanics of a hydrogel injectate and infarct during the diastolic filling. The injectate caused the end-diastolic fibre stresses in the infarct zone to decrease from 22.1 to 7.7 kPa in the 7 day infarct and from 35.7 to 9.7 kPa in the 28 day infarct. This stress reduction effect declined as the stiffness of the biomaterial increased. It is suggested that the gel works as a force attenuating system through micromechanical mechanisms reducing the force acting on tissue layers during the passive diastolic dilation of the left ventricle and thus reducing the stress induced in these tissue layers.