<p>Controllable continuous feeding of biomass feedstock in a biorefinery is critical to upscaling current ethanol conversion techniques to a commercial scale. Mechanical pretreatment of biomass feedstock performed using a compression feed screw (CFS) improves the ethanol yield but is subject to flowability issues, especially the plugging of biomass. The mechanical behavior, and hence, the flowability of biomass feedstock, is strongly affected by several factors, including preparation method, moisture content, physical composition, and particle size distribution. In addition, the current design of CFS is guided by limited experimentation and even fewer theoretical correlations. This thesis aims at developing computational methods to model the flow of densified feedstock in a CFS and experimental techniques to characterize the mechanical properties required for the model. We adopted a modified Drucker-Prager Cap constitutive (mDPC) law for milled corn stover (a widely used feedstock for bioethanol production) to model the material’s rate-independent bulk behavior in a CFS. The mDPC elastoplastic law captures the frictional shear and permanent volumetric changes in corn stover using a continuous porosity-dependent yield surface. The parameters of the mDPC model are calibrated using a unified set of single-ended die compaction and multiple shear failure tests. In addition, we quantified the changes in the mDPC parameters with moisture content up to the water-holding capacity of corn stover particles. A Coupled Eulerian-Lagrangian Finite Element Method model developed for the CFS geometry predicts the deformation of the material using the calibrated mDPC parameters. We model the interaction between the material and the CFS surface using a Coulomb wall friction coefficient calibrated using the Janssen-Walker method for a punch and die system. A laboratory-scale compression feed screw is designed and fabricated to characterize the flow of dense granular materials in collaboration with undergraduate students in the School of Mechanical Engineering. FEM model predictions of feeding torque and mass flow rate are validated against the laboratory-scale feeder for microcrystalline cellulose Avicel PH-200 and milled corn stover. The model predictions agree with the experiments for Avicel PH-200 but have a higher error in the case of corn stover. Some physical effects, such as shear hardening and particle erosion observed in milled corn stover, are not captured using the current implementation of the mDPC model, which explains the different model accuracies for both materials. The continuum model is used to uncover material density distribution, torque, and pressure inside the CFS, otherwise challenging through experiments. The FEM model showed a significantly higher sensitivity of the feeder performance to two material properties, namely the hydrostatic yield stress and the wall friction coefficient. The characterized variation of material properties with moisture content and the effect of each material property on the feeder performance provide strategies to engineer the feedstock for better flowability. Further, the continuum model offers a method to study design changes before manufacturing the equipment. Finally, we propose the possibility of a reduced-order analytical model based on the critical material properties and the material deformation mechanism demonstrated by the FEM model.</p>

In light of the world‟s growing demand for energy that is environmentally friendly and sustainable, energy sources such as hydrogen have been considered potential contenders. Hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) thermo-chemical process consisting of a decomposition and an electrolysis step. During the HyS electrolysis step, SO2 and H2O are converted to H2 and H2SO4, which implies that the proton exchange membranes (PEMs) to be used for this process should have a high proton conductivity, limited SO2 cross-over and good H2SO4 stability. In order to find alternatives to the costly and high-temperature unstable Nafion®, the aim of this study was to evaluate the H2SO4 stability of various novel membranes. To structure the study, the novel PEM materials were grouped according to the PBI-type base component within the blend membranes, resulting in three groups comprising non-PBI based membranes, PBIOO based membranes and F6-PBI based membranes. Nafion®212 was included as reference PEM. By repeating the H2SO4 treatment with three different Nafion®212 samples, the obtained Nafion® data was also used to determine the experimental and analytical error margins for the study. The stability of all membranes was determined by submerging the membrane samples in 80 wt% H2SO4 at 80 °C for 120 hours. To determine the influence of the acid on the membranes, all samples were characterised before and after the H2SO4 treatment and compared in terms of their acid stability. Physical characterisation of the PEMs included the evaluation of weight and thickness changes, while IEC, SEM-EDX, FTIR and TGA were used to elucidate possible chemical changes due to the H2SO4 treatment. According to the Nafion®212 data, which had been obtained in triplicate for each of the analytical techniques, the experimental error of both the analytical and H2SO4 treatment remained below 10 %, except for the SEM-EDX sulfur-content where significantly larger errors were observed. In spite of the high error margins of the SEM-EDX data (S-content), its results, combined with the results from the other analytical techniques, resulted in a better understanding (both physical and chemical) of the effect the H2SO4 had on the membrane. This further facilitated the evaluation and comparison of the various blended PEM materials in terms of their H2SO4 stability, and the subsequent relation obtained between the observed stability and the chemical constitution and cross-linking of the membranes. After the 80 wt% H2SO4 treatment, significant weight losses were reported for the non-PBI based and PBIOO based membrane groups in comparison with the minimal changes noted for the F6-PBI based group and Nafion®212. Furthermore, significant thickness changes were reported for most of the PBIOO based membranes. The small weight and thickness changes observed for the F6-PBI confirmed the improved stability of this group of membranes in an H2SO4 environment, most likely due to the protective role of the partially fluorinated basic polymer and the known strength of the C-F bonds present. The results showed a clear correlation between the H2SO4 stability and the specific polymers present in the PEM blends investigated. Specific effects found included sulfonation, salt formation, hydrolysis and the accompanied dissolution of membrane fragments. Significant physical changes, for example ascribed to sulfonation of the concerned polymers, were supported by increased IEC measurements and peak intensities of the FTIR spectra, corresponding to the additional –SO3H groups present, while a variation in TGA signals served to further support the altered membrane composition and structure due to the H2SO4 treatment. In the case of dissolution, the corresponding chemical changes (analytical techniques) were supported by the decreased peak intensities of FTIR spectra, IEC measurements and TGA signals associated with degradation of the polymer backbone. It was shown that the stability of the blended membranes depended on the composition (blend components) of the membrane and the effective cross-linking (interaction) between the blend components. For all three groups examined, it became apparent that blend components sFS and sPSU were, for example, more stable than sPEEK and that ionical cross-linking seemed more effective than covalent cross-linking of blend components. When considering all membranes tested, the non-PBI based blend membranes consisting of (s)PSU and PFS copolymers in the presence of fluorinated cross-linkers and the PBIOO-sPSU blended membranes including most of the F6-PBI based membranes showed sufficient stability to be recommended for SO2 electrolysis. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Concentrated solar power (CSP) is an efficient means of renewable energy that makes use of solar radiation to produce electricity instead of making use of conventional fossil fuel techniques such as burning coal. The aim of this study is the simulation and characterisation of a CSP plant in order to gain a better understanding of the dominant plant dynamics. Due to the nature of the study, the dissertation is divided into two main parts namely the simulation of a CSP plant model and the characterisation of the plant model. Modelling the CSP plant takes the form of developing an accurate Flownex® model of a 40 MW combined cycle CSP plant. The model includes thermal energy storage as well as making use of a duct burner. The Flownex® model is based on an existing TRNSYS model of the same plant. The Flownex® model is verified and validated, by making use of a bottom-up approach, to ensure that the developed model is in fact correct. The characterisation part of this dissertation involves evaluating the dynamic responses unique to that of a CSP plant as stated in the literature. This involves evaluating the dominant dynamic behaviour, the presence of resonant and anti-resonant modes found within the control bandwidth, and the change in the dynamics of the plant as the plants’ operating points change throughout the day. Once the developed model is validated, characterisation in the form of evaluating the open loop local linear models of the plant is implemented. In order to do so, these models are developed based on model identification processes, which include the use of system identification software such as Matlab® SID Toolbox®. The dominant dynamic behaviour of the plant model, obtained from the developed local linear models, represents that of an over damped second order system that changes as the operating points of the plant change; with the models’ time responses and the bandwidth decreasing and increasing respectively as the thermal energy inputs to the plant increases. The frequency response of the developed local linear models also illustrates the presence of resonant and antiresonant modes found within the control bandwidth of the solar collector field’s temperature response. These modes however are not found to be present in the mechanical power output response of the plant. The use of adaptive control, such as feedforward and gain-scheduled controllers, for the plant should be developed to compensate for the dynamic behaviours associated with that of a CSP plant. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2015

Dust is a well-known occupational hygiene challenge and has been throughout the years, especially in the coal mining industry. The hazards arising from coal dust will differ between geographical areas due to the unique characteristics of dust from the coal mining environment. It is therefore of upmost importance to identify these qualities or characteristics of coal dust in order to understand the potential hazards it may pose. It is also important to consider the presence of nanoparticles which until recently remained neglected due to the absence of methods to study them. Aim: The aim of this study was to collect significant quantities of airborne dust through static sampling to characterise the physical, morphological as well as elemental properties of inhalable and respirable dust produced at two South African underground and two opencast coal mines. Personal exposure quantification was therefore not the primary concern in this study. Method: Static dust sampling was done at two mining areas of the two opencast and underground coal mines using four Institute of Occupational Medicine (IOM) and four cyclone samplers per area at each mine. A condensation particle counter (CPC) was also used at the opencast areas. The opencast areas included blast hole drilling, drag line and power shovel operations. The underground areas included the continuous miner and roof bolter operations. Gravimetric analyses of the cyclone and IOM samples were done as well as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis. Results: Mine A (opencast and underground) produces higher grade coal in comparison to mine B (opencast and underground). Gravimetric analysis indicated higher average inhalable (55.35 mg/m3) and respirable (2.13 mg/m3) concentrations of dust in the underground areas when compared to the opencast areas (34.73 mg/m3 and 0.33 mg/m3). Blast hole drilling operations indicated higher average inhalable and respirable dust concentrations (39.02 mg/m3 and 0.41 mg/m3) when compared to the drag line and power shovel operations (30.44 mg/m3 and 0.246 mg/m3). CPC results showed higher average concentrations of sub-micron particles at the blast hole drilling areas per cubic metre (63132 x 106) compared to the drag line and power shovel operations (38877 x 106). EDS analysis from the opencast areas indicated much higher concentrations of impurities (with lower concentrations of carbon – 33.33%) when compared to samples taken from the underground mining activities (65.41%). The EDS results from the opencast areas differed substantially. The highest concentrations of silica were found at the blast hole drilling areas. EDS results from the underground areas indicated that mine A has slightly higher concentrations of carbon (66.2%) with less impurities when compared to mine B (64.62%). The continuous miner operations showed a higher concentration of impurities when compared to the dust from the roof bolter. SEM results from the opencast areas revealed that the majority of particles are irregularly shaped and the presence of quartz and agglomerations are evident. SEM results from the underground areas were similar except that the roof bolter produced smaller sized particles when compared to the continuous miner. It also seemed that the areas with higher levels of impurities produced more sub-micron particles. Conclusions: It is possible to identify the majority of physical and elemental characteristics of coal dust by means of gravimetric analysis, particle counting, SEM and EDS. There were differences found, regarding the morphological; chemical and physical characteristics, between the different opencast and underground areas at mine A and mine B due to the type of mining activity and amount of overburden present. Silicosis, Pneumoconiosis and Chronic obstructive pulmonary disease are some of the possible health concerns. It has been seen that dust from higher grade coal mines contributed to more developed stages of these diseases. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2015

In light of the world‟s growing demand for energy that is environmentally friendly and sustainable, energy sources such as hydrogen have been considered potential contenders. Hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) thermo-chemical process consisting of a decomposition and an electrolysis step. During the HyS electrolysis step, SO2 and H2O are converted to H2 and H2SO4, which implies that the proton exchange membranes (PEMs) to be used for this process should have a high proton conductivity, limited SO2 cross-over and good H2SO4 stability. In order to find alternatives to the costly and high-temperature unstable Nafion®, the aim of this study was to evaluate the H2SO4 stability of various novel membranes. To structure the study, the novel PEM materials were grouped according to the PBI-type base component within the blend membranes, resulting in three groups comprising non-PBI based membranes, PBIOO based membranes and F6-PBI based membranes. Nafion®212 was included as reference PEM. By repeating the H2SO4 treatment with three different Nafion®212 samples, the obtained Nafion® data was also used to determine the experimental and analytical error margins for the study. The stability of all membranes was determined by submerging the membrane samples in 80 wt% H2SO4 at 80 °C for 120 hours. To determine the influence of the acid on the membranes, all samples were characterised before and after the H2SO4 treatment and compared in terms of their acid stability. Physical characterisation of the PEMs included the evaluation of weight and thickness changes, while IEC, SEM-EDX, FTIR and TGA were used to elucidate possible chemical changes due to the H2SO4 treatment. According to the Nafion®212 data, which had been obtained in triplicate for each of the analytical techniques, the experimental error of both the analytical and H2SO4 treatment remained below 10 %, except for the SEM-EDX sulfur-content where significantly larger errors were observed. In spite of the high error margins of the SEM-EDX data (S-content), its results, combined with the results from the other analytical techniques, resulted in a better understanding (both physical and chemical) of the effect the H2SO4 had on the membrane. This further facilitated the evaluation and comparison of the various blended PEM materials in terms of their H2SO4 stability, and the subsequent relation obtained between the observed stability and the chemical constitution and cross-linking of the membranes. After the 80 wt% H2SO4 treatment, significant weight losses were reported for the non-PBI based and PBIOO based membrane groups in comparison with the minimal changes noted for the F6-PBI based group and Nafion®212. Furthermore, significant thickness changes were reported for most of the PBIOO based membranes. The small weight and thickness changes observed for the F6-PBI confirmed the improved stability of this group of membranes in an H2SO4 environment, most likely due to the protective role of the partially fluorinated basic polymer and the known strength of the C-F bonds present. The results showed a clear correlation between the H2SO4 stability and the specific polymers present in the PEM blends investigated. Specific effects found included sulfonation, salt formation, hydrolysis and the accompanied dissolution of membrane fragments. Significant physical changes, for example ascribed to sulfonation of the concerned polymers, were supported by increased IEC measurements and peak intensities of the FTIR spectra, corresponding to the additional –SO3H groups present, while a variation in TGA signals served to further support the altered membrane composition and structure due to the H2SO4 treatment. In the case of dissolution, the corresponding chemical changes (analytical techniques) were supported by the decreased peak intensities of FTIR spectra, IEC measurements and TGA signals associated with degradation of the polymer backbone. It was shown that the stability of the blended membranes depended on the composition (blend components) of the membrane and the effective cross-linking (interaction) between the blend components. For all three groups examined, it became apparent that blend components sFS and sPSU were, for example, more stable than sPEEK and that ionical cross-linking seemed more effective than covalent cross-linking of blend components. When considering all membranes tested, the non-PBI based blend membranes consisting of (s)PSU and PFS copolymers in the presence of fluorinated cross-linkers and the PBIOO-sPSU blended membranes including most of the F6-PBI based membranes showed sufficient stability to be recommended for SO2 electrolysis. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Concentrated solar power (CSP) is an efficient means of renewable energy that makes use of solar radiation to produce electricity instead of making use of conventional fossil fuel techniques such as burning coal. The aim of this study is the simulation and characterisation of a CSP plant in order to gain a better understanding of the dominant plant dynamics. Due to the nature of the study, the dissertation is divided into two main parts namely the simulation of a CSP plant model and the characterisation of the plant model. Modelling the CSP plant takes the form of developing an accurate Flownex® model of a 40 MW combined cycle CSP plant. The model includes thermal energy storage as well as making use of a duct burner. The Flownex® model is based on an existing TRNSYS model of the same plant. The Flownex® model is verified and validated, by making use of a bottom-up approach, to ensure that the developed model is in fact correct. The characterisation part of this dissertation involves evaluating the dynamic responses unique to that of a CSP plant as stated in the literature. This involves evaluating the dominant dynamic behaviour, the presence of resonant and anti-resonant modes found within the control bandwidth, and the change in the dynamics of the plant as the plants’ operating points change throughout the day. Once the developed model is validated, characterisation in the form of evaluating the open loop local linear models of the plant is implemented. In order to do so, these models are developed based on model identification processes, which include the use of system identification software such as Matlab® SID Toolbox®. The dominant dynamic behaviour of the plant model, obtained from the developed local linear models, represents that of an over damped second order system that changes as the operating points of the plant change; with the models’ time responses and the bandwidth decreasing and increasing respectively as the thermal energy inputs to the plant increases. The frequency response of the developed local linear models also illustrates the presence of resonant and antiresonant modes found within the control bandwidth of the solar collector field’s temperature response. These modes however are not found to be present in the mechanical power output response of the plant. The use of adaptive control, such as feedforward and gain-scheduled controllers, for the plant should be developed to compensate for the dynamic behaviours associated with that of a CSP plant. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2015

Dust is a well-known occupational hygiene challenge and has been throughout the years, especially in the coal mining industry. The hazards arising from coal dust will differ between geographical areas due to the unique characteristics of dust from the coal mining environment. It is therefore of upmost importance to identify these qualities or characteristics of coal dust in order to understand the potential hazards it may pose. It is also important to consider the presence of nanoparticles which until recently remained neglected due to the absence of methods to study them. Aim: The aim of this study was to collect significant quantities of airborne dust through static sampling to characterise the physical, morphological as well as elemental properties of inhalable and respirable dust produced at two South African underground and two opencast coal mines. Personal exposure quantification was therefore not the primary concern in this study. Method: Static dust sampling was done at two mining areas of the two opencast and underground coal mines using four Institute of Occupational Medicine (IOM) and four cyclone samplers per area at each mine. A condensation particle counter (CPC) was also used at the opencast areas. The opencast areas included blast hole drilling, drag line and power shovel operations. The underground areas included the continuous miner and roof bolter operations. Gravimetric analyses of the cyclone and IOM samples were done as well as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis. Results: Mine A (opencast and underground) produces higher grade coal in comparison to mine B (opencast and underground). Gravimetric analysis indicated higher average inhalable (55.35 mg/m3) and respirable (2.13 mg/m3) concentrations of dust in the underground areas when compared to the opencast areas (34.73 mg/m3 and 0.33 mg/m3). Blast hole drilling operations indicated higher average inhalable and respirable dust concentrations (39.02 mg/m3 and 0.41 mg/m3) when compared to the drag line and power shovel operations (30.44 mg/m3 and 0.246 mg/m3). CPC results showed higher average concentrations of sub-micron particles at the blast hole drilling areas per cubic metre (63132 x 106) compared to the drag line and power shovel operations (38877 x 106). EDS analysis from the opencast areas indicated much higher concentrations of impurities (with lower concentrations of carbon – 33.33%) when compared to samples taken from the underground mining activities (65.41%). The EDS results from the opencast areas differed substantially. The highest concentrations of silica were found at the blast hole drilling areas. EDS results from the underground areas indicated that mine A has slightly higher concentrations of carbon (66.2%) with less impurities when compared to mine B (64.62%). The continuous miner operations showed a higher concentration of impurities when compared to the dust from the roof bolter. SEM results from the opencast areas revealed that the majority of particles are irregularly shaped and the presence of quartz and agglomerations are evident. SEM results from the underground areas were similar except that the roof bolter produced smaller sized particles when compared to the continuous miner. It also seemed that the areas with higher levels of impurities produced more sub-micron particles. Conclusions: It is possible to identify the majority of physical and elemental characteristics of coal dust by means of gravimetric analysis, particle counting, SEM and EDS. There were differences found, regarding the morphological; chemical and physical characteristics, between the different opencast and underground areas at mine A and mine B due to the type of mining activity and amount of overburden present. Silicosis, Pneumoconiosis and Chronic obstructive pulmonary disease are some of the possible health concerns. It has been seen that dust from higher grade coal mines contributed to more developed stages of these diseases. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2015

This dissertation investigates the extent and type of influence the Shona folktale has had on the writing of the Shona novel. Of particular interest is how much influence the folktale has had on the early writers of Shona novels as compared to the modern writers. The study investigates folktale influence on the development of plot, setting and characterisation in targeted novels. With regard to the development of plot, the study focuses on folktale influence on the following aspects; the exposition, complication, climax and resolution. Looking at setting, the study investigates folktale influence on setting as place, time or social circumstances in which the stories happen. The study also investigates the type of characters the novelists portray and seek to detect any folktale influence on characterisation. / African Languages and Literature / Thesis (M.A.)

This thesis investigates the behaviour and failure of simple aerospace type carbon fibre composite structures. The work focused on Acoustic Emission (AE) wave propagation in composite materials, the use of advanced AE techniques to detect, characterise and locate damage and their application to the monitoring of buckling and impact failure in large scale structures. The novelty in the work is highlighted below:

The replacement of chromate conversion coatings for zinc coated components has been necessitated by the materials finishing industries due to the inherent toxicity issues with Cr(VI) and the legislative enforcement of WEEE and ELV Directives by the European Union. Current replacements are based on non-chromate , Cr(III) systems, these may be perceived by some to be problematic as they still contain chromium . Molybdate based conversion coatings have long been viewed by many researchers to be a viable non-chromium alternative due to their low toxicity. An extensive literature review of the research carried out in the last 20 years was carried out, highlighting areas of interest for improving the corrosion resistance of the coatings studied. These were, primarily, the synergesis that exists with molybdate and phosphate compounds for corrosion resistance and the incorporation of nanoparticle silica into treatment solution. Also discovered was the importance of the acid used to adjust treatment solution pH, immersion time, oxidising agent additions and the incorporation of rare earth metal species. Silicate sealant layers were also highlighted as a post treatment. Molybdate-based coatings were formed on commercial electrodeposited acid zinc surfaces. Many treatment conditions were investigated, and initially performance analysed using DC Linear Polarisation Resistance (LPR) trials. Subsequently, the highest performing coatings were subjected to the more aggressive, industry standard, ASTM B 117 Neutral Salt Spray (NSS) corrosion test. The highest performing molybdate coatings were found to have an average LPR of ~ 9 000 Ω. cm2, in contrast to ~ 12 000 Ω. cm2 for the Cr(VI) based reference. NSS results were amongst the highest performing for molybdate based coatings documented, at 24 h until 5% white rust, however remained inferior to Cr(VI) coatings, which lasted 120 h. The highest performing coatings were characterised using FEG-SEM, Cryofracture EDXA and site specific AES. These techniques revealed that the enhanced molybdate coatings had a columnar structure that was around 300 nm thick, with pores that appeared to expose the substrate. AES showed this type of coating to have a mixed Mo, P and Zn oxide surface. Corrosion initiation was also studied; this can be thought of as an investigation to determine the point(s) of weakness or the mechanism that causes coating failure. Coatings were immersed in 5 % wt/ vol NaCl(aq) until they showed any surface change. Initial signs of corrosion were deemed to be any appearance of pitting or discolouration of the film, not a voluminous corrosion product. Untreated Zn, Cr(VI) and simple molybdate coatings were studied as well as enhanced molybdate coatings. There were clear differences in the way the coatings behaved at the onset of corrosion. Cr(VI) coatings delaminated, leaving an area of decreased Cr concentration. The enhanced molybdate coatings failed by the appearance of localised pores of ~ 70 µm in diameter. Substrate exposure was indisputably the reason for coating failure in chloride environments. In light of the work carried out in the present thesis the outlook for the use of molybdate as a potential replacement for chromate for the conversion coating of electrodeposited zinc surfaces is a positive one.