Research Doctorate - Doctor of Philosophy (PhD)

The characteristics of single- and binary-phase turbulence in an oscillating grid system were investigated experimentally by using time-resolved, non-intrusive particle image velocimetry (PIV) technique. Experiments were conducted in three different fields of view (FoV) namely: 10 mm × 10 mm, 30 mm × 30 mm and 60 mm × 60 mm in the center of the tank for grid oscillation frequency 0 to 5 Hz. The grid Reynolds number (Re_g) and Taylor Reynolds number (Re_λ) ranges were 1080–10800 and 12–60, respectively. Specifically, the focus was on: (i) characterisation of single-phase homogeneous isotropic flow based on specific energy dissipation rate; (ii) modulation of turbulence due to particle-fluid and bubble-fluid interaction; and (iii) quantification of scaling properties of pressure spectrum for single- and binary-phase flow. In order to understand the homogeneous and isotropic turbulence inside the oscillating grid system turbulent length scales, isotropy ratio (IR = v_rms/u_rms), specific energy dissipation rate, and energy spectra were determined from the measured experimental fluctuating velocity field for different grid Reynolds numbers. Fluctuating velocity was found to increase linearly with increasing Re_g which was in agreement with the previous reported results. It was found that the turbulence length scale decreased with increase in grid oscillation frequency. The isotropy ratio ranged from 0.77-0.85 which indicated the presence of isotropic homogeneous turbulence in the system. The energy dissipation rate of single-phase flow was determined using the following methodologies: (i) dimensional analysis; (ii) velocity gradient; (iii) structure function; and (iv) energy spectrum. In general, the specific energy dissipation rate increased with increase in grid oscillation frequency. It was found that the specific energy dissipation rates were different for each of the four methodologies. Whilst the analysis identified uncertainties in all four approaches, it was concluded that the energy spectrum methodology was likely to be most reliable since it was able to satisfy the energy balance of the system—this was not possible for other three methods. Moreover, the energy spectra exhibited a slope close to Kolmogorov’s -5/3 in the inertial subrange. White noise was observed in the dissipation range, which was able to be removed by an exponential filter. The modulation of homogeneous and isotropic turbulence was experimentally investigated in the presence of a single stationary particle. The particle diameter varied in the range of 1 to 8 mm (~ 10 to 77 times larger than the flow Kolmogorov length scale). It was found that the fluid-only fluctuating velocity increased by up to 2-25 percent depending upon the particle diameter. The isotropy ratio of the fluid-only phase also increased with the size of the particle; but was much less influenced by the Reynolds number of the grid, Re_g. The energy dissipation rate of…

Research Doctorate - Doctor of Philosophy (PhD)

This thesis provides an assessment of the toxic pollutants formed during the thermal decomposition of polychlorinated (PCBs) and mixed halogenated (i.e., simultaneously chlorinated and brominated) biphenyls (PXBs; X = Cl/Br), under gas phase conditions similar to those occurring in fires, and in other combustion processes. (For convenience, in this thesis, the term polychlorinated biphenyls also comprises monochlorinated biphenyls.) In particular, we have investigated the oxidation of 4-chlorobiphenyl (4-CB), 4,4’-dichlorobiphenyl (4,4’-DCB) and 4-bromo,4’-chlorobiphenyl (4,4’-BCB), at temperatures lower than those leading to complete conversion of PCBs and PXBs to HBr, HCl, H2O and CO2. The presence of chlorine and bromine in the molecules indicates the propensity for releasing highly toxic chlorinated and mixed halogenated volatiles (VOCs) in combustion processes. In addition, previous studies reported polychlorinated biphenyls, which were widely used as transformer oil in capacitors, to form polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The work covered by this thesis was designed to examine the type and abundance of pollutants formed in incomplete oxidation of PCBs and PXBs and to gain an understanding into the effect of structural differences among the reactants on the reaction mechanisms responsible for the formation of pollutants. In addition, we examined the effect of three materials of construction of the reactors: alumina (99.5 %), quartz (99.95 %) and quartz with boron-oxide coating on the reactor walls. Initially, we studied the same reactant (4-CB) in the three reactors, to understand the effect of impurities (trace amount of transition metals) and surface generated singlet oxygen on the reaction mechanisms responsible for the pollutant formation. We established a laboratory-scale apparatus that consisted of a laminar flow reactor equipped with a sampling system for intercepting the volatile and condensable products. A XAD-2 cartridge served to trap the volatile organic compounds (VOCs) and PCDD/Fs. The analysis of VOCs involved high resolution gas chromatography – quadrupole mass spectrometry (GC-QMS) while HRGC – ion trap MS (GC-ITMS) quantitated the PCDD/Fs produced. The development of reaction mechanisms involved the application of Gaussian 09 suite of programs. We optimised structures and calculated the zero point vibrational energies (ZPVE) at the B3LYP/6-31G(d), B3LYP/6-311G(d,p) and M062X/6-311+G(d,p) levels of theory. Stationary points located were either minima or transition states (TSs) determined by vibrational frequency analysis wherein a transition structure contained just one imaginary frequency along the specified reaction coordinates. Intrinsic reaction coordinate (IRC) analysis afforded linking the reactants and products with their TSs. The thermal decomposition of 4-CB in the alumina reactor produces a number of volatile pollutants, including chlorophenols and chlorobenzenes, which are important…

Research Doctorate - Doctor of Philosophy (PhD)

This research presents ENSO forecasting and explores ENSO impact by investigating climate and catchment forcing on hydrological response (streamflow). Climate is used as a donor input into catchment types both similar to, and substantially different from the original catchment type. This approach allows catchment response in ENSO phases to be explored with and without implicit climate differences. Research outcomes are: Reliable forecasting (by reducing false positive predictions); That climate is dominant over catchment characteristics in driving hydrological response; That catchment groups have implicit climate differences; The action of La Nina and IPO increasing flood risk, is through increased frequency/duration of events, not increased rainfall intensity

Professional Doctorate - Doctor of Philosophy (PhD)

Polychlorinated dibenzo-p-dioxins and dibenzofuran (PCDD/Fs) constitute a major toxic component of environmental pollutants. It is well documented that formation of these compounds accelerates in the presence of transition metals especially copper and iron. It has also been established that chlorinated phenols and chlorinated benzenes play a vital role in their formation. Numerous studies have been reported regarding surface-mediated formation of PCDD/Fs from reactions of chlorinated phenols. However, fewer experimental studies have been performed on alumina and iron oxide as active sites, in spite of being the most abundant compounds in fly ash. In this thesis, we have investigated the catalytic decomposition of 2-chlorophenol (2-CPh) into toxic products including polychlorinated dibenzo-<i>p</i>-dioxin and polychlorinated dibenzofuran (PCDD/Fs, dioxins). The catalysts that have been investigated for 2-CPh decomposition consist of silica, alumina, silica-supported iron oxide and alumina-supported iron oxide. To gain a thorough and more comprehensive understanding of the PCDD/Fs formation we arranged a series of reactions using a bench tubular reactor, with the main focus on varying temperature and time on stream. The reaction products were identified and quantified with a gas chromatogram quadrupole time of flight mass spectrometer (GC-QTOF), micro gas chromatogram (µGC) and an ion chromatogram (IC). In addition, we identified the bonds formed on the surface of the catalysts due to the decomposition of 2-CPh with an <i>in-situ</i> Fourier transform infrared (<i>in-situ</i> FTIR) spectrometer. Additionally, X-ray photoelectron spectroscopy (XPS), temperature program desorption (TPD), NO gas adsorption by in-situ FTIR, CO chemisorption, catalyst surface area measurement and inductively coupled plasma optical emission spectrometry (ICP-OES) have been performed for catalyst characterisation. Initially, we studied 2-CPh decomposition on the surface of neat silica. We have identified chlorinated phenols as volatile organic compounds (VOCs) and detected chlorinated and non-chlorinated DD/Fs including dibenzo-<i>p</i>-dioxin (DD), 1- and 2-monochlorodibenzo-p-dioxin (1-, 2-MCDD), 1,6-, 1,9-, 1,3-dichlorodibenzo-p-dioxin (1,6-, 1,9-, 1,3-DCDD), 4-monochlorodibenzofuran (4-MCDF) and 4,6-dichlorodibenzofuran (4,6-DCDF). In this chapter we showed that silica has the ability for chlorination/dechlorination and the dioxin products are formed by self-condensation of chlorophenoxy radicals on the surface and coupling of chlorophenoxy radicals on the surface with chlorinated phenols, also we proved that even in the absence of transition metals, PCDD/Fs could form on the surface of neat silica. Oxidative decomposition of 2-CPh on the surface of silica-supported iron oxide revealed the production of phenol, benzene, chlorinated phenols and chlorinated benzenes. Silica-supported iron oxide has a greater ability for chlorination/dechlorination of dioxin condensation products and…

Research Doctorate - Doctor of Philosophy (PhD)

Advanced porous materials are a new group of materials where the desired properties can be controlled and even tailored. These interesting materials offer a vast field of applications, thanks to their multi-functional abilities. Several types of advanced porous structures including cellular metals and ceramic porous materials are the focus of the present investigation. Corevo® foam and perlite metallic syntactic foam are investigated in this thesis and manufactured from infiltration casting. In addition, advanced pore morphology foam elements are addressed that are fabricated using thermal expansion of a thin wire-shaped precursor. Ceramic porous structures specially developed (via foam replication) for tissue engineering scaffolds are also studied within the scope of this work. Given the similarity of the geometrical structure of all these materials, the same mechanical characterisation approaches are adopted to assess their mechanical properties. The materials properties are determined for quasi-static and dynamic compression for both small and large strain deformation. Numerical simulations are performed by making use of the highly accurate models obtained from micro-computed tomography data. Where possible, numerical results are verified by the findings of experimental testing. Detailed analysis is included in each chapter elaborating the result from the numerical simulations and the compressive loading test. Versatile tools such as electron microscopy, image based geometry analyser software and IR-thermal imaging are utilised to assist the study. The results show that all cellular metals investigated in this thesis exhibit the characteristic stress-strain curve of metallic foams. This means that a linear slope is found in the beginning of the compression loading, this is followed by a long plateau region indicating energy absorption capability and ends with a steep slope at the end representing the densification. Corevo® foam exhibits a significant amount of mechanical anisotropy in casting direction under quasi-static compressive loading. The degree of mechanical anisotropy is considered mild for perlite metallic syntactic foam in the casting direction under the same loading condition. Foam materials (Corevo® and advanced pore morphology foam element) characterised under dynamic loading show a strain-rate dependence property. Last, but not least, a possible extension of the present research is proposed at the end of this thesis in the Conclusions and Outlook section.

Research Doctorate - Doctor of Philosophy (PhD)

Water injection is the most commonly used method to increase the yield from oil and gas reservoirs. Seawater is typically the most convenient water source, and aquifer water and produced water (recovered from crude oil) or some combination is also used. The water injection pipelines (WIP) usually are carbon steel and often are many kilometres long. Because the insides of the pipes usually are not coated, the adverse operational environment means that internal corrosion is an on-going problem for many water injection pipelines. A corrosion problem of much concern in practice is the severe internal corrosion at the lower part of water injection pipelines in near-horizontal positions, in some cases, severe metal loss threatening the integrity of the pipelines. This type of corrosion is known variously as channelling corrosion, 6 o’clock corrosion, and bottom of the line corrosion. The examination of field observations suggests both under-deposit corrosion (UDC) and microbiologically influenced corrosion (MIC) are likely to be associated with the phenomenon. However, the mechanism of this phenomenon is still not fully understood. This thesis reports the observations of long-term corrosion of model steel pipes in a pilot laboratory study aimed at improving the understanding of development of channelling corrosion in offshore water injection pipelines. Half-pipe steel specimens were exposed continuously to stagnant and simulated deoxygenated seawater in the presence of mixed deposits for up to 365 days. The relative contributions of MIC, UDC and nitrate addition to corrosion development were investigated using four different test environments. The steel specimens were recovered after 12, 180 and 365 days of exposure and the changing surface topography was examined by Scanning Electron Microscopy (SEM) and optical microscope. The evolution of corrosion products were analysed by SEM and Energy-dispersive X-ray spectroscopy (EDS). The pit depths were measured by digital Linear Variable Differential Transformer (LVDT). These techniques present detailed graphical, morphological and chemical results of the corrosion process of mild steel in presence of deposits exposed to deoxygenated seawater. The observations show the synergistic effect of MIC and under-deposit corrosion led to severe localized corrosion. Nitrate addition caused most severe localized corrosion. This is linked to the enhanced MIC and the added nitrate plays the role of a source of critical nutrient. The progression of maximum pitting depth with increased exposure period was evaluated and a preliminary extreme value analysis of variability in maximum pit depth is presented. It is found that extreme value distribution examination shows Gumbel function is not appropriate to describe all the pit depth data. Frechet distribution is a better model to deal with the variability of the deepest pits. Finally, it is proposed that the continuous propagation of broad pits with the initiation of newer pits may explain the…

Research Doctorate - Doctor of Philosophy (PhD)

In today’s knowledge oriented economy, the ability to make accurate decisions becomes crucial for any organization or individual for adapting to new demands and conditions in the environment. Additionally, technology allows for ubiquitous access to knowledge and information from different places and devices at any time, which has created a new generation of highly informed customers and enterprises; thus, precise decisions have become more important in order to increase customer fidelity, maintain competitive advantage, and reduce reaction times and costs. In spite of all the advances in the field of Knowledge Management, and more specifically in the area of Knowledge Sharing, most of the existing solutions for capturing, storing, and reusing knowledge require a high degree of expert intervention; for instance, expert forums or document bases. Moreover, the process of finding an appropriate solution for a given problem becomes complex when the amount of information and knowledge available increase everyday. Furthermore, unlike traditional organizational assets, knowledge has a unique intangible nature and is highly embedded in the workforce and the business processes, making it hard to measure and estimate its actual availability. The e-Decisional Community aims at proposing a set of guidelines for the development of a large scale platform to share knowledge and experience in order to support decision-making processes in organizations. The main idea behind the platform is that experiential knowledge is gathered from the constant interaction between users and organizations and from the software applications that they use on a daily basis. Knowledge exchange and evaluation is performed in a semiautomatic way by using smart agent technology, a set of indicators that reflect human behaviour, and an automatized knowledge-based market environment. Additionally, the most important contribution of this research is the definition of a semi-automatic way of assessing quantity and quality of knowledge. The e-Decisional Community is able to provide estimated measures of quantity and quality of knowledge, endowing organizations with a novel set of tools for assessing the knowledge that resides in their workers and business processes. Several conceptual elements of this thesis have been implemented in a testing prototype, and the experimental results that were obtained show that the platform has a great potential for reducing the workload on experts, as well as response times for providing accurate solutions. Consequently, overall organizational efficiency is increased because workers can focus on their core tasks without worrying about additional management duties for their knowledge-based systems, such as solution classification, or knowledge quality assessment.

Research Doctorate - Doctor of Philosophy (PhD)

Within the scope of this thesis different cellular materials such as sintered metallic hollow sphere structure, sintered metallic fibre structure, lotus-type material, open-cell sponge m.pore® and closed-cell foam Alporas® are investigated. Mechanical properties at small deformation (e.g. Young’s modulus and 0.2 % offset yield stress) and the effective thermal conductivity of these materials are studied. These properties are determined with the help of a novel method which is capable of simulating the real structure of the material. In this, the real sample is scanned and the micro-computed tomography images obtained are transformed into a computational model by converting the 2D images into a 3D structure and generating a volume mesh. Then the simulation model is defined by assigning material properties, boundary conditions and the appropriate load case. The advantage of this simulation method over experimental testing is the repetition of calculations and therefore a precise characterisation of the complex material structure is possible by investigating different spatial directions on the same sample. The accuracy of the simulation models is verified with a numerical convergence analysis and experimental testing. In the case of experimental testing, mechanical properties are determined with an uniaxial compression test and the thermal conductivity with steady-state plate method and transient plane source method (i.e. Hot-Disk® method).

Research Doctorate - Doctor of Philosophy (PhD)

In the last two decades a great deal of research has been focused on the development and characterisation of metallic foams for special purpose applications. Due to their high strength to weight ratios and highly porous structures, metallic foams have unique energy absorption, damping, and thermal properties. However, these materials have not yet been widely used in industry, simply because of their higher costs when compared to their polymeric competitors in the market. In recent years, researchers have shown considerable interest in metallic syntactic foams, which are produced by embedding hollow or porous low density heat resistant particles in a metallic matrix. Owing to their relatively simple manufacturing processes, metallic syntactic foams have lower costs when compared to other foams. However, the typical aluminium syntactic foams have significantly higher densities (reportedly more than 1.4 g/cm³). This is mainly due to the high densities of the filler particles (typically more than 0.6 g/cm³) and the failure of particles during the manufacturing process. In this thesis, the major limitations of the metallic syntactic foams, i.e., their high densities and relatively high costs, are addressed by introducing a novel light porous filler material, Expanded Perlite (EP). A large volume fraction of internal porosity (≥95%) reduces the density of this natural volcanic glass down to only 0.18 g/cm³. Being mined in large quantities, to the author’s knowledge EP has the lowest price when compared to its competitors. The large particle size range, from 300 μm to 6 mm, allows for the simple, cost efficient manufacture of foams with the desired properties. EP/A356 aluminium syntactic foams were successfully fabricated using a melt infiltration technique. Depending on the manufacturing parameters, the densities of the foams may vary between 0.7 and 1.05 g/cm³, which are the lowest among the typical syntactic foams. The produced foams were then subjected to a wide range of microstructural, structural, and mechanical testing for a comprehensive characterisation of the material. With a special focus on the energy absorption capabilities of the foams, attempts were made to improve the mechanical responses of the foams by adjusting their structures and microstructures. Heat treatment, a smaller EP particle size, and a higher sphericity of the particles were shown to be effective parameters which increase the mechanical strength and energy absorption capacities of the foams. The positive strain rate sensitivity of the compressive properties makes this foam attractive for crash cushioning applications. The foams also showed outstanding performances under cyclic compressive loading conditions. Following the major characterisations, an application of EP/aluminium syntactic foam, as the core of hollow steel tubes, was investigated. The compressive and bending properties of the foam filled tubes improved considerably when compared to empty tubes. A second novel filler material,…

Research Doctorate - Doctor of Philosophy (PhD)

Water distribution (WD) systems throughout the world are deteriorating, most commonly due to external corrosion ‘pitting’ on cast iron pipes. Replacing an entire aging pipe infrastructure is likely to be prohibitively expensive so it is worthwhile to seek incremental improvements in these systems. By developing a deeper understanding of WD operational states associated with water pipe failures, system managers will be better informed to propose operational improvements that extend asset life and reduce long term costs. A novel framework was developed that describes the process of forensic systems analysis (FSA) to investigate how system operations are associated with large diameter trunk-main failures. FSA utilises a water utility’s pipe failure database and its historical supervisory control and data acquisition technology to analyse operating states at the failure time. Using FSA about 313 large diameter (≥250 millimetres) trunk-main failures were investigated in three real urban WD subsystems in Newcastle, Australia. Significant insights into system operations association with failure were developed resulting in discovery of a previously unknown system failure mode called ‘pump off-peak (POP) increasing static pressure’. POP was characterised by high speed pumping (greater than 80% of the maximum pump rotational speed) or fixed speed pumping from the central pump stations in low demand periods, and with limited pressure relief from downstream reservoirs. POP was shown to be the dominant system failure mode in two of the three investigated subsystems. Frequency analyses of POP conditions associated with failure were conducted. It was found in one of the investigated subsystems that between 2002 and 2012 in the off-peak period between 10:00pm and 6:00am, trunk-main failures were four to five times more likely to occur in the presence of POP conditions. Inexpensive operational changes were investigated to reduce off-peak system pressure and hence, by association, reduce the frequency of POP failures. FSA can assist in identifying activities and characteristics of the WD system that increase the risk of discontinuity of water supply. Furthermore, it was shown that system failure mode diagnoses of trunk-main failures can be used to prioritise pipeline rehabilitation. FSA has been successfully tested on three WD subsystems suggesting that practicing WD engineers can now utilise FSA in the investigation of recent and historical trunk-main failures.

Research Doctorate - Doctor of Philosophy (PhD)

Global radiation is an important input for evaporation calculations; however, limited measurements exist. Current models for estimating global radiation are deterministic and do not give an estimate of the errors associated with the predicted radiation amounts. In this thesis, five stochastic models are developed to estimate the mean amount and associated uncertainty of global, direct and diffuse radiation from sunshine duration data. The modelled global radiation is used to estimate evaporation amounts using a variety of models, including the Penman-Monteith model, radiation-based models, and temperature-based models. Evaporation estimates are compared to determine the influence of uncertainty in the global radiation estimate on evaporation amounts. The second part of this thesis deals with the relationship between temperature and evaporation, with implications for anthropogenic climate change studies. The influence of temperature on evaporation amounts is analysed using a combination of empirical evaporation models and a more physically-based planetary boundary layer model. The results indicate that global radiation can be accurately estimated using all of the developed radiation models (average error = 9%), when compared with measured data. The variance of the errors is greater for cloudy days compared with clear days. The diffuse radiation component is best modelled using a quadratic model (average error = 22%). The direct radiation component is best modelled using a linear model (average error = 23%). Two types of regional models are also developed to calculate radiation amounts at any location. These models have only a small loss of accuracy compared to the locally calibrated models. While the variance of the errors for the locally calibrated models is shown to be location dependent, these regional models allow for the model parameters and the error variance to be estimated at any location, as there is a statistically significant relationship between the model and error parameters and latitude. The regional models are also comparable in accuracy to satellite estimates of global radiation. It is also found that the uncertainty in global radiation leads to considerable uncertainty in evaporation rates, up to ±31% for the radiation-based models. The locations with greater uncertainty in the radiation estimate have an associated greater uncertainty in the evaporation estimate. Temperature increases are shown to have minor influences on evaporation rates. Soil moisture is the most dominant influence. Consequently, temperature-based models are shown to lead to unreasonable estimates of evaporation when temperatures are increased.

Research Doctorate - Doctor of Philosophy (PhD)

Nitrosation reactions sparked interest in the biochemical field following the discovery of nitric oxide (NO) as a signalling molecule in many biological functions in the 1990s. This prompted a flurry of research in different areas of biochemistry including S-nitrosothiols as NO· donors in vivo as well as in N-nitrosamines due to carcinogenic properties. Diverse industrial functions of nitrosation chemistry are also found in azo-dye production and in chemical gassing of emulsion explosives. In the latter, a substrate and a nitrosating agent react to generate nitrogen (N₂) gas bubbles in situ providing sensitisation of the emulsion prior to detonation. The decomposition of nitrosated compounds to either NO· or N₂often poses challenges due to differing roles of products. Therefore, it is important to determine the kinetics and mechanisms of nitrosation in substrates as well as decomposition fates of nitroso species to N₂ and NOx to optimize processes that are relevant to specific applications. This work studied nitrosation reactions in a class of compounds that contain sulfur and an amine group, using a two pronged approach combining experimental measurements with theoretical calculations. These species are particularly interesting due to the inherent structural flexibility that allows intra- and inter-molecular transnitrosation. In these compounds, initial nitrosation occurs at the sulfur atom due to its greater nucleophilicity and the subsequent ON⁺ transfer to a deprotonated amine group results in rapid release of N₂. Previous studies proposed that nitrous acid initiated reactions with amino-thiones proceed via two parallel pH-dependent pathways. The first pathway leads to the formation of benign N₂consequent of the S- to N-transnitrosation in S-nitroso compounds and was earlier studied within the narrow range of pH 3.8−4.1 for thiourea. The second pathway forms disulfide and toxic NO· and is thought to occur at a lower pH but has not been studied in detail. Despite the long history of kinetic studies for S-nitrosation of aminothiols and aminothiones, there remain significant discrepancies between kinetic rate constants in reported literature. At high acidities where the nitrosating agent is either nitrous acidium and/or nitrosonium ion, rate constants are perceived to approach a diffusion limit of 7 000 M⁻¹∙s⁻¹ for neutral species. Revisiting analysis on the true nature of nitrosating agent reveals that the nitrosonium ion pathway is not adequate to explain the kinetic rate constants observed for neutral species. Moreover, the expected encounter limit for the nitrous acidium pathway is two orders in magnitude higher than the observed kinetic rate constants in literature. The early part of this work delved on kinetics of S-nitrosation of thioacetamide and thiourea. In acidic solutions, reactions proceed via nucleophilic attack on the electrophilic nitrous acidium or nitrous acidium by the electron dense sulfur sites. Using stopped-flow UV-vis spectrophotometry, the…

Research Doctorate - Doctor of Philosophy (PhD)

The objective of this study is to document the development of a computational procedure for the analysis of coupled geotechnical problems involving finite deformation, inertia effects and changing boundary conditions. The procedure involves new finite element (FE) algorithms that were formulated and implemented into SNAC—a FE code developed by the geomechanics group at the University of Newcastle, Australia. The numerical scheme was then utilised to analyse some important offshore geotechnical problems. The first development concerns the implementation of the governing equations of two-phase saturated porous media in a mixed form, allowing predictions of solid displacement, pore fluid pressure and Darcy velocity. The generalised-α method was chosen to integrate the governing equations in the time domain. The formulation was extended to consider geometrical nonlinearity within the framework of the Arbitrary Lagrangian–Eulerian approach. Suitable absorbing boundary conditions were also incorporated to model the radiation of bulk waves towards infinity at the truncated FE mesh boundaries. Some closedform solutions were also developed, which are suitable to verify the implementation of dynamic consolidation algorithms. The second development involves the formulation and implementation of a high-order contact algorithm for solid–fluid mixtures accounting for large deformations and inertia effects. The contact algorithm is based on a mortar segment-to-segment approach formulated for cases of frictionless and frictional interfaces. The node-to-segment approach was also employed to compare and highlight the merits of the mortar method when dealing with dynamic coupled problems. The computational procedure was evaluated by modelling some numerical exercises and comparing the predicted results with alternative numerical and analytical solutions where possible. In the last part of the thesis, the computational framework was employed to successfully model the problems of dynamically penetrating anchors and offshore pipeline-seabed interactions. The analysis of dynamically penetrating anchors comprises the simulation of the penetration process and consolidation of the soil surrounding the penetrometer. The analysis of the pipeline-seabed interaction involves the simulation of the laying process and the largeamplitude lateral motion of the pipe.

Research Doctorate - Doctor of Philosophy (PhD)

Froth flotation is a widely used separation technique in the mineral processing industry. It consists of capturing valuable, hydrophobic particles with air bubbles, which rise to the surface. The bubbles segregate at the surface to form a froth zone. Valuable particles are recovered by the overflowing/skimming of the froth phase. The froth phase plays a crucial role in upgrading the concentrate by draining out non-valuable particles. The stability of the froth phase is partly controlled by chemical factors (e.g. surfactants) and physical factors (e.g. particles) among others. Inherent to the process, froth stabilising particles are depleted, which compromises the stability of the froth phase in subsequent flotation cells. This thesis details the stabilisation of flotation froth by the addition of hydrophobic silica nanoparticles and salt to improve flotation performances in the presence of non-ionic frothers. With this objective in mind, a system of nanoparticle, non-ionic surfactants, and inorganic electrolytes were characterised by their performance in a binary coalescence apparatus and a bubble column before being tested in flotation. The effect of the chemical reagents on the coalescence of bubbles was determined using the bubble-pair technique developed by Ata. The four non-ionic surfactants (i.e. 1-pentanol, 4-metyl-2-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) 425) were characterised using bubbles of 2 mm in diameter. Among the selected surfactants, the polyglycols were found to provide greater resistance to coalescence. It was also found that a minimum concentration is required to have any effect on the coalescence time. This is opposite to the results with alcohols, which showed a smoother transition from coalescing to non-coalescing. The oscillation of the projected area of the resultant bubble was quantified using the damping coefficient of the oscillation. It was noticed that an elasticity of approximately 1 mN m-1 was needed to immobilise the surface. Too much surfactant could reduce the stability of the bubbles and the surface due to a fast relaxation of the surface. Some inorganic electrolytes are known to prevent bubble coalescence. Chloride and sulphate electrolytes were tested. There appeared to be two regions; a low and a high concentration region. At low concentrations, the resistance to coalescence was in the order of milliseconds whereas coalescence was prevented for seconds at higher concentrations. The two regions observed could be the result of a transition affected by the relative speed of approach of the capillary bubbles. Using sodium chloride as a typical inorganic electrolyte, the oscillation of the resultant bubble showed no significant variation with increasing concentration. The dynamic foaming and gas dispersion properties of 1-pentanol, tri(propylene glycol) methyl ether, poly(propylene glycol), sodium chloride, and octanol-esterified nanoparticles were investigated by sparging N2 gas in solutions…

Research Doctorate - Doctor of Philosophy (PhD)

This thesis is concerned with investigating the application of the Inverted REFLUX™ Classifier (IRC™) for separating positively buoyant particles from other negatively buoyant particles. This innovative technology was investigated here for the first time to recover valuable cenospheres, less dense than water, from the fly ash waste of a coal fired power station. Annually, millions of tonnes of fly ash generated from burning coal are discarded to the land surrounding power stations, causing long-lasting environmental and health issues. Fly ash contains valuables components such as cenospheres, unburnt carbon, metals and trace elements. The cenospheres are hollow micro-shells consisting of oxides of silicon and aluminium. These particles represent one of the most valuable components found in fly ash, but at low levels of order 1 wt.%. The particles offer superior properties such as high insulation, high strength, and low density, and hence are valued sometimes up to $ 2000 per tonne. They are positively buoyant in water, and hence wet gravity separation offers the potential for their separation from the negatively buoyant fly ash particles. In this study, wet gravity separation in an Inverted REFLUX™ Classifier was investigated to recover and concentrate cenospheres. The Inverted REFLUX™ Classifier (IRC™) consisted of 1-metre long parallel inclined channels located underneath a 1-metre long vertical liquid fluidized bed. Downwards fluidization was supplied through a distributor at the top for the purpose of washing high density slimes from the low density cenospheres. The inclined channels enhanced the segregation rate of the cenosphere particles leading to a throughput advantage over a conventional fluidized bed. Following preliminary experiments it was shown, using the correlation derived by Laskovski et al. (2006), the throughput advantage of the IRC™ was 32. In other words, for a given separation performance, the feed rate per unit of vessel area to the IRC™ can be increased to a level 32 times higher than for a conventional fluidized bed. These preliminary studies were based on using a model feed, a mixture of commercial cenospheres and silica flour. Then, a real fly ash feed containing around 0.51 wt.% cenospheres was used. At a solids throughput of about 2.3 t/(m² h), a product grade of 76 wt.% and a recovery of about 42 wt.% were obtained, corresponding to an upgrade of about 151. By increasing the product rate, the recovery of cenospheres increased to about 64 wt.%, while the upgrade was reduced to 33. A more systematic study was then conducted using a new feed consisting of about 1 wt.% cenospheres, focussed on the role of the solids concentration in effecting enhanced segregation. Based on the study by Batchelor and Van Rensburg (1986), it was hypothesised that a bulk streaming phenomenon should develop in the inclined channels at sufficiently high cenosphere and fly ash concentrations. Different feed solids concentrations from 10 wt.% to 46 wt.% were used,…

Research Doctorate - Doctor of Philosophy (PhD)

Oxygen constitutes 30% share of the global industrial gas market and is the second largest-volume chemical produced in the world after sulfuric acid. Commercial applications of oxygen can be found in industry sectors as diverse as metallurgical industry, chemical synthesis, glass manufacturing, pulp and paper industry, petroleum recovery / refining, and health services. Advanced power generation systems, such as integrated gasification combined cycle (IGCC), Oxy-fuel combustion and solid oxide fuel cells, SOFC represent emerging markets for oxygen. Oxygen is commonly produced at industrial scales by air separation using cryogenic distillation and adsorption based technologies. Advanced technologies such as membrane separation (e.g. ion-transport membrane, ITM) and in-situ air separation are also being developed for small-volume point-of-use oxygen generation. While conventional cryogenic and adsorption air separation methods are matured technologies, their energy intensity and high costs can no longer be tolerated under the current economic, energy, and environmental crises. Membrane separation methods whilst less energy intensive remain expensive due to challenges associated with their fabrication, installation and integration. In view of the above, a team of researchers led by Prof Moghtaderi at the University of Newcastle devised the Chemical Looping Air Separation (CLAS) process and its variants including: (i) Integrated Chemical Looping Air Separation (ICLAS) process for oxy-fuel applications and (ii) Redox Energy Storage (RES) process for thermo-chemical energy storage. Depending on the operating temperature and frontend conditions, the energy input into the CLAS process is 50% - 80% lower than that required for the cryogenic process and, as such, the CLAS family of processes has a relatively small energy footprint. CLAS works in a cyclic fashion by continuous recirculation of metal oxide particles between a set of two interconnected reactors, where oxidation (O₂ coupling) and reduction (O₂ decoupling) of carrier particles take place, respectively. In the original version of the CLAS process the reduction half cycle is carried out in presence of steam so that the desired oxygen product can be obtained by condensing out the steam. However, the production and condensation of steam is energy consuming and if it can be replaced by an alternative method the overall energy footprint of the CLAS process can be further reduced. Motivated by this, Prof Moghtaderi and his team turned their attention on to yet another variant of CLAS named Membrane Integrated Chemical Looping Air Separation (MICLAS) where the oxygen product from the reduction reactor is separated from steam or other suitable reducing agents (e.g. N₂) using an oxygen transport membrane (OTM) system. The combination of the OTM and CLAS in the MICLAS process creates an air separation platform which is far more cost effective than the standalone OTM based processes because of the smaller volume of gases…

Research Doctorate - Doctor of Philosophy (PhD)

This thesis focuses on a fundamental study of hybrid geothermal energy systems, in which geothermal energy is hybridised with other energy sources, such as solar, biomass and fossil fuels, in an integrated technology platform. The motivation behind this study was to use hybridisation to reduce the cost and improve the thermal efficiency of geothermal resources, especially hot dry rock (HDR) resources. Once proven, the hybrid concept will offer a better approach to replacing fossil fuels with clean energy, thereby increasing the renewable energy share in the world’s current energy mix and reducing greenhouse gas emissions. The objective of this project was to undertake a systematic techno-economic assessment of hybrid geothermal energy systems for low emission power generation. The ultimate goal was to explore the potential benefits from the synergies between geothermal and other energy resources. The scope of the thesis, however, was limited to addressing mainly the surface engineering problems faced by geothermal energy systems, particularly Enhanced Geothermal System (EGS), by treating the geothermal energy as an “engineering approximation” to the complex reality where the subsurface geology of geothermal energy is subject to great uncertainties/difficulties. To achieve the broad objectives of this project, the research mainly focused on a theoretical investigation of the two main themes of hybrid geothermal energy systems: hybrid solar–geothermal energy systems and hybrid geothermal–fossil fuel energy systems. A comprehensive set of thermodynamic and economic analyses were undertaken. The thermodynamic studies were based on the first and second law of thermodynamics analyses, examining the technical feasibility of the hybrid systems. The proposed economic assessments were performed using established economic practices to: 1. Compare the capital and operating costs of hybrid geothermal energy systems. 2. Estimate the electricity production costs for each alternative technology option based on a plant cash flow analysis encompassing the total annual expenses and revenues. The cost of electricity approach, net present value and sensitivity analysis were employed as economic tools to examine the economic feasibility of the hybrid systems. In addition, figure of merit analyses were performed to evaluate the superiority or inferiority of the hybrid plants compared to two stand-alone plants, from both technical and economic viewpoints. Lastly, Australian case studies were performed to examine the hybrid system in more realistic technical and economic conditions. The process simulation package, Aspen HYSYS, was employed for all simulation purposes. Analyses of the hybrid solar–geothermal power plant showed that this plant was significantly affected by resource quality and weather conditions. Particularly on partially clear and partially cloudy days, the performance of the solar heating system was found to drop by 40 to 60%, significantly affecting the feasibility of the…

Research Doctorate - Doctor of Philosophy (PhD)

This study investigated the heat transfer behaviour of nanofluids with focus on a magnetite nanofluid as an alternative for the next generation of cooling applications. The very first aim of this study was to shed light on conflicting data reported in the literature about the thermal conductivity of conventional nanofluids (non-magnetic). For this purpose, the thermal conductivity of different nanofluid samples were measured under different conditions (namely particle volume fractions, temperature and pH) and results were compared with theoretical prediction of mixture theory. Shortcomings of different hypotheses were examined, analysed and explained. All of the experimental data were within the ±10% boundary of theoretical mixture theory (i.e. Maxwell model). It was shown that higher thermal conductivity in the conventional nanofluids can be achieved by controlling the aggregation size (i.e. pH value). To test this hypothesis, artificial aggregates were generated by applying an external magnetic field to the magnetite nanofluid. Thermal conductivity enhancement by up to 160% was observed for 0.86 vol% magnetite nanofluids (Fe3O4-water), subjected to the magnetic field intensity of 32 mT parallel to the temperature gradient. On the other hand, the thermal conductivity of magnetite nanofluid is almost constant under the applied magnetic field perpendicular to the temperature gradient. Convective heat transfer coefficient of magnetite nanofluid under laminar flow condition was also considered in the absence and presence of an external magnetic field. Heat transfer in magnetite nanofluids with and without magnetic field has been performed previously. However, the extent of the experiments and analysis is the main goal which has been achieved through this study. It has been shown that the experimental data in the absence of an external magnetic field follows the prediction of standard correlation for laminar flow heat transfer (Shah equation) using the thermophysical properties of nanofluid. Up to 300% enhancement in convective heat transfer enhancement has been observed at Re=745 and the magnetic field gradient of 32.5 mT/mm. Moreover, the effect of magnetic field on pressure drop was insignificant. It is concluded here that aggregation is the main mechanism of heat transfer in nanofluids. The thermal conductivity and convective heat transfer coefficient of magnetite nanofluids can be altered far beyond the prediction of traditional theories by applying an external magnetic field.

Research Doctorate - Doctor of Philosophy (PhD)

Food security and hence access to environmentally sustainable food resources is one of the key global challenges in the 21st century. In this context and from an agronomic perspective, the role of soil amendments (e.g. fertilisers) for enhanced food production cannot be overstated. One such soil amendment is biochar: a carbon-rich organic substance derived from biomass that has great potential to improve soil health by improving nutrient retention, particularly in coarsely textured soils. In addition, biochar can be used as a carbon sink and thus can be considered as an alternative means of reducing atmospheric carbon dioxide. Meanwhile, with the ever-increasing rates of coal production in Australia and around the world, management of mine waste, in particular coal tailings, is becoming a pressing issue. Given that both coal and biomass are organic substances with somewhat similar characteristics, the concept of ‘chailings’, a char created from coal tailings rather than biomass, for use as a soil amendment was proposed by our research team in 2009 and formed the basis of this thesis. As a result, the primary objectives of this thesis were to produce, characterise and apply chailings to soil and ultimately assess the concept for future work and scaled-up production. Chailings were produced via a slow pyrolysis process from tailings sourced from two coal mines (Mine A and Mine B) in New South Wales, Australia. Pyrolysis conditions were varied in terms of maximum heating temperature (400 °C to 850 °C) and holding time (0–6 hours) to create chailings with varying properties. Chailings were characterised using a number of techniques. X-ray diffraction and x-ray fluorescence techniques identified the primary mineral constituents as silica (i.e. quartz) and aluminosilicates (i.e. kaolinite or illite). Clear morphologic changes were observed via optical and scanning electron microscopy for increasing pyrolysis temperature, with evidence of particle swelling and devolatilisation apparent at high temperatures (>600°C). Proximate analyses indicated near complete devolatilisation was apparent at 800 °C for both mines, with thermogravimetric analysis revealing that peak devolatilisation occurred at 454 °C for Mine A and 464 °C for Mine B. Increases in pH and decreases in electrical conductivity (EC) and total acidic capacity were observed when pyrolysis temperature increased primarily due to the volatilisation of acidic compounds. A substantial increase in surface area with increasing pyrolysis temperature was observed for Mine A chailings, from 2.7 m²/g at 400 °C to 75.3 m²/g at 800 °C, because of the development of microporosity. However, a decrease was observed for Mine B chailings, from 2.4 m²/g at 400 °C to 1.2 m²/g at 800 °C, attributed to macroporosity and aggregation of particles. Overall, characterisation of chailings revealed that the physical and chemical properties of chailings were highly dependent on tailings sources and pyrolysis temperature, while holding time had…

Research Doctorate - Doctor of Philosophy (PhD)

Micromechanics has been a popular scientific topic since the late 19th century. The anisotropic mechanical properties of crystals and the complexity of the interaction across grain boundaries were obstacles for revealing a rigorous connection between macroscopic and microscopic stresses and strains. The development of neutron and synchrotron diffraction enables practitioners to accurately measure the internal strains for certain groups of crystallites with the same orientation. This provides us experimental possibilities for analysing the micromechanical response of individual grains to external load. Eshelby's study on ellipsoidal inclusions in a matrix material gave us the theoretical foundation of how the individual grains interact with the surrounding material. By considering the polycrystalline material as an isotropic or transversely isotropic medium in terms of the macroscopic scale, it is possible to determine the internal stress and strain under an external load. Incorporated with the in situ loading neutron diffraction, the relationship between the measured strains as a reaction to the external load can be quantitatively analysed. This helps us to understand the micromechanical state of polycrystalline materials. The initial objective of this research was the micromechanical analysis for determining the single crystal elastic constants (SCEC) from polycrystals. Inspired from the hypothesis that ductile materials are more Reuss-like whilst brittle materials are more Voigt-like, we started research from the background and literature review, experimental methods and quantitative texture analysis. Following this a practical method was analytically developed for quantifying the micromechanical stress for individual groups of grains. Based on this method, a few differently categorised materials (e.g. alumina, MAX phases and metal alloys) were studied in order to determine the SCEC from the experimentally measured microscopic strains. Eventually, we concluded that the method developed based on Eshelby's theory and the self-consistent micromechanical model is capable of determining the micromechanical state for a material without any non-elastic deformation under external load. Anelastic deformation plays a significant role in determining the micromechanical state of a material therefore the proper precautions must be taken in order to apply the method developed to applications such as determination of SCEC from polycrystals or residual stress analysis.

Research Doctorate - Doctor of Philosophy (PhD)

One of the most important technical issues of recent pneumatic conveying technology development is the new approach for better modelling of fine powder flow performance. This presents a significant challenge in ensuring the model adequately reflects the physical nature of the flow, and the predicted results are comparatively more accurate than the conventional empirical based methods. Instead of empirically based methods, this research adopted a fluid rheology based technique to assess the flow performance of fine powders within pneumatic conveyors. The approach stemmed from the liquid-analogy characteristics of fluidised powder materials where the critical property to determine the flow performance of a liquid is its rheological response. This liquid analogy principle can be applied to fine powder pneumatic flows. Therefore, the objective of this research was focused on following specific aspects: theoretical modelling of fine powder pneumatic flow from a rheology perspective, experimental determination of the rheological properties for aerated powders, validations of the proposed conveying models, and transient characteristics of fine powder pneumatic flows. Initially, conveying models based on the rheology of aerated powders were derived for straight pipelines. This was achieved by analysing a continuous flow system using classic fluid mechanics. By inputting the rheological and conveying parameters, models capable of predicting the pressure drops were proposed. Experimental investigations on the rheology of aerated powder materials (alumina, cement and flyash) were subsequently conducted. These investigations were predominantly focused on the hydrostatic yield stress at low aeration and viscous characteristics at high aeration. Two purposely designed and built experimental apparatuses were utilised to examine the rheology of aerated powders accordingly. Empirical power-law and yield power-law rheological correlations were subsequently formulated based on the quantitative results obtained through testing. Rheology based conveying models were finally evaluated and validated by comparing the pressure drop produced from conveying models with the pressure drop measured from a 7-metre long pilot scale pneumatic conveyor. Results showed good agreements between the model predictions and experimental observations for alumina with overall error around 11.7 %. However, for flyash, only the results in low to intermediate dense states (m* <130) were found to be close the experimental results. Transient flow behaviours of the flyash powder were also investigated using a non-invasive imaging device-Electrical Capacitance Tomography (ECT). A 20-metre long pilot scale pneumatic conveyor was designed and set up to conduct various tests with the ECT embedded in the pipeline. Flow patterns reconstructed from the ECT results indicated that the dense flyash pneumatic flows were naturally unsteady and pulsatile. Structural and statistical analyses on the pulse structures were…

Research Doctorate - Doctor of Philosophy (PhD)

Many major city water supply distribution networks consist of buried cast iron pipes. In many cases, the pipes are internally cement lined and the predominant corrosion is by external pitting. This may cause leakage and eventually structural failure. Predicting the remaining life of older pipes is, therefore, a matter of interest both for engineers and asset managers. An accurate predictive model requires an estimation of the probability of failure and would be useful for reducing the costs of maintenance and for protection against unexpected failures. Since the pipes are buried, and thus cannot be inspected visually, there is considerable uncertainty about their condition. Indirect inspection techniques also have a high degree of uncertainty. For these reasons, there is an interest in long-term asset management to develop realistic models for the depths and areas of pitting corrosion in order to aid the estimation of the probability of failure of older pipes. It is generally considered that the deepest pits are of most interest in relation to failure. It is thus conventional to use the Gumbel Extreme Value distribution to represent the statistics of the maximum pit depths and to use it to estimate the probability of pipe wall perforation. Herein, the data obtained for the maximum pit depths for large sized (1 2m long) samples of 24 pipes exhumed from different, apparently randomly selected, locations after 34 to 129 years of service are examined for consistency with the Gumbel probability distribution. This was the case for the deepest pits, but the data for less deep pits showed a consistent pattern of departure from the Gumbel distribution. Some extreme pit depth data, inconsistent with the rest, are interpreted as being possibly caused by material imperfections. The likely pit size is also of interest in estimating leakage losses, and for assessing the mechanical behaviors and failure probabilities of pipes. However, to date, limited statistical models for the sizes of the pits have been proposed. Current work aimed at statistically modeling the progression of pit sizes for cast iron water pipes is also reported, again using data from actual pipes exposed for long periods. The present study thus examines pit area and pit length data computed from pit depth data. To investigate the progression of pitting corrosion, the relationships between the pit areas and the pit depths of each pipe is described. These results, and the results of the Extreme Value Analysis of the maximum pit lengths of old cast iron pipes, supports previous observations that the growth of pits is not a continuous process but occurs in stages, with each stage involving lateral growth and the amalgamation of pits, and then the formation of new pits in the plateaus formed by earlier corrosion.

Research Doctorate - Doctor of Philosophy (PhD)

Oxy-fuel combustion is an emerging technology intended to mitigate CO₂ emissions from power plants. Compared with other CO₂ capture technologies, non-CO₂ components in Oxy-fuel flue gas are highly concentrated, among which SO₂ is of concern. Sodium based quench units have been used in Oxy-fuel projects to directly cool the gas prior to compression and to also remove SO₂. However, the high concentration of CO₂ in the flue gas can interfere with the capture of SO₂. This study considers the mechanisms by which SO₂ in CO₂ is absorbed by sodium containing liquids, using laboratory experimentation and experiments at the Callide Oxy-fuel Project. Conditions for the operation of Oxy-fuel scrubbers are recommended, including operational pH levels based on both the SO₂ absorption rate and the effective use of Na⁺ in liquid. In the laboratory evaluation, dynamic experiments were designed to elucidate the reaction mechanisms of SO₂ absorption from gas mixtures of SO₂/N₂, SO₂/CO₂, SO₂/N₂/O₂ and SO₂/CO₂/O₂ when introduced into solutions of NaOH, Na₂CO₃ and NaHCO₃ with known initial concentrations and pH. Correspondingly, the steady state experiments were designed to understand the absorption rate of SO₂ from gas mixtures of SO₂/CO₂ when introduced into sodium solutions with known mixtures of NaHCO₃ and NaHSO₃. The SO₂ concentration of the exhaust gas and the changes in the pH of the liquid were obtained during experiments in both dynamic and steady state processes. The changes in both parameters were recorded during experiments for dynamic processes; whereas both parameters were controlled to reach target values during experiments for steady state processes. Additionally, liquid samples were obtained on a regular basis for the analysis of HCO₃-, S (IV) and S (VI) in both dynamic and steady state processes. The absorption rate of SO₂ in dynamic experiments was found to be reduced in CO₂ in the gas phase controlled region primarily due to the reduced diffusivity of SO₂ in CO₂ and reduced kinematic viscosity of CO₂ compared to N₂. The dynamic absorption results for gas mixtures of SO₂/CO₂ demonstrated three pH regions of absorption rate behaviour and the absorption rate of SO₂ was correlated with speciation in these regions, as pH decreased during the experiments. The steady state experiments of SO₂ absorption into mixtures of NaHCO₃ and NaHSO₃ investigated solution chemistry at various pH values, the significance of solution pH and the concentration of SO₂ on the absorption rate of SO₂. The absorption rates of SO₂ obtained in steady state experiments were predicted by the model based on the instantaneous reaction assumption. The model generally overestimates the absorption rates of SO₂ at pH values below pH 6 indicating a kinetic limitation of SO₂ and water reaction at low pH values. Experiments at the Callide Oxy-fuel Project yielded both gas and liquid analyses. Gas analysis for SO₂, CO₂, O₂, CO, NO and NO₂ were obtained at three positions: before, at the intermediate location of,…

Research Doctorate - Doctor of Philosophy (PhD)

Biomass is an important primary and renewable energy resource which is widely distributed around the world. Bioenergy derived from biomass is a form of renewable energy that may be used to generate power, heat and to synthesize liquid fuels for transport or chemical production. Among the different biomass utilisation processes, thermo-chemical conversion methods, such as pyrolysis or gasification, are the most efficient way to convert biomass to fuels or fine chemicals. Biomass gasification is generally favoured as it can be used for the production of syngas (H₂ and CO) in differing H₂/CO ratios, which can be used as a fuel, or for chemical synthesis. However, existing gasification units, suffer from a major technical hurdle that is tar formation. Tar components, especially smaller molecule aromatic ring components such as toluene, xylene and naphthalene etc., are still present in syngas after primary and secondary tar removal treatments. This seriously influences the efficiency of subsequent syngas application in either gas turbines or chemical synthesis. As such tar removal technologies are imperative for the purification of raw syngas generated during biomass gasification. Catalytic cracking is currently considered the most attractive method for tar removal, as cooling of the raw syngas can be avoided and hence minimal energy is lost. A further advantage lies in that tars can be cracked and reformed into light gaseous components, such as H₂, CO and CH₄, increasing the overall gasification efficiency and improving the lower heating value (LHV) of the product syngas. Among the various catalysts available such as alkali metal catalysts, nickel-based catalysts and transition metal catalysts, calcium based catalysts were selected for systematic investigation. Calcium based catalysts were evaluated as the most attractive due to their low cost and ability for simultaneous catalytic tar cracking and CO₂ capture at moderate temperatures. In order to utilise a calcium based catalyst for tar cracking in a biomass gasification process, with a primary focus on syngas production and power generation, two configurations of a novel calcium looping based biomass gasification process were proposed in this thesis; (i) an ex-situ calcium looping (ECL) process for biomass gasification and (ii) a calcium looping based biomass integrated gasification combined cycle (CL-BIGCC). To assess the technical merits of the proposed processes, a fundamental understanding of bio-tar formation during biomass gasification, as well as, bio-tar cracking in the presence of calcium-based catalysts was necessary. Accordingly, a series of experimental and theoretical modelling investigations were conducted to assess the performance of the proposed processes. An experimental investigation of tar cracking behaviour during biomass partial oxidative gasification in the presence of CaO was conducted. The amount of tar cracked was proportional to the oxygen…

Research Doctorate - Doctor of Philosophy (PhD)

Subsidence is one of the most challenging and controversial problems in rock mechanics and geotechnical engineering. In particular, the expansion of urbanised areas over abandoned mining excavations has brought about several questions concerning the long term stability of such excavations and the duration of the subsidence development. This study, therefore, aims to investigate the mechanisms of post mining subsidence. The role of the effective factors on the mechanisms of excavation induced ground movements are assessed through some case studies of actual subsidence incidents. Clearly, one of the fundamental stages of conducting numerical or theoretical analyses for calculating the magnitudes of subsidence is to reliably estimate the mechanical parameters of rock masses. A simple and practical approach is developed in this study, based on the concept of rock mass classification methods to approximate the rock mass parameters. Additionally, the mechanisms of mining induced subsidence in sloping terrain are investigated through numerical modelling. An interesting example of mining beneath escarpments in New South Wales, Australia, is investigated to capture the effects of the surface topography on the mechanisms of subsidence. Furthermore, the role of the gradual deterioration of a rock mass on the duration of the subsidence development in shallow abandoned coal mines is investigated. The conventional Tributary Area Method (TAM) is augmented to incorporate the effects of the gradual deterioration on the loads of pillars. Moreover, the conventional pillar strength methods are modified to take into account the effects of the gradual deterioration. The combination of these two approaches provides a suitable ground for assessing the life times of pillars. Furthermore, a simple and practical approach is proposed to take into account the role of gradual deterioration in the numerical modelling. The proposed approach is then employed for assessing the formation of subsidence over an abandoned shallow coal mine around the village of Dolphingstone, UK. The outcomes of the numerical modelling are then verified against the results of the empirical methods for estimating the stand up time of room and pillar mining excavations. Creep is the other time dependent behaviour of rocks, controlling the long term stability of excavations. The role of this factor on the mechanisms of post mining subsidence is also investigated in this study. The theories of visco elasticity and visco plasticity are employed in the frameworks of the analytical and numerical modelling to study the effects of creep on the gradual development of subsidence over abandoned room and pillar mines. The outcomes of the study show that creep plays a pronounced role on the values of the time dependent displacements over mining excavations. Moreover, a procedure is developed to take into account the effects of gradual weakening due to mechanical factors (e.g., creep) or environmental factors (e.g., weathering and…

Research Doctorate - Doctor of Philosophy (PhD)

Compared to high velocity dilute phase, low velocity dense phase conveying offers additional benefits of reduced wear and higher material throughputs; while maintaining all the benefits pneumatic conveying has to offer including enclosed conveying, flexible routing and low maintenance. The complexity of the flow; however, is the major limiting factor when it comes to widespread implementation of dense phase systems. The still unknown mechanisms responsible for the flow have resulted in universally unreliable design procedures resulting in reluctance from industry in employing this profitable flow type. The work presented in this thesis aims to shed light on the unknown mechanisms, specifically within horizontal slug flow, through an experimental and theoretical analysis of the key parameters of the flow. Experimentally the relationship between the key slug properties was investigated at two pipe locations allowing the evolution of the parameters to be tracked and correlated for individual slugs. The ‘Ergun porosity’ approach was expanded as well as a physical and theoretical review of the method resulting in a modified form of the Ergun equation for slug flow. Further investigations on the slug porosity resulted in a simple model developed along with a tuning procedure for the model constant to account for the effects of air supply. The gas dynamics were considered as a function of time and an unsteady model was developed for the interstitial gas velocity. Preliminary examinations suggest that dynamic changes in slug porosity and pressure only impact the magnitude of the interstitial velocity and not the trend. Future work should involve experimental porosity data and more robust numerical approaches to further examine these findings. Lastly, an investigation on the layer fraction resulted in the development of a new predictive model that addresses the drawbacks of the readily applied model of Konrad. Three sets of experimental data were utilised to validate and compare to the model of Konrad while also investigating the layer fraction as a function of air supply, pipe location and bulk material. Overall three models; for the porosity, interstitial gas velocity and the layer fraction were developed as well as a modification to an existing Ergun inspired approach. When combined, the developed models enable prediction of the porosity, interstitial gas velocity and slug velocity profiles in time, as well as the layer fraction deposited at the rear of the slug; all with only a pressure drop/gradient input.

Research Doctorate - Doctor of Philosophy (PhD)

Rockfalls represent a serious hazard in surface mining that affects the safety of working personnel at the base of highwalls and in the vicinity of underground portal entries. The research presented in this thesis focuses on the numerical investigation of the dynamic response of granular and composite rockfall mi-ti-gation structures for the protection of underground portal entries. The study numerically investigates the energy absorption capacity of small scale waste rock piles (or muckpiles) and the application of an innovative damping module system as an alternative mitigation measure. The first part of the research focuses on the dynamic response of a muckpile upon rockfall impact. A simplified discrete element model of a muckpile is developed. The influence on the rebound characteristics of the contact parameters and different mixtures of spheres and elongated rigid aggregates composed of two spheres is investigated. The study highlights that a realistic representation of the granular material using clumps is essential to capture the correct rebound behaviour. These findings are then used for the development of a more detailed model which is used to perform a parametric study on the muckpile geometry and the impact conditions. The study allows presenting critical observations for the design of the portal structure and the exclusion zones around a portal. The second aim of this research is the numerical investigation of the potential application of damping modules as an alternative cost-effective solution to muckpiles for the protection of underground portals against rockfall. A damping module system consists of cylindrical modules made of a wire mesh, steel rings, an optional boundary rope and a geotextile lining filled with granular material. Starting with an accurate numerical representation of each component of the damping module, a novel discrete element formulation for the modelling of deformable structures is presented. In particular, a new deformable triangular element, a so-called PFacet, is developed and implemented into the open-source framework YADE. The model is extremely versatile and its application to the accurate modelling of deformable structures and geotextiles is shown. Then, the model is extended to simulate damping modules by incorporating a stochastically distorted wire model into the PFacet formulation. The dynamic response of the damping module is validated using experimental results and the capabilities of the model are investigated by considering various design and impact configurations. Starting from the initial numerical investigation of the energy absorption capacity of rockfall mitigation measures currently used in surface mining for the protection of underground portal structures, the study articulates a general numerical approach to the modelling of more complex composite structures such as damping modules. By combining experimental observations from the scientific literature, detailed numerical investigations and innovative…

Research Doctorate - Doctor of Philosophy (PhD)

Since the era of industrialization, the handling of materials in bulk form has become a necessary process for a range of industries throughout the world. Bulk handling and storage facilities should be designed and operated to obtain both maximum reliability and efficiency as well as encourage economy. A better understanding of the stress field and arching behavior and an accurate assessment of the bin wall pressure are essential steps to achieving reliable design of the storage bins or the feeder system. To date, the determination of the critical mass-flow hopper opening dimensions to prevent blockages due to the formation of stable, cohesive arches has been based on the radial stress field generated in the lower region of the hopper. The surcharge loads on the hopper have not been taken into account. Non-linear effects caused by the hopper surcharge loads in mass-flow analysis need to be addressed. In this study, a large number of experiments were conducted to investigate the influence of the surcharge pressure and the filling level on the hopper wall pressure during arching. The failure mechanism of the arches is discussed by means of studying the arch profile in the mass-flow hopper. In this study, to ensure efficient feeding, the hopper and feeder geometry are designed as an integral unit. The stress field at the hopper/feeder interface is of particular interest due to the role that it plays in estimating the feeder loads. In reality, the two-dimensional stress field assumed in the mass-flow hopper is influenced by the shear force due to the feeder operation. The combination of the active stress field and the passive stress field in the mass-flow hopper is suggested. This study also attempts to provide an accurate estimation of the feeder loads by investigating the feeder loads given by a combination of two methods. Apart from the comparisons between the experimental and theoretical results, numerical simulations using the discrete element method were carried out additionally to assist in the investigation of the hopper wall pressures and feeder loads. The influences of the various parameters on the hopper wall pressure, such as filling heights and outlet dimensions, are presented in this thesis. For the feeder system, the effects of the clearance between the hopper and feeder, the belt speed and other areas are also studied.

Research Doctorate - Doctor of Philosophy (PhD)

This thesis describes the development and experimental verification of a three dimensional finite element analysis model that can be used to predict the indentation rolling resistance performance of steel cord conveyor belt.

Research Doctorate - Doctor of Philosophy (PhD)

Dynamic Compaction (DC) is conducted by dropping heavy weights on the ground surface. It has the advantage of providing rapid improvement of the geotechnical properties of soil at relatively large depths; hence, it can reduce the overall time of the soil improvement process dramatically. Furthermore, this method does not usually need any off-site disposal of excess materials. Despite the wide use of DC as an economically attractive ground improvement technique and the abundance of experimental data for dynamic compaction, few detailed predictive methods for DC are available. There is a demand for a reliable theory to predict and explain the complicated nature of DC. As previous numerical simulations were mostly unable to accurately study the problem of dynamic compaction on unsaturated soils, the primary aim of the provided thesis is presenting and implementing a general finite element framework to investigate the response of partially saturated soils subjected to dynamic compaction. This would enhance the understanding of this mechanism together with providing a useful tool for studying the determinative parameters of this problem. Partially saturated soils are characterised by the simultaneous deformation of a porous soil, and its pore water and pore air and usually exhibit more complex behaviour than some other porous materials, as they often experience non-linear plastic (irrecoverable) deformation. This makes their computational modelling less straightforward than for some other coupled problems. In recent decades numerical modelling the response of partially saturated soils to external loadings within the so-called mixture theory has received increasing attention. In such analyses the mixture-theory (with or without some simplifying assumptions, e.g., considering an iso-thermal environment and immiscibility of fluid phases) has formed the basis for analysing thermo-hydro-mechanical and even chemical coupling in partially saturated soils. A challenge in modelling unsaturated soil as a three-phase material arises in solving the global equations of motion, where the presence of different phases, together with the existence of inertia forces in each phase, makes the solution of the coupled dynamic system computationally demanding. The selection of a consistent constitutive model within the theory of mixtures, that can incorporate suction forces into the description of stress, provides a further complication. The necessity of such incorporation has frequently been reported in experimental studies of unsaturated soils. Moreover, in cases of large deformations analyses, the infinitesimal strain theory should be replaced by an algorithm which can explain the occurrence of large deformations in the numerical framework. These require the adoption of a unique strategy for integration of the constitutive model for an unsaturated soil. This thesis will address the aforementioned challenges. The generalised-𝛼 method is introduced and implemented for solving the global…