Research Doctorate - Doctor of Philosophy (PhD)

The present thesis is concerned with geothermal energy and specifically focuses on engineered geothermal systems (EGS), which are among a portfolio of technology options for power generation from geothermal resources. In this cyclic approach (also known as hot-dry-rocks or enhanced geothermal systems), high pressure water (i.e. "geofluid") is first pumped down a borehole (known as injection well) into a bed of hot fractured rock and forced to travel through the bed, capturing the heat content of the rocks. The hot water is then extracted from a second borehole (known as production well) and sent into a binary power plant, where its thermal energy is converted to electricity. The cooled water exiting the power plant is then injected back into the ground to resume the cycle. The aim of this thesis is to advance the understanding of CO₂ based EGS power generation process and verify the merits of using CO₂ rather than water for heat extraction from fractured hot dry rocks. The work has been largely driven by the suitable thermodynamic and transport properties of supercritical CO₂ (scCO₂), which makes it a desirable candidate for harnessing geothermal energy from hot dry rocks, particularly in regions where water resources are scarce. However, only a limited number of studies were carried out in the past to assess the viability of the CO₂ based EGS concept. Most of these studies were theoretical examinations of the heat extraction and exergy analysis under a limited range of operational parameters. In addition, research work on the fluid-rock interactions relevant to CO₂ based EGS is also limited and needs further investigation. The present thesis addresses the above knowledge gaps through a combined experimental and theoretical study, resulting to an accurate description of the entire CO₂ based EGS power generation process encompassing the reservoir, wellbore and power plant cycle as well as the fluid-rock geochemical interaction. The specific objectives of the project underlying this thesis were: (1) model development and simulation of the entire CO₂ and H₂O based EGS and the associated power plant cycles, (2) optimisation studies and sensitivity analysis of operating and design parameters affecting CO₂ and H₂O based EGS performance, (3) performance comparison of CO₂ based EGS and H₂O based EGS under the same operating and reservoir conditions, (4) examination of the effect of reservoir parameters on both CO₂ and H₂O based EGS concepts through detailed 3D reservoir simulations, (5) design and fabrication of a fluid-rock interaction apparatus capable of simulating EGS conditions, and (6) experimental investigation of the fluid-rock interactions at reservoir conditions and its likely impact on the performance characteristics of CO₂ and H₂O based EGS. One dimensional (1D), 2D, and 3D models of integrated reservoir-wellbore-power plant cycle were developed to provide an overall description of fluid flow in fractured reservoir (channel flow) and in radial fluid flow in…

Research Doctorate - Doctor of Philosophy (PhD)

Predicting the behaviour of unsaturated soils, and in particular compacted high plasticity clays, is a pre-requisite for the safe and reliable functioning of civil infrastructure. However, the complex behaviour of high plasticity clayey soils subjected to changes in their hydraulic and stress states are not well understood in engineering design. This thesis-by-publication focuses on an experimental investigation of the volumetric and microstructural behaviour of compacted clays. The following significant contributions to an understanding of unsaturated soil behaviour have been made through the journal articles that comprise this thesis-by-publication: Identification of the microstructure properties that are common between compacted and reconstituted soils. ; Proposal of a new method for delineating micro and macro components of the void ratio. ; Identification of the water retention behaviours that are common between compacted and reconstituted soils. ; Proposal of a new approach to unsaturated soil testing using the axis-translation technique, where the degree of saturation is controlled directly.

Masters Research - Master of Philosophy (MPhil)

Fatigue life predictions associated with S–N curves have been largely based on empiricism due to the complexity involving multiple variables such as fatigue life, applied stress, number of loading cycles and stress ratio. A damage model proposed by Palmgren in1924 and popularised by Miner in 1945 may be one of the most important milestones in the history of fatigue damage research. However, its validity and the principle it adopts have been questioned, and many researchers have attempted to refine the model without much success. The ultimate objectives of the current work were to provide a validity framework theory for fatigue damage associated with the S–N curve and to derive a damage function capable of predicting fatigue life. The validity framework is designed as the fundamental basis to ensure the validity of a damage function in the development process. In the current work, a validity framework theory consisting of axioms, relative conditions for compatibility and boundary conditions is developed for fatigue damage on an S–N plane at a stress ratio of zero. The compatibility in fatigue damage was conceptualised. Manifestation points for accumulated damage were defined and conceptualised for boundary conditions by differentiating between damage accumulated before failure, and failure caused by damage. A selected equation for damage at failure as the reference damage was theoretically validated for further validation of damage on the S–N plane. Also, a damage function capable of predicting fatigue damage is proposed following the validation process. Comparisons between experimental results from two stress level sequence loading and theoretical fatigue life predictions were made and a close agreement between them was found. An evaluative review on conventional fatigue damage models is presented along with the benefits of the new compatibility concept and criteria developed here.

Research Doctorate - Doctor of Philosophy (PhD)

Multiagent systems are an increasingly popular approach to software engineering, offering a fundamentally different design technique for software development based around the creation and deployment of autonomous software components. One of the leading models for the development of agent-based software is the Belief-Desire-Intention (BDI) model. This model provides a method for developing software based around the concepts used in human reasoning. BDI provides not just a useful model for developing software agents, but promises a whole new paradigm for software development, occurring at a higher level of abstraction than traditional techniques. In order to effectively develop BDI systems, a software development process is required that takes advantage of the concepts and abstractions offered by the BDI model. This thesis presents the Newcastle University Multi-Agent Process (NUMAP), a modular development process for BDI multi-agent systems. The process is practical, usable, and intuitive, operating at a level of abstraction suited to BDI agent development, focusing on the use of concepts associated with human reasoning throughout the development lifecycle. A support tool for use with NUMAP is also presented, assisting developers as they progress through each phase of the process. This support tool offers code template generation for popular agent implementation platforms, and provides a novel dependency tracking mechanism. A new evaluation framework is presented for assessing the completeness of development processes for multiagent systems, and NUMAP is assessed in comparison with other leading design processes, showing advantages in terms of its coverage of agent modelling concepts, and in terms of its usage and practicality.

Research Doctorate - Doctor of Philosophy (PhD)

This thesis addresses issues associated with using ever-increasing amounts of information and knowledge more effectively, and taking advantage of knowledge generated through experience. With very fast expansion of the Internet has created several problems and challenges linked to the increasing amount of information in Web content. These challenges are related mainly to the difficulty of extracting potentially useful information and knowledge from Internet pages. Data mining is a tool that enables enterprises to learn from existing experience by providing them with useful and accurate trends about their customers’ behaviour, and assists organisations in predicting which products their customers may be interested in buying. Moreover, in the real world, it is common to face optimisation problems that have two or more objectives that must be optimised at the same time, that are typically explained in different units, and are in conflict with one another. The evolutionary algorithm can use experience that is derived from a former decision event to improve the evolutionary algorithm’s ability to find optimisation solutions rapidly and efficiently. A hybrid structure, the Smart Experience-based Knowledge Analysis System (SEKAS), is put forward in this thesis to address issues of knowledge management and use. SEKAS combines a set of experience knowledge structures (SOEKS) with multiple techniques to provide a comprehensive knowledge management approach capturing, discovering, reusing and storing knowledge for the users. The SEKAS integrates a novel Decisional DNA (DDNA) knowledge structure with the traditional web crawler technologies. DDNA, as a knowledge representation platform, can help deal with noisy and incomplete data, with learning from experience, and with making precise decisions and predictions in vague and fuzzy environments. This thesis outlines the investigation of the combination of DDNA and feature selection algorithms to guarantee the future performance for prediction. The proposed approaches are general and extensible in terms of both designing novel algorithms, and in the application to other domains. The SEKAS integrates the evolutionary algorithm, Non-dominated Sorting Genetic Algorithm II (NSGA-II) (Deb et al. 2002), using experience that is derived from a former decision event, to improve the evolutionary algorithm’s ability to find optimal solutions rapidly and efficiently. The SEKAS application to solve a travelling salesman's problem shows that this new proposed hybrid model can find optimal, or close to true, Pareto-optimal solutions in a fast and efficient way. Several conceptual elements for this thesis have been implemented in the testing prototype, and the experimental results that were obtained show that the SEKAS system has great potential for managing knowledge, as well as improving the response times for providing accurate solutions. Consequently, the SEKAS can provide a universal knowledge management platform for mass autonomous…

Research Doctorate - Doctor of Philosophy (PhD)

Flash flooding is considered as one of the most disastrous natural hazards, which has had significant impact on human, infrastructure and environment throughout history. By definition, flash flooding occurs within a very short time (usually few hours) of the beginning of rainfall, which results in a limited time frame to issue warnings or prepare for evacuation. Risk assessment can be done using a hydrological model. However, most models require catchment specific data and take considerable execution time. Modelling techniques and the understanding of flash flooding are getting improved with the availability of better quality data such as high resolution Digital Elevation Models (DEM). DEMs allow the automated characterization of the influence of geomorphology on the hydrologic response of catchments. They are particularly useful for small ungauged catchments where available hydrologic data (e.g. rainfall, runoff) are sparse and where site specific studies are rarely done unless some evidence of high risk is available. This research presents new relationships between catchment hydrologic response and instantaneous unit hydrograph (IUH), which led to derive risk indicators that can be used to identify flash flooding risk areas within catchments. New measures are related to the rate of rise of the hydrograph and the catchment response time. Standard terrain analysis methods (pit filling, flow direction, local slope, contributing area, flow velocity and travel time) were used to produce time-area diagram and subsequently IUH, which was calculated for every individual pixel in the catchment. When computing the IUHs, each pixel was considered as the outlet of its own catchment bounded by its contributing area. This allows presenting the hydrological response and risk areas at the finest scale possible for a DEM. To perform this analysis, a fully distributed hydrological model was developed using Python programming language. The model is quite computationally efficient and can be completely automated. The study area includes 37 major river basins covering a 1700km long by 50km wide coastal strip of Eastern Australia. The analysis was done using a high resolution (1 arc second) DEM. Two types of output maps were produced; 1) flash flood risk areas at catchment scale, 2) spatial distribution of hydrologic response within catchments (e.g. high and low responsive areas). Moreover, results were validated using the data of severe flash flooding that occurred around Toowoomba (at the northern end of the coastal strip studied) in January 2011.

Research Doctorate - Doctor of Philosophy (PhD)

In the near future, Uninhabited Aircraft Systems (UAS) will bring significant benefits to a rapidly growing number of operations beyond defence. When it comes to national security, UAS could be used for border patrol, policing, detecting trafficking and smuggling, rapid emergency response, search and rescue, bushfire and flooding monitoring, and early detection of threats to national assets that could be targeted by terrorism. In civilian applications, UAS have the potential to be used for airborne mineral explorations, crop-yield monitoring, traffic monitoring in transportation systems, digital mapping, inspection of power-grid lines, and data collection for environmental and climate research. Due to this potential, nations worldwide are seeking to develop further their UAS capabilities. Over the past ten years, research activities in industry and academia have been growing, and companies are designing and developing the next generation of UAS. A global market with a worth close to 50 billion $USD is projected within the next decade. There is, however, a fundamental challenge that needs to be addressed before we can realise the full potential of routine UAS operations. This challenge is the integration of UAS into the National Airspace System (NAS). This integration requires UAS to demonstrate levels of reliability and safety equivalent to current aviation standards. As the level of autonomy in UAS operations increases, UAS must be able to either continue operating in the presence of faults and anomalous conditions, or shut down safely, whilst not beaching a minimum level of safety - this characteristic is described as robust autonomy. Most of the recent research effort in UAS has been focused on improving robust autonomy as well as aircraft ability to conduct different missions. This thesis takes a different approach and focuses on how robust autonomy in UAS can be quantified so National Airworthiness Authorities (NAA) can certify UAS for operations in the NAS. A novel framework is proposed whereby characteristics related to missions, aircraft, and operational and weather conditions are used in a Bayesian probabilistic assessment of how the autonomy handles anomalous conditions. The end result is a set of predicted probabilities of satisfactory performance called Measures of Robust Autonomy. To demonstrate the proposed framework, a general reconnaissance mission of a UAS is considered and measures of robust autonomy in relation to actuator faults and autonomous decision-making about control re-configuration are computed. To achieve this, the design of a low-computational complexity autopilot with capability for actuator reconfiguration is considered. We propose a design for joint control allocation and motion control scheme whereby the actuator configuration is used to map actuator constraints into the space of the aircraft generalised forces. This allows one to constrain the output of the flight controller and consider an unconstrained allocation problem since the…

Research Doctorate - Doctor of Philosophy (PhD)

The Bayesian Total Error Analysis (BATEA) framework permits model calibration and prediction to be informed by estimates of data and model uncertainty, and allows assessment of the relative contribution of various sources of error to the total uncertainty within the conceptual hydrologic modelling system. However, full BATEA applications are presently limited to studies with relatively short record lengths. This is because batch calibration rapidly becomes computationally infeasible as the number of inferred input and/or model structural errors grows. This thesis presents the development of a recursive implementation of the BATEA framework based on particle filtering techniques. Particle filtering techniques, traditionally used in automatic control and signal processing, are a group of sequential Monte Carlo methods which can be adapted to provide a robust recursive implementation of the BATEA framework within the non-linear and non-Gaussian conditions presented by conceptual hydrologic models. The particle filter developed in this thesis is designed to preserve the constraints and relationships between time-invariant parameters and latents which exist in most conceptual hydrologic models. This is achieved in a fully recursive manner through careful selection of appropriate Importance Sampling proposals, design and selection of Markov Chain Monte Carlo (MCMC) proposals which permit efficient regeneration of time-invariant parameters and the construction of an approximation to the Metropolis-Hasting acceptance probability which avoids the need for batch evaluation. The resulting particle filter is capable of efficiently performing an approximate recursive BATEA analysis for a conceptual hydrological model subject to observation, structural and parameter uncertainty with the parameters of both the error model and the hydrological model requiring inference. The performance of the approximate BATEA analysis technique is demonstrated with synthetic case studies ranging from well-posed to highly ill-posed problems and is shown to produce practically useful results at a small fraction of the computational effort required in batch calibration.

Research Doctorate - Doctor of Philosophy (PhD)

The experimental results presented in this thesis were obtained by using hot-wire anemometry with single- and X-wire probes. The experiments were carried out at low to moderate Reynolds numbers (6 ≤ R_λ ≤ 100) in grid turbulence and turbulent boundary layers to investigate the effects of non-homogeneities on small scale turbulence. Four different flows were extensively investigated: the homogeneous and isotropic turbulence (HIT), the turbulent shearless mixing layer (TSLML), and the turbulent shear mixing layer (TSML), all three flows generated by the three different classical and two different composite grids. The fourth flow was a turbulent boundary layer over a rough wall. Classical grid turbulence measurements were made with the aim of ascertaining whether the decay of q² follows a power law. It was found that the conventional turbulence power law decay (q² ∼ xⁿ, with n is constant) does not describe the entire decay period (the initial to final period of decay, including the transition period). A family of the power law of the form xⁿⁱ, where nⁱ is a different constant over a restrained portion of decay is more appropriate. It was also found that the Kolmogorov scaling holds down to R_λ ≃ 25; below this value, it breaks down. The effects of R_λ on the energy distribution across the different scales of motion and the validity of the local isotropy, were investigated. It also was found that the assumption of self-preservation (SP) in the classical grid turbulence was not valid. The grid generated turbulent shearless mixing layer (TSLML) was investigated with the aim of studying the turbulence decay with non-homogeneous turbulence,and in particular whether or not SP could be satisfied. The SP analysis was carried out using the transport equation of the second-order velocity structure function or the scale-by-scale (SBS) energy budget equation. It was observed that the SBS energy budget on the centreline of the grid is similar to that found in the decaying HIT. Moreover, the measurements on the centreline showed that the complete SP was achieved at all scales of motion. This mean that the Taylor microscale Reynolds number (R_λ = u′λ/ν) is constant and decay power law exponent n is equal to - 1. A grid generated turbulent with a mean shear (TSML) was used to study the effect of a mean shear on the turbulence decay. The one-point statistics showed that the distribution of the mean velocity and the Reynolds stresses u^′2, v^′2, w^′2 and uv across the shear layer collapsed when x/M_L ≥ 50, suggesting SP is approximated for one-point statistics. The power law decay exponent n was about zero on the centreline of the grid, but differed from zero outside the shear layer region. The SBS energy budget equation was shown that the TSML flow did not conform to SP conditions (e.g., R_λ is not constant). For the turbulent boundary layer over a rough wall,…

Research Doctorate - Doctor of Philosophy (PhD)

Soil is one of the most important resources on planet Earth and soil properties heavily influence various processes in geomorphological, hydrological and climatic systems. Understanding the formation and the global distribution of soil is imperative in the quest for sustainable use of this resource. While spatial characterization of soil properties is important, understanding the evolution of soil properties on a dynamic landform is also crucial. Over the years, various statistical and mechanistic models have been formulated to understand both landform evolution and soil development. However throughout history, soil modelling and landform modelling have developed independent of each other with minimal consideration of the influence of one on the other. In order to fully appreciate the development and evolution of soil on a dynamic landform, coupling landform evolution and pedogenesis is necessary. This thesis tries to address this issue. This work describes the development of State Space Soil Production and Assessment Model (SSSPAM), a soilscape and landform evolution model that integrates soil profile dynamics and landform evolution. First a computationally efficient soil evolution model was formulated by extending the mARM3D modelling framework to explore the soil profile self-organization in space and time, and dynamic evolution. Then the landform evolution was integrated into SSSPAM by incorporating elevation changes incurred due to erosion and deposition. The complexities of physically based process equations were simplified by introducing state-space matrix methodology which allows efficient simulation of mechanistically linked landscape and pedogenesis processes in catena scale spatial extents. The modelling approach and the physics underpinning the modelled processes are described in detail. SSSPAM explicitly describes the particle size grading of the entire soil profile at different soil depths, tracks the sediment grading of the flow, and calculates the elevation difference caused by erosion and deposition at every point in the soilscape at each time step. This allows comprehensive analysis of soil landform interactions and soil self-organization. SSSPAM simulates fluvial erosion, armouring, physical weathering, and sediment deposition. The modular nature of SSSPAM framework allows integration of other pedogenesis processes in follow-on research projects. The pedogenesis module of SSSPAM was first used to explore, through a parametric study, the sensitivity of the area-slope-soil grading relationship first identified by <i>Cohen et al.</i> [2009]. The parametric study confirmed the generality of this area-slope-soil grading relationship and showed that the relationship was present throughout the soil profile. Using the same methodology the dynamics of soil profile evolution on a static hillslope with different depth dependent weathering functions was also studied. This study showed that although the soil surface properties may reach similar equilibrium with…

Research Doctorate - Doctor of Philosophy (PhD)

This research aims at developing a regional assimilation barotropic tidal model for the Great Barrier Reef (GBR) and Coral Sea, Australia. For this, all available satellite altimeter, coastal and marine datasets have been used to constrain the shallow water tidal equations in order to estimate tidal constants for 37 long-period, major and shallow water constituents. The resulting model is called University of Newcastle Great Barrier Reef (UoNGBR) model that has a spatial resolution of 2' x 2'. In this process the recent bathymetry model gbr100 with spatial resolution of 3.6" x 3.6" is used as the source of depth information for the assimilation model. In addition, in order to address the role of reefs in shaping tidal regime of the area, spatially variable drag coefficients are adopted from the GBR1 Hydrodynamic Model. According to GBR1 model, drag coefficient varies from 0.0025 to 0.0049 in the GBR and Coral Sea. The modelling procedure is split into three main phases: (1) assessment of the performance of existing tidal models, (2) development of an empirical tidal model, and (3) tidal assimilation procedure. According to the assessment results, all existing tidal models show large uncertainties in the central and southern GBR, where complex bathymetry and coral reefs exist. Therefore, an assimilation approach is selected to develop the tidal model, with consideration of the effect of bathymetry and sea bottom complexities. The Oregon state university Tidal Inversion Software (OTIS) is chosen for this purpose. The OTIS has an efficient algorithm and can handle all different input data including information from sea current meters. To provide OTIS with the initial values needed in its forward solution, an empirical tidal model is developed based on Remove-Compute-Restore method for the GBR and Coral Sea. In order to create the empirical tidal model, tide gauge data is directly analysed using a harmonic analysis to extract tidal constants for 37 components, while the Remove-Compute-Restore method is used for satellite altimetry observations. The FES2014 model, which has implemented more tidal constituents in comparison to other existing models, is used as the background model. The calculated Sea Level Anomalies (SLAs) are analysed using a combination of the harmonic analysis and response method to estimate the tidal constant corrections. The estimated tidal constants are spread over a regular 2' x 2' grid using a depth dependent Least Squares Collocation (LSC) method. This empirical model is used in calculation of the forward solution in OTIS software. The estimated tidal constituents through analysing data from coastal tide gauges, altimetry (including only pure ocean tides) and current meters are used as the open boundary conditions, which are assimilated into the tidal shallow water equations using OTIS software. A sensitivity analysis is performed to investigate how bathymetry and drag coefficients affect the assimilation model. The results reveal that the use of…

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…