The aim of this research project is to provide the academic and industrial community with a numerical tool that can be used for describing extreme flow cavitation scenarios and the atomisation process of these multiphase jets in a low-pressure environment. The research lies in the intersection of Numerical Analysis, Applied Physics and programming. From the physical point of view, the project has two different strands: The first is developing a methodology for channel flows due to a rapid pressure drop which is possible to result into various flow regimes inside the channel. The second step is to track the liquid fragmentation of the liquid jet downstream the channel exit and describing the atomisation process to liquid ligaments and blobs to droplets. Using a fully Eulerian approach, this research aims towards a holistic approach that addresses some of the major challenges that govern superheated jets atomisation. The finite volumes method in a compressible framework is used utilising various models for modelling the underpinning physics of flashing jets. Flashing occurs either if a liquid follows an isothermal depressurisation or isobaric heating. In both cases, the fluid fails to adjust to the local changes in pressure and temperature admitting a metastable state which makes the process more challenging to understand. The Homogeneous-Relaxation-Model (HRM) is used for modelling the heat transfer under sudden depressurisation conditions accounting for the non-equilibrium vapour generation. A new pressure equation is proposed which employs the continuity equation indirectly. The pressure responds to compressibility and density changes due to the rapid phase change and includes the surface tension contribution in the pressure-velocity coupling algorithm. The coupling of the continuity and momentum equation with the HRM and the interface tracking method is thoroughly described. The result of this coupling is a conserved numerical method that is capable of characterising the flow regimes and the impact of bubble nucleation on the mass flow rate. The present study presents a numerical approach for simulating the atomisation of flashing liquids accounting for the distinct stages, from primary atomisation to secondary break-up to small droplets Following the Eulerian-Lagrangian-Spray-Atomisation approach, the concept of the surface density Σ is introduced into the methodology for the spray dynamics. The proposed approach has the advantage of avoiding the unrealistic common assumption of pure liquid at the nozzle exit. It models the change in the regime inside the nozzle treating flashing in a unified approach simulating the metastable jet both inside and outside the nozzle. Important mechanisms such as thermal non-equilibrium, aerodynamic break-up, droplet collisions and evaporation are modelled in a novel atomisation model. The modified Σ- equation employed a new source term proposed for cryogenic jets. A wide range of numerical tests is presented for validation and obtaining insights for the underlying physics. Short and long nozzle geometries are tested for both low and high-pressure releases for flashing water, R134A, liquid nitrogen and LNG. Results for turbulent flows for both sub-cooled and superheated liquids are presented showing that the proposed approach can accurately simulate the primary atomisation.

<p> Unstable failure in underground mining occurs when a volume of material is loaded beyond its strength and displaces suddenly. It is recognized on various scales, from small rock bursts to the collapse of pillars or entire sections of a mine. The energy that is released during smaller scale events is manifested through the ejection of material, which can pose a hazard to the safety of miners. Larger scale events generate seismic waves as mine workings are damaged and may entrap miners or terminate production. </p><p> This dissertation focuses on the analysis of unstable failure in an underground room and pillar mining environment. The potential for violent pillar failure is assessed using numerical modeling techniques and a parametric approach to loading conditions and material strength properties. The magnitude of instability is quantified by calculating the release of kinetic energy that occurs as failure progresses in each simulation. </p><p> Fundamental mechanisms associated with the release of kinetic energy are analyzed in a series of finite difference models, and the results are compared with analytical solutions to illustrate the applicability of the energy calculations to increasingly complex modes of failure. Back analyses are performed on two room and pillar mine collapse events from the western United States by constructing large-scale models and reproducing widespread failure. The values of energy released in two-dimensional models are extrapolated by assuming a depth of failure in the third direction, and the total energy values are compared to the documented seismic magnitudes from each collapse through empirical equations. With further development of this numerical modeling approach, energy consideration may be used to study the potential for instability in a wide variety of mining excavations and identify the associated range of hazards.</p>

Vermiculite is a clay mineral that is generally used for a wide range of applications such as in agricultural, horticultural and construction industries. This is due to its various properties which include high porosity, lightweight, thermo-insulating, non-toxic and good absorption capacity when exfoliated. The objective of this research was to critically evaluate the fundamental interaction of electromagnetic waves with vermiculite from different source locations and to understand the mechanism of exfoliation in an applied microwave field. When vermiculite minerals are placed under the influence of high electric fields, they expand due to the rapid heating of their interlayer water, which subsequently builds up pressure that pushes apart the silicate structure. The degree of exfoliation is directly related to the intensity of the applied electric field. The principal areas covered in this thesis include: a detailed review of the fundamentals of microwave processing and issues surrounding scale up; a critical literature review of vermiculite mineralogy, and previous methods of vermiculite processing and their limitations; understanding the interaction of microwave energy with vermiculite by carrying out mineralogical and dielectric characterisation; microwave exfoliation tests of vermiculite minerals from different source locations and a comparative energy and life cycle analysis of microwave and conventional exfoliation of vermiculite. A detailed review of the literature revealed that conventional exfoliation of vermiculite by gas or oil fuelled furnaces has significant limitations such as emissions of greenhouse gases, high-energy requirements (greater than 1 GJ/t), health and safety issues and poor process control. All work reported so far on microwave exfoliation of vermiculite has been limited to laboratory scale using domestic microwave ovens (2.45 GHz, power below 1200 W) and the route to scale up the process to industrial capacity has not given due consideration. Mineralogical characterisation of vermiculite from different geographical locations (Australia, Brazil, China and South Africa) revealed that only the sample from Brazil is a pure form of vermiculite while the other samples are predominantly hydrobiotite. All the samples have varying degrees of hydration with the Brazilian sample having the highest total water content. The presence of water in any form in a material influences its dielectric response and ultimately the microwave absorbing properties. The dielectric characterisation carried out on the different vermiculite samples shows that the vermiculite mineral structure is effectively transparent to microwave energy, but it is possible to selectively heat microwave absorber, which is the interlayer water in the vermiculite structure. The continuous microwave exfoliation tests carried out at both pilot scale at 53-126 kg/h and the scaled up system at 300-860 kg/h demonstrated that microwave energy can be used for the industrial exfoliation of vermiculite at high throughputs and is able to produce products below the specified product bulk densities standard required by The Vermiculite Association (TVA). The degree of vermiculite exfoliation depends on factors such as power density, feedstock throughput, energy input, interlayer water content, particle size of the feedstock, and vermiculite mineralogy. The highest degree of exfoliation was recorded for the Brazilian sample, which also had the highest water content. Life cycle analysis (LCA) frameworks by the International Organisation for Standardisation (The ISO 14040: principles and framework and ISO 14044: Requirements and guidelines) and British standards institution (PAS2050) were used to carry out comparative life cycle analysis of vermiculite exfoliation using microwave heating and conventional (industrial and Torbed) heating systems. The results showed that the microwave system potentially can give an energy saving of about 80 % and 75 % over industrial and Torbed Exfoliators respectively, and a carbon footprint saving potential of about 66 % and 65 %. It can be concluded that the reduced dust emission and noise from the microwave system would improve the working conditions, health and safety. Furthermore, the methodology discussed in this project can be used to understand the fundamental of microwave interaction with perlite and expanded clay, which are minerals with similar physical and chemical compositions as vermiculite.

Single crystal Ni-based superalloys are used in the highest temperature components in jet turbine engines owing to their excellent properties under creep conditions. These alloys owe their properties greatly to their chemical composition, and in particular the addition of slow diffusing elements like Re delays the creep deformation significantly. Vacancy diffusion has been suggested to be the rate-controlling process for creep deformation at high temperatures, and elements like Re are expected to interact with the vacancies in slowing them down. This has been investigated in the present work using ab initio calculations. Specifically, dilute as well as non-dilute binary alloys of Re, W and Ta in Ni were considered to study the effect of chemical composition on the rate of vacancy diffusion. Analytical formulations were used to describe the diffusion equations, however their applicability was restricted to the dilute regime. For the calculation of diffusion coefficients particularly in the non-dilute regime, kinetic Monte Carlo simulations were performed. The energies and the diffusion barriers were described using the cluster expansion method. Results suggested appreciable modifications of the vacancy diffusion coefficients, suggesting that the beneficial role of slow-diffusing elements in Ni-based superalloys could be partly explained by their effect on vacancy diffusion.

Chemical composition of structural steels with a ferrite-pearlite microstructure has been developing towards decreasing carbon content, to increase weldability, with increased microalloying element content, to provide grain refinement, solid solution and precipitation strengthening. During the UOE forming of large diameter (more than 400 mm) welded pipes the strength drop from plate to pipe, as a result of reverse deformation (the Bauschinger effect), depends on steel grade, namely microalloying element content, and processing. In this project the microstructure of two Nb- and V-microalloyed steels has been studied with optical, scanning and transmission electron microscopy. The dislocation density and (Ti,Nb,V,Cu)-rich particle diameter, volume fraction and number density were measured for as-rolled and annealed (30 min. at 400 \(^0\)C and 550 \(^0\)C) steels. The Bauschinger effect was measured during compression-tension testing for the same steel conditions. The yield stress drop during reverse deformation has been found to increase with an increase in forward pre-strain, dislocation density and particle number density within the effective particle diameter range of 12-50 nm. On the basis of dislocation-particle interaction analysis, a quantitative model of work-hardening behaviour dependence on particle number density and dislocation density has been derived for the reverse deformation of studied steel grades.

The main focus of the current study was to design, construct and evaluate a common platform to enable the integration of multiple sensing systems for cure monitoring. An Abbe refractometer was selected to house a custom-made cell which accommodated the following optical sensors: (i) Fresnel reflection sensor; (ii) near-infrared transmission sensor; (iii) evanescent wave sensor; and (iv) fibre Bragg grating sensor. The cell was designed such that it was also possible to simultaneously acquire conventional refractive index data during the cross-linking process. Thus, the cross-correlation of data on refractive index, cross-linking kinetics, strain and temperature was facilitated. It was found that the trends observed in the qualitative (intensity-based refractive index monitoring via the Fresnel reflection sensor) and quantitative (optical fibre-based transmission FTIR spectroscopy) approaches were similar during the cure of common thermosetting resin systems. Furthermore, for the first time, S-2 glass® fibres were used to obtain evanescent wave spectra during cross-linking, and excellent correlation was observed with the transmission FTIR spectral data. Fibre Bragg grating sensors were used to infer the magnitude of the residual fabrication strain. Excellent correlation was observed between the refractive index data generated using the Abbe refractometer and Fresnel reflection sensor.

A literature survey on the whole field of pore formation is assembled into the form of a general theory of the causes of porosity in castings. The conventionally accepted modes of feeding are assessed: liquid-, mass-, and interdendritic- feeding; and two further mechanisms are proposed: burst- and solid-feeding. The latter is investigated theoretically using various flow models: elastic-plastic, viscous, creep and Bingham flow. A new theory is proposed for the origin of layer porosity in castings. Experimental work on a wide variety of alloys: Al-Cu, Fe-C, Complex Ni- and Co-base alloys, cast both in air and in vacuum are investigated for the effect of section thickness, taper, and mould and metal temperatures. The formation of porosity appears to change from a non-nucleation to a nucleation mechanism as section thickness increases. A new method of interpreting radiographs based upon a longitudinal line count reveals that solid feeding becomes important in reducing porosity at high mould temperatures. Experiments on the effect of composition of an alloy on porosity cast doubt on the widely accepted theory that the presence of non-equilibrium eutectic liquid reduces porosity, but indicate that the non-equilibrium freezing range of the alloy may be the critical parameter. The effect of pressure on porosity is investigated utilising pressures below atmospheric; the results are inadequately explained by current theories and are discussed in terms of the nucleation and growth of pores; the effect would also appear to have considerable industrial potential for reducing porosity in vacuum cast components.

Aluminium and their alloys readily react with air to form surface oxides and films. If they become entrained in a casting, they form double oxide film defects that reduce the mechanical properties of the component. It is important to determine the nature and behaviour of the films formed, so that defects can be avoided or their internal gas volumes reduced. The reaction of common additions and impurities that may be present in aluminium alloys were melted at 750 °C in air and nitrogen, to determine thickness, composition and structure of possible films that may form in a defect. The effects of molybdenum were also investigated. It has also been suggested that oxides formed on aluminium alloys may act as heterogeneous nucleation points for solidification. Spinel containing copper layers were manufactured by electro-codeposition, and added to commercial purity aluminium to test its potential as a grain refiner. It was compared with non-refined aluminium and aluminium refined with standard Tibor refiner. The lattice parameters of oxides formed were also compared with that of aluminium to ascertain their potential as nucleation centres. The results are discussed in this work.

Pitting corrosion of iron has been studied via artificial pits. Solid corrosion products were observed within the pit, which was characterised as disordered-carbon and Fe\(_3\)C, acted as diffusion barriers for metal ions and slightly increased the solution resistance. Its formation depends upon the interfacial potential. High purity iron was used to calculate an effective diffusion coefficient for metal ions (a combination of self-diffusion and electrical migration) in different MgCl\(_2\) concentrations. The contribution of self-diffusion increases with increasing MgCl\(_2\) concentration if Mg\(^2\)\(^+\) depletion in the pit is considered. The Tafel kinetics of iron dissolution in metal ion saturated solutions was studied in different MgCl\(_2\) concentrations. The Tafel slope (56 to 70 mV/decade) was independent of MgCl\(_2\) and FeCl\(_2\) concentration when FeCl\(_2\) is saturated. The effect of nitrate on the composition/structure of salt layers was characterised. The salt layer is composed of FeCl\(_2\).4H\(_2\)O in chloride-based solutions (isotropic in HCl and anisotropic in HCl with trace nitrate), and Fe(NO\(_3\))\(_2\).6H\(_2\)O in nitrate-based solutions. The dissolution behaviour of iron in chloride/nitrate solutions was studied. Dissolution is uniform under a salt layer, but crevice formation and surface roughening. Potentiodynamic measurements can induce abrupt dissolution/ passivation transitions, resulting in deep and localised attack.

An investigation into the optimisation of magnetic properties of two types of magnetic alloys based on Sm(Co,Cu,Fe,Zr)_z (z = 7.4) and Nd₁₅Fe₇₇B₈ has been carried out. The optimum heat treatment which gave the best magnetic properties for the Sm(Co,Cu,Fe,Zr)_z alloy depended primarily on the sintering and solid solution temperatures. After quenching the alloy from the solid solution temperature, and then ageing isothermally, it was found that the intrinsic coercivity, microhardness and electrical resistance changed with ageing time, and the ageing temperature also affected the rate of these changes. The magnetic properties of specimens produced from the Nd-Fe-B type alloy were also shown to be affected by different heat treatments. The microhardness, microstructure and intrinsic coercivity were affected by an isothermal ageing treatment and the temperature of the treatment. Two routes were used for powder preparation 1n the production of the sintered specimens: i. Mechanical ball milling of crushed ingot material. ii. Hydrogenation followed by ball milling. It was found that higher energy products were achieved in the ball milled material for the two alloys investigated. Two reasons for this were proposed: i. The hydrogenated and ball milled powder had a larger size than the ball milled only powder. ii. The surfaces of the hydrogenated powder were highly reactive in air and some oxidation of the surfaces occurred. Optical and electron microscope studies showed that the variations in the ageing behaviour of both the alloys was concurrent with subtle differences in the microstructure between the samples aged at different isothermal ageing temperatures.