A technique has been developed that allows the gasification reaction rates of representative samples of carbon-carbon composite materials to be examined. The technique involves heating the sample in a controlled and monitored environment; the product gases of the reaction are then analysed by a mass spectrometer, allowing their identification and quantification. The technique was used to characterise the oxidation reactions of cathode carbons. These materials are composites and so the oxidation reactions of their constituent raw materials were also examined. Surface area was determined for each sample, allowing specific rates of reaction to be determined, normalising surface area effects. The anodes, cathodes and sidewalls of aluminium smelting cells are made of composite carbon materials comprising filler materials (such as coke, anthracite and graphite) and a binder (almost exclusively coal tar pitch). Whilst the oxidation of anode carbons has received extensive study the oxidation reactions of cathodes have been neglected largely because they have not been a cause of smelting cell failure. However, with the longer lives now being achieved from smelting cells the long term degradation reactions, such as oxidation, will have to be considered. Oxidation of cathodes in the area of the collector bar will increase resistance and affect the heat balance of the cell. Gasification reactions of carbon materials are frequently characterised using techniques such as thermal gravimetric analysis (TGA). These techniques are accurate for examining such reactions when the sample is of small size and a single carbon type. To characterise composite carbons correlations have been made between the overall oxidation resistance (determined by weight loss) and the ignition temperature of one of the constituent materials (determined by TGA). The results obtained using the new technique of product gas analysis (PGA) revealed an exponential dependence of oxidation rate on temperature for the carbons examined. At higher rates the limiting condition appeared to be mass transfer through the pores of the sample. Arrhenius plots of reaction rates allowed the activation energy of oxidation to be determined for each material. When the rate was controlled by the chemical reactivity of the material the activation energies determined agreed well with values obtained from the literature. The two graphites examined had activation energies of 164 and 183 kJ.mol-1, Ea of graphite has been measured in the range 175-281 kJ.mol-1, the latter figure being for a highly pure graphite. For the two anthracites Ea was ll3 and 118 kJ.mol-1, literature values have it between 100 and l5l kJ.mol-1. The pitches, used as binders of cathode carbons, had Ea equal to 112 and 123 kJ.mol-1, values from the literature range from 121-165 kJ.mol-1. Activation energies were determined for the cathode materials, and were clearly influenced by the reactivity of the constituent materials. An amorphous cathode carbon, having nominally 30% graphite, had an activation energy of 121 kJ.mol-1. A semigraphitic cathode material comprising 100% graphite in a pitch binder had an activation energy of 123 kJ.mol-1. The similarity of these values to those for Ea of the pitch and anthracite indicates that the binder phase is having a strong influence on cathode reactivity. These values of Ea accord well with values determined for similar samples, reported in the literature ranging from 114 to 138 kJ.mol-1. A semigraphitised cathode material had an activation energy of 176 kJ.mol-1 in the same range as that of graphite. This sample oxidised significantly less rapidly at all temperatures. The variation in reactivity of the constituent materials of cathode carbons accounts for the highly selective oxidation behaviour observed in these materials. Porosity development is rapid as binder matrix is preferentially oxidised, leading to an acceleration of oxidation rate with increasing burnoff. The rate begins to decelerate once all the binder matrix has been oxidised, the residue being less reactive than the starting material. The structure of the materials was quantified using X-ray diffraction (XRD). A peak ratio method was employed, comparing the intensify of the 4oz peaks of cathode carbons and a standard electrographite. Once effects of cathode porosity had been normalised an excellent correlation between increasing peak intensity ratio and increasing oxidation resistance was found.

Whole document restricted, see Access Instructions file below for details of how to access the print copy. / Correct coagulant dosage is necessary for the efficient operation of conventional drinking water treatment plants, yet no accurate or automated way of determining this exists. Streaming current (SC) is a measurement of charge on particles in water and is useful in feedback control of coagulant dosage. Analysis of the movement of change within a SC sensor can provide some explanation of its slow response, while signal processing utilising Fourier analysis improves the instrument's bandwidth. Presently inaccurate manual jar tests are the only way determine the SC required for best coagulation. An online automated jar tester is presented to improve on this. It uses an automatic sampling system that takes a sample from the process stream. An optimisation algorithm makes repeated step adjustments to the SC set point and gradually moves it in the direction of improving jar test results. The system was evaluated on both a small-scale model and a full-scale plant. Noise in the test measurements means the optimal set point cannot be located accurately enough, but the results indicate that this is possible. Greater accuracy would allow optimisation of turbidity and costs for multiple chemicals. A representative neural network model can be made of the dynamic relationship between coagulant dosage and streaming current in a scale model, with an alkali dosed to simulate a disturbance. In a rapid mixer, the measured response is significantly slower than the true response. Several common types of linear controller are designed and their performance at set point tracking and disturbance rejection is compared on this system. Model predictive control with a Kalman filter performs best in these tests, while the self-tuning regulator has benefits when the rate of set point change is slower. A non-linear feed-forward radial basis function network that adapts to the system's steady-state inverse can effectively augment a linear controller for this system. Adaptation rules based on vector eligibility are derived from dynamic back-propagation and extended to the general dynamic non-linear case. This can result in a useful and efficient feed-forward neural controller for dosing systems that can be represented by a Wiener model.

Methodologies of implementing nonlinear constitutive models of soil in FLAC are studied in order to reduce numerical distortion, which has been found to occur in nonlinear dynamic analysis when a nonlinear soil model is implemented using an ‘apparent modulus’ approach. Analyses undertaken using several simple nonlinear soil models indicate that use of ‘plastic correction’ approach can eliminate or minimize the problem. This approach is therefore adopted in the thesis to implement in FLAC a bounding surface bubble soil model, i.e. the Bubble model. Satisfactory performance of the Bubble model has been obtained in dynamic analysis without using any of the additional mechanical damping given in FLAC. An analytical study on the Bubble model is carried out with FLAC. On the basis of the study, the hardening function is modified to better incorporate size ratio effects of the yield surface and is explored to eliminate abrupt transition in stiffness from elastic region to yielding. Pore water pressure is formulated with the assumption that the pore water pressure is generated as a response to the constant volume constraint which prevents the tendency for volume change when plastic volumetric strain takes place. The formulation is added to the Bubble model so that pore water pressure can be generated automatically by the model for fully saturated and undrained soil. FLAC analyses indicate that the Bubble model is generally in good agreement with published experimental data. The parameters and initial conditions associated with the Bubble model are studied with FLAC analyses in triaxial stress space to investigate their influence on the model and to investigate their effective ranges. Both large and small strain behaviors of the model are explored in the parametric study. Finally, the Bubble model is applied in the modeling of vertical vibration of rigid strip foundations. The influence of soil nonlinearity on vertical compliance of rigid foundations is investigated. Some major factors are considered, which include initial stress level in soil, level of excitation and mass ratio of foundation.

In this thesis, the forward problem of electrocardiography is investigated from a cellular level through to potentials on the surface of the torso. This integrated modelling framework is based on three spatial scales. At the smallest spatial resolution, several cardiac cellular models are implemented that are used to represent the underlying cellular electrophysiology. A bidomain framework is used to couple multiple individual cells together and this provides a mathematical model of the myocardial tissue. The cardiac geometry is described using finite elements with high order cubic Hermite basis function interpolation. An anatomically based description of the fibrous laminar cardiac microstructure is then defined relative to the geometric mesh. Within the local element space of the cardiac finite elements, a fine collocation mesh is created on which the bidomain equations are solved. Each collocation point represents a continuum cell and contains a cellular model to describe the local active processes. This bidomain implementation works in multiple coordinate systems and over deforming domains, in addition to having the ability to spatially vary any parameter throughout the myocardium. On the largest spatial scale the passive torso regions surrounding the myocardium are modelled using a generalised Laplace equation to describe the potential field and current flows. The torso regions are discretised using either finite elements or boundary elements depending on the electrical properties of each region. The cardiac region is coupled to the surrounding torso through several methods. A traditional dipole source approach is implemented that creates equivalent cardiac sources through the summation of cellular dipoles. These dipoles are then placed within a homogeneous cardiac region and the resulting potential field is calculated throughout the torso. Two new coupling techniques are developed that provide a more direct path from cellular activation to body surface potentials. One approach assembles all of the equations from the passive torso regions and the equations from the extracellular bidomain region into a single matrix system. Coupling conditions based on the continuity of potential and current flow across the myocardial surfaces are used to couple the regions and therefore solving the matrix system yields a solution that is continuous across all of the solution points within the torso. The second approach breaks the large system into smaller subproblems and the continuity conditions are iii iv imposed through an iterative approach. Across each of the myocardial surfaces, a fixed point iteration is set up with the goal of converging towards zero potential and current flow differences between adjacent regions. All of the numerical methods used within the integrated modelling framework are rigorously tested individually before extensive tests are performed on the coupling techniques. Large scale simulations are run to test the dipole source approach against the new coupling techniques. Several sets of simulations are run to investigate the effects of using different ionic current models, using different bidomain model simplifications, and the role that the torso inhomogeneities play in generating body surface potentials. The main question to be answered by this study is whether or not the traditional approach of combining a monodomain heart with an equivalent cardiac source in a two step approach is adequate when generating body surface potentials. Comparisons between the fully coupled framework developed here and several dipole based approaches demonstrate that the resulting sets of signals have different magnitudes and different waveform shapes on both the torso and epicardial surface, clearly illustrating the inadequacy of the equivalent cardiac source models. It has been found that altering the modelling assumptions on each spatial scale produces noticeable effects. At the smallest scale, the use of different cell models leads to significantly different body surface potential traces. At the next scale the monodomain approach is unable to accurately reproduce the results from a full bidomain framework, and at the largest level the inclusion of different torso inhomogeneities has a large effect on the magnitude of the torso and epicardial potentials. Adding a pair of lungs to the torso model changes the epicardial potentials by an average of 16% which is consistent with the experimental range of between 8 and 20%. This provides evidence that only a complex, coupled, biophysically based model will be able to properly reproduce clinical ECGs.

An experimental and theoretical investigation of heat transfer to liquid mixtures has been performed using binary and ternary mixtures of acetone, isopropanol and water. Two data-bases were established which contain measurements of the heat transfer coefficient under saturated pool boiling and subcooled flow boiling conditions. A third database comprises measurements of heat transfer and pressure drop in a plate heat exchanger. The performance of two heat transfer enhancement techniques, namely the coating of the heat transfer surface with teflon and a perforated brass foil, was studied under saturated pool boiling conditions. A model was developed, which can be used to predict the heat transfer coefficient. The model is based on the additive superposition of convective and boiling heat transfer coefficients. It is applicable for heat transfer to mixtures and single component fluids under saturated and subcooled boiling conditions. The empirical parameters in the correlations used in the model were not altered to fit the measurements of this study. The predictions of the model were compared to the experimental data, which covers the convective heat transfer regime, the transition region and the fully developed nucleate boiling regime. It was found that the best agreement between predicted an measured values was achieved, if the linear mixing law was used to calculate the ideal heat transfer coefficient rather than the correlations by Stephan-Preußer or Stephan-Abdelsalam. The heat transfer coefficient under saturated pool boiling conditions could be predicted with an accuracy of 12.6 %. A comparison between over 2000 measured heat transfer coefficients under subcooled flow boiling conditions in an annulus and the predictions of the model showed good agreement with a mean error of 10.3 %. The accuracy of the model was found to be independent of the fluid velocity and composition, as well as of the magnitude and mechanism of heat transfer. The heat flux in a plate heat exchanger could be predicted with a mean error of 6.9 % for a wide range of fluid velocities, subcoolings and compositions. The heat transfer coefficient on the test liquid side of the exchanger could be predicted with a mean error of 10 %. The heat transfer model was used for a theoretical study of the heat transfer to mixtures boiling on a finned surface. It was found that the fin geometry and thermal conductivity have a distinct influence on the local and mean heat transfer coefficients. The results indicate that the application of fins is more effective for boiling of mixtures than for boiling of single component liquids.

This thesis describes research undertaken as an initial step in the development of a nationwide land mobile coverage area prediction model for New Zealand. The most suitable approach is shown to be a computer-based method which includes corrections for both environmental and terrain features. Extensive field trials performed in Auckland at 76 and 465MHz to develop a propagation data base are described. Measurements have been made in a variety of environments over unobstructed, obstructed and mixed land-sea paths. An analysis of these measurements indicates that, subject to the availability of suitable topographic and environmental data bases and with the exception of two special cases, a plane earth based prediction method is suitable for incorporation in a nationwide land mobile coverage area prediction model for New Zealand. Recommendations are made for the implementation and further development of this model.

A new method for the synthesis of broadband impedance transformers having predictable passband frequency response is presented. The technique is based on the use of non-commensurate (i.e. unequal element length) transmission line networks. Through the use of approximations and computer optimization studies non-commensurate circuits are shown to be advantageous in distributed circuit design. The new method derives a non-commensurate circuit from a conventional commensurate prototype in such a way that the transmission matrix of pairs of elements in both circuits is made equal at one frequency. The transformation used ensures that the frequency response of the derived circuit closely matches that of the prototype circuit. Limitations on section characteristic impedances imposed either by constructional constraints or other practical realizability considerations are more easily met using the new design technique than when using conventional commensurate networks alone, Moreover, wide harmonically related passbands are largely avoided. The method finds greatest application where there are circuit length (or size) restrictions which must be met. Where such restrictions do not apply, conventional commensurate techniques are usually sufficiently flexible. The non-commensurate technique can however still provide benefits of even greater flexibility or better stop-band attenuation. The method presented is only an approximate equivalence and so an analysis of the technique is presented. The analysis establishes the degree of approximation. The use and application of the non-commensurate design technique are supported by an experimental investigation.

Thermal plasma technology is potentially useful for a range of materials processing applications, such as the synthesis of sub-micron, ultra-pure ceramic powders. Thermal plasma reactors are characterised by short residence times (between 10 and 100 ms). Consequently, for chemical reactions to proceed to completion, reactants must be in the gas phase. Reaction rates of solids and liquids are too slow to proceed to any great degree in a thermal plasma, and unvaporised particles can contaminate product material. However, many useful reagents for plasma synthesis are available in particulate form, and thus particles must be completely vaporised if they are to be effective. In this thesis, vaporisation of particles in thermal plasmas was investigated both numerically and experimentally. A numerical model of particle vaporisation in a thermal plasma was developed, which considers the effects of particle vapour on thermodynamic and transport properties of the plasma. This was compared with a simpler model which neglects vapour contamination effects on the plasma. Results showed that the simpler model greatly over-estimated vaporisation times of copper, aluminium, and tungsten particles in argon plasmas at temperatures less than 11000 K, but reasonable accuracy was obtained at higher temperatures. It was found that heat and mass fluxes, and vaporisation time could be expressed in a reduced form which is independent of initial particle diameter. Heat and mass fluxes during vaporisation were found to be linear functions of the inverse of particle radius. Gas-vapour property data are generally difficult to obtain, and guidelines are recommended for using pure argon properties to estimate vaporisation time. The two major types of thermal plasma are the DC (direct current) arc, and the RF (radio-frequency), or induction, plasma. The RF plasma has several advantages over other techniques for the synthesis of powders. Reactions occur in primarily in the gas phase, resulting in good mixing between reactants. Rapid quenching of the tail flame can be used to promote homogeneous nucleation and fine particle size. There is no source of external contamination, because the RF plasma torch lacks electrodes, and a wide variety of reactants can be used, including corrosive and oxidising reagents. The plasma has a relatively low velocity and large diameter, and axial feeding of particles results in better vaporisation of particulate reagents than other thermal plasma torches. In the experimental programme, two RF plasma torches were designed and constructed using the same 13.5 MHz, 15 kW power supply. Fluidised bed feeders and a vibratory feeder were constructed to feed low flow rates (less than 0.2 g/min) of powders, and other apparatus were designed for collecting product particles and quenching the plasma tail flame. The final torch design was used to study heat transfer to particles of a range of materials and particle sizes in the plasma. The materials studied covered a range of boiling points and heats of vaporisation, so that the effects of these properties could be investigated. Particles of alumina, titanium carbide and magnesium oxide smaller than 38 μm diameter were found to vaporise completely. Condensation of vapour produced particles approximately 100 nm diameter which were probably agglomerates of smaller particles formed by homogeneous nucleation. Inspection of morphologies of unvaporised particles showed that the treatment of particles in the plasma is not always uniform, as particles follow a wide range of trajectories and experience various temperature histories. From a semi-empirical analysis of partial vaporization of a range of particle sizes it was estimated that the mean residence time of particles was 18 ms and the mean plasma temperature was 9400 K A heat transfer coefficient of 8000 W/m2K was estimated for partially vaporising particles, which was similar to heat transfer coefficients obtained by numerical modelling. These three parameters may be used to predict the degree of vaporization of particles in an RF plasma torch. Thermodynamic analyses of plasma synthesis of titanium carbide and nitride were performed, indicating the feasibility of the synthesis of these materials in thermal plasma reactors and possible reactant combinations which may be used.

Whole document restricted, see Access Instructions file below for details of how to access the print copy. / Although pinched sluice concentrators have been used for the concentration of heavy minerals for many centuries, their mechanisms involved have not been fully understood. Previous studies on the performance of pinched sluices have been of a purely empirical nature. In the present analysis, an attempt has been made to explain the behaviour of a pinched sluice in terms of the established theories of fluid mechanics and minerals processing. In spite of the inherently complex nature of two phase flow, a method has been developed to calculate the underflow discharge by assuming a logarithmic velocity distribution and free gravity fall through the discharge slot. The concentration profile of solids over the depth of flow has been shown to comply with Bagnold's theory of dispersive shear, rather than turbulent sediment transfer. Even although the results can be explained qualitatively by the Bagnold's theory, their complete quantitative analysis will not be possible until more work is done. Consequently, an empirical equation has been developed to predict underflow pulp densities. The segregation process of the heavier mineral beneath the lighter has been shown to obey a first order law, as was originally proposed by Mayer in relation to jigging. In the light of the results obtained, a computer model of the pinched sluice has been developed. This predicts the underflow grade, pulp density and flow rate in terms of the feed and operating conditions. The model can also be used to determine the effect of a change in operating conditions, and for the optimisation of rougher, cleaner and scavenger circuits.

Reducing oil content, minimizing any carcinogenic acrylamide in the high temperature frying process for potato crisps, and producing good products with considerable crispiness and acceptable color were the objectives of this research. Vacuum frying with pre-treatment of potato crisps was investigated as an effective process for oil content reduction. Pre-drying and subsequent dipping (PSSD) in a sugar solution (‘sugar dipping’) were considered as an advantageous procedure for the treatment of potato crisps before frying in order to reduce oil uptake during frying. Vacuum frying was observed as an excellent process to decrease significantly the acrylamide formation at low temperature frying of potato crisps. In this study, potato crisps were respectively blanched, pre-dried, and dipped in a solution of sugar (23.07 wt %) for two seconds, before vacuum frying at 120oC, 110oC under different vacuum pressures (170mbars, 150mbars, 100mbars and 50mbars in separate experiments). Conventional frying at 180oC was also used as the control to benchmark the reductions in the oil contents and acrylamide formation among various techniques. There was a significant reduction in oil content of the potato crisps observed when the new techniques were applied. The crisps that had been pre-treated and fried with conventional frying have given the result of 30 wt % reduction. The crisps that were fried under vacuum frying achieved greater oil reduction with varying percentages when applying different pretreatments. The lowest oil content was achieved when the potato crisps were fried at 110oC and 150 mbars giving 58 % reduction on the dry basis compared with control samples. There are various advantages of the technique with PSSD as we have discovered: it is simple and can be applied in potato crisp industries in continuous mode in both vacuum and conventional frying systems. The crisps that had been treated with pre-drying and subsequent sugar solution dipping and then fried were crunchier and possibly had better perceived taste to the consumer, due to the small sugar addition. Pre-drying and vacuum frying have all turned out to be excellent techniques to reduce acrylamide formation in potato crisps as we have found in this study. Vacuum frying at 120oC and 150 mbars reduced acrylamide formation by 80 to 85%. The 95% reduction was obtained when the crisps had been pre-dried. Acrylamide was undetectable when crisps were pre-dried and vacuum fried at 110oC, 150 mbars. The crisps with pre-drying subsequent sugar dipping and vacuum fried at low temperature had improved color compared with the control samples, which were produced by conventional frying at high temperatures. / Note: Part 3 publication restricted due to copyright restrictions.