Supported olefin polymerisation catalysts are used to produce more than 20 million tonnes of polyethylene a year. In this thesis, the application of non- equilibrium plasmas to Phillips, Ziegler-Natta, and metallocene catalysts is described. A Cr(acetate)/silica Phillips catalyst precursor was activated using either thermal, plasma, or combined activations. Oxygen plasma activation was found to completely oxidise the acetate ligands, but left a low chromium dispersion and high hydroxyl population on the support. This large hydroxyl population caused the resulting catalyst to display a low activity. Plasma dehydroxylation of the silica support was then studied with the aim of increasing the activity of the plasma activated catalyst. Non-isothermal CF4 plasma treatment of mesoporous silica decreased the total hydroxyl population to a level comparable to a 773 K thermal treatment. These optimum conditions were then applied to the catalyst precursor, which in combination with oxygen plasma activation, produced an active polymerisation catalyst. Also, it has been found that combined thermal and plasma activations produce catalysts of lower activity than when solely calcined, but the resulting polymers have a narrower molecular weight distribution. Next, it was shown that Zeigler-Natta catalyst supports can be prepared by ccl(_4) plasma chlorination of a dibutylmagnesium/silica precursor. This approach offers the benefits of fast reaction times and less chemical waste compared to conventional solution phase chlorination. Finally, the replacement of conventional inorganic supports by polymer analogues has been investigated. It has been shown that plasma fluorination can be used to passivate the internal pores of high surface area polystyrene beads, thereby providing an ideal inert high surface area medium for high activity metallocene catalysts. Overall, this work has demonstrated how non-equilibrium plasmas can be highly effective at chemically modifying porous media.

Isotope separation is an important field of scientific research. Many methods have been used to separate elements and isotopes. The two main processes used at present are diffusion and centrifuging. In the second category, rotating plasmas may be of importance due to the high rotational velocities which can be obtained. This thesis describes an experimental study of isotopic enrichment in a rotating neon plasma. Some of the theoretical considerations are also presented and a new theory of isotopic separation in rotating plasmas is formulated.

The main object of this thesis is to attempt to derive an adequate description of the origin and nature of thermal oscillations induced in fluids of low Prandtl number. Chapter One reviews the hydrodynamic stability of a fluid layer heated from below (results which are equally applicable to a fluid heated from the side) and surveys the current state of theory which is pertinent and linked to the Rayleigh-Benard convection. The next section examines the current state of crystal growth especially problems focusing attention on the induced thermal oscillations. Chapter Two commences with an introduction to the basic flow state. If we are going to consider the salient features of thermal oscillations in an annular configuration, a model should be developed and this is the main area of concentration in this chapter. However, certain approximations are introduced to reduce the complexity of the proposed model and still obtain meaningful results. Turning now to Chapter Three we examine the stability characteristics and transformation of the basic eighth order differential equation describing the fundamental flow pattern into non-dimensional form. The final section of the chapter is concentrated on allowing the converted basic equation of flow be truncated to the small Prandtl number limit. The final Chapter concentrates on the experimental apparatus: five different annular boats were employed with both mercury and gallium as the working fluid. The final section comprises the experimental results and the comparison between theory and experiment. The main conclusions are as follows:- The structural state is a pre-requisite for the existence of large amplitude temperature oscillations, to be initiated and sustained. Furthermore, this links both high and low Prandtl number fluids that together, for specific Rayleigh numbers, exhibit rolls, hexagons et sequ. The square rolls are certainly prominent for liquids whose cell length is greater than its depth. There is a critical temperature which must be exceeded before oscillations can commence. A comparison between the Lorentz model and the wave lengths in the structured state is good. Finally, an estimate of the velocities in a range of fluids is compared. The essential conclusion is that for high Prandtl numbers the magnitude of the t velocity, induced in the fluid by Rayleigh-Benard convection, is not large enough to provide a suitably large vertical shear. Likewise, the stabilizing effect of the vertical temperature gradient becomes too large for oscillations to occur.

No description available.

The subject of this thesis concerns the development of a non-contact instrument for measuring the flow of gaseous effluent from 1.ron and steelmaking vessels. This effluent is a high temperature, dust laden gas and existing techniques for its flow measurement are reviewed and shown to be inade qua te • Following a study of alternative techniques it is concluded that a time of flight measurement, obtained by the cross-correlation of signals observed by infra-red detectors, is the most propitious method. In Chapter 2 preliminary investigations are presented which established the feasibility of this technique for measuring both regional and mean velocities. The results demonstrated that to ensure the signals observed are a true representation of the flow noise, careful consideration must be given to the optical properties of the fume and the characteristics of the infra-red sensors employed. In Chapter 3 the optical properties of the exhaust fume and the characteristics of infra-red sensors are examined. This information is used in the design of the prototype transducer employed throughout the rest of the development work. Circuit diagrams for several signal conditioning units are also presented, together with a brief description of their function.The experimental results obtained are presented in Chapter 4. Correlation flows measured under production plant conditions are shown to be in close agreement with results obtained uS1ng other flow measurement techniques. These results gave the confidence to construct an experimental flame tube in order to explore further development under controlled conditions. Two experiments, conducted on the experimental flame tube are described. These were designed to determine: i) The effect of varying the transducer angular field of view along the direction of flow on the correlation bandwidth. ii) The transducer spacing which gives the best accuracy. The application and performance of the flowmeter on two production plant investigations is the subject of Chapter 5. The first of these investigations is concerned with the performance of the conditioning tower and dry electrostatic precipitator of an arc furnace extraction plant. The second study 1S concerned with establishing the design parameters for future arc furnace direct extraction systems. The final Chapter contains the conclusions of the work and summarises the way in which an infrared cross-correlation flow measurement system can be designed using the information in this thesis. In addition, areas in which the research and development might continue are suggested.

No description available.

Free energy is the criterion of stability and is essential for determining phase equilibrium properties, for example. However, calculation of free energies for complex systems, such as fluids by computer simulation, is extremely difficult. In this thesis, we show how the partition function of fluids can be calculated directly from simulations; this allows us to obtain the absolute Helmholtz free energy (F) via F- -k8TInQ. Our method radically simplifies the process of calculating absolute free energies of continuous systems. As the method has been developed in the past few months, we have not yet applied it to the study of phase equilibria. This task will be part of our future work. In the rest of the thesis, we have focused on the application of more established simulation techniques to the urgent problem of finding environmentally friendly refrigerant fluids. Methane and fluoromethanes are possible candidates. However, they are flammable. 1-1-1-2-tetrafluoroethane, on the other hand, has for a long time been used in domestic refrigeration and automobile air-conditioning systems. However, it will be banned in Europe from 2011, due to concerns about its global warming impact. Carbon dioxide has received much attention as a fluid that can be used in combination with other refrigerants to minimise flammability and toxicity, and has a very low global warming potential. Thus, it could be mixed with those refrigerants to form new environmentally friendly refrigerant mixtures. Unfortunately, little information on the thermophysical properties of these mixtures is available. We simulate the thermophysical properties of these important industrial refrigerants and their mixtures with carbon dioxide using both empirical and in-house firstprinciples potentials. Simulations also provide a microscopic-level understanding of the structure of liquids, which is not accessible via experiment. Our high-quality ab initio force fields have reproduced the thermophysical properties for carbon dioxide, methane, fluorinated methanes, and mixtures of carbon dioxide and methane and carbon dioxide and fluorinated methanes. Multi-body effects play a crucial role in determining the thermophysical properties of fluids and inclusion of a three-body effect substantially improves the prediction of the phase-coexistence properties. Our studies should be of relevance to a broad range of mixtures of fluoroalkanes and carbon dioxide. Our efforts in making the first-principle force fields for carbon dioxide and fluorinated methanes pave the way for larger fluorinated hydrocarbons to come in the future.

No description available.

This work describes the design and implementation of an algorithm for solving the compressible turbulent flow equations, in two-dimensional space, using two-equation turbulence models. The basic governing equations of the fluid flow are presented and the transport equations for the turbulence kinetic energy and dissipation energy are given for both the k-epsilon and the k-omega models. Some basic physical concepts of turbulence are explained and several different versions of both the k-epsilon and the k-omega models are considered. The principle of upwind discretisation is discussed and some physical and mathematical aspects of the Euler equations are presented. Roe's flux-difference splitting scheme and the ideas behind a MUSCL higher-order extension are introduced. A brief discussion is also included on the concept of limiting. The finite element formulation employed in solving the governing equations is presented and some numerical issues regarding boundary conditions, time integration and robustness are discussed. Several test cases are solved and the effects of the limiters, mesh resolution, shock-boundary layer and shock-shock interactions and turbulence models are studied. Finally, some conclusions are drawn and a few guidelines for future research are presented.

No description available.