Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ed. D.)--Northern Illinois University, 1997. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ed. D.)--Northern Illinois University, 1997. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 206-210). Available also in a digital version from Dissertation Abstracts.

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.

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.

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.

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.