A mathematically consistent algorithm for simulating interfacial turbulent flows is devised in this work. To minimize numerical errors for imposing dynamic boundary conditions at the interface locations, piezometric pressure is used to limit the effect of gravity forces in a flow field. Consequently, suitable and consistent numerical schemes are designed to accurately implement the new forms of interfacial forces. The proposed numerical methods are challenged for low Froude number flows which tend to trouble conventional algorithms. To capture the effect of turbulence on the interface, standard large eddy simulation techniques are reviewed and discussed. It is shown the standard filtered flow equations encounter numerical and mathematical inconsistencies. To remedy the irregularities of the conventional methods, a new framework for large eddy simulations is grounded. Purely mathematical models are derived and correlated with the conventionally more physical models. Semi implicit SIMPLE method is used to discretize the final flow equations. Taking advantage of the implicit feature of SIMPLE algorithm, an error correction technique is devised by which numerical cost of a turbulent simulation is substantially reduced. The entire framework is finally discussed toward simulating a turbulent interfacial flow.

A mathematically consistent algorithm for simulating interfacial turbulent flows is devised in this work. To minimize numerical errors for imposing dynamic boundary conditions at the interface locations, piezometric pressure is used to limit the effect of gravity forces in a flow field. Consequently, suitable and consistent numerical schemes are designed to accurately implement the new forms of interfacial forces. The proposed numerical methods are challenged for low Froude number flows which tend to trouble conventional algorithms. To capture the effect of turbulence on the interface, standard large eddy simulation techniques are reviewed and discussed. It is shown the standard filtered flow equations encounter numerical and mathematical inconsistencies. To remedy the irregularities of the conventional methods, a new framework for large eddy simulations is grounded. Purely mathematical models are derived and correlated with the conventionally more physical models. Semi implicit SIMPLE method is used to discretize the final flow equations. Taking advantage of the implicit feature of SIMPLE algorithm, an error correction technique is devised by which numerical cost of a turbulent simulation is substantially reduced. The entire framework is finally discussed toward simulating a turbulent interfacial flow.

Multiphase pumping with twin-screw pumps is a relatively new technology that has been proven successful in a variety of field applications. By using these pumps to add energy to the combined gas and liquid wellstream with minimal separation, operators have been able to reduce capital costs while increasing overall production. In many cases, such as subsea operations, multiphase pumping is the only viable option to make remote wells economic. Despite their many advantages, some problems have been encountered when operating under conditions with high gas volume fractions (GVF). Twin-screw multiphase pumps experience a severe decrease in efficiency when operating under wet-gas conditions, GVF over 95%. Field operations have revealed severe vibration and thermal issues which can lead to damage of the pump internals, requiring expensive maintenance. The research presented in this thesis seeks to investigate two novel methods of improving the performance of twin-screw pumps under wet-gas conditions. The first involves increasing the viscosity of the liquid stream. We propose that by increasing the viscosity of the liquid phase, the pump throughput can be increased. Tests were conducted at high GVF using guar gel to increase the viscosity of the liquid phase. Along with results from a multiphase pump model the pump behavior under wet-gas conditions with increased liquid viscosity was evaluated. The experimental results indicate that at high GVF, viscosity is not a dominant parameter for determining pump performance. Possible reasons for this behavior were proposed. These results were not predicted by current pump models. Therefore, several suggestions for improving the model’s predictive performance were suggested. The second method is the direct injection of liquid into the pump casing. By selectively injecting liquid into specific pump chambers, it is believed that many of the vibration issues can be eliminated with the added benefit of additional pressure boosting capacity. Since this method requires extensive mechanical modifications to an existing pump, it was studied only analytically. Calculations were carried out that show that through-casing liquid injection is feasible. More favorable pressure profiles and increased boosting ability were demonstrated.

The use of twin-screw pumps for moving fluids is not new technology but its application to wet gas compression (high gas volume fraction [GVF]) is still considered relatively new. There are many advantages for using twin-screw pumps for oil field applications; three of the immediate improvements include reducing hardware costs, reducing well bore pressure, and producing a pressure boost to move the product to a central collection facility. While there are many advantages to using twin-screw pumps in wet gas applications, there are some problems that have been encountered while operating at high GVFs. When operating at high GVF, over 95 percent twin-screw pumps experience a severe loss of efficiency and an increase of operating temperature. A common way to increase the efficiency while operating in the high GVF range includes adding a liquid recirculation system where a portion of liquid is stored downstream of the pump and is injected into the pump inlet. These systems lower the effective GVF of the multiphase fluid below 95 percent in order to increase the pump efficiency. The first objective is to characterize the performance of a twin-screw pump fitted with a liquid recirculation system while operating under high GVF conditions. The second objective is to investigate the transient heat rise associated with high GVF operation. While traditional twin-screw pumps can be fitted with a liquid recirculation system to allow them to operate under high GVF conditions the pumps themselves are not optimized for wet gas compression and still suffer performance penalties. The results of this investigation show that the liquid recirculation system can allow the pump to operate under high GVF but the heat added to the system reduces the systems efficiency. Without a method of removing the heat generated in the pumping process the pump will not run at its optimal efficiency. The following investigation provides recommendations for further research in area of multiphase pumping using twin-screw pumps based on the characterization and transient studies provided in this thesis.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 144-155). Available also in a digital version from Dissertation Abstracts.

Polymer nanocomposites with organoclay fillers offer improved performance and opportunities for commercial applications. The key to significant property enhancement is to exfoliate the individual organoclay platelets into the polymer matrix to utilize their high aspect ratio and modulus. The affinity between the polymer matrix and the organoclay is one of the most important factors for determining the exfoliation level. To a certain extent, the affinity can be enhanced by optimizing the organoclay structure for a given polymer matrix. Numerous studies have demonstrated that nanocomposites provide significant enhancements in stiffness and strength, flame retardancy, gas barrier properties, thermal stability and ionic conductivity. However, most polymer nanocomposites have decreased toughness relative to that of the matrix polymer. One exception to this general rule was found for nanocomposites based on poly(ethylene-co-methacrylic acid) ionomer prepared by melt compounding. My initial work investigated this system using an instrumented impact test. The data were analyzed using the essential work of fracture (EWF) methodology. Transmission electron microscopy (TEM) revealed that the clay platelets were well exfoliated in this matrix. It has also been observed that addition of organoclays to polymer blends can greatly reduce the size of the dispersed phase in some cases. It was thought that this feature might be useful for controlling rubber particle size, and, therefore, the toughness of polyamide/elastomer blends. Initially, I investigated the effect of the organoclay structure on the extent of exfoliation and properties of the nanocomposites. Nanocomposites based on the organoclays with one alkyl tail and hydroxyl ethyl groups gave well-exfoliated structures and high matrix reinforcement while nanocomposites from two-tailed organoclay contain a considerable concentration of intercalated stacks. Nanocomposites from the organoclays with one alkyl tail showed slightly better exfoliation and matrix reinforcement than those from the organoclays with hydroxyl ethyl groups. Based on this research result, the toughening response of amorphous polyamide nanocomposites using two types of elastomers, EOR and EOR-g-MA, four types of organoclays, M3(HT)1, M2(HT)2, M1H1(HT)2 and (HE)2M1T1, and two mixing protocols, has been investigated. Glass fibers (diameter ~ 12 m) are frequently used to reinforce polyamides. However, there is a practical limit to the amount of fiber that can be added while maintaining processability. Another possible use of organoclays is as an additional filler that acts on the nanoscale to complement the micro-scale reinforcement of the glass fibers. The possible synergies of simultaneous reinforcement at these very different length scales were explored and the composite moduli were compared to theoretical predictions using aspect ratios determined from TEM images. / text

Multiphase flow in porous media is a wide-ranging phenomenon, covering such topics as the motion of immiscible fluids, where the interaction with the medium is by exchange of heat and/or mass between phases, to fluid-solid phase flow accompanied by clogging and leaching. The present study is limited to the flow of immiscible fluids (oil and surfactant), where fine solids (clay) migration occurs during the motion. It is divided into two parts: (a) experimental and (b) theoretical. / The experimental investigations have been performed in order to evaluate: (a) the factors (e.g., porosity, temperature and injection pressure) that affect the injected surfactant flow rate through oil/soil mixtures, (b) the role of clay mineral concentration on the uptake and displacement of oil by the injected surfactant, (c) the portion of the oil displaced by the injected surfactant in the medium, under the testing conditions, (d) the effect of injection head on the rate of oil uptake during the injection process. / The theoretical analysis leads to a new diffusion model which accounts for the simultaneous movement of oil, fines and surfactant. The conclusion to be drawn from this part is that the new simplified model, together with further refinement, lead to a better understanding of the behaviour and prediction of the multiphase flow through a porous medium.

Multi-phase flows can be found in a range of processes in vanous industries. Ironrnaking blast furnace is one of the typical examples. With high pulverized coal injection rates, complete combustion within the raceway of blast furnace becomes difficult, giving rise to a large amount of powder flow together with gases into the furnace. Thus, the performance of a modern blast furnace with high PCI strongly depends on the characteristics of a multiphase system which involves gas, powder, and liquid superimposed on the motion of solid particles. For this multiphase flow system, the solid (coke, sinter/pellets, etc) movement and liquids (hot metal and slag) and powders (unbumt coal and coke ash) accumulation in the lower region of the furnace are believed to play an important role. This thesis presents an experimental study focus on quantifying the hydrodynamics of gas-powder and gas-powder-liquid flows through packed beds with special reference to blast furnace. The effects of process variables including fluid flowrate and some material properties on powder hold-up, pressure gradient and phase interaction are examined. An experimental study of the hydrodynamics of gas-powder flow in packed beds has been carried out. Glass powder and spherical/non-spherical particles are used to simulate pulverized coal and coke particle respectively. It is found that solid motion, powder flowrate and particle spericity affect powder hold-up and pressure gradient significantly. New correlations are proposed for static and dynamic powder hold-ups to account for these effects based on experimental results. A hydrodynamic model is proposed for gas-powder flow in packed beds with spherical and non-spherical particles. Incorporation these correlations and porosity function into the existed Fanning and Ergun equations, the pressure gradients in fixed and moving beds can be reasonably estimated. The gas-powder-liquid flow through the moving beds is studied. The effects of fluid variables and some material properties on total powder hold-up and pressure gradients have been examined experimentally within the so-called operational regime. The normal and non-wetting treated glass beads, glass powder and water or mixture of water and glycerin are used to simulate coke, pulverized coal and hot metal/slag in a blast furnace. The results indicates that steady-state gas-powder-liquid flow in moving packed beds can be achieved under certain flow conditions since particle motion gives main contribution while it provides a higher bed porosity, enhances powder and liquid flow and removes the accumulation of the powder. The fluid variables and liquid viscosity significantly affect the total powder hold-up and hence pressure gradient but the wettability does not. Based on the experimental results, new correlations for powder hold-up and pressure gradient are proposed for blast furnace modelling in terms of dimensionless number of flowrates for different phases. Incorporation of these correlations and the existed empirical correlations of phase interactions, a hydrodynamic model is proposed to quantify the interaction force between liquid and powder. The results show that this force plays an important role for stable gas-powder-liquid flow in moving beds though it is ignored by most of the previous researchers.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Diss., 2004 / Title from document title page. Includes bibliographical references. Available in PDF format via the World Wide Web.