Polycarbonate polyurethane (PCPU) has been studied as a novel polymer impregnated with nanoparticles for improved mechanical, thermal and adhesion properties [4]. This study investigates the synthesis of polycarbonate polyurethane (PCPU) polymeric nanofiber membranes by the process of electrospinning. This study further examines all the parameters associated with electrospinning a novel PCPU polymeric solution impregnated with nanofillers, such as nanoparticles, to produce fiber membranes. Tetrahydrofuran (THF) and N, N dimethylformamide (DMF) are used as solvents to dissolve PCPU polymer. One percent (1%) of nanofillers like silver and silica nanoparticles are added to PCPU polymer solution to investigate the impact on polymer solution properties, which in turn affects the fiber formation. Process parameters are studied by evaluating the impact each parameter has on the fiber formation. PCPU polymer concentrations of three polymer solutions (PCPU, PCPU + 1% silver and PCPU + 1% silica) with the appropriate solvent mixture ratio are achieved to produce polymeric fiber membranes with minimal bead formation. Polymeric nanofiber membranes of PCPU, PCPU + 1% silver and PCPU + 1% silica are produced using THF/DMF: 70/30 (V/V) solvent mixture. The polymeric nanofiber membranes obtained are characterized by using a scanning electron microscopy, rotational viscometer, tensiometer, contact angle measurement device, fourier transform infrared spectroscopy (FTIR). A comparative life cycle assessment (LCA) is performed to evaluate environmental impacts associated with solvents in the process of producing PCPU polymeric nanofiber membranes. The LCA is completed to gauge the potential impacts PCPU nanofiber membranes may have when utilized for various applications. This study discusses the successful production and characterization of good quality (no beading) polymeric nanofiber membranes of PCPU and novel composites of PCPU + 1% silver and PCPU + 1% silica. This two dimensional production of impregnated PCPU in nanofiber form will give researchers the opportunity to capitalize on the large surface areas of PCPU nanofibers versus PCPU thin films.

Free energy techniques provide the basis for an analysis of aspects of the liquid-vapour interface undertaken in this study. The main focus of this work is an extensive theoretical investigation into properties of the surface tension, including curvature dependence and supersaturation effects, using Monte Carlo computer simulation techniques.

This thesis presents an axisymmetric numerical model to simulate interfacial flows near a sharp corner, where contact line pinning occurs. The method has been used to analyze drop imbibition into a capillary. To evaluate the performance of the numerical method, for a liquid drop initially placed partially within a capillary, a thermodynamic model has also been developed, to predict equilibrium states. The first part of this thesis presents an axisymmetric VoF algorithm to simulate interfacial flows near a sharp corner. (1) A new method to exactly calculate the normals and curvatures of any circle with a radius as small as the grid size is presented. This method is a hybrid least squares height function technique which fits a discretized osculating circle to a curve, from which interface normals and curvature can be evaluated. (2) A novel technique for applying the contact angle boundary condition has been devised, based on the definition of an osculating circle near a solid phase. (3) A new flux volume construction technique is presented, which can be applied to any split advection scheme. Unlike the traditional approach where the flux volumes are assumed rectangular, the new flux volumes can be either trapezoidal or triangular. The new technique improves the accuracy and consistency of the advection scheme. (4) Explicit PLIC reconstruction expressions for axisymmetric coordinates have been derived. (5) Finally, a numerical treatment of VoF for contact line motion near a sharp corner is presented, base on the idea of contact line pinning and an edge contact angle. The second part of the thesis is on the imbibition of a drop into an open capillary. A thermodynamic analysis based on minimization of an interfacial surface energy function is presented to predict equilibrium configurations of drops. Based on the drop size compared to the hole size, the equilibrium contact angle, and the geometry of the capillary, the drop can be totally imbibed by the capillary, or may not wet the capillary at all. The thesis concludes with application of the numerical scheme to the same problem, to examine the dynamics of wetting or dewetting of a capillary. All of the simulations yield results that correspond to the equilibrium states predicted by the thermodynamic analysis, but offer additional insight on contact line motion and interface deformation near the capillary edge.

The classical theory of linear elastic fracture mechanics for a quasi-static crack in an infinite linear elastic body has two significant mathematical inconsistencies: it predicts unbounded crack-tip stresses and an elliptical crack opening profile. A new theory of fracture developed by Sendova and Walton, based on extending continuum mechanics to the nanoscale, corrects these erroneous effects. The fundamental attribute of this theory is the use of a dividing surface to describe the material interface. The dividing surface is endowed with an excess property, namely surface tension, which accounts for atomistic effects in the interfacial region. When the surface tension is taken to be a constant, Sendova and Walton show that the theory reduces the crack-tip stress from a square root to a logarithmic singularity and yields a finite angle opening profile. In addition, they show that if the surface tension depends on curvature, the theory completely removes the stress singularity at the crack-tip, for all but countably many values of the two surface tension parameters, and yields a cusp-like opening profile. In this work, we develop a numerical model using the finite element method for the Sendova-Walton fracture theory applied to the classical Griffith crack problem in the case of constant surface tension. We show that the numerical model behaves as predicted by the theory, yielding a reduced crack-tip singularity and a finite opening angle for all nonzero values of the constant surface tension. We also lay the groundwork for the numerical implementation of the curvature-dependent model by constructing an algorithm to determine the appropriate threshold values for the surface tension parameters that guarantee bounded crack-tip stresses. These values can then be directly applied to the forthcoming numerical model.

This thesis presents an axisymmetric numerical model to simulate interfacial flows near a sharp corner, where contact line pinning occurs. The method has been used to analyze drop imbibition into a capillary. To evaluate the performance of the numerical method, for a liquid drop initially placed partially within a capillary, a thermodynamic model has also been developed, to predict equilibrium states. The first part of this thesis presents an axisymmetric VoF algorithm to simulate interfacial flows near a sharp corner. (1) A new method to exactly calculate the normals and curvatures of any circle with a radius as small as the grid size is presented. This method is a hybrid least squares height function technique which fits a discretized osculating circle to a curve, from which interface normals and curvature can be evaluated. (2) A novel technique for applying the contact angle boundary condition has been devised, based on the definition of an osculating circle near a solid phase. (3) A new flux volume construction technique is presented, which can be applied to any split advection scheme. Unlike the traditional approach where the flux volumes are assumed rectangular, the new flux volumes can be either trapezoidal or triangular. The new technique improves the accuracy and consistency of the advection scheme. (4) Explicit PLIC reconstruction expressions for axisymmetric coordinates have been derived. (5) Finally, a numerical treatment of VoF for contact line motion near a sharp corner is presented, base on the idea of contact line pinning and an edge contact angle. The second part of the thesis is on the imbibition of a drop into an open capillary. A thermodynamic analysis based on minimization of an interfacial surface energy function is presented to predict equilibrium configurations of drops. Based on the drop size compared to the hole size, the equilibrium contact angle, and the geometry of the capillary, the drop can be totally imbibed by the capillary, or may not wet the capillary at all. The thesis concludes with application of the numerical scheme to the same problem, to examine the dynamics of wetting or dewetting of a capillary. All of the simulations yield results that correspond to the equilibrium states predicted by the thermodynamic analysis, but offer additional insight on contact line motion and interface deformation near the capillary edge.

Thin liquid films driven by surface tension gradients are studied in diverse applications, including the spreading of a droplet and fluid flow in the lung. The nonlinear partial differential equations that govern thin films are difficult to solve analytically, and must be approached through numerical simulations. We describe the development of a numerical solver designed to solve a variety of thin film problems in two dimensions. Validation of the solver includes grid refinement studies and comparison to previous results for thin film problems. In addition, we apply the solver to a model of surfactant spreading and make comparisons with theoretical and experimental results.

The molten pool shape and thermocapillary convection during melting or welding of metals or alloys are self-consistently predicted from scale analysis. Determination of the molten pool shape and transport variables is crucial due to its close relationship with the strength and properties of the fusion zone. In this work, surface tension coefficient is considered to be negative, indicating an outward surface flow, whereas high Prandtl number represents a thinner thickness of the thermal boundary layer than that of momentum boundary layer. Since Marangoni number is usually very high, the domain of scaling is divided into the hot, intermediate and cold corner regions, boundary layers on the solid-liquid interface and ahead of the melting front. The results find that the width and depth of the pool, peak and secondary surface velocity, and maximum temperatures in the hot and cold corner regions can be explicitly and separately determined as functions of working variables or Marangoni, Prandtl, Peclet, Stefan, and beam power numbers. The scaled results agree with numerical data, different combinations among scaled equations, and available experimental data.

The study applies the phase-field method to simulate the behavior between bubble and liquid-solid front in the solidification. During the process, the two-phase flow module is used to match up with temperature and phase-field function to determine the percentage of- solid, liquid, and gas- in the domain. The governing equations for mass, momentum and energy contain coefficients which are related to percentage of phases.The result show that the surface tension and the temperature difference will influence the shape of bubble and the velocity of solidification.

Recent technoligical advancement demands new robust micro-components made out of engineering materials. The prevalent methods of manufacturing at micro-nano level are established mostly for silicon structures. Therefore, there is interest to develop technologies for micro-fabrication of non silicon materials. This research studies microend-milling of 316L stainless steel. Machine tool requirement, tool modeling, cutting fluid evaluation, and effect of cutting parameters are investigated. A machine tool with high rigidity, high spindle speed, and minimal runout is selected for successful micro-milling. Cumulative tool wear and tool life of these micro-tools are studied under various cutting conditions. Ideal abrasive wear is observed when applying mist cooling whereas inter-granular shearing is the major failure mode while flood cooling or dry cutting during micro-machining. Various experiments and computational studies suggest an optimal position of the mist nozzle with respect to a tool that provides maximum lubrication at the cutting edge. Mist droplets effectively penetrate the boundary layer of a rotating tool and wet the cutting edge and significantly improve the tool life.

Low-pressure, low-producing natural gas wells commonly encounter liquid loading during production. Because of the decline in the reservoir pressure and the flow capacity, wells can fall below terminal velocity. Identifying and predicting the onset of liquid loading allows the operators to plan and prepare for combating the liquid loading hence saving valuable reserves and downtime. The present industrial applications of artificial lift, wellhead pressure reduction by compressor installation at the wellheads and reduction in tubing size are costly and often intermittent. The thesis examines the above aspects to generate a workflow for identifying and predicting the liquid loading conclusively and also assessing the application of Auger Tool and foam combination towards achieving a cost effective and more efficient solution for liquid unloading. In chapters I-IV, I describe the process of using production surveillance software of Halliburton Digital Consulting Services, named DSS (Dynamic Surveillance Software), to create a workflow of identifying the liquid loaded wells based on well data on daily basis for field personnel and engineers. This workflow also decides the most cost effective solution to handle it. Moreover, it can perform decline analysis to predict the conditions of liquid loading. In chapters V-VIII of the thesis, I describe the effort of handling the problem of liquid loading in a cost effective manner by introduction of an inexpensive Auger Tool in the bottomhole assembly and using WhiteMax surfactant soapstick from J&J Solutions. Four different combinations of well completion and fluid were tested for performance in respect to liquid hold up, pressure loss in the tubing, unloading efficiency and critical flow requirement. The test facilities and instruments, along with the operational methods, are discussed in chapter VI. Except for the reduction of the operational envelope with the inclusion of Auger Tool, the performance improved with the insertion of Auger Tool. The best combination of Auger and foam system could be a result of flow modification by the Auger Tool caused by reduced pressure loss and increase in drag coefficient and also by reduced density and surface tension of foam.