The hydrodynamic phenomena occurring inside the enclosed downcomer section of a plunging jet bubble column are described in the study. The gas entrainment rate for a plunging liquid jet was found to consist of two components, namely the gas trapped within the effective jet diameter at the point of impact, and the gas contained within the film between the jet and induction trumpet surface at the point of rupture. Entrainment within the effective jet diameter has been examined by McCarthy (1972). In this study, a model was supported by the experimental results, provided the film attained a region of constant thickness. When the induction trumpet was ruptured prior to a constant film thickness being reached, the measured rate of filmwise entrainment was higher than the prediction. Filmwise entrainment was found to be initiated once a critical velocity along the surface of the induction trumpet was reached. The critical velocity was a function only of the liquid physical properties and was independent of the jet conditions and downcomer diameter. The velocity of the free surface of the induction trumpet was obtained from the velocity profile for the recirculating eddy generated by the confined plunging liquid jet. The jet angle used to describe the expansion of the submerged jet inside the downcomer was predicted from the radial diffusion of jet momentum into the recirculation eddy. The model was able to predict the jet angle when it was assumed that the radial diffusion of jet momentum was a function of the Euler number based on the jet velocity and absolute pressure in the headspace at the top of the downcomer. The model was also developed to predict the maximum stable bubble diameter generated within the submerged jet volume, where the energy dissipation attributed to bubble breakup was given by the energy mixing loss derived for the throat section of a liquid-jet-gas-pump. Good agreement was found between the measured and predicted maximum bubble diameter values. The average experimental Sauter mean/maximum diameter ratio was found to be 0.61, which was similar to that for other bubble generation devices. It was found that for turbulent liquid conditions in the uniform two-phase flow region, a transition from bubble to churn-turbulent flow occurred at a gas void fraction of approximately 0.2 when the gas drift-flux was zero. Under laminar liquid flow, this transition took place at a gas void fraction above 0.3. For the bubbly flow regime the Distribution parameter Co used by Zuber and Findlay (1965) to describe the velocity and gas void fraction profile, was found to be a function of the liquid Reynolds number. For laminar liquid flow, values of Co greater than unity were obtained. As the liquid Reynolds number was increased it was found that Co decreased, until a constant value of unity was obtained for fully turbulent flow. For the churn-turbulent regime it was found that the gas void fraction measurements for all of the experimental runs could be collapsed onto a single curve when a modified gas void fraction was plotted against the gas-to-liquid volumetric flow ratio. The modified gas void fraction included a correction factor to account for the difference in the bubble slip velocity between the experimental runs. The experimental results also indicated that the value of the constant in the gas void fraction correction factor was different for laminar and turbulent flow. Prior to bubble coalescence, it was found that the experimental drift-flux curves could be predicted from the measured bubble diameter, using the separated flow model development by Ishii and Zuber (1979). After the onset of coalescence the drift flux measurements departed from the original drift-flux curves at a rate which increased linearly with increasing gas void fraction. It was found that the slope of the line fitted to the coalesced region of the drift-flux curves increased with increasing liquid Reynolds number and reached a constant value under fully turbulent flow conditions. The model developed, together with the implications of the experimental results, are discussed with regard to optimising the design of an industrial plunging jet bubble column. / PhD Doctorate

Extending the use of Doppler spectroscopy as an important plasma diagnostic -- by developing a multi-channel system capable of tomography -- is the foundation of this thesis. A system which can simultaneously measure the emissivity, temperature and flow velocity of plasma ions has been installed, calibrated and operated on the H-1NF heliac, yielding comprehensive and interesting results. The measurements are time-resolved, made from a large range of viewing positions and, using scalar tomographic inversion methods, can be unfolded to give two-dimensional images of ion emissivity and temperature. The flow velocity profiles, while not inverted, nevertheless lead to a greater understanding of the plasma behaviour.¶ Fifty-five lens-coupled optical fibres, mounted on a large rotatable stainless steel ring, encircle the plasma poloidally and transport light to a multi-channel Fourier-transform spectrometer. This `coherence-imaging' spectrometer employs an electro-optically modulated birefringent crystal plate to monitor the coherence of an isolated spectral line. Measurement of the intensity, fringe visibility and phase of the resulting interferogram leads to values for the emissivity, ion temperature and flow velocity. Using a multi-anode photomultiplier assembly, allows the time-resolved detection of all optical channels simultaneously.¶ The system has been fully calibrated, including a measurement of the spatial response of each line-of-sight. The calibration procedure accounts for the relative channel sensitivities, the response of the line filter and the removal of detector cross-talk. In situ light sources are installed provide routine and accurate relative intensity calibration of the system.¶ Methods of tomography provide the unfolding of the measured plasma parameters to construct two-dimensional images of ion temperature and emissivity. Methods of inversion include the iterative ART routine -- using projection data gathered with the light-collecting optics rotated to different viewing positions -- and linear composition of Fourier-Bessel basis functions -- with the data obtained from a single unrotated viewing position. ART reconstructions of the emissivity are performed without the need for a priori information while those of the ion temperature are computed using regularising functions to help stabilise the inversion.¶ This new system -- named ToMOSS for Tomographic Modulated Optical Solid-state Spectrometer -- enables a more detailed study of various plasma phenomena observed in H-1NF. Among other results, this thesis presents the first tomographic reconstructions of emissivity and temperature fluctuations associated with a large-scale coherent instability.

The self-similar evolution of a turbulent Rayleigh-Taylor (R-T) mix is investigated through experiments and numerical simulations. The experiments consisted of velocity and density measurements using thermocouples and Particle Image Velocimetry techniques. A novel experimental technique, termed PIV-S, to simultaneously measure both velocity and density fields was developed. These measurements provided data for turbulent correlations, power spectra, and energy balance analyses. The self-similarity of the flow is demonstrated through velocity profiles that collapse when normalized by an appropriate similarity variable and power spectra that evolve in a shape-preserving form. In the self-similar regime, vertical r.m.s. velocities dominate over the horizontal r.m.s. velocities with a ratio of 2:1. This anisotropy, also observed in the velocity spectra, extends to the Taylor scales. Buoyancy forcing does not alter the structure of the density spectra, which are seen to have an inertial range with a -5/3 slope. A scaling analysis was performed to explain this behavior. Centerline velocity fluctuations drive the growth of the flow, and can hence be used to deduce the growth constant. The question of universality of this flow was addressed through 3D numerical simulations with carefully designed initial conditions. With long wavelengths present in the initial conditions, the growth constant was found to depend logarithmically on the initial amplitudes. In the opposite limit, where long wavelengths are generated purely by the nonlinear interaction of shorter wavelengths, the growth constant assumed a universal lower bound value of

With the use of grand canonical molecular dynamics, we studied the slow ompression(0.01m/s) of very thin liquid films made of equimolar mixtures of short and long alkane chains (hexane and hexadecane), and branched and unbranched alkanes (phytane and hexadecane). Besides comparing how these mixtures behave under constant speed compression, we will compare their properties with the behavior and structure of the pure systems undergoing the same type of slow compression. To understand the arrangement of the molecules inside the confinement, we present segmental and molecular density profiles, average length and orientation of the molecules inside well layered gaps. To observe the effects of the compression on the fluids, we present the number of confined molecules, the inlayer orientation, the solvation force and the inlayer diffusion coefficient, versus the thickness of the gap. We observe that pure hexadecane, although liquid at this temperature, starts presenting strong solid-like behavior when it is compressed to thicknesses under 3nm, while pure hexane and pure phytane continue to behave liquid-like except at 1.3nm when they show some weak solid-like features. When hexadecane is mixed with the short straight hexane, it remains liquid down to 2.8nm at which point this mixture behaves solid-like with an enhanced alignment of the long molecules not seen in its pure form; but when hexadecane is mixed with the branched phytane the system does not present the solid-like features seen when hexadecane is compressed pure.

Studies show that dynamical properties of ultra-thin polymer films deviate from those of bulk materials. Despite some controversial issues, there is growing evidence indicating that the interfacial properties play a key role for observed dynamical anomalies. However, how and how much the interfacial properties affect the average dynamics of the nanometer scale systems are still elusive. In this work, we developed several novel techniques to investigate near-free-surface dynamics of thin polymer films. We studied surface dynamics of glassy i-PMMA films using a nano surface hole relaxation technique: a strong substrate property dependence and an unexpected molecular weight dependence were observed; we found that a local Tg of ~40K below bulk Tg could be assigned to the surface region. We used nano gold particle embedding to study PS surface dynamics: enhanced surface dynamics and weak temperature dependence were observed for the surface region; a depth profile with the nm resolution was observed; viscous liquid-like and soft solid-like properties were observed in the first 5.5nm and next 3.3 nm regions in PS films; no molecualr weight dependence was found in glassy PS films. We built a low level noise measurement system to study the thermal polarization noise in PVAc films: cooperative rearranging dynamics were evidenced; the noise power spectral density (PSD) is found to fluctuate around a certain average level without discernable peak shift; we observed some relatively big jumps or fluctuations in successive integrated PSD’s, which indicate some energy exchange between different microscopic domains in glassy polymer systems. We developed a novel nano rheology AFM technique to study the near-free-surface dynamics of thin polymer films: enhanced near-free-surface dynamics with weak temperature dependence are observed for PVAc films, which is similar with the PS case.

Studies show that dynamical properties of ultra-thin polymer films deviate from those of bulk materials. Despite some controversial issues, there is growing evidence indicating that the interfacial properties play a key role for observed dynamical anomalies. However, how and how much the interfacial properties affect the average dynamics of the nanometer scale systems are still elusive. In this work, we developed several novel techniques to investigate near-free-surface dynamics of thin polymer films. We studied surface dynamics of glassy i-PMMA films using a nano surface hole relaxation technique: a strong substrate property dependence and an unexpected molecular weight dependence were observed; we found that a local Tg of ~40K below bulk Tg could be assigned to the surface region. We used nano gold particle embedding to study PS surface dynamics: enhanced surface dynamics and weak temperature dependence were observed for the surface region; a depth profile with the nm resolution was observed; viscous liquid-like and soft solid-like properties were observed in the first 5.5nm and next 3.3 nm regions in PS films; no molecualr weight dependence was found in glassy PS films. We built a low level noise measurement system to study the thermal polarization noise in PVAc films: cooperative rearranging dynamics were evidenced; the noise power spectral density (PSD) is found to fluctuate around a certain average level without discernable peak shift; we observed some relatively big jumps or fluctuations in successive integrated PSD’s, which indicate some energy exchange between different microscopic domains in glassy polymer systems. We developed a novel nano rheology AFM technique to study the near-free-surface dynamics of thin polymer films: enhanced near-free-surface dynamics with weak temperature dependence are observed for PVAc films, which is similar with the PS case.

Buckle arrestors are devices placed along an offshore pipeline for the purpose of arresting an incoming propagating buckle. Typically, buckle arrestors locally increase the pipe’s bending rigidity in the hoop direction. Spiral buckle arrestors are rods closely wound around the pipe for a number of turns and then welded at the ends to secure it in place. Spiral buckle arrestor have some key advantages to other designs in that they provide limited resistance to axial bending of the pipeline, and they can be wound on a continuous line away from free ends. This thesis uses a combination of experiments and modeling to study the effectiveness of spiral buckle arrestors. A series of experiments are conducted using 1.25-inch diameter SS-304 tubes with diameter-to-thickness ratios of 19 and 25. Stainless steel rods of four diameters are wound on tubes for a chosen number of turns and secured in place. A propagating buckle is subsequently initiated in the tube, engages the arrestor quasi-statically, is temporarily arrested, and eventually crosses the arrestor at a pressure defined as the crossover pressure. The crossover pressure was found to depend on the tube D/t and mechanical properties; and the rod diameter, number of turns, and mechanical properties. Finite element models are developed that enable the simulation of rod winding, buckle propagation, and buckle crossover. Local collapse is induced by external pressure and is propagated quasi-statically until it engages the arrestor. The pressure is increased until the buckle crosses the arrestor. The model is shown to reproduce the experimental observations and a large number of the measured crossover pressures with sufficient accuracy. Additional simulations were performed varying the rod diameter, numbers of turns, and tube D/t in order to enrich the database developed. This database was subsequently used to develop an empirical design formula for the arresting efficiency based on key nondimensional parameters of the problem. As was the case for the slip-on buckle arrestor, the arresting efficiency is bounded by the confined propagation pressure of the pipe. / text

This thesis numerically studied mass transfer during fully confined liquid jet impingement on a rotating target disk of finite thickness and radius. The study involved laminar flow with jet Reynolds numbers from 650 to 1500. The nozzle to plate distance ratio was in the range of 0.5 to 2.0, the Schmidt number ranged from 1720 to 2513, and rotational speed was up to 325 rpm. In addition, the jet impingement to a stationary disk was also simulated for the purpose of comparison. The electrochemical fluid used was an electrolyte containing 0.005moles per liter potassium ferricyanide (K3(Fe(CN6)), 0.02moles per liter ferrocyanide (FeCN6?4), and 0.5moles per liter potassium carbonate (K2CO3). The rate of mass transfer of this electrolyte was compared to Sodium Hydroxide (NaOH) and Hydrochloric acid (HCl) electrochemical solutions. The material of the rotating disk was made of 99.98% nickel and 0.02% of chromium, cobalt and aluminum. The rate of mass transfer was also examined for different geometrical shapes of conical, convex, and concave confinement plates over a spinning disk. The results obtained are found to be in agreement with previous experimental and numerical studies. The study of heat transfer involved a microchannel for a composite channel of trapezoidal cross-section fabricated by etching a silicon wafer and bonding it with a slab of gadolinium. Gadolinium is a magnetic material that exhibits high temperature rise during adiabatic magnetization around its transition temperature of 295K. Heat was generated in the substrate by the application of magnetic field. Water, ammonia, and FC-77 were studied as the possible working fluids. Thorough investigation for velocity and temperature distribution was performed by varying channel aspect ratio, Reynolds number, and the magnetic field. The thickness of gadolinium slab, spacing between channels in the heat exchanger, and fluid flow rate were varied. To check the validity of simulation, the results were compared with existing results for single material channels. Results showed that Nusselt number is larger near the inlet and decreases downstream. Also, an increase in Reynolds number increases the total Nusselt number of the system.

The self-similar evolution of a turbulent Rayleigh-Taylor (R-T) mix is investigated through experiments and numerical simulations. The experiments consisted of velocity and density measurements using thermocouples and Particle Image Velocimetry techniques. A novel experimental technique, termed PIV-S, to simultaneously measure both velocity and density fields was developed. These measurements provided data for turbulent correlations, power spectra, and energy balance analyses. The self-similarity of the flow is demonstrated through velocity profiles that collapse when normalized by an appropriate similarity variable and power spectra that evolve in a shape-preserving form. In the self-similar regime, vertical r.m.s. velocities dominate over the horizontal r.m.s. velocities with a ratio of 2:1. This anisotropy, also observed in the velocity spectra, extends to the Taylor scales. Buoyancy forcing does not alter the structure of the density spectra, which are seen to have an inertial range with a -5/3 slope. A scaling analysis was performed to explain this behavior. Centerline velocity fluctuations drive the growth of the flow, and can hence be used to deduce the growth constant. The question of universality of this flow was addressed through 3D numerical simulations with carefully designed initial conditions. With long wavelengths present in the initial conditions, the growth constant was found to depend logarithmically on the initial amplitudes. In the opposite limit, where long wavelengths are generated purely by the nonlinear interaction of shorter wavelengths, the growth constant assumed a universal lower bound value of

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