Two-phase flow experiments at vertical pipes are much suitable for studying the action of different constitutive relations characterizing the momentum exchange at the gas/liquid interface as well as the dynamic behaviour of the gas/liquid interface itself. The flow can be observed in its movement along the pipe and, in particular, within the shear field close to the pipe wall over a considerable vertical distance and, consequently, over a comparatively long time without the immediate separation of gas and liquid characteristic for horizontal flows. Wire-mesh sensors, which were the working horse in the described experiments, supplied sequences of instantaneous two-dimensional gas fraction distributions with a high-resolution in space and time. This allows to derive from the data not only void fraction and bubble velocity profiles, but also bubble size distributions, bubble-size resolved radial gas fraction profiles as well as the axial evolution of these distributions. An interfacial surface reconstruction algorithm was developed in order to extract the extension of interfacial area from the wire-mesh sensor data. The sensors were upgraded to withstand parameters that are close to nuclear reactor conditions. Most of the experiments were performed for both air/water flow at ambient pressure and steam/water flow of up to 6.5 MPa at identical combinations of the gas and liquid superficial velocities. This offers excellent conditions for studying the influence of the fluid properties.

Computational fluid dynamics (CFD) modeling was used to predict the hydrodynamics of a column reactor. Bubble columns have applications across many engineering disciplines and improved modeling techniques help to increase the accuracy of numerical predictions. An Eulerian-Eulerian multi-fluid model was used to simulate fluidization and to capture the complex physics associated therewith. The commercial code ANSYS Fluent was used to study two-dimensional gas-liquid bubble columns. A comprehensive parameter study, including a detailed investigation of grid resolution was performed. Specific attention was paid to the bubble diameter, as it was shown to be related to cell size have significant effects on the characteristics of the flow. The parameters used to compare the two-dimensional (2D) cases to experimental results of Rampure, et. al. were then applied to a three-dimensional (3D) geometry. It was demonstrated that the increase in accuracy from 2D to 3D is negligible compared to the increase in CPU required to simulate the entire 3D domain. Additionally, the reaction chamber of a microbial fuel cell (MFC) was modeled and a preliminary parameter study investigating inlet velocity, temperature, and acetate concentration was conducted. MFCs are used in wastewater treatment and have the potential to treat water while simultaneously harvesting electricity. The spiral spacer and chemical reactions were modeled in a 3D geometry, and it was determined that inlet velocity was the most influential parameter that was simulated. There were also significant differences between the 2D and 3D geometries used to predict the MFC hydrodynamics. / Master of Science

Aerosols are a major source of uncertainty in estimates of anthropogenic effects on global radiative forcing and can pose serious health concerns. While many instrumental techniques capable of analyzing aerosol samples are available, individual-particle spectromicroscopic techniques like the ones presented here are the only ones to offer morphological and compositional measurements together. Studying the composition and mixing state of aerosol populations allowed for important aspects to be uncovered, such as: aerosol source, formation mechanism, hygroscopicity, optical properties, level of aging, and inhalation dangers. Ambient aerosols from the Amazon, both biogenic and anthropogenic, were apportioned based on their individual composition. Recently discovered organic aerosols from the central United States were identified and their chemical properties were characterized. The lead fraction of mixed lead- and zinc-rich particles from Mexico City was speciated to determine the lead’s solubility and possible bioavailability. It is through the use of these powerful spectromicroscopic techniques that a better understanding of complex mixed aerosols was achieved.

No / The development of kerosene–water up-flow in a vertical pipe of 77.8 mm inner diameter and 4500 mm, length downstream of a 90◦bend, hasbeen investigated using a Pitot tube and dual optical probe. The CFD ANSYS Fluent 12.0 is used to model the flow and the results are comparedwith experimental data. The CFD provides detailed information on flow structure which is difficult to obtain in experiments. The experimentalmeasurements of the local parameters demonstrate that the single phase and two-phase flows reached the fully developed axisymmetricalconditions at L/D = 54. These results also show the severe asymmetry distributions of the two-phase flow parameters at the entrance region(L/D = 1). The predictions from Fluent are found to be in close agreement with experimental data for L/D ≥ 16 but there is a significant discrepancyat L/D = 1.

No / The local parameters for kerosene–water upward flow are measured in a vertical pipe of 77.8 mm inner diameter at 4200 mm from the inlet(L/D = 54) using hot-film and dual optical probes. The effect of superficial water velocity and volumetric quality on radial distribution of two-phaseflow parameters is investigated. The results show the following: (i) the profiles of volume fraction and drop frequency are very similar, and increasing superficial water velocity at low volumetric qualities (<18.6%) change the profile from a convex shape with peak at the pipe centreline to uniform then to concave shape with peak near the wall; (ii) the profiles of drop cut chord change from a parabolic shape with peak at centreline for lows uperficial water velocities to a flat shape at higher superficial water velocity, and the area-averaged drop diameter decreases with higher superficial water velocities for all volumetric qualities; (iii) velocity profiles for both phases have shapes similar to single phase flow, flatter at higher values of superficial water velocity and volumetric quality and centreline peaked at low superficial water velocities and volumetric qualities; (iv) the slip velocity decreases with radial distance having a peak at centreline and zero values near the wall; (v) introducing kerosene drops into single phasewater flow results in a sharp increase in turbulent intensity, particularly at low water velocity, and the difference between the single phase and two-phase flow turbulence intensities decreases with higher superficial water velocities and (vi) the results show that interfacial area concentration increased with higher volumetric quality and higher number of bubbles thereby increases the contact area between the two phases.

No description available.

A study is carried out into fracture behavior of steel/steel laminates both experimentally and through finite element analysis (FEM). The laminates produced by hot pressing consisted of low carbon and medium carbon steels with two volume fractions / 0.41 and 0.81. Fracture toughness, JIC has been measured using partial unloading technique assuming a critical value of crack extension. The technique is initially applied to monolithic material and then to the laminates in crack divider orientation. Evaluation of fracture toughness of laminates indicates that there is a substantial improvement of JIC with increase in the volume fraction. The systems under study were also evaluated by FEM modeling with the use MARC package program. To evaluate JIC, the problem has been evaluated in several steps / first two-dimensional plane strain problem is considered. This is followed by three-dimensional case and then by an artificially layered system, all for monolithic materials. Values of JIC derived were close to one another in all cases. Following this verification, the method, as implemented in layered monolithic system, was applied to laminates. This has shown that JIC of laminates can be predicted using FEM analysis, including the delamination. Values of JIC varied in the same manner as the experiment verifying that fracture toughness in the current system increases with increase in volume fraction. It has been concluded that modeling as implemented in this work can be used for useful composite systems incorporating hard/brittle reinforcements both in crack divider and crack arrester orientation.

The extensive experimental results presented in this report provide a high-quality database for air-/water flows in a vertical pipe with a nominal diameter of 200 mm. This database can be used for the development and validation of CFD-like models for two-phase flows, e.g. for bubble coalescence and fragmentation. In particular, the investigations aim on the evolution of the two-phase flow along the pipe height. Therefore, up to 18 single measurements with varying distances between the gas injection and measurement plane were realised for each of the 92 combinations of gas and water flow rates. The pressure at the position of the activated gas injection was kept constant at 0.25 MPa(a). This boundary condition has the advantage that the measured data represent exactly the evolution of the flow along the pipe, i.e. they reflect a configuration at which the gas injection is at a fixed height position, while the measurement plane varies. Important results of this test series are time averaged radial profiles of the gas fraction, and the gas velocity, as well as the time and cross-section averaged bubble size distributions. Furthermore, gas fraction data resolved regarding the bubble size and spatial distribution are presented. As in previous test series, flow patterns were analysed, whereby the classification results from the bubble size. A substantial part of these new air/water experiments were quality and plausibility checks of the measured data. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. The influence of the orifice diameter of the gas injection on flow patterns is also discussed in the report.

Die im Rahmen dieser Versuchsserie erzielten umfangreichen experimentellen Ergebnisse bilden eine hochwertige Datenbasis für Luft-Wasser-Strömungen in einem vertikalen DN200-Rohr, die für die Entwicklung und Validierung von CFD-Modellen, beispielweise bzgl. Blasenkoaleszenz und -fragmentierung, genutzt werden können. Besonderes interessant ist die Untersuchung der Entwicklung der Zweiphasenströmung über der Rohrhöhe. Aus diesem Grund wurden für jede der 92 betrachteten Kombinationen aus Gas- und Wasser-Volumenstromdichten bis zu 18 Messungen mit variablen Abständen zwischen Gaseinspeisung und Messebene durchgeführt. Dabei wurde der Druck an der Gaseinspeisestelle konstant auf 0,25 MPa(a) gehalten. Diese Randbedingung bietet den Vorteil, dass die so gemessenen Daten die Entwicklung der Strömung über der Rohrhöhe widerspiegeln, d.h. eine Konfiguration beschreiben, bei der das Gas an einer festen Höhenposition eingespeist wird und die Messungen in verschiedenen darüberliegenden Ebenen erfolgen. Wesentliche Ergebnisse dieser Messserie sind radiale zeitgemittelte Profile für den Gasgehalt und die Gasgeschwindigkeit sowie zeit- und querschnittsgemittelte Blasengrößenverteilungen. Außerdem liegen blasengrößen- und ortsaufgelöste Gasgehaltsdaten vor. Wie bereits bei früheren Versuchsserien wurden auch in diesem Fall die Strömungsformen analysiert, wobei die Klassifizierung anhand der Blasengröße erfolgte. Ein wesentlicher Bestandteil dieser neuen Luft/Wasser-Versuche war die Qualitäts- und Plausibilitätsprüfung der Messdaten. Es konnte festgestellt werden, dass die Daten einen eindeutigen, widerspruchsfreien Trend bzgl. ihrer Entwicklung mit zunehmendem Abstand von der Gaseinspeisung aufweisen. Zur Plausibilitätsprüfung wurden Vergleiche des Gasgehaltsverlaufes über der Rohrhöhe mit theoretisch zu erwartenden Kurven durchgeführt. Zusätzlich zu diesen Ergebnissen enthält der Bericht eine Einschätzung des Einflusses des Bohrungsdurchmessers an der Gaseinspeisung auf die sich einstellende Strömung.

<p>Void growth and coalescence in a single layer model material with holes were visualized by the environmental electron scanning microscope coupled with in situ tensile test. Single sheet model materials were manufactured with a line of laser drilled holes through thickness. In order to investigate the effect of shear localization, the line of holes were oriented with the misorientation angle <em>θ </em>= 0°, 15°, 30°, and 45°. The α-brass samples were studied to introduce the work hardening effect in comparison with the pure copper samples.</p> <p>By taking images at intervals with small strain increments, the void growth behaviors were visualized during the interrupted tensile testing. The void coalescence (defined consistent with Hosokawa et al (2011), as the point at which the voids stopped shrinking laterally) was successfully captured for the first time in the two dimensional studies. The evolutions of void shape change and void rotation during deformation were also studied quantitatively. The results showed that the higher work hardening behaviors can suppress the void coalescence. It also showed that the effect of local volume fraction dominated the coalescence event rather than the void spacing and shear localization. A comparison of the classic models with the experimental results were also made.</p> / Master of Science in Materials Science and Engineering (MSMSE)