Impinging jets are a flow geometry that is of interest in many chemical and processing engineering applications for a wide range of industries. Of particular interest in the current research is their application to particle re-suspension in nuclear reprocessing activities such as the HAS (highly active storage) tanks at Sellafield, UK. The challenging nature of these operations and their environment means that in-situ experimental work is impossible. Therefore, when designing and optimising equipment such as HAS tanks, engineers often turn to computational modelling to help gain an understanding about what effects certain modifications may have on the performance of the jet. The challenge then becomes obtaining physically realistic predictions using the methods available to industry. Impinging jets are complex and complicated flow geometries that have caused a number of problems for computational modellers over the years. Indeed, several turbulence models and approaches have been developed specifically with impinging jets in mind to help overcome some of the more difficult aspects of the flow. The work presented herein compares Reynolds-averaged Navier-Stokes (RANS) commercial codes readily available to industrial users for single- and multi-phase flows with RANS and large eddy simulation (LES) codes developed in an academic research environment. The intention is to contrast and compare and highlight where industrial-based computational models fall short and how these might be improved through implementing schemes with fewer simplified terms. The work conducted for this Engineering Doctorate has modelled a series of impinging jets with varying jet heights and Reynolds numbers using a range of RANS turbulence models within commercial and academic-based codes. This allows not only the discussion of the performance of the applied turbulence models, but also the effects of varying jet height. The predictions are validated against available experimental data for assessment of the performance of the scheme used. The degree of alignment with real, physical data is an indication of the performance of a model and is used to conclude where a particular model has failed or whether it is more suited than another. Different particle sizes have also been considered to determine the ability of different particle tracking schemes to predict particle behaviour based on their response to the continuous phase. Multi-phase data is also validated against limited available experimental data. Finally, LES has been used to demonstrate the next step in complexity in terms of simulation and prediction of continuous phase flows in difficult engineering applications and how these can greatly improve upon predictions from RANS methods.

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(工学) / 乙第12650号 / 論工博第4078号 / 新制||工||1547(附属図書館) / 29728 / (主査)教授 辻 伸泰, 教授 落合 庄治郎, 教授 乾 晴行 / 学位規則第4条第2項該当

This thesis investigates violent air-water flows in two and three dimensions using a smoothed particle hydrodynamics (SPH) model accelerated using the parallel architecture of graphics processing units (GPUs). SPH is a meshless Lagrangian technique for CFD simulations, whose major advantage for multi-phase flows is that the highly nonlinear behaviour of the motion of the interface can be implicitly captured with a sharp interface. However, prior to this thesis performing multi-phase simulations of large scale air-water flows has been prohibitive due to the inherent high computational cost. The open source code DualSPHysics, a hybrid central processing unit (CPU) and GPU code, is heavily modified in order to be able to handle flows with multiple fluids by implementing a weakly compressible multi-phase model that is simple to implement on GPUs. The computational runtime shows a clear improvement over a conventional serial code for both two- and three dimensional cases enabling simulations with millions of particles. An investigation into different GPU algorithms focuses on optimising the multi-phase SPH implementation for the first time, leading to speedups of up to two orders of magnitude compared to a CPU-only simulation. Detailed comparison of different GPU algorithms reveals a further 12% improvement on the computational runtime. Enabling the modelling of cases with millions of fluid particles demonstrates some previously unreported problems regarding the simulation of the air phase. A new particle shifting algorithm has been proposed for multi-phase flows enabling the air, initially simulated as a highly compressible liquid, to expand rapidly as a gas and prevent the formation of unphysical voids. The new shifting algorithm is validated using dam break flows over a dry bed where good agreement is obtained with experimental data and reference solutions published in the literature. An improvement over a corresponding single-phase SPH simulation is also shown. Results for dam break flows over a wet bed are shown for different resolutions performing simulations that were unfeasible prior to the GPU multi-phase SPH code. Good agreement with the experimental results and a clear improvement over the single-phase model are obtained with the higher resolution showing closer agreement with the experimental results. Sloshing inside a rolling tank was also examined and was found to be heavily dependent on the viscosity model and the speed of sound of the phases. A sensitivity analysis was performed for a range of different values comparing the results to experimental data with the emphasis on the pressure impact on the wall. Finally, a 3-D gravity-driven flow where water is impacting an obstacle was studied comparing results with published experimental data. The height of the water at different points in the domain and the pressure on the side of the obstacle are compared to a state-of-the-art single-phase GPU SPH simulation. The results obtained were generally in good agreement with the experiment with closer results obtained for higher resolutions and showing an improvement on the single-phase model.

This thesis presents the study of nanocomposites based on immiscible polymer blend of polycarbonate and acrylonitrile-butadiene-styrene (PC/ABS) filled with multi-walled carbon nanotubes (MWCNT). The aim is to achieve an improvement of mechanical properties and electrical conductivity of the nanocomposites. In an initial stage, a twin-screw extruder was used to obtain nanocomposites by melt compounding. Three methods of carbon nanotubes addition were studied: direct addition, dilution from a masterbatch and feeding of MWCNT suspension in ethanol. For each method, the influence of nanofiller content and processing parameters on morphology and final properties of the nanocomposite was analyzed. Furthermore, the influence of two types of carbon nanotubes modifications was studied: covalent modification by surface-oxidation (MWCNT-COOH) and non-covalent modification by an addition of surfactant promoting the nanofiller-matrix interactions. A good dispersion of the MWCNT was obtained for masterbatch dilution and suspension feeding. Both methods showed preferential localization of carbon nanotubes in polycarbonate phase (PC). Samples processed by masterbatch dilution showed the 30 % increase of rigidity and a decrease of ductility of PC/ABS for 0.5 wt. % MWCNT. Electrical conductivity was influenced by processing temperature and carbon nanotubes type. The percolation threshold value was 2.0 wt. % for pristine MWCNT and 1.5 wt. % for modified MWCNT-COOH. Better balance of mechanical properties and electrical conductivity was achieved in the samples obtained by the masterbatch route. These properties were studied in a subsequent phase, when the extruded nanocomposite was injection molded in order to obtain a defined geometry. / Wegrzyn, M. (2014). Nanocomposites of Multiphase Polymer Blend Reinforced with Carbon Nanotubes: Processing and Characterization [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36869 / TESIS

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22047号 / 工博第4628号 / 新制||工||1722(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 後藤 仁志, 教授 細田 尚, 准教授 KHAYYER,Abbas / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

his thesis deals with the problems of cavitation flow in a Venturi tube. It is made for a multi-phase (water-vapour) flow calculation of two geometry tubes. Results of numerical calculations for the flow geometry (dimensions) are compared with performed experiment. Numerical flow calculation was performed in the Fluent 2.3.26.

Nach einer kurzen technischen Beschreibung der Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW und der verwendeten Messtechnik werden die theoretischen Grundlagen zur Modellierung der Kondensation von Dampf in einer Wasserströmung erläutert. Dabei gehen die Autoren besonders auf die Auswahl geeigneter Modelle zur Beschreibung des Wärmeübergangs und der Zwischenphasengrenzfläche im Druckbereich zwischen 10 und 65 bar detailliert ein. Außerdem werden verschiedene Drift-Flux-Modelle auf ihre Tauglichkeit anhand von experimentellen Daten geprüft. Da Veränderungen thermodynamischer und strömungstechnischer Parameter hauptsächlich in axialer Richtung stattfinden, wurden diese Modelle in einen eindimensionalen Code eingebettet, mit dem der Strömungsverlauf entlang einer vertikalen Rohrleitung mit einer Länge von 8 m und einem Nenndurchmesser von 200 mm berechnet werden kann. Anschließend werden Aufbau und Funktion dieses Programms vorgestellt. Nachfolgend vergleichen die Autoren experimentelle und berechnete Strömungsverläufe bei der Kondensation von Dampf sowohl in einer unterkühlten Wasserströmung als auch nahe der Siedetemperatur. Dabei wird der Einfluss wichtiger Randbedingungen, wie z.B. Druck oder Primärblasengröße, auf die Kondensationsintensität analysiert. Eine Einschätzung der Fehlerbanden für die experimentellen Daten, die verwendeten Gittersensoren und die numerische Simulation schließen den Bericht ab.

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The numerical computer models that simulate municipal solid waste (MSW) bioreactor landfills have mainly two components--a biodegradation process module and a multi-phase flow module. The biodegradation model describes the chemical and microbiological processes of solid waste biodegradation. The models available to date include predefined solid waste biodegradation reactions and participating species. In a bioreactor landfill several processes, such as anaerobic and aerobic biodegradation, nitrogen and sulfate cycling, precipitation and dissolution of metals, and adsorption and gasification of various anthropogenic organic compounds, occur simultaneously. These processes may involve reactions of several species and the available biochemical models for solid waste biodegradation do not provide users with the flexibility to selectively simulate these processes. This research work includes the development of a generalized biochemical process model, BIOKEMOD-3P, which can accommodate a large number of species and process reactions. This model is able to simulate bioreactor landfill processes in a completely mixed condition; when coupled with a multi-phase model it will be able to simulate a full-scale bioreactor landfill. This generalized biochemical model can simulate laboratory and pilot-scale operations which are important to determine biochemical parameters important for simulation of full-scale operations. To illustrate application of BIOKEMOD-3P, two sets of laboratory MSW bioreactors were simulated in this research work. The first demonstrated simulation of data from anaerobic biodegradation of MSW in experimental bioreactors. In another application, simultaneous nitrification and denitrification processes in MSW bioreactors were simulated. The results from these simulations generated information about various modeling parameters that would help implement these processes in a full-scale bioreactor landfill operation.

ABSTRACT Digitally-Controlled Two-Phase Zero-Voltage-Switching Quasi-Resonant Buck Converter Brian Luc This thesis entails the design, construction, and performance analysis of a digitally-controlled two-phase Zero-Voltage Switching Quasi-Resonant (ZVS-QR) buck converter. The converter is aimed to address the issues associated with powering CPUs operating at lower voltage and high current. To evaluate its performance, the Two-Phase ZVS-QR buck converter is compared against a traditional Two-Phase buck converter. The design procedure required to implement both converters through utilizing the characterization curve and formulas derived from their circuit configurations will be presented. Computer simulation of the Two-Phase ZVS-QR buck converter is provided to exhibit its operation and potential for use in low voltage and high current applications. In addition, hardware prototypes for both ZVS-QR and traditional buck converters are constructed utilizing a Programmable Interface Controller (PIC). Results from hardware tests demonstrate the success of using digital controller for the 60W 12VDC to 1.5VDC ZVS-QR buck converter. Merits and drawbacks based on the operation and performance of both converters will also be assessed and described. Further work to improve the performance of ZVS-QR will also be presented. Keywords: Buck Converter; Zero-Voltage-Switching; Multi-Phase; Efficiency; Switching Loss