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Measurements of Film Flow Rate in Heated Tubes with Various Axial Power DistributionsAdamsson, Carl January 2006 (has links)
<p>Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions.</p>
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Escoamento anular não estabelecido de óleo ultraviscoso e água em dutos curvados: análises hidrodinâmica e energética.SILVA, Bruno Ferreira. 26 April 2018 (has links)
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Previous issue date: 2016-02-29 / Capes / Na indústria de petróleo, o transporte de óleos pesados em oleodutos requer altas potências de bombeamento devido a sua alta viscosidade, sendo este um dos inconvenientes na produção de óleos dessa natureza; surge assim a necessidade de desenvolvimento de novas tecnologias que otimize tais processos. Uma técnica economicamente viável e que pode ser usada, é o core anular flow, onde uma camada de água é responsável pela lubrificação do óleo que escoa no centro do duto. Desse modo, o presente trabalho apresenta um estudo energético e hidrodinâmico envolvendo o transporte de óleos pesados e água em dutos de conexões curvadas, através de simulação numérica via software ANSYS CFX® Release 15.0. Foi utilizado um modelo matemático que considera o modelo de mistura para tratar o escoamento bifásico águaóleo pesado, tridimensional, transiente e isotérmico, assumindo regime laminar para fase óleo e turbulento para a fase água adotando o modelo de turbulência k . Uma análise energética envolvendo as bombas também foi realizada. Resultados de campos de pressão, velocidade e fração volumétrica para as duas fases são apresentados e analisados. Verifica-se que o uso da técnica core-flow proporciona uma redução de 95,4% na queda de pressão por fricção comparado ao escoamento monofásico de óleo pesado, e que o desligamento e repartida das bombas de óleo e água afetam a queda de pressão por fricção. / In the oil industry, the transport of heavy oils in pipelines requires high power pumping due to its high viscosity, which is one of the drawbacks in oils production of this nature, thus emerge a need to develop new technologies that optimize such processes. An economically viable technique that can be used is the core annular flow, where a water layer is responsible for oil lubrication flowing in the center of the duct. In this way, this work presents an energy and hydrodinamic study of the heavy oils transportation in curved connections by numerical simulation via software ANSYS CFX® Release 15.0. It used a mathematical model that considers the mixture model to treat heavy oil-water two-phase flow, three-dimensional, transient and isothermal, assuming laminar flow to oil phase and turbulent flow to water phase, using k-ε turbulence model. An energy analysis involving pumps was performed. Results of pressure, velocity and volumetric fraction fields for the two phases are show and analysed. It was verified that the use of core-flow technique has decreased in 95.4% friction pressure drop as compared to monophase heavy oil flow and that stop-and-go from the oil and water pumps affect pressure drop by friction
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Modelagem e projeto de um sistema de controle aplicado ao escoamento bifasico de oleo viscoso e agua em padrão anular / Modeling and design of a control system applied to two-phase annular flow of viscous oil and waterGranzotto, Desiree Grenier 15 August 2018 (has links)
Orientador: Antonio Carlos Bannwart / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociencias / Made available in DSpace on 2018-08-15T14:50:36Z (GMT). No. of bitstreams: 1
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Previous issue date: 2008 / Resumo: As grandes reservas mundiais de óleo pesado e os elevados preços do barril de petróleo tornam essencial o desenvolvimento de tecnologias de elevação e transporte desses óleos. O óleo pesado, com suas características desfavoráveis de alta viscosidade (100 - 10000 cP) e de densidade (abaixo de 20° API), necessita de métodos específicos que viabilizem sua movimentação em dutos a altas vazões. Para isto, um dos métodos mais simples e que não requer utilização de calor ou diluentes é oferecido pelo escoamento anular óleo-água (core-flow). Entre as questões ainda não resolvidas sobre esse escoamento está o controle do escoamento bifásico, de modo a se obter uma operação segura com a razão água-óleo adequada. Neste trabalho é apresentada uma modelagem do escoamento anular de óleo viscoso e água em regimes permanente e transiente no interior de um duto horizontal. Das possíveis estratégias de controle, optou-se, por simplicidade, pelo controle da vazão de água a uma dada vazão de óleo (desejada para a linha), através da atuação na rotação da bomba d'água. A modelagem permanente da perda de carga em escoamento anular foi ajustada aos dados experimentais colhidos em uma linha de aço de 2,5 polegadas de diâmetro nominal e comprimento 30 m, para diversas combinações de vazões de óleo e água, devido a certa aderência do óleo na parede do duto. A modelagem transiente satisfaz o critério clássico de estabilidade de Ledinegg. Esses resultados possibilitaram projetar e testar um sistema de controle para a vazão de água em duas versões: proporcional-integral (PI) e fuzzy. As comparações permitiram concluir pelo melhor desempenho do controlador fuzzy, por suas características e robustez / Abstract: The significant heavy oil reserves worldwide and the presently high crude oil prices make it essential the development of technologies for heavy oil production and transportation. Heavy oils, with their inherent features of high viscosity (100-10,000 cP) and density (below 22°API) require specific techniques for pipe flow at high flow rates. For this purpose, one of the simplest methods, which does not require use of heat or diluents, is provided by oil-water annular flow (core-flow). Among the still unsolved issues regarding core-flow is the two-phase flow control, in order to obtain a safe operation of the line at the lowest possible water-oil ratio. In this work a model of the viscous oil-water annular flow in a horizontal pipe for both steady and unsteady regimes is presented. From the possible strategies, the water flow rate control for a given oil flow rate was selected for simplicity. Due to the observation of some oil adherence to the wall, the steady state flow model was adjusted to experimental data collected in a 2.5 inches, 30 meters long steel pipe at several combinations of oil and water flow rates. On the other hand the transient model is shown to satisfy the well-known Ledinegg stability criterion. These features made it possible to design and testing a control system for the water flow rate in two different versions: proportional-integral (PI) and fuzzy. Comparisons indicate that the fuzzy controller performs better due to its features and robustness / Mestrado / Explotação / Mestre em Ciências e Engenharia de Petróleo
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Measurements of Film Flow Rate in Heated Tubes with Various Axial Power DistributionsAdamsson, Carl January 2006 (has links)
Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions. / QC 20101108
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Experimental Study and Modelling of Spacer Grid Influence on Flow in Nuclear Fuel AssembliesCaraghiaur Garrido, Diana January 2009 (has links)
The work is focused on experimental study and modelling of spacer grid influence on single- and two-phase flow. In the experimental study a mock-up of a realistic fuel bundle with five spacer grids of thin plate spring construction was investigated. A special pressure measuring technique was used to measure pressure distribution inside the spacer. Five pressure taps were drilled in one of the rods, which could exchange position with other rods, in this way providing a large degree of freedom. Laser Doppler Velocimetry was used to measure mean local axial velocity and its fluctuating component upstream and downstream of the spacer in several subchannels with differing spacer part. The experimental study revealed an interesting behaviour. Subchannels from the interior part of the bundle display a different effect on the flow downstream of the spacer compared to subchannels close to the box wall, even if the spacer part is the same. This behaviour is not reflected in modern correlations. The modelling part, first, consisted in comparing the present experimental data to Computational Fluid Dynamics calculations. It was shown that stand-alone subchannel models could predict the local velocity, but are unreliable in prediction of turbulence enhancement due to spacer. The second part of the modelling consisted in developing a deposition model for increase due to spacer. In this study Lagrangian Particle Tracking (LPT) coupled to Discrete Random Walk (DRW) technique was used to model droplet movements through turbulent flow. The LPT technique has an advantage to model the influence of turbulence structure effect on droplet deposition, in this way presenting a generalized model in view of spacer geometry change. The verification of the applicability of LPT DRW method to model deposition in annular flow at Boiling Water Reactor conditions proved that the method is unreliable in its present state. The model calculations compare reasonably well to air-water deposition data, but display a wrong trend if the fluids have a different density ratio than air-water.
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Experimental Study of Annular Two-phase Flow on 3x3 Rod-bundle Geometry with Spacers / スペーサー付3×3模擬燃料ロッドバンドル内における環状二相流の実験的研究Pham Hong Son 24 September 2014 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18589号 / 工博第3950号 / 新制||工||1607(附属図書館) / 31489 / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 中部 主敬, 講師 河原 全作 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
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Refinement and testing of CTF for annular flow regime and incorporation of fluid propertiesShahid, Usama January 2021 (has links)
The current study focuses on improving and testing the CTF thermalhydraulics computer code. CTF is a thermalhydraulic code used for subchannel analysis of nuclear power reactors developed as part of the US DOE CASL program and distributed by North Carolina State University. Subchannel analyses are used to predict the local fuel temperatures and coolant conditions inside a complex nuclear fuel assembly. Such calculations are used to improve designs of nuclear fuel, improve operating margins, or perform safety analysis. An important part of the code development process is the verification and validation for its intended use. In this work validation activities are performed using the RISO experiments are modeled in CTF for adiabatic and diabatic cases in annular flow regimes and a limited set of tests in CANDU geometries. The CTF predictions significantly overpredicted the pressure drop for cases involving annular flow conditions. Depending on the application, such overprediction can result in significant errors in the computation of fuel element dryout and other figures of merit. For example, an analysis using fixed pressure boundary conditions CTF predicts much lower subchannel flows and hence fuel element temperatures may be overestimated. On the other hand, for a scenario with mass flux and inlet pressure as boundary conditions, the impact of pressure drop discrepancies on dryout predictions may be lower. Therefore, there is a particular focus in this thesis on the two-phase pressure drop models and the RISO experiment specifically, since the RISO tests involve a range of annular flow conditions which is prototypical of many CANDU accident analysis conditions.
In addition to the RISO experiments, 28-element CANDU full scale rod bundle experiments are modeled in CTF for single-phase and two-phase flow conditions. Cases are modeled for crept and uncrept conditions with different bearing pad heights i.e., 1.17 mm and 1.35mm. Pressure drop predictions are compared with the experimental results where single-phase comparisons are in good agreement while an overprediction of ~25% is observed for two-phase conditions. The effect of bearing pads on the subchannel local parameters, like mass flow rate, are also studied. Furthermore, the effect of turbulent mixing rate on subchannel enthalpy distribution in the bundle and CHF in different subchannels is also analyzed.
Based on the comparison to the RISO and CANDU 28 element test databases, the overprediction of pressure drop in the annular flow regime needs improvement in the current version of CTF. This overprediction of the frictional pressure drop results from either wall drag or interfacial shear stress phenomena. In this study, it is demonstrated that the issue occurs mostly as a result of interfacial friction factor modelling this work examines several alternative approaches. The results show the Ju’s and Sun’s interfacial friction factor better predicts the results among all the other six correlations implemented in CTF.
The major impediment in further testing of CTF is that it lacks the capability to simulate R-134a fluids. Given there is a large database of R-134a two-phase tests, another aspect of this thesis is to extend CTF for application and validation using refrigerants. The current CTF version only supports fluid properties for water and FLiBe salts. By adding R-134a fluid properties the testing and validation range of CTF is broadened for different experiments performed using R-134a fluids. CHF experiments are modeled in CTF and results are compared with experimental data. For local conditions correlation, 2006 water LUT are used to predict CHF and DNBR. The fluid-to-fluid scaling method is applied in CTF when using CTF with R-134a fluid properties for CHF and DNBR predictions to account for the difference in fluid properties between R-134a and the CHF look-up table. / Thesis / Master of Applied Science (MASc) / COBRA-TF (CTF) is a thermalhydraulic code, based on the historical code COBRA-TF, used for subchannel analysis of nuclear power reactors. Subchannel analysis can be used to predict the local fuel temperatures and coolant conditions inside a complex nuclear fuel assembly. CTF is a transient code that simultaneously solves conservation equations for mass, momentum, and energy for the three coolant phases present, i.e. vapor, continuous liquid, and entrained liquid droplet phases.
The scope of the current study includes 1) testing the code for conditions relevant to CANDU accident analysis, 2) refinement of the models that are used in two-phase interfacial friction calculations, and 3) inclusion of alternate fluid properties. The testing of CTF is performed with different experimental databases covering CANDU thermalhydraulic conditions. The refinement is done by improving the pressure drop prediction in the annular flow regime by using different interfacial friction factor correlations from earlier studies in the literature. The current CTF version includes water and liquid salt properties (FLiBe) for coolant fluids. Freon (R-134a) fluid properties have been added in CTF in order to broaden the testing range of CTF for different experimental database using R-134a as working fluid.
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Experimental and numerical investigation of high viscosity oil-based multiphase flowsAlagbe, Solomon Oluyemi 05 1900 (has links)
Multiphase flows are of great interest to a large variety of industries because flows of two
or more immiscible liquids are encountered in a diverse range of processes and
equipment. However, the advent of high viscosity oil requires more investigations to
enhance good design of transportation system and forestall its inherent production
difficulties.
Experimental and numerical studies were conducted on water-sand, oil-water and oilwater-
sand respectively in 1-in ID 5m long horizontal pipe. The densities of CYL680 and
CYL1000 oils employed are 917 and 916.2kg/m3 while their viscosities are 1.830 and
3.149Pa.s @ 25oC respectively. The solid-phase concentration ranged from 2.15e-04 to
10%v/v with mean diameter of 150micron and material density of 2650kg/m3.
Experimentally, the observed flow patterns are Water Assist Annular (WA-ANN),
Dispersed Oil in Water (DOW/OF), Oil Plug in Water (OPW/OF) with oil film on the
wall and Water Plug in Oil (WPO). These configurations were obtained through
visualisation, trend and the probability density function (PDF) of pressure signals along
with the statistical moments. Injection of water to assist high viscosity oil transport
reduced the pressure gradient by an order of magnitude. No significant differences were
found between the gradients of oil-water and oil-water-sand, however, increase in sand
concentration led to increase in the pressure losses in oil-water-sand flow.
Numerically, Water Assist Annular (WA-ANN), Dispersed Oil in Water (DOW/OF), Oil
Plug in Water (OPW/OF) with oil film on the wall, and Water Plug in Oil (WPO) flow
pattern were successfully obtained by imposing a concentric inlet condition at the inlet of
the horizontal pipe coupled with a newly developed turbulent kinetic energy budget
equation coded as user defined function which was hooked up to the turbulence models.
These modifications aided satisfactory predictions.
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Experimental Investigations of Flow Development, Gap Instability and Gap Vortex Street Generation in Eccentric Annular ChannelsChoueiri, George H. 02 May 2014 (has links)
Isothermal flow development, gap instability, and gap vortex street generation in eccentric annular channels have been studied experimentally. A representative paradigm of a flow in a highly eccentric annular channel was examined for a channel having an inner-to-outer diameter ratio d/D = 0.50 and an eccentricity e = 0.8 for a Reynolds number Re = 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth region and the rapid-mixing region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60% of the bulk velocity. The dependence on inlet conditions, d/D, e and Re on the development and structure of flows was also investigated. Experimental conditions covered the ranges: 0 ≤ Re ≤ 19000, 0 ≤ e ≤ 0.9 and d/D = 0.25, 0.50 and 0.75. For Re < 7000, the Strouhal number, the normalized mid-gap axial flow velocity and the axial and cross-flow fluctuation intensities at mid-gap were found to increase with increasing Re and to depend strongly on inlet conditions. At higher Re, however, these parameters reached asymptotic values that were only mildly sensitive to inlet conditions. A map was constructed for the various stages of periodic motions vs. e and Re and it was found that, for e < 0.5 or Re < 1100, the flow was unconditionally stable as far as gap instability is concerned. For e ≤ 0.5, transition to turbulence occurred at Re ≈ 6000, whereas, for 0.6 ≤ e ≤ 0.9, the critical Reynolds number for the formation of periodic motions was found to increase with eccentricity from 1100 for e = 0.6 to 3800 for e = 0.9. The use of an empirically derived "mixing layer Strouhal number" permitted a universal description of gap vortex street periodicity in eccentric annular channels. This study has contributed to our understanding of the physical mechanisms that lead to gap instability and the development of a gap vortex street and the dependence of these flow phenomena on the channel geometry and the dynamic conditions of the flow.
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Estudo Experimental e de Simulação por CFD de Escoamentos em Seções AnularesVieira Neto, José Luiz 31 May 2011 (has links)
The increasing activity of oil and gas extraction in deep water has stimulated several
studies to solve problems encountered in drilling wells. During the drilling operation, a fluid
(drilling mud) is pumped through the column to the bottom, carrying to the surface the drill
cuttings generated, through the annular space formed between the column and the borehole
wall. In this type of flow may appear a kind of hydrodynamic instability characterized by the
appearance of toroidal vortices. This type of instability (Taylor-Couette) may profoundly alter
the pressure drop of the flow, the shear stress at the borehole wall and the ability of carrying
the solids. Moreover, during the process of drilling a well it is necessary promotes the well
cementing and coating to provide a mechanical support, as well as, to isolate it from different
rock formations traversed. For this step to be successful, the drilling mud must be completely
removed from the annular space, and this removal may be impaired in wells which have
varying eccentricity along the tube. Due to high costs of correction transactions and loss of
drilling time, it is crucial to predict the mud flow around the annular. The effects of this
variation of the eccentricity have not been much discussed in the literature, and they may have
great influence on the displacement of the mud in the annular space. As an initial phase of
work, numerical simulations were performed to study the flow and the emergence of Taylor-
Couette instabilities in a concentric annular section, in order to compare them with literature
data. Numerical simulations were developed in annular periodic sections, concentric and
eccentric (E = 0.5) in order to obtain average profiles of axial and tangential velocities using
different turbulence models, aiming at a comparison of simulated results with experimental
data from literature. Later, it was made an experimental study and simulation to assess the
effect of internal axis rotation on the pressure drop in the flow of non-Newtonian fluids
(aqueous solutions of xanthan gum and carboxymethyl cellulose with 0.2% by weight) in a
section annular concentric and the other with fixed eccentricity (E = 0.75). Finally, it was
elaborated an experimental design (3k) with four variables, such as, xanthan gum
concentration (0.05%, 0.10% and 0.15% by weight), eccentricity (0.0, 0.23 and 0.46), fluid
flow rate (5, 7 and 9 m3/h) and internal rotation axis (0, 100 and 200 rpm). Following this
planning, experimental data of pressure drop were collected, as well as, numerical simulations
(CFD) in periodic annular sections to get results of axial velocity, in order to evaluate the
effect of variable eccentric rotation on the fluid dynamics of non-Newtonian flows in annular
spaces. / A crescente atividade de extração de petróleo e gás em águas cada vez mais profundas
tem impulsionando diversos estudos para solucionar problemas encontrados na perfuração de
poços. Durante a operação de perfuração, um fluido (lama de perfuração) é bombeado através
da coluna até o fundo do poço, retornando à superfície carreando os cascalhos gerados pela
broca, passando pelo espaço anular formado entre a coluna e a parede do poço. Neste tipo de
escoamento pode ocorrer um tipo de instabilidade hidrodinâmica caracterizada pelo
aparecimento de vórtices toroidais. Este tipo de instabilidade (Taylor-Couette), pode alterar
profundamente a perda de carga do escoamento, a tensão cisalhante na parede do poço e a
capacidade de carreamento de cascalho. Além disto, durante o processo de perfuração de um
poço é necessário promover o revestimento e a cimentação do poço para fornecer a sua
sustentação mecânica, bem como, para isolá-lo das diferentes formações rochosas
atravessadas. Para esta etapa ser bem sucedida, a lama de perfuração deve ser completamente
removida do anular, sendo que, esta remoção pode ser prejudicada em poços que apresentem
excentricidade variando ao longo do tubo. Devido aos altos custos das operações de correção
e a perda de tempo de perfuração, é fundamental prever este deslocamento da lama ao redor
do anular. Os efeitos desta variação da excentricidade ainda não foram muito abordados na
literatura e podem apresentar grande influência no deslocamento da lama no espaço anular.
Como etapa inicial do trabalho, foram realizadas simulações numéricas para estudar o
escoamento com surgimento de instabilidades do tipo Taylor-Couette em uma seção anular
concêntrica, com intuito de compará-las com trabalhos da literatura. Depois foram
desenvolvidas simulações numéricas em seções anulares periódicas, concêntrica e excêntrica
(E = 0,5), a fim de obter perfis médios de velocidades axial e tangencial usando diferentes
modelos de turbulência, visando uma comparação dos resultados simulados com os dados
experimentais da literatura. Posteriormente, foi feito um estudo experimental e de simulação
para avaliar o efeito da rotação do eixo interno sobre a queda de pressão no escoamento de
fluidos não-Newtonianos (soluções aquosas de Goma Xantana e de Carboximetilcelulose a
0,2% em peso) numa seção anular concêntrica e outra com excentricidade fixa (E = 0,75).
Finalmente, elaborou-se um planejamento fatorial de experimentos do tipo 3k com quatro
variáveis, tais como, concentração de Goma Xantana (0,05%, 0,10% e 0,15%), excentricidade
(0,0; 0,23 e 0,46), vazão volumétrica (5, 7 e 9 m3/h) e rotação do eixo interno (0, 100 e 200
rpm). Seguindo este planejamento foram levantados dados experimentais de queda de pressão,
bem como, simulações numéricas (CFD) em seções periódicas para obtenção de resultados de
velocidade axial, com intuito de avaliar efeito do movimento de rotação excêntrica variável
sobre a dinâmica do escoamento de fluidos não-Newtonianos em espaços anulares. / Doutor em Engenharia Química
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