Dissertations / Theses on the topic 'Annual flow'
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1
Lam, Yung-chun Nelson, and 林勇進. "Annual distribution of phytoplankton in Tolo Harbour: a flow cytometry approach." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B3124192X.
2
Lam, Yung-chun Nelson. "Annual distribution of phytoplankton in Tolo Harbour a flow cytometry approach /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22718874.
3
O, Dohonova K., and Bortnik Y. V. "Construction of dependence function of annual passenger flow and GPD per capita." Thesis, National Aviation University, 2021. https://er.nau.edu.ua/handle/NAU/50700.
Abstract:
1. Higher Mathematics: manual. Theory of Probability and Elements of Mathematical Statistics / V.P. Denisiuk, V.M. Bobkov, L.A. Grishina – K.: NAU, 2013. 210-216 pages.
2. Пасажиропотік аеропортів України [Electronic source] - https://www.wikiwand.com/uk/Пасажиропотік_аеропортів_України/Загальний_пасажиропотік_аеропортів_України.
3. Валовой внутренний продукт (ВВП) в Украине 2021[Electronic source] -https://index.minfin.com.ua/economy/gdp/In many problems of physics, economics, medicine, engineering, etc. we have to experimentally study the dependence of a random variable Y, observed, on one or more other random or non-random variables Х_1,Х_2,…,Х_n. Regression analysis is a branch of mathematical statistics that studies the dependence between random variables using regression equations, and regression is the functional dependence on average of any random variables.
4
Sukheswalla, Zubin Rohinton. "A statistical model for estimating mean annual and mean monthly flows at ungaged locations." Texas A&M University, 2003. http://hdl.handle.net/1969.1/192.
Abstract:
Prediction of flow is necessary for planning and management of water resources. The objective of this study is to estimate mean annual flows for the USA and mean monthly flows for the rivers of central Texas based on the precipitation and their watershed characteristics. Flow varies largely with topographic and climatic parameters and hence generalization of runoff models is difficult. This model aims at providing a prediction at
ungaged locations with very few parameters that are easily available and measurable.
Scatter in predicted data will be seen at the annual and monthly time scale in the range selected for each data. This model will work on annual and monthly means to reduce the scatter and produce better estimates.
5
Guo, Zhenyi. "CFD Simulation of Annular Flow Boiling in Microchannels." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14428.
Abstract:
Flow boiling in microchannels has received enormous interest over the past few decades because of its importance in the thermal management of micro-structured devices. Few of previously published studies focus specifically on microchannel annular flow boiling which is very important due to its prevalence in this system. This thesis provides understanding of the heat and mass transfer in microchannel annular flow boiling via the use of a computational fluid dynamics (CFD) approach. The commercial software ANSYS Fluent was chosen to perform the CFD simulations. A modified height function (HF) method was implemented into the default CSF model to improve the performance of surface tension modelling. Simulation of an inviscid parallel flow demonstrated successful prediction of the onset of Kelvin-Helmholtz (K-H) instability in close accord with the analytical criterion. Studies of imposed numerical perturbations in laminar annular air-water flow showed that viscosity does not affect the stability of interfacial waves but has large impacts on the growth rates. A phase change model was formulated using a kinetic-based model to calculate the interphase mass flux. An established numerical smoothing procedure was used to improve numerical stability. A detailed study of a laminar annular flow boiling was performed using water at 160 kPa in a 0.5 mm diameter channel with constant fluid mass flux G = 60 kg m−2 s−1 and inlet vapour quality x = 0.1. Interfacial waves were observed and flow recirculation and a localised increase of heat transfer coefficient occurred at the interfacial wave troughs, where the liquid film was very thin. A parametric analysis showed that boiling heat transfer coefficient increases with increasing mass flux, system pressure, vapour quality and heat flux but decreases with increasing tube diameter.
6
Meyer, Lucie. "The annual ragweeds (Ambrosia artemisiifolia L. - Ambrosia trifida L.) : adaptive response to chemical weeding and population genetics in agricultural environments." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCK005.
Abstract:
Ce travail a eu pour but premier d’étudier le risque d’évolution de la résistance aux herbicides inhibiteurs de l’acétolactate synthase (ALS) chez l’ambroisie à feuilles d’armoise (Ambrosia artemisiifolia L.) à travers quatre points : (i) la pression de sélection (étude de l’efficacité d’une gamme d'herbicides inhibiteurs de l’ALS), (ii) la capacité de réponse adaptative de l’adventice (détermination de la variation de la sensibilité aux inhibiteurs de l’ALS entre plantes et mise en place d’un programme de sélection récurrente), (iii) une étude de terrain (recherche de résistance aux inhibiteurs de l’ALS au champ en France), (iv) l’étude des mécanismes de résistance (liée à la cible – RLC – et non liée à la cible – RNLC – par une approche de transcriptomique). Le second objectif fut d’étudier la connectivité des populations d’A. artemisiifolia dans des paysages agricoles à l’aide de marqueurs microsatellites développés lors de ce travail afin de déterminer les facteurs qui pourraient faciliter la dispersion de cette espèce et de la résistance à l’échelle du paysage agricole.En ce qui concerne la résistance aux herbicides :-La réponse de d’A. artemisiifolia aux herbicides inhibiteurs de l’ALS est très variable entre substances.-Des plantes ayant survécu à la dose maximale autorisée et à des doses supérieures de metsulfuron ont été sélectionnées pour débuter un programme de sélection récurrente. Après deux cycles de sélection, on observe une intensification de la résistance au metsulfuron et une émergence de la résistance à l’imazamox et au tribénuron.-Trois cas de résistance à l’imazamox ont été identifiés au champ dont deux cas de pure RNLC et un cas de coexistence RLC – RNLC.-Un transcriptome d’A. artemisiifolia a été généré grâce à la technique de séquençage PacBio pour rechercher des gènes impliqués dans les mécanismes de RNLC (approche RNAseq). 62 gènes candidats ont été identifiés dont des transporteurs ABC, des cytochromes P450 ainsi que des glutathione-S-transférases connus pour être impliqués dans la dégradation des herbicides.Pour l’étude de la connectivité des populations agricoles :-26 marqueurs microsatellites ont été développés et ont révélé une forte variabilité génétique. La structuration génétique a été étudiée à grande échelle pour des populations d’A. artemisiifolia d’Europe (aire d’invasion) et d’Amérique du Nord (aire d’origine).-À une échelle plus fine (paysage agricole), la structure génétique des populations reste influencée par les événements de colonisation. Les événements de migration qui ont été identifiés entre zones de présence de l’ambroisie suggèrent des flux de gènes (pollen/semences) et une connectivité modérés à l’échelle d’un territoire agricole. Dans les environnements agricoles, la dispersion des allèles de résistance aux herbicides pourrait se faire facilement de proche en proche via les flux de pollen, et également à plus longue distance via des dispersions de graines. Les activités anthropiques jouent un rôle majeur dans la dispersion des semences (machineries agricoles, lots de semences contaminés…).-L’analyse du système de reproduction a confirmé que cette espèce est allogame ce qui entraîne des flux de gènes intra- et inter-populations importants.Les connaissances acquises au cours de ce travail pourront aider à développer des stratégies de contrôle mieux adaptées, pour lutter efficacement contre A. artemisiifolia afin de limiter son expansion, telles que :-Des stratégies de désherbage diversifiées : combinaison de lutte mécanique (dont faux semis) et chimique (diversification des modes d’action herbicides).-Un allongement et une diversification des rotations de cultures en favorisant des cultures d’hiver et/ou des cultures couvrantes et compétitrices.Ces connaissances pourront aussi être utilisées dans la lutte contre une autre espèce adventice du genre Ambrosia, Ambrosia trifida.Mots-clés (6) : Ambrosia artemisiifolia L., ambroisies, résistance aux herbicidesThe first aim of this work was to investigate the risk for the evolution of resistance to acetolactate synthase inhibitor (ALS) herbicides in the common ragweed (Ambrosia artemisiifolia L.) through four points: (i) the selection pressure (effectiveness of a range of ALS inhibitor herbicides), (ii) the adaptive response of Ambrosia artemisiifolia (recurrent selection experiment), (iii) a resistance monitoring in fields in France, and (iv) the investigation of the mechanisms underlying herbicide resistance (target-site (TSR) and non-target-site resistance (NTSR) using transcriptomic analyses). The second aim was to study the connectivity of A. artemisiifolia populations in agricultural landscapes using microsatellite markers developed during this work, to determine factors that could facilitate the spread of this invasive weed species and the spread of herbicide resistance.In regards to herbicide resistance:-The sensitivity of A. artemisiifolia to ALS-inhibiting herbicides is variable between active ingredients.-Plants that survived the French maximum authorized field rate and higher rates of metsulfuron were selected to implement a recurrent breeding program. After two selection cycles, the resistance level to metsulfuron increased and resistance to imazamox and tribenuron emerged.-Three cases of imazamox resistance were identified in the field, including two cases of pure NTSR and one case of TSR - NTSR coexistence.-A transcriptome for A. artemisiifolia, AMBELbase, was generated using the PacBio sequencing technology to search for genes involved in NTSR mechanisms (RNAseq approach). 62 candidate contigs were identified including ABC transporters, cytochromes P450 and glutathione S-transferases known to be involved in the degradation of herbicides.In regards to population connectivity:-26 microsatellite markers were developed and revealed high genetic variability. Genetic structuring has been studied on a large scale for populations of A. artemisiifolia from Europe (invasion range) and North America (native range).-On a finer scale (agricultural landscape), the genetic structure of populations was influenced by colonization events. Migration events detected among the areas colonized by A. artemisiifolia suggested moderate pollen/seed flows and connectivity at the farmland scale. In agricultural environments, herbicide resistant alleles could be easily spread among neighbouring populations via pollen flow, and also at longer distances via seed dispersal. Human-related activities play a major role in the dispersal of seeds (agricultural machinery, contaminated seed lots, etc.).-The mating system analysis confirmed that A. artemisiifolia is an obligate outcrossing species which leads to important intra- and inter-population gene flow.The knowledge acquired during this work may help to foster the development of better management strategies to effectively control A. artemisiifolia to limit its spread, such as:-Diversified weed control strategies: combination of mechanical (including false-seed) and chemical weeding (diversification of herbicide modes of action).-Longer diversified crop rotations including more winter crops and/or cover and competitive crops to break the life cycle of A. artemisiifolia.These knowledge may also be used to better control of another weed species of the genus Ambrosia, Ambrosia trifida L
7
Al-Yarubi, Qahtan. "Phase flow rate measurements of annular flows." Thesis, University of Huddersfield, 2010. http://eprints.hud.ac.uk/id/eprint/9104/.
Abstract:
In the international oil and gas industry multiphase annular flow in pipelines and wells is extremely important, but not well understood. This thesis reports the development of an efficient and cheap method for measuring the phase flow rates in two phase annular and annular mist flow, in which the liquid phase is electrically conducting, using ultrasonic and conductance techniques. The method measures changes in the conductance of the liquid film formed during annular flow and uses these to calculate the volumetric and mass flow rates of the liquid film. The gas velocity in the core of the annular flow is measured using an ultrasonic technique. Combined with an entrainment model and the liquid film measurements described above, the ultrasonic technique enables the volumetric flow rate of the gas in the core and the volumetric and mass flow rates of entrained liquid droplets to be measured. This study was based on experimental work and the use of modelling techniques. The practical investigation comprised a series of experiments conducted on a purpose built flow loop in which the test section was a Perspex pipe of 50mm ID. The experimental work was limited to two-phase air-water flow. The flow loop was specifically designed to accommodate the different instruments and subsystems designed in this investigation including bespoke flow meters and a film extraction system. Most flow loop controls were automated using a MATLAB program. Reference measurement of the total water flow rate was made using a calibrated turbine flow meter and of the air flow rate using a calibrated rotameter. For the combined ultrasonic/conductance method investigated in this thesis, the velocity of the gas in the core was found using a novel Ultrasonic Flow Meter (USFM). The positioning and arrangement of the transducers have never been used previously. The flow velocity of the liquid film and the thickness of the film were measured using a novel Conductance Flow Meter (CFM). The CFM measured the liquid film thickness using novel wall conductance probes. By cross correlating the signals from a pair of such probes the film velocity was obtained. Good agreement of the experimental results obtained from the CFM and USFM with results published in the literature was found. Although not investigated experimentally in the work described in this thesis, annular flows encountered in the oil industry may contain a liquid phase comprising a mixture of oil and water. For such flows, the volume fractions of the oil and water can be measured using an automated bypass system developed during this project. The bypass system periodically extracts part of the liquid film, measures its density and then releases the sample back into the pipeline. The liquid phase volume fractions are determined from this density measurement which can be performed more than once per minute. An entrainment model was developed, which is required by the ultrasonic/conductance flow metering technique described in this thesis, in which the mass fraction of the liquid flowing as entrained droplets in the core can be determined from the liquid film thickness and velocity measurements. A mathematical model was also developed to describe the properties of the liquid film, such as liquid velocity profile within the film, and the model’s results were found to agree with the experimental results obtained during the project and also with previous work cited in the literature. The complexity of this latter model was reduced by making a number of simplifying assumptions, which are presented and discussed in the thesis, including the assumption that in annular flow there is a dynamic balance liquid entrainment and droplets being deposited back onto the film. The combination of the designed CFM and USFM with the bypass tube and the entrainment model offer the opportunity for a ‘wet gas’ flow meter to be developed to measure two and three phase annular flows at relatively low cost and with enhanced accuracy. Such a device would have the advantage that it would by substantially smaller than systems using separators and it could even be retrofitted onto off-shore platforms. The integration of the subsystems developed in this project into a single system capable of giving on-line measurements of annular flow would be a major benefit to the author’s sponsor, Petroleum Development of Oman.
8
Mekanik, Abolghasem. "General solution for unsteady annular flows between concentric cylinders and annular flow-induced instabilities." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28844.
Abstract:
The aim of this Thesis is to obtain time-accurate solutions of the Navier-Stokes equations for laminar incompressible unsteady flows generated by oscillating boundaries in an annular region made from two concentric cylinders. For this, a time-dependent coordinate transformation is first used to obtain a fixed computational domain. The resulting governing equations in the fixed domain are discretized in real time based on a three-time-level implicit scheme. A pseudo-time integration with artificial compressibility is then used to reduce the resulting coupled discretized equations in delta form to set a decoupled scalar tridiagonal systems.The method of solution has been applied to various 3-D unsteady flows in annular geometries, as well as to 2-D annular flows. The numerical results obtained are compared with those based on a mean position analysis, without transformation, for small-amplitude oscillation. This comparison shows that the time-dependent coordinate transformation is necessary to obtain accurate solutions for larger-amplitude oscillations.
The mean-position approach has also been applied to the analysis of axially variable annular configurations. The results obtained show more pressure recovery after a diffuser section with 6$ sp circ$ half-angle than in the case of 20$ sp circ$ half-angle.
A comprehensive experimental study was conducted to validate the theoretical results in the range of laminar flow. The results obtained were in good agreement with the numerical results, specially with those obtained by the time-dependent coordinate transformation. Experiments were also conducted for turbulent flow.
Based on the theoretical models developed, a computational method has been used to study fluid-structure interaction phenomena. It was applied to several cylindrical annular configurations in which one side of the annulus, the outer cylinder, is assumed to be flexibly supported, and thus to be susceptible to flow-induced instabilities. The structural and N-S equations were solved simultaneously by employing the numerical method developed for the unsteady flow and a fourth-order Runge-Kutta scheme for the structural motion. The numerical results thus obtained have predicted the stability of the structure for different annular geometries. The structure having a uniform annular geometry was shown to be more damped, while the annular geometry with a backward facing step is less damped. The study of the structure for a uniform annular geometry in the case of the rocking motion of the outer cylinder predicts an instability in the form of flutter of the outer cylinder.
9
Luo, Yuejin. "Non-Newtonian annular flow and cuttings transport through drilling annuli at various angles." Thesis, Heriot-Watt University, 1988. http://hdl.handle.net/10399/1477.
Abstract:
This thesis presents the results of the investigations in two areas, i.e. non-Newtonian annular flow and cuttings transport in drilling annuli at various angles. In the first part of the thesis, a review of the fundamentals and the previous studies on laminar concentric annular flow of non-Newtonian fluids is given at first. Then two parallel theoretical studies are performed, respectively, on: a. Laminar eccentric annular flow of power-law and Bingham plastic fluids. In this analysis, a new method is used which treats an eccentric annulus as infinite number of concentric annuli with variable outer radius. The analytical solutions of the shear stress, shear rate, velocity and the volumetric flowrate/pressure gradient are obtained over the entire eccentric annulus. This analysis is useful in design of any engineering operations related to eccentric annular flow such as oil drilling operations. b. Laminar helical flow of power-law fluids through concentric annuli. A group of dimensionless equations are derived in this analysis for the profiles of the apparent viscosity, angular and .axial velocities, and for the volumetric flowrate. These equations are essential when one needs to simulate the helical flow conditions in various engineering operations. In addition, another group of dimensionless equations are also derived for pressure gradient calculations which can be used directly by drilling engineers to predict the reduction of the annular friction pressure drop caused by drillpipe rotation during drilling operations. The second part of the thesis is dedicated to the investigations into the problems directly related to cuttings transport through drilling annuli at various angles. First, both theoretical and experimental studies on settling velocities of drilled cuttings in drilling fluids are conducted using new approaches to account for the non-Newtonian nature of drilling fluids and for the shape irregularity of drilled cuttings. Based on experimental results, a generalised model is developed for calculating settling velocities of variously shaped particles in power-law fluids. Then, the effects of various parameters on cuttings transport during drilling operations are analysed based on the previous and the present studies. After that, an extensive theoretical analysis for the previous studies on the minimum transport velocity (MTV) in solid-liquid mixture flow through pipelines, on initiation of sediment transport in open channels and on MTV for cuttings transport in deviated wells is presented. At last, theoretical studies on the minimum transport velocity for cuttings transport in drilling annuli at various angles are conducted and two parallel general correlations are developed. When these correlations are experimentally verified and numerically established in the future, they can be served as general criteria for evaluating and correlating the effects of various parameters on cuttings transport, and as a guideline for cuttings transport programme design during directional drilling.
10
Hawkes, Neil. "Wispy-annular flow." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/12043.
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Jedwab, M. R. "Flow in annular diffusers." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233255.
Abstract:
An experimental study was performed to investigate the mechanics of fluid flow in a 30o annular diffuser, and to study the periodicity of flow oscillations in this region. Surface oil-flow patterns and smoke-flow visualisation experiments were performed with a centrebody concentric and eccentric in the diffuser. Above a threshold offset, the measurements revealed two contra-rotating periodic vortices in antiphase with each other, symmetrically disposed about the plane of minimum clearance in the annulus, and originating in the 30o diffuser. Steady pressure measurements indicated that the steady fluid forces acting on the centre body are decentralising, and any small perturbation will result in the centrebody being pushed towards the wall of the diffuser. Unsteady pressure and force measurements showed that for a mean eccentric centrebody position, there was a predominantly tangential unsteady vortex force present with the centre body both fixed and vibrating. This vortex force scaled linearly with flow velocity, indicating a Strouhal-type mechanism. The magnitude of the vortex force was independent of both amplitude and frequency of vibration of the centrebody, indicating a forced vibration effect. The exception was when the centre body frequency approached the vortex shedding frequency, in which case lock-on occurred. For the geometry considered, lock-on does not significantly increase the unsteady forces acting on the centrebody. During lock-on it was found that the vortices could not only be influenced by centrebody motion, but could be completely suppressed by closely controlling the amplitude and frequency of the centrebody. The effect that shaking the centrebody has on the different flow regimes in which the annular diffuser operates is explained. The vortices could also be eliminted by a) attaching a small helical fence to the surface of the centrebody, and b) by inserting a perforated liner within, and downstream of, the diffuser section. A small perturbation theoretical analysis of the unsteady flow in the diffuser has been developed. The flow was computed numerically, and the predicted self-induced forces examined. The analysis predicted mainly negative damping for the configurations examined. The predicted magnitude of the unsteady forces agreed with experimental results. Finally, the flow was also predicted analytically, and a good level of agreement with the numerical study was found.
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Wang, Xiaohang. "Large eddy simulation of turbulent pipe/annular supercritical CO₂ flow with heat transfer and perfect gas flow in a ribbed annuli passage." [Ames, Iowa : Iowa State University], 2006.
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Dillon, Chad Michael. "Two-Phase Flow Within Narrow Annuli." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5097.
Abstract:
A study of two-phase flow in annular channels with annular gaps of less than 1 mm is useful for the design and safety analysis of high power density systems such as accelerator targets and nuclear reactor cores. Though much work has been done on pressure drop in two-phase flow, designers rely mostly on empirical models and correlations; hence, it is valuable to study their applicability for different channel sizes, geometries, and gas qualities.
The pressure drop along a concentric annular test section was measured for cases of either constant quality or variable quality along its length (such as in sub-cooled and flow boiling). A porous tube was used to inject gas along the inner surface of the annular channel, thereby simulating the case of flow boiling along the inner surface. The data were compared to predictions of various models and correlations. Additionally, the effect of wall vibrations on the pressure drop was examined. Experiments were conducted by imposing vibrations of known amplitudes and frequencies on the outer tube of the annulus. Wall vibrations were thought to be important for flow in microchannels where the vibration amplitudes may be significant compared to the channel hydraulic diameter.
The results obtained in this investigation indicate that the pressure drop correlation given by Beattie and Whalley provides the best agreement with the data for both porous tube gas injection (i.e. variable quality) and constant quality two-phase flow within the narrow annulus. Furthermore, the results show that there is a minimal effect of vibrations on two-phase pressure drop over the range of frequencies and amplitudes studied.
14
Wolf, Arne. "Film structure of vertical annular flow." Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/8178.
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Badie, Shahrokh. "Horizontal stratifying annular gas liquid flow." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249385.
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McQuillan, K. W. "Flooding in annular two-phase flow." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354843.
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Willetts, I. P. "Non-aqueous annular two-phase flow." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393120.
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Flores, Aaron G. (Aaron Guerrero). "Dryout limits in horizontal annular flow." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12872.
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Teixeira, Jose Carlos Fernandes. "Turbulence in annular two phase flow." Thesis, University of Birmingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570318.
Abstract:
The structure of turbulent flow in vertical upwards annular air water two-phase flow was examined. Experiments were carried out in a 32 mm internal diameter tube using laser Doppler anemometry. Simultaneous measurements of the two velocity components and the Reynolds stress were obtained by the use of two colours (blue and green) of a 50 mW argon ion laser. The gas core was seeded by polystyrene particles of 1 um diameter which were believed to follow the gas turbulent fluctuations. The characteristics of the signal were used to discriminate these tracer particles from the water droplets. The gas velocity profiles were shown to be more peaked at the centre of the tube than those observed in turbulent single phase flow. Comparative analysis with other data suggested that both interfacial roughness and, particularly, the momentum interchange between the droplets and the gas core, are the most important factors affecting the gas velocity profile in annular flow. Turbulent fluctuations of the gas velocity were found to be significantly higher than those typical of single phase flow, for similar gas Reynolds numbers. The interfacial shear, droplet size and concentration and the presence of disturbance waves at the interface were identified as being the most important factors affecting the gas turbulence in annular flow. A model was developed to predict the axial component of the turbulent fluctuations at the centre of the tube. The turbulence transport properties were observed to differ from those typical of single phase flow: i.e., higher production of turbulent energy (associated with higher anisotropy ratios), higher turbulence length scales and comparativelly lower dissipation ratios. Extrapolation of the mixing length theory to annular flow appeared to be inappropriate. Droplet size measurements showed that the gas velocity and the droplet concentration are the most important parameters affecting droplet size. At low droplet concentrations (where the gas-droplet interaction is more important than that between the droplets), a modified Weber number based on the homogeneous gas core momentum describes the maximum droplet diameter. At high droplet concentrations, the data suggests that coalescence is the dominant factor. Droplet velocity was found to be related to the size of the droplets: i.e., large droplets travel slower than small ones. The difference in velocity between large and small droplets was found to depend on the liquid and gas flow rates. This observation is related to conditions where droplet coalescence occurs. The effect of inserts on droplet size and the entrained fraction was examined. Disturbances in the channel geometry were found to affect the mean droplet size due to the creation of a new droplet population. The entrained fraction of liquid downstream of the insert was also affected. A model was formulated to describe the liquid interchange in the presence of a vertical plate.
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Shlyubsky, Dmitry Iosifovich. "Flow control in an annular-return flow using combustion-driven actuators." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/36537.
Abstract:
The annular-return flow and the utility of small-scale, combustion-based actuators for its control are investigated experimentally. The annular return flow is generated by an axial primary round jet, which impinges normally on a bounded end wall of a concentric tube, subsequently reverses direction, and exits the tube in a countercurrent flow to the primary jet. The combustion-based actuator generates a momentary (pulsed) jet that is produced by the ignition of a mixture of gaseous fuel and oxidizer in a small (cubic centimeter scale) combustion chamber. The operating frequency and the phase can be continuously varied by independently controlling the flow rate of the fuel/oxidizer and the ignition frequency. Two radially-opposing actuators are mounted on the wall of the annular return tube and are used to trigger flow transients that alter the global flow through strong feedback.
The characteristics of the baseline flow and the effects of actuation are investigated using particle image velocimetry (PIV) as well as static and unsteady pressure measurements. The baseline flow is highly unstable, exhibiting very high rates of flow recirculation. The actuator jet acts as an azimuthal obstruction deflecting the primary jet and causing it to flow around the actuator jet. Furthermore, the interaction of the primary jet with the actuator jets generates large-scale circulation domains.
21
Mohri, K. "Supersonic flow over rectangular-section annular cavities." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501753.
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Ekberg, Nathanial Paul. "Two-phase flow in horizontal thin annuli." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17250.
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Yapici, Sinan. "Electrochemical mass transfer in annular swirl flow." Thesis, University of Exeter, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303777.
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Blasick, Ann Marie. "Onset of flow instability in heated horizontal annuli." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19538.
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Jepson, D. M. "Vertical annular flow : the effects of physical properties." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316862.
26
Qiu, Yue. "Computational Investigation of Annular Flow Condensation in Microgravity." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1561039399443141.
27
Lorenz, David Joseph. "Wave-mean-flow interaction and the annular mode /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10036.
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Mohapatra, Chinmoy Krushna. "Computational Study of Internal Two Phase Flow in Effervescent Atomizer in Annular Flow Regime." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470741568.
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Curran, Stephen J. "Hydrodynamics and mass transport in an annular flow bioreactor." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508496.
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Altunbas, Ayse. "Study of two-phase annular flow in inclined pipes." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301659.
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Chong, Li Yean. "Annular two phase flow in straight and serpentine channels." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403700.
32
TARAZONA, VICTOR MANUEL CARDENAS. "FLOW OF PSEUDOPLASTIC FLUID IN ANNULAR WITH VARIABLE ECCENTRICITY." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8743@1.
Abstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO estudo de escoamentos em espaço anular é de fundamental importância para o entendimento e otimização do processo de perfuração de poços. A lama de perfuração deve possuir propriedades reológicas e termofísicas tais que garantam um bom desempenho no carreamento de cascalho, na lubrificação e refrigeração das brocas, na limpeza do poço, manutenção da pressão da coluna de líquido para equilibrar a pressão das formações atravessadas e estabilizar as paredes do poço. Uma análise completa desta situação é extremamente complexa; o cilindro interno (coluna) pode estar girando, a geometria da parede do poço não é um cilindro perfeito, o espaço anular é excêntrico e a excentricidade varia ao longo do poço. Além disto, lamas de perfuração possuem um comportamento pseudoplástico, isto é a viscosidade é função decrescente da taxa de deformação. Os modelos que levam em conta todos esses fatores são extremamente complexos e caros computacionalmente. Os modelos disponíveis na literatura utilizam hipóteses simplificadoras para tornar a análise menos complexa. Muitos trabalhos consideram a rotação do cilindro interno e o comportamento não Newtoniano, mas desprezam a variação da excentricidade ao longo do poço. Mesmo com esta simplificação, os modelos apresentados, que consistem na solução da equação bidimensional para determinar o campo de velocidade axial e tangencial do escoamento desenvolvido em um espaço anular, possuem alto custo computacional. O modelo apresentado neste trabalho leva em conta a variação da excentricidade ao longo do poço, bem como o comportamento pseudoplástico da lama e a rotação do cilindro interno. As equações que governam o problema foram simplificadas utilizando a teoria de lubrificação. As equações diferenciais parciais que descrevem o perfil de velocidade e a pressão ao longo do poço foram resolvidas pelo método de diferenças finitas (diferenças centrais) e linearizadas pelo método de Newton. O modelo de lubrificação foi validado através da comparação dos resultados obtidos com trabalhos na literatura para escoamentos com excentricidade constante. Os resultados mostram o efeito da variação da excentricidade ao longo do poço, da rotação na coluna, das propriedades não Newtonianas no padrão do escoamento e no fator de atrito.
Helical flow in annular space occurs in drilling operation of oil and gas wells. The correct prediction of the flow of the drilling mud in the annular space between the wellbore wall the the drill pipe is essential to determine the variation in the mud pressure within the wellbore, the frictional pressure drop and the efficiency of the transport of the rock drill cuttings. A complete analysis of this situation is extremely complex; the inner cylinder is usualy rotating, the wellbore wall will depart significantly from cylindrical, during driling operation the drill pipe is eccentric, and the eccentricity varies with position along the well. Moreover, drilling muds present pseudoplastic behavior, the viscosity is a strong function of the deformation rate. A complete analysis of this situation would require the solution of the three-dimensional momentum equation and would be computationally expensive and complex. Models available in the literature to study this situation do consider the rotation of the inner cylinder and the non Newtonian behavior of the liquid, but assume the position of the inner and outer cilinders fixed, i.e. they neglect the variation of the eccentricity along the length of the well, and assume the flow to be well developed. This approximation leads to a two-dimensional model to determine the three components of the velocity field in a cross-section of the annulus. The resulting differential equations have to be solved by some numerical method. The model presented in this work takes into account the variation of the eccentricity along the well; a more appropriate description of the geometric configuration of directional wells. As a consequence, the velocity field varies along the well length and the resulting flow model is three-dimensional. Lubrication theory is used to simplify the governing equations into a non-linear, two-dimensional Poisson Equation that describes the pressure field. Lubrication model was validated by comparing the predictions to reported results on fully developed flow on eccentric annular space. The results show the effect of varying eccentricity, non Newtonian behavior and inner cylinder rotation on the flow field and on the friction factor.
33
Bremner, Sherry. "A granular flow model of an annular shear cell." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20304.
Abstract:
Machinery such as an IsaMillTM used in communition to produce fine particle sizes that allow minerals to be extracted are best modelled using granular flows. A single rheological description that captures all the features of granular flows has not yet been realised, although considerable progress towards a complete theory has been made. Existing models of such horizontally stirred mills are empirical, tend to be extremely dependent on boundary conditions and do not allow for confident extrapolation beyond their window of design. As a first step to understanding the dynamics inside the IsaMillTM,a constitutive stress model of a horizontal annular shear cell is developed. This shear stress model was used in an athermal energy balance to develop a description of the power dissipation, which drives the communition purpose of the IsaMillTM. The key ingredients (velocity, shear rate and volume fraction distributions) to the granular ow model are extracted from experiments using Positron Emission Particle Tracking (PEPT), as well as Discrete Element Method (DEM) simulations. 5mm glass beads were used to fill an annulus 51mm wide. In the PEPT experiments, two different surfaces of the driving wall (the inner cylinder of the shear cell) were used, over two shearing velocities. The effect of two friction coefficients over a range of shearing wall velocities were examined in the DEM simulations. The data were examined over 3 selected radial lines and utilised to calculate the shear stress distribution and the power dissipation from the developed models. It was found that even the usually simple relations describing the dynamics within a vertical shear cell are greatly modified by changing the orientation of the rotation axis.
34
Wang, Hengliang. "Numerical study of turbulent flow in eccentric annular pipe." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6349.
Abstract:
An eccentric annular duct is a prototype element in many applications, for example in close-packed tubular heat exchangers and coolant channels of nuclear reactors. From a fundamental viewpoint, turbulent flow in eccentric annular ducts is an ideal model for investigating inhomogeneous turbulence. It is also a convenient model to study the laminar and turbulent interface and may serve as a test case for turbulence modelling of flows with partly turbulent regimes. Based on the approach of direct numerical simulation, numerical investigations of turbulent flow in eccentric annular pipes are carried out in this thesis. We first investigated the case of fully turbulent flow. A detailed statistical analysis of turbulent flow and heat transfer was performed. Simulation results, such as friction factors, mean velocity profiles and the secondary-motion pattern, are in overall qualitative and quantitative agreement with the existing experimental data. The components of the Reynolds stress tensor, temperature-velocity correlations and some others were obtained for the first time for such kind of a flow. The study of the partly turbulent flow case was then carried out. Three approaches for detecting interfaces between laminar and turbulent regimes in partly turbulent flow in rotating eccentric pipes were compared and discussed. Positions of laminar-turbulent and turbulent-laminar interfaces obtained from profiles of perturbation enstrophy are the same as those obtained from production terms of enstrophy. Using patterns of streaks defined by wall shear stresses to determine the locations of interfaces showed similar results. The growth rate of a small disturbance in partly turbulent flow case was also analyzed. Small perturbations were introduced into the initial flow field in two different ways. Both cases show that the global growth rate of the small disturbance normalized by the global viscous time scale is constant. This constant value is in a good agreement with that obtained in channel flows and tube flows. A new approach was proposed to distinguish the interface between laminar and turbulent flow by introducing the global and local disturbance growth rate.
35
Al-Aufi, Yousuf Abdullah. "Vertical annular flow characteristics for air/silicone oil system." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49216/.
Abstract:
Annular flow is one of the most common two-phase flow regimes observed in industrial applications. In annular flow, the liquid flows partly as a thin film along the pipe wall and partly as droplets entrained in the turbulent gas core. Most of the previous studies about the characteristics of annular flow and the developed correlations were conducted using an air/water system. This thesis reports an investigation about the characteristics of the annular flow regime and a development of liquid film thickness measurement using an ultrasonic technique in air/water and air/silicone oil systems. Experiments were carried on an upward vertical annular flow test facility with 34.5 mm inner diameter (ID) using air/water and air/silicone oil two-phase systems. Time-varying of total pressure drop, liquid film thickness and wall shear stress were measured. The total pressure drop was measured using a remote seal differential pressure transducer and the wall shear stress was measured using a glue-on hot film sensor. An ultrasonic technique was developed to measure the liquid film thickness. It was evaluated using static and dynamic measurements. For static measurements, it was compared with the liquid film thickness calculated based on knowledge of liquid volume and area of the test rig. For dynamic measurements, it was compared with two well-known conductance measurement techniques (Multi Pin Film Sensor and concentric probe) in falling film and upward vertical annular flow test facilities respectively. The relative error between the ultrasonic technique and the other two techniques was within ±5%. A new processing method for ultrasonic measurement called Baseline removal method was developed for measuring liquid film thickness less than 0.5 mm. The influence of gas and liquid superficial velocities, viscosity and surface tension on the measured parameters was studied using both systems. Both systems showed similar trend behavior with increasing gas and liquid superficial velocities even there was a difference in fluid properties. The results were also compared with the existing correlations developed using an air/water system to predict each one of the measured parameters. Most of the tested correlations predicted the total pressure drop, liquid film thickness and wall shear stress with relative deviation of ±50% or even higher in some cases.
36
Fernelius, Mark H. "Effect of Full-Annular Pressure Pulses on Axial Turbine Performance." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3825.
Abstract:
Pulse detonation engines show potential to increase the efficiency of conventional gas turbine engines if used in place of the steady combustor. However, since the interaction of pressure pulses with the turbine is not yet well understood, a rig was built to compare steady flow with pulsing flow. Compressed air is used in place of combustion gases and pressure pulses are created by rotating a ball valve with a motor. This work accomplishes two main objectives that are different from previous research in this area. First, steady flow through an axial turbine is compared with full annular pulsed flow closely coupled with the turbine. Second, the error in turbine efficiency is approximately half the error of previous research comparing steady and pulsed flow through an axial turbine. The data shows that a turbine driven by full annular pressure pulses has operation curves that are similar in shape to steady state operation curves, but with a decrease in turbine performance that is dependent on pulsing frequency. It is demonstrated that the turbine pressure ratio increases with pulsed flow through the turbine and that this increase is less for higher pulsing frequencies. For 10 Hz operation the turbine pressure ratio increases by 0.14, for 20 Hz it increases by 0.12, and for 40 Hz it increases by 0.06. It is demonstrated that the peak turbine efficiency is lower for pulsed flow when compared with steady flow. The difference between steady and pulsed flow peak efficiency is less severe at higher pulsing frequencies. For 40 Hz operation the turbine efficiency decreases by 5 efficiency points, for 20 Hz it decreases by 9 points, and for 10 Hz it decreases by 11 points. It is demonstrated that the specific power at a given pressure ratio for pulsed flow is lower than that of steady flow and that the decrease in specific power is lower for higher pulsing frequencies. On average, the difference in specific power between steady and pulsed flow is 0.43 kJ/kg for 40 Hz, 1.40 kJ/kg for 20 Hz, and 1.91 kJ/kg for 10 Hz.
37
Skoog, Erik. "CFD Annular Flow Modelling Based on a Three-Field Approach." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80165.
Abstract:
This master thesis aim to model the annular flow that occurs in the final section between the fuel rods inside Boiling Water Reactors, by approximating the geometry to a cylindrical pipe. Simulations were performed in the software ANSYS Fluent, as a step in the development of replacing the 1D correlations currently used in the nuclear industry with CFD models in 3D. An Eulerian-Lagrangian approach was used for the three fields of steam, liquid film and liquid droplets in the model. Entrainment was modeled based on 1D correlations from Okawa [7] and deposition with the built in Discrete Phase Model in ANSYS Fluent. The work focused on making the process less time consuming, and increasing accuracy of the model by comparing the results with empirical data based on experimental values. A transverse velocity was applied on the droplets at the point of entrainment with better correlating results with the Okawa model.
38
Agostinelli, Giulia. "Advancement of closure relations for annular flow modeling in CFD." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129364.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, September, 2020Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 118-124).
In Boiling water Reactors (BWRs), the presence of a liquid film in contact with the heated rod surface is crucial to ensure an efficient heat removal and prevent the threatening occurrence of dryout. The accurate prediction of the complex multidimensional liquid film behavior in advanced BWR fuel assemblies is critical to guarantee improved reactors performance and safety. Multiphase- CFD (M-CFD) brings the ability to model the complex three-dimensional flow structures in annular flow regime [1], while physics-based constitutive equations are needed to accurately represent the phase interactions, particularly at the liquid film interface. The development of closure relations for droplet deposition and entrainment as well as wave-induced interfacial shear, is a major priority for the modeling of annular flow in M-CFD. In annular flow conditions, liquid is continuously exchanged at the interface between the bulk steam and the film on the walls.
While liquid droplets deposit onto the film driven by turbulent diffusion, new ones are entrained from the waves appearing on the film surface. A modeling approach is proposed and assessed to represent the local subgrid-scale deposition in CFD, showing comparable results with existing integral correlations, and an average error of 30%. Available closures are also evaluated for their ability to represent entrainment in the CFD implementation. Finally, in order to drive the advancement of the representation of interfacial shear, as well as physics-based droplet entrainment, the work focuses on the analysis and modeling of disturbance waves. The recent high resolution film measurements collected by Robers [2] are analyzed and leveraged to propose a physical representation of disturbance waves, which can be implemented into a complete model.
The proposed model is successfully assessed against the experimental measurements of Sawant [3], while a large disagreement is found in comparison with the high pressure data evaluated at the RISO facility [4]. The new model predictions are consistent with existing integral correlations, demonstrating the need for further advancement of high pressure experiments with high resolution, necessary to drive more general representations. The complete set of closures is implemented in a commercial CFD software, and demonstrated adopting data from the Robers experiments. While the lingering limitations of the CFD implementation to transport thick films lead to overprediction of the local film thickness, the formulation shows promising performance towards more fundamental modeling of annular flow in M-CFD.
by Giulia Agostinelli.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
39
Raddino, Salvatore. "CFD modeling of annular flow with a three-field approach." Thesis, KTH, Fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-214546.
40
Pohner, John A. "Analysis of separated, non-parallel, axisymmetric, annular two-phase flows." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/15838.
41
Stridh, Madeleine. "Material flow : An analysis of a production area for improved material flow." Thesis, Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80193.
Abstract:
Focus in the world today is quality and customer orientation. An organization needs to understand the concept of value from the perspective of a customer in order to keep up with expectations on quality, and the turbulent and global environment of today characterized by rapidly changing conditions. This master thesis project was conducted at ABB in Sweden during spring 2020. It is essential for ABB to have an ongoing focus on improvement to maintain a successful organization and enable a competitive future of quality and innovation. The aim of this project was to identify ways to improve material flow and reduce the amount of non-value-added activities that exist in a particular assembly process today. The objective of the project was to conduct proposals on realistic actions for improvement for implementation. Initially in the project a current state was performed and compiled into a specification of requirements and visualized through overall mapping of the material and communication flow. Two of the requirements were reducing the total lead time and ensure the same, or improved, physical and psychosocial work environment. The result of the current state showed that material is not available when needed, material shelves are not structured, and material flow is not optimal. Analysis methods used for analyzing the current state were material flow charts, value stream mapping and spaghetti diagrams. The outcome of the performed analyzes were then used as the foundation for a compiled list of problem areas. All previous performed work was then summarized, discussed and developed into a list of actions for improvement. This phase was performed by initially generating a great amount of ideas, which were then reviewed and evaluated in consideration of the specification of requirements. In addition to the final list of actions, a mapping of the future state was conducted to support the actions and visualize what a future state could look like if the actions are implemented. Lastly, the final list of actions was complemented with another list – a living document of the actions. This document gives the opportunity on a regular basis to monitor progress and should be regularly reviewed and updated. To ensure a successful implementation of improvement work based on the conducted action list, it is recommended to define and clarify responsibility for each action as well as target date and end date. Furthermore, the list should be continuously modified to ensure implementation. It is as well recommended to acknowledge implemented improvements in parallel with performing actions to maintain motivation. Additionally, participation in implementation and promoting dialogue, transparency and respect are valuable factors reducing the negative effects of the implementation of improvement concepts and contributes to a sustainable development of the improvement work.
42
Pan, Shunqi. "An experimental study of swirl development along the annulus between a rotor and a stator." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1407.
43
Tkaczyk, Piotr. "CFD simulation of annular flows through bends." Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556100.
Abstract:
There is particular interest in the oil industry, in gas/liquid distribution in pipe line systems. The presence of bends has a significant effect on gas/liquid flows. Bends are often necessary to fit the equipment into limited spaces e.g. in plants or on oil rig platforms. As part of designing industrial systems, it is therefore important to be able to understand how liquid and gas move around bends. The aim of this research is to develop a method for predicting gas/liquid annular flows. A 3D CFD-based method is therefore developed to solve for annular flows in pipes and is applied to a range of pipe bends. In the presented study, the two-phases are gas and liquid. Multiphase fields can be handled as a continuum gas field, continuum liquid filed and as liquid droplets of varied diameters. The liquid travels along the walls as a film and in the gas core in the form of droplets. The presented approach accounts for the dynamics of the droplets flow in the gas core and their interaction between them. The liquid film is solved explicitly by means of a modified Volume of Fluid (VOF) method. The droplets are traced using a Lagrangian technique. The film to droplets (entrainment) and droplets to film (splashing, spread, bounce and stick) interactions are taken into account using sub- models to complement the VOF model. In free surface flows, a high velocity gradient at the gas/liquid interface results in high turbulence generation. In order to improve the momentum transfer between the phases at the interface, a correction to VOF is also implemented based on the work of Egorov [1]. A detailed comparison between the model and experimental data for vertical, Wolf et al. [2], and horizontal annular flows, Butterworth and Pulling [3], show reasonable agreement. The model is then applied to annular flow in bends, Maddock et al. [4], Anderson and Hills [5], Sakamoto et al. [6]. The comparison between the model and experimental data found in the literature show a good agreement. The model is also successfully applied to medium size (127mm) pipe configurations run at Nottingham University as part of a parent project. The model is finally applied to large pipe diameters encountered in industrial oil/gas applications to investigate scale issues and the model potential in industry.
44
Chochua, Gocha. "Computations of gas annular damper seal flows." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE1000115.
Abstract:
Thesis (Ph. D.)--University of Florida, 2002.Title from title page of source document. Document formatted into pages; contains xix, 103 p.; also contains graphics. Includes vita. Includes bibliographical references.
45
Donovan, William Howard. "Experimental and computational investigation of flow through an annular turbine cascade." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA302953.
46
Thomas, Gregory David. "Measurement and prediction of the flow through an annular turbine cascade." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA272530.
47
Omurlu, Cigdem. "Mathematical Modeling Of Horizontal Two-phase Flow Through Fully Eccentric Annuli." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607243/index.pdf.
Abstract:
iv
The primary objective of this study is to understand the mechanism, the
hydraulics and the characteristics, of the two-phase flow in horizontal annuli.
While achieving this goal, both theoretical and experimental works have been
conducted extensively. The METU-PETE-CTMFL (Middle East Technical
University, Petroleum and Natural Gas Engineering Department, Cuttings
Transport and Multiphase Flow Laboratory) multiphase flow loop consists of
4.84 m long eccentric horizontal acrylic pipes having 0.1143m inner diameter
(I.D) acrylic casing - 0.0571m outer diameter (O.D) drillpipe and 0.0932m I.D
acrylic casing - 0.0488m O.D drillipipe geometric configurations. During each
experiment, differential pressure loss data obtained from digital and analog
pressure transmitters at a given liquid and gas flow rate were recorded. The
flow patterns were identified visually. Meanwhile a mechanistic model has been
developed. The flow pattern identification criteria proposed originally for twophase
flow through pipes by Taitel and Dukler1 has been inherited and modified
for the eccentric annular geometry. The complex geometry of eccentric annuli
has been represented by a new single diameter definition, namely
representative diameter dr. The representative diameter has been used while
calculating the pressure losses. A computer code based on the algorithm of the
proposed mechanistic model has been developed in Matlab 7.0.4. Both the flow
pattern prediction and the frictional pressure loss estimation are compared with
the gathered experimental data. Moreover, friction factor correlations have
been developed for each flow pattern using experimental data and statistical
methods. The performance of the proposed model and the friction factor
correlations has been evaluated from experimental data. The mechanistic
model developed in this study accurately predicts flow pattern transitions and
frictional pressure losses. The model&rsquos pressure loss estimations are within ±
30% for two different annular flow geometries.
48
Anghel, Ionut Gheorghe. "Experimental Study of Post-Dryout Heat Transferin Annuli with Flow Obstacles." Licentiate thesis, KTH, Reaktorteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-44071.
Abstract:
An experimental study on post dryout heat transfer regime in annuli with flow obstacles was conducted in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. An annulus consisting of two concentric heated pipes (12.7x24.3) mm, with total heated length equal to 3650 mm was employed as a test section. Three kinds of flow obstacles were used: pin-spacers, cylindrical obstacles and grid obstacles. The experiments performed in the test section with pin-spacers only were considered as the reference case. In two consecutive sets of runs, additional obstacles were placed inside the flow channel while keeping the pin spacers in the same positions. In that way the net effect of obstacles on heat transfer was measured. The experimental investigations were performed in a wide range of the operational conditions: mass flux (500-1750) kg/(m2s), inlet subcooling (10-40) K and system pressure (5-7) MPa. The wall superheat was measured at 88 different axial positions (40 on the inner tube and 48 on the outer tube) for the conditions mentioned above. A local heat transfer coefficient was calculated based on the measured annulus wall temperatures and the saturated fluid (water) properties. The results show an enhancement of the heat transfer coefficient downstream of flow obstacles. The most significant influence has been observed in case of pin spacers. This result is consistent with blockage area of various obstacles, which was the highest in case of pin spacers. The data obtained in more than 200 runs were compared with two pre-dryout and post-dryout correlations. The correlations show a slight over-prediction of the heat transfer coefficient in both pre-dryout and post-dryout regions. The thesis contains a detailed description of experimental procedures as well as an analysis of the results of measurements.QC 20111024
SKC: Post Dryout Regime
49
Tse, David Gar Nile. "Flow and combustion characteristics of model annular and can-type combustors." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/8941.
50
Barbosa, Jader Riso. "Phase change of single component fluids and mixtures in annular flow." Thesis, Imperial College London, 2001. http://hdl.handle.net/10044/1/11558.
Abstract:
This thesis is dedicated to the study of flow boiling of single component fluids and multicomponent mixtures in vertical pipes at high qualities. Both theoretical and experimental investigations were carried out with the objective of improving fundamental knowledge of hydrodynamics and phase change heat transfer in annular flow. The diabatic experiments had the objective of studying the nature of nucleate boiling in upward steam-water annular flow. A specially constructed, electrically heated, annulus visualisation test section (deq = 12.9 mm) was used to observe directly the interaction between disturbance waves and bubble nucleation through the analysis of high-speed video recordings. It was found that disturbance waves seem to locally trigger off the activity of nucleation sites as they travel along the channel. Local measurements of the heater wall temperature, and hence of heat transfer coefficient, were carried out using a radiation equilibrium thermocouple which could be traversed along the heated section. An analysis of the Onset of Nucleate Boiling (ONB) in climbing films was also implemented. Adiabatic experiments were carried out to investigate the behaviour of the fraction of the liquid entrained as droplets in the region of transition between the churn and annular flow regimes. An isokinetic probe was used, which enabled the simultaneous measurement of the gas and entrained liquid mass fluxes. The campaign was performed in a 10.8 m long, 31.8 mm internal diameter test section (LOTUS facility) over a wide range of flow conditions. The profiles of local droplet concentration characterise churn flow as a region in which the radial gradients of concentration tend to disappear with increasing gas flowrate. As annular flow takes place, the local concentration is virtually constant with respect to radial position and gas flowrate. As far as the determination of the fraction of liquid entrained as droplets at the onset of annular flow is concerned, the experimental results are of particular interest to annular flow computer simulation codes as it provides a basis for calculating the initial condition for the mass conservation equations. With that objective in mind, an empirical correlation was developed to predict the fraction of liquid entrained as droplets at the onset of annular flow. The modelling work on heat transfer deals with phase change of multicomponent mixtures at high qualities. A differential phenomenological model of the annular flow regime is proposed so as to describe the deterioration of the heat transfer coefficient observed by Kandlbinder (1997) for boiling of binary and ternary hydrocarbon mixtures in a 25.4 mm internal diameter, vertical pipe. The set of correlations for droplet entrainment and deposition by Govan (1990) was extended to cope with the so-called mixture effects. Use was also made of a Colburn-Drew type formulation for calculation of interfacial parameters (mass fluxes, compositions and temperature). The formulation gives a very good prediction of bulk and wall temperatures and of heat transfer coefficients determined experimentally. A simple mathematical model to describe the formation of waves characteristic of the churn flow regime is also proposed. Previous work (Govan, 1990), in which high-speed video recordings were carried out, used a test section with a specially constructed transparent liquid inlet and showed clearly the process of wave formation. The model, which is based on integral mass and momentum conservation principles, predicts the wave velocity and distance travelled by the waves. It also provides estimates of wave parameters, such as critical amplitude, length and flow rates that are consistent with the experimental observations.