Дисертації з теми "Single fluid flow"
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1
McPhail, Stephen John. "Single-phase fluid flow and heat transfer in microtubes." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-36182.
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2
Bolour-Froushan, Abol Hassan. "Prediction of single-phase turbulent flow in agitated mixing vessels." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37946.
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3
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.
Повний текст джерелаАнотація:
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.
4
Hosseinian, Armin. "Numerical simulations of fluid flow through a single rough walled fracture." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1764.
Повний текст джерелаАнотація:
The morphological properties of rock fractures may have a significant influence on their hydromechanical behaviour. Fracture surface roughness could change the fluid flow regime from laminar to turbulent, while it causes the flow properties to deviate from cubic law for smooth channels due to a change in fracture equivalent hydraulic aperture. Different empirical (including the well known Joint Roughness Coefficient, JRC) and statistical methods have been proposed for surface roughness characterisation in an attempt to link them to the hydromechanical behaviour of fractures.This thesis aims to investigate the potential for assessment of fluid behaviour by studying its surface geometrical properties. D[subscript]R[subscript]1 and D[subscript]R[subscript]2, the 2D and 3D roughness parameters developed recently using Riemannian geometry, were used to correlate fracture geometry to its flow behaviour. Also, the 2D Riemannian isotropy parameter (I[subscript]R[subscript]2) was used to correlate surface roughness anisotropy with directionality in fluid flow behaviour along different directions.Numerical simulations in both 2D and 3D were performed assuming the laminar flow regime using FLUENT software. This assumption is, to a large extent, acceptable for situations where the height to length ratios of a fracture is very small. 2D analysis of synthetic profiles with different geometries demonstrated how a change in profile roughness can affect flow response, for example, the pressure drop. JRC flow channels developed in this work as combinations of pairs of JRC profiles were simulated numerically. The analysis results indicated that channels with a similar JRC average for the upper and lower walls but a different JRC profile number responded differently when they were subjected to fluid flow. Therefore, assuming special fluid properties, correlations developed using the pressure drop of a fracture can be estimated by its analogy to JRC flow channels.3D simulations of a corrugated plane were performed assuming different asperity height distributions, for fluid travelling along different directions with respect to surface geometry and at different shear displacements. No asperity contact and failure is assumed in the analysis performed in this work. D[subscript]R[subscript]2 analysis results of the corrugated plane indicated how fluid flow could be related to surface geometry. For instance, it was observed that the pressure drop was maximised along the direction of maximum roughness and reduced to its minimum along a perpendicular direction which shows anisotropy in fluid flow behaviour. Significant changes in pressure drop due to shear offset indicated the importance of fracture wall displacements with respect to each other. A detailed analysis of one synthetically generated surface, and also five surfaces with identical statistical parameters except their correlation distances being different, further confirmed the above concepts. This was followed by analysing a real rock like fracture which was studied elsewhere for fracture shear tests in the lab. Simulation of this surface was performed with particular interest in identifying the locations where the velocity magnitude reduced to nearly zero after the fracture was subjected to a shear offset corresponding to maximum shear stress. These areas were found to be very similar to the locations of asperity degradations as observed through lab experiments. The roughness analysis of the surface was in agreement with the correlation found between the mechanical and hydraulic behaviour of the surface.The results of this research demonstrate how detailed analysis of surface geometry could provide valuable information with respect to surface flow behaviour. Detailed discussions and interpretations of the results will be presented and various conclusions will be made.
5
Alfred, Dicman. "Modeling fluid flow through single fracture using experimental, stochastic, and simulation approaches." Texas A&M University, 2003. http://hdl.handle.net/1969.1/324.
Повний текст джерелаАнотація:
This research presents an approach to accurately simulate flow experiments through a fractured core using experimental, stochastic, and simulation techniques. Very often, a fracture is assumed as a set of smooth parallel plates separated by a constant width. However, the flow characteristics of an actual fracture surface are quite different, affected by tortuosity and the impact of surface roughness. Though several researchers have discussed the effect of friction on flow reduction, their efforts lack corroboration from experimental data and have not converged to form a unified methodology for studying flow on a rough fracture surface.
In this study, an integrated methodology involving experimental, stochastic, and numerical simulations that incorporate the fracture roughness and the friction factor is shown to describe flow through single fractures more efficiently. Laboratory experiments were performed to support the study in quantifying the flow contributions from the matrix and the fracture. The results were used to modify the cubic law through reservoir simulations. Observations suggest that the fracture apertures need to be distributed to accurately model the experimental results.
The methodology successfully modeled fractured core experiments, which were earlier not possible using the parallel plate approach. A gravity drainage experiment using an X-ray CT scan of a fractured core has also validated the methodology.
6
Park, Jinyong. "Experimental and Numerical Investigations of Fluid Flow for Natural Single Rock Fractures." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1385%5F1%5Fm.pdf&type=application/pdf.
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7
Starnoni, Michele. "Modelling single and two-phase flow on micro-CT images of rock samples." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232293.
Повний текст джерелаАнотація:
In this Thesis, numerical simulations of single and two-phase pore-scale flow on three dimensional images obtained from micro-CT scanning of different reservoir rocks are presented. For single-phase flow, the petrophysical properties of rocks, namely Representative Elementary Volume (REV), mean pore and grain size, and absolute permeability, are calculated using an integrated approach comprising image processing, statistical correlation and numerical simulations. Two rock formations, one carbonate and one sandstone, are used throughout this Thesis. It is shown that REV and mean pore and grain size are effectively estimated using the two-point spatial correlation function. A comparison of different absolute permeability estimates is also presented, showing a good agreement between the numerical value and the experimentally determined one for the carbonate sample, but a huge discrepancy for the sandstone. For two-phase flow, the Volume-of-fluid method is used to track the interfaces. The surface tension forces are modelled using a filtered sharp formulation, and the Stokes equations are solved using the PISO algorithm. A study on the snap-off mechanism, investigating the role of several parameters including contact angle and viscosity ratio, is presented. Results show that the threshold contact angle for snap-off increases from a value of 28◦ for a circular cross-section to 30-34◦ for a square cross-section and up to 40◦ for a triangular one. For a throat of square cross-section, increasing the viscosity of the injected phase results in a drop in the threshold contact angle from a value of 30◦ when µ = 1 to 26◦ when µ = 10 and down to 24◦ when µ = 20, where µ is the viscosity ratio. Finally, a rigorous spatial averaging procedure is presented, leading to a novel definition of the macroscopic capillary pressure. Simulations results of drainage on the scanned images of the rock samples are used to compare different estimates of the macroscopic capillary pressure. The comparison reveals that, contrary to what is commonly done following the traditional approach, use of surface average for the pressures is more appropriate than that of volume average, when averaging the microscopic balance equations relevant for pore-scale two-phase flows in porous media.
8
Hellum, Aren. "Intermittency and the viscous superlayer in a single stream shear layer." Diss., Connect to online resource - MSU authorized users, 2006.
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9
Steinke, Mark E. "Single-phase liquid flow and heat transfer in plain and enhanced silicon microchannels /." Link to online version, 2005. http://hdl.handle.net/1850/999.
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10
Dhaubhadel, Manoranjan N. "Experimental and finite-element investigation of flow past single and multiple cylinders." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/50006.
Повний текст джерелаАнотація:
Fluid flows past single and multiple cylinders in different configurations are investigated both experimentally and numerically. Three and five in-line cylinders and in-line and staggered bundles of cylinders with different pitch-to-diameter ratios are considered. Experimental work comprises of laser-Doppler velocimetry and flow visualization obtained in a water tunnel and skin friction, pressure, lift, drag and hot-wire measurements obtained in a wind tunnel. Both steady and pulsed flows are considered. Numerical work consists of finite element analysis of Navier-Stokes and energy equations governing viscous fluid flow past single and multiple cylinders. Detailed measurements of the fluid dynamic quantities for flow past cylinders reveal that flow pulsation at frequencies which induce lock-on increases the organization of the flow in gaps between cylinders. A new pattern of flow field is found for flow past a triad and a pentad of cylinders with a pitch-to-diameter ratio of l.8. The numerical analysis generates important integral characteristics like flow resistance and heat transfer. A staggered square arrangement of finite bundle of cylinders is found to have better heat transfer characteristics compared to the in-line or staggered equilateral-triangular arrangements.Ph. D.
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11
Nadim, Nima. "Fluid and thermal behaviour of multi-phase flow through curved ducts." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/794.
Повний текст джерелаАнотація:
Fluid flow through curved ducts is influenced by the centrifugal action arising from duct curvature and has behaviour uniquely different to fluid flow through straight ducts. In such flows, centrifugal forces induce secondary flow vortices and produce spiralling fluid motion within curved ducts. Secondary flow promotes fluid mixing with intrinsic potential for thermal enhancement and, exhibits possibility of fluid instability and additional secondary vortices under certain flow conditions. Reviewing published numerical and experimental work, this thesis discusses the current knowledge-base on secondary flow in curved ducts and, identifies the deficiencies in analyses and fundamental understanding. It then presents an extensive research study capturing advanced aspects of secondary flow behaviour in single and two-phase fluid flow through curved channels of several practical geometries and the associated wall heat transfer processes.As a key contribution to the field and overcoming current limitations, this research study develops a new three-dimensional numerical model for single-phase fluid flow in curved ducts incorporating vortex structure (helicity) approach and a curvilinear mesh system. The model is validated against the published data to ascertain modelling accuracy. Considering rectangular, elliptical and circular ducts, the flow patterns and thermal characteristics are obtained for a range of duct aspect ratios, flow rates and wall heat fluxes. Results are analysed for parametric influences and construed for clearer physical understanding of the flow mechanics involved. The study formulates two analytical techniques whereby secondary vortex detection is integrated into the computational process with unprecedented accuracy and reliability. The vortex inception at flow instability is carefully examined with respect to the duct aspect ratio, duct geometry and flow rate. An entropy-based thermal optimisation technique is developed for fluid flow through curved ducts.Extending the single-phase model, novel simulations are developed to investigate the multiphase flow in heated curved ducts. The variants of these models are separately formulated to examine the immiscible fluid mixture flow and the two-phase flow boiling situations in heated curved ducts. These advanced curved duct flow simulation models are validated against the available data. Along with physical interpretations, the predicted results are used to appraise the parametric influences on phase and void fraction distribution, unique flow features and thermal characteristics. A channel flow optimisation method based on thermal and viscous fluid irreversibilities is proposed and tested with a view to develop a practical design tool.
12
Davis, Staci Ann. "The manipulation of large- and small-scale flow structures in single and coaxial jets using synthetic jet actuators." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17313.
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13
Sundararaj, Vivekanandhan. "Computational fluid dynamic analysis of unsteady compressible flow through a single cylinder internal combustion engine /." Available to subscribers only, 2006. http://proquest.umi.com/pqdweb?did=1240704871&sid=3&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Повний текст джерелаАнотація:
Thesis (M.S.)--Southern Illinois University Carbondale, 2006."Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (leaves 171-174). Also available online.
14
Hattingh, Shane Kenneth Francis. "The simulation of single phase, compressible fluid flow in fractured petroleum reservoirs using finite elements." Doctoral thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/4888.
Повний текст джерелаАнотація:
Summary in English.Bibliography: leaves 181-193.
In this thesis, commonly used equations governing the flow of fluids are reviewed, from first principles where appropriate. The assumptions that are made in the process are critically assessed and their limitations are discussed. The equations deal with flow through a porous and permeable medium, a single fracture, a network of fractures, and with the coupling of the fracture network and blocks of matrix material.
15
Koyama, Tomofumi. "Numerical modelling of fluid flow and particle transport in rough rock fracture during shear." Licentiate thesis, Stockholm : Mark och vatten, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-512.
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16
Everts, Marilize. "Single-phase mixed convection of developing and fully developed flow in smooth horizontal tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes." Thesis, University of Pretoria, 2017. http://hdl.handle.net/2263/64045.
Повний текст джерелаАнотація:
The laminar and turbulent flow regimes have been extensively investigated from as early as 1883, and research has been devoted to the transitional flow regime since the 1990s. However, there are several gaps in the mixed convection literature, especially when the flow is still developing. The purpose of the study was to experimentally investigate the heat transfer and pressure drop characteristics of developing and fully developed flow of low Prandtl number fluids in smooth horizontal tubes for forced and mixed convection conditions.
An experimental set-up was designed and built, and results were validated against literature. Two smooth circular test sections with inner diameters of 4 mm and 11.5 mm were used, and the maximum length-to-diameter ratios were 1 373 and 872 respectively. Heat transfer measurements were taken at Reynolds numbers between 500 and 10 000 at different constant heat fluxes. A total of 648 mass flow rate measurements, 70 301 temperature measurements and 2 536 pressure drop measurements were taken. Water was used as the test fluid and the Prandtl number ranged between 3 and 7.
It was found that a longer thermal entrance length was required for simultaneously hydrodynamically and thermally developing flow. Therefore, a coefficient of at least 0.12 (and not 0.05 as advised in most literature) was suggested. Because free convection effects decreased the thermal entrance length, correlations were also developed to calculate the thermal entrance length for mixed convection conditions. The boundaries between the flow regimes were defined mathematically, and terminology to define transitional flow characteristics was presented. For laminar flow, three different regions (forced convection developing, mixed convection developing and fully developed) were identified in the local heat transfer results and nomenclature and correlations were developed to define and quantify the boundaries of these regions. Correlations were also developed to calculate the local and average laminar Nusselt numbers of mixed convection developing flow. The laminar-turbulent transition along the tube length occurred faster with increasing Reynolds number, and was also influenced by free convection effects. As free convection effects became significant, the effect was first to disrupt the fluctuations inside the test section, leading to a slower laminar-turbulent transition along the tube length compared with forced convection conditions. However, as free convection effects were increased, the fluctuations inside the test section increased and caused the laminar-turbulent transition along the tube length to occur faster.
The Reynolds number at which transition started was found to be independent of axial position for both developing and fully developed flow. However, the end of transition occurred earlier as the flow approached fully developed flow. When the flow was fully developed, the end of transition became independent of axial position. Furthermore, free convection effects affected both the start and end of the transitional flow regime, and caused the Reynolds number range of the transitional flow regime to decrease. Correlations were therefore developed to determine the start and end of the transitional flow regime for developing and fully developed flow in mixed convection conditions. The transitional flow regime across the tube length was divided into three regions. In the first region, the width of the transitional flow regime decreased significantly with axial position as the thermal boundary layer thickness increased, and free convection effects were negligible. In Region 2, the width of the transitional flow regime decreased with axial position, due to the development of the thermal boundary layer, as well as with increasing free convection effects. In the fully developed region (Region 3), the width of the transitional flow regime was independent of axial position, but decreased significantly with increasing free convection effects. At high Grashof numbers, free convection effects even caused the transitional flow regime of fully developed flow to become negligible.
It was found that the boundaries of the different flow regimes were the same for pressure drop and heat transfer, and a relationship between pressure drop and heat transfer existed in all four flow regimes. In the laminar flow regime, this relationship was a function of Grashof number (thus free convection effects), while it was a function of Reynolds number in the other three flow regimes. Correlations to predict the average Nusselt numbers, as well as the friction factors as a function of average Nusselt number, for developing and fully developed flow in all flow regimes were developed.
Finally, flow regime maps were developed to predict the convection flow regime for developing and fully developed flow for a wide range of tube diameters and Prandtl numbers, and these flow regime maps were unique for four reasons. Firstly, they contained contour lines that showed the Nusselt number enhancements due to the free convection effects. Secondly, they were valid for a wide range of tube diameters and Prandtl numbers. Thirdly, the flow regime maps were developed as a function of temperature difference (Grashof number) and heat flux (modified Grashof number). Finally, four of the six flow regime maps were not only valid for fully developed flow, but also for developing flow.Thesis (PhD)--University of Pretoria, 2017.
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Stellenbosch University/University of Pretoria
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Mechanical and Aeronautical Engineering
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Unrestricted
17
Bapat, Akhilesh V. "Experimental and numerical evaluation of single phase adiabatic flows in plain and enhanced microchannels /." Online version of thesis, 2007. http://hdl.handle.net/1850/5536.
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18
Celik, Sitki Berat. "Analysis Of Single Phase Fluid Flow And Heat Transfer In Slip Flow Regime By Parallel Implementation Of Lattice Boltzmann Method On Gpus." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614943/index.pdf.
Повний текст джерелаАнотація:
In this thesis work fluid flow and heat transfer in two-dimensional microchannels are studied numerically. A computer code based on Lattice Boltzmann Method (LBM) is developed for this purpose. The code is written using MATLAB and Jacket software and has the important feature of being able to run parallel on Graphics Processing Units (GPUs). The code is used to simulate flow and heat transfer inside micro and macro channels. Obtained velocity profiles and Nusselt numbers are compared with the Navier-Stokes based analytical and numerical results available in the literature and good matches are observed. Slip velocity and temperature jump boundary conditions are used for the micro channel simulations with Knudsen number values covering the slip flow regime. Speed of the parallel version of the developed code running on GPUs is compared with that of the serial one running on CPU and for large enough meshes more than 14 times speedup is observed.
19
Claretti, Roberto. "Heat and fluid flow characterization of a single-hole-per-row impingement channel at multiple impingement heights." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5920.
Повний текст джерелаАнотація:
The present work studies the relationship between target and sidewall surfaces of a multi-row, narrow impingement channel at various jet heights with one impingement hole per row. Temperature sensitive paint and constant flux heaters are used to gather heat transfer data on the target and side walls. Jet-to-target distance is set to 1, 2, 3, 5, 7 and 9 jet diameters. The channel width is 4 jet diameters and the jet stream wise spacing is 5 jet diameters. All cases were run at Reynolds numbers ranging from 5,000 to 30,000. Pressure data is also gathered and used to calculate the channel mass flux profiles, used to better understand the flow characteristics of the impingement channel. While target plate heat transfer profiles have been thoroughly studied in the literature, side wall data has only recently begun to be studied. The present work shows the significant impact the side walls provide to the overall heat transfer capabilities of the impingement channel. It was shown that the side walls provide a significant amount of heat transfer to the channel. A channel height of three diameters was found to be the optimum height in order to achieve the largest heat transfer rates out of all channels.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermo-Fluids
20
Sundareswaran, Kartik Sivaram. "Characterizing single ventricle hemodynamics using phase contrast magnetic resonance imaging." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/31748.
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Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Yoganathan, Ajit; Committee Member: Fogel, Mark; Committee Member: Kanter, Kirk; Committee Member: Oshinski, John; Committee Member: Skrinjar, Oskar. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Roberts, Peter John. "Numerical modelling of single and two phase fluid flow and energy transport in rigid and deforming porous media." Thesis, Swansea University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.644360.
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Balakrishnan, Mahalingam III. "The Role of Turbulence on the Entrainment of a Single Sphere and the Effects of Roughness on Fluid-Solid Interaction." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30732.
Повний текст джерелаАнотація:
Incipient motion criterion in sediment transport is very important, as it defines the flow condition that initiates sediment motion, and is also frequently employed in models to predict the sediment transport at higher flow conditions as well. In turbulent flows, even a reasonably accurate definition of incipient motion condition becomes very difficult due to the random nature of the turbulent process, which is responsible for sediment motion under incipient conditions. This work investigates two aspects, both of which apply to incipient sediment transport conditions. The first one deals with the role of turbulence in initiating sediment motion. The second part deals with the nature of sediment-fluid interaction for more general and complex flows where the number of sediment particles that form the rough surface is varied.
The first part of this work that investigates the role of turbulence in initiating sediment motion, uses a video camera to simultaneously monitor and record the sediment (glass ball) motion and corresponding fluid velocity events measured by a three-component laser Doppler Velocimeter (LDV). The results of the single ball experiment revealed that the number of LDV flow measurements increase dramatically (more than four folds) just prior to the ball motion. The fluid mean velocity and its root-mean-square (rms) values also are significantly higher than the values that correspond to the flow conditions that yield no ball motion.
The second part of the work, investigation of the fluid-sediment interaction, includes five tests with varying number of sediment particles. In order to understand the nature and extent of fluid-solid interaction, velocity profile measurements using the 3-D laser system were carried out at three locations for each of these five cases. Plots of mean velocities, rms quantities located the universal layer at about 1.5 ball diameters above the porous bed. However, at higher sediment particle concentrations, this distance reduced and the beginning of the universal layer approached the top of the porous bed.Ph. D.
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Rattner, Alexander S. "Single-pressure absorption refrigeration systems for low-source-temperature applications." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53912.
Повний текст джерелаАнотація:
The diffusion absorption refrigeration (DAR) cycle is a promising technology for fully thermally driven cooling. It is well suited to applications in medicine refrigeration and air-conditioning in off-grid settings. However, design and engineering knowhow for the technology is limited; therefore, system development has historically been an iterative and expensive process. Additionally, conventional system designs require high-grade energy input for operation, and are unsuitable for low-temperature solar- or waste-heat activated applications.
In the present effort, component- and system-level DAR engineering analyses are performed. Detailed bubble-pump generator (BPG) component models are developed, and are validated experimentally and with direct simulations. Investigations into the BPG focus on the Taylor flow pattern in the intermediate Bond number regime, which has not yet been thoroughly characterized in the literature, and has numerous industry applications, including nuclear fuel processing and well dewatering. A coupling-fluid heated BPG design is also investigated experimentally for low-source-temperature operation. Phase-change simulation methodologies are developed to rigorously study the continuously developing flow pattern in this BPG configuration. Detailed component-level models are also formulated for all of the other DAR heat and mass exchangers, and are integrated to yield a complete system-level model. Results from these modeling studies are applied to develop a novel fully passive low-source-temperature (110 - 130°C) DAR system that delivers refrigeration grade cooling. This design achieves operation at target conditions through the use of alternate working fluids (NH3-NaSCN-He), the coupling-fluid heated BPG, and a novel absorber configuration. The complete DAR system is demonstrated experimentally, and evaluated over a range of operating conditions. Experimental results are applied to assess and refine component- and system- level models.
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Chalfi, Toufik Yacine. "Pressure loss associated with flow area change in micro-channels." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/24725.
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Ates, Ahmet Muaz. "Experimental Comparison Of Fluid And Thermal Characteristics Of Microchannel And Metal Foam Heat Sinks." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613577/index.pdf.
Повний текст джерелаАнотація:
Doubling transistor count for every two years in a computer chip, transmitter and receiver (T/R) module of a phased-array antenna that demands higher power with smaller dimensions are all results of miniaturization in electronics packaging. These technologies nowadays depend on improvement of reliable high performance heat sink to perform in narrower volumes. Employing microchannels or open cell metal foam heat sinks are two recently developing promising methods of cooling high heat fluxes. Although recent studies especially on microchannels can give a rough estimate on performances of these two methods, since using metal foams as heat sinks is still needed further studies, a direct experimental comparison of heat exchanger performances of these two techniques is still needed especially for thermal design engineers to decide the method of cooling.
For this study, microchannels with channel widths of 300 µm, 420 µ
m, 500 µ
m and 900 µ
m were produced. Also, 92% porous 10, 20 and 40 ppi 6101-T6 open cell aluminum metal foams with compression factors 1,2, and 3 that have the same finned volume of microchannels with exactly same dimensions were used to manufacture heat sinks with method of vacuum brazing. They all have tested under same conditions with volumetric flow rate ranging from 0,167 l/min to 1,33 l/min and 60 W of heat power. Channel height was 4 mm for all heat sinks and distilled water used as cooling fluid. After experiments, pressure drops and thermal resistances were compared with tabulated and graphical forms. Also, the use of metal foam and microchannel heat sinks were highlighted with their advantages and disadvantages for future projects.
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Niehus, Mark T. "An Experimental Study of Temperature Sensor Noise Analysis in Evaluating the Velocity of Single-Phase Air and Water Flows." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1213385038.
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Obuseh, Chukwuyem Charles. "Quasi-Three Dimensional Experiments on Liquid-Solid Fluidized Bed of Three Different Particles in Two Different Distributors." Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc12173/.
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This thesis is an experimental study of the fluidization of binary mixture in particulate flows. A fluidized bed with two distributors was built with water being used as carrying fluid. Three types of solid particles of nylon, glass and aluminum of the same size and different densities are used in the experiments. The wall effect on a single particle fluidization, the fluidization of binary mixture of large density difference (nylon and aluminum of density ratio of 0.42), and the fluidization of binary mixture of close density (glass and aluminum with density ratio of 0.91) were investigated. Also, the effect of distributors on mono-disperse and bi-disperse particle fluidization was investigated. Results show that the presence of narrow walls reduces the minimum fluidization velocity for a single particle by as much as nearly 40%. Also, in the case of binary mixture of close density particles, uniform mixing was easily achieved and no segregation was observed, but in the case of large density difference particles, there exists significant segregation and separation. At high velocity, the uniform distributor behaves like a transport bed. To achieve a full bed in the single jet, it requires 1.5 times velocity of the uniform distributor. This behavior determines their application in the industries.
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Wickizer, Gabriel Benjamin. "Experimental System Effects on Interfacial Shape and Included Volume in Bubble Growth Studies." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337716075.
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Blume, Martin [Verfasser]. "3D Flow Simulation for the Investigation of Cavitation and Its Relationship To Erosion, Turbulence and Primary Breakup in Hydraulic Components by Single-Fluid Multi-Phase Methods / Martin Blume." Düren : Shaker, 2021. http://d-nb.info/1238497381/34.
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Suara, Kabir Adewale. "Development and use of GPS-based technology to study dispersion in shallow water." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/102841/1/Kabir%20Adewale_Suara_Thesis.pdf.
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This project was a step forward for the measurement and management of shallow water estuaries using satellite technology. Newly developed Global Positioning System (GPS) high resolution drifters were used to investigate the flow field and the spreading behaviours of passive particles. It identified the dominant mechanisms responsible for the tidal scale spreading with a focus on tidal estuaries in Southeast Queensland. Importantly, this study provides a unique moving sensor (Lagrangian) approach to strengthen current modelling efforts in prediction of the transport of materials in tidal estuaries. This new approach provides a unique complement to the traditional fixed sensor (Eulerian) approach.
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Blanch, Ojea Roland. "Numerical and experimental analyses of single and two-phase microfluidic flows with implications in microreactors." Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/63824.
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Aquesta tesi centra els seus esforços en l'àmbit de la microfluídica, un camp relativament recent dins de la Mecànica de Fluids, amb un futur prometedor i amb un ritme d'investigació intens en les seves diferents especialitzacions.
En aquest sentit, la tesi presenta dos aportacions científiques principals. Primer, aporta una eina numèrica d'elaboració pròpia per realitzar simulacions de fluxos reactius en microcanals. Eina que s'aplica satisfactòriament a la identificació dels principals processos de transport involucrats en la oxidació parcial del metà per a produir gas de síntesi, i a l'estudi de l'efecte que tenen alguns paràmetres d'operació en aquest procés reactiu. Segon, estén el coneixement dels fluxos multifàsics en microunions en T, estudiant experimentalment fluxos de dues fases amb fluids principalment miscibles i en condicions supercrítiques, que son portats al seu equilibri vapor-líquid. Durant aquest estudi, a més, reporta un succés inesperat que presenta futurs reptes en l'aplicació d'aquest tipus de fluxos multifàsics.The present thesis focuses on microfluidics, a relatively recent field of Fluid Mechanics with promising expectations and with an intense scientific interest on its different areas. In this regard, the thesis aims to provide two main scientific contributions. First, it presents an in-house numerical tool to carry out simulations of reactive flows within microchannels. The tool is successfully applied to the identification of the main transport phenomena involved on the partial oxidation of methane to produce synthesis gas, and to the analysis of the effect of several operating parameters on this reactive process. Second, it extends the knowledge on multiphase flows in microfluidic T-junctions with an experimental study of two-phase flows of mixtures of potentially miscible fluids, in supercritical conditions and in vapour-liquid equilibrium. In this study it is also reported an unexpected phenomenon, which brings new challenges to the application of these kind of multiphase flows.
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Moncalvo, Davide [Verfasser]. "The influence of fluid properties on single and two-phase two-component flows in safety valves / Davide Moncalvo." Aachen : Shaker, 2010. http://d-nb.info/109804035X/34.
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Wang, Yuan. "Liquid-vapour phase change and multiphase flow heat transfer in single micro-channels using pure liquids and nano-fluids." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5752.
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Heat management in high thermal-density systems such as CPU chips, nuclear reactors and compact heat exchangers is confronting rising challenges due to ever more miniaturized and intensified processes. While searching for heat transfer enhancement, micro-channel flow boiling and the usage of high thermal potential fluids such as nanofluids are found to be efficient heat removal approaches. However, the limited understanding of micro-scale multiphase flows impedes wider applications of these techniques. In this thesis work, liquid-vapour phase change and multiphase flow heat transfer in micro-channels were experimentally investigated. Included are studies on the single phase friction, vapour dynamics, liquid meniscus evaporation, two-phase flow instabilities and heat transfer. An experimental system was built. Rectangular microchannels with different hydraulic diameters (571 μm, 762 μm and 1454 μm) and crosssectional aspect ratios were selected. Transparent heating was utilised by coating the micro-channels with a layer of tantalum on the outer surfaces. FC-72, n-pentane, ethanol, and ethanol-based Al2O3 nanofluids were used as working fluids. Pressures and temperatures at micro-channel inlet and outlet were acquired. Simultaneous visualisation and thermographic profiles were monitored. Single phase friction of pure liquids and nanofluids mostly showed good agreement with the conventional theory. The discrepancies were associated with hydrodynamic developing flow and the early transition to turbulent flow, but nanoparticle concentration showed minor impact. After boiling incipient, the single vapour bubble growth and flow regimes were investigated, exploring the influences of flow and thermal conditions as well as the micro-channel geometry on vapour dynamics. In addition, liquid meniscus evaporation as the main heat transfer approach at thin liquid films in micro-channels was studied particularly. Nanoparticles largely enhanced meniscus stability. Besides, flow instabilities were analyzed based on the pressure drop and channel surface temperature fluctuations as well as the synchronous visualization results. Moreover, study on flow boiling heat transfer was undertaken, the corresponding heat transfer characteristics were presented and the heat transfer mechanisms were elucidated. Furthermore, ten existing heat transfer correlations were assessed. A modified heat transfer correlation for high aspect ratio micro-channel flow boiling was proposed. The crucial role of liquid property and microchannel aspect-ratio on flow boiling heat transfer was highlighted.
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Morente, Antoine. "Développement d'une méthode de pénalisation pour la simulation d'écoulements liquide-bulles." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19922/1/MORENTE_Antoine.pdf.
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Ce travail est dédié au développement d'une méthode numérique pour la simulation des écoulements liquide-bulles. La présence des bulles dans l'écoulement visqueux et incompressible est prise en compte via une méthode de pénalisation. Dans cette représentation Euler-Lagrange, les bulles supposées indéformables et parfaitement sphériques sont assimilées à des objets pénalisés interagissant avec le fluide. Une méthode VOF (Volume Of Fluid) est employée pour le suivi de la fonction de phase. Une adaptation de la discrétisation des équations de Navier-Stokes est proposée afin d'imposer la condition de glissement à l'interface entre le liquide et les bulles. Une méthode de couplage entre le mouvement des bulles et l'action du liquide est proposée. La stratégie de validation est la suivante. Dans un premier temps, une série de cas-tests est proposée; les objets pénalisés sont supposés en non-interaction avec le fluide. L'étude permet d'exhiber la convergence et la précision de la méthode numérique. Dans un second temps le couplage est testé via deux types de configurations de validation. Le couplage est d'abord testé en configuration de bulle isolée, pour une bulle en ascension dans un liquide au repos pour les Reynolds Re=17 and Re=71. Les résultats sont comparés avec la théorie établie par la corrélation de Mei pour les bulles sphériques propres décrivant intégralement la dynamique de la bulle. Enfin, des simulations en configurations de nuage de bulles sont présentées, pour des populations mono- et bidisperses dans un domaine entièrement périodique pour des taux de vide s'établissant entre 1% et 15%. Les statistiques fournies par les simulations caractérisant l'agitation induite par les bulles sont comparées à des résultats expérimentaux. Pour les simulations de nuages de bulles bidisperses, de nouveaux résultats sont présentés.
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Fernandes, Hipolito Ana Isabel. "Étude des phénomènes de transport dans un réacteur catalytique pilote de type filaire." Thesis, Lyon 1, 2010. http://www.theses.fr/2010LYO10285/document.
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L’extrapolation des réacteurs catalytiques nécessite l’acquisition des données cinétiques sur des réacteurs à petite échelle dans les conditions opératoires industrielles. Le critère de dimensionnement utilisé lors de la réduction d’échelle est la conservation de la vitesse volumique horaire, ce qui conduit à des vitesses de circulation très faibles dans les réacteurs pilotes à lit-fixe. A ces vitesses, les flux de transfert de matière externes peuvent devenir limitant par rapport au flux de réaction. Dans ce contexte, une nouvelle géométrie de réacteur a été imaginée pour intensifier les transferts de matière et chaleur et pour augmenter les vitesses de circulation des fluides : le réacteur "filaire". Il s’agit d’un réacteur dont le diamètre est égal ou proche de celui des grains de catalyseur et avec un ratio longueur sur diamètre très élevé. Le principal objectif de cette thèse est de caractériser ce réacteur en termes d’hydrodynamique et de transferts de matière externes pour définir ses limites d’utilisation. En écoulement diphasique, ce réacteur est relativement piston et la rétention liquide est élevée, ce qui permet d'assurer un mouillage total du catalyseur. En ce qui concerne les vitesses des transferts de matière externe, celles-ci sont proches de celles d'un réacteur agité avec panier et sont supérieures à celles caractéristiques d'un réacteur pilote à lit-fixe conventionnel. Cette observation est liée à l’augmentation des vitesses locales du liquide et à la présence d'un écoulement du type Taylor modifié. En conclusion, le réacteur "filaire" constitue une alternative efficace aux réacteurs pilotes à lit-fixe pour l’étude de catalyseurs mis en formeSmall size fixed-bed reactors are a common choice for testing industrial supported catalyst under industrial operating conditions. The most common criterion for reactor’s scale-down is based on the conservation of the liquid hourly space velocity which leads to a very low fluid flow velocity at the laboratory scale. Under these conditions, the external mass transfer flux can become the limiting step of the process. In this context, a new reactor geometry was proposed to intensify mass and heat transfers and to increase fluid flow velocities: the single pellet string reactor. This reactor is composed of a tube with an internal diameter close to that of the catalyst particles and with a high length over diameter ratio. The main goal of this thesis is to characterise the hydrodynamic and external mass transfer performances of this new reactor in order to define its application domain. In two-phase gas-liquid flow, the reactor flow is plug flow and the liquid hold-up values are high, which insures a complete wetting of the catalyst particles. The mass transfer coefficients were quantified and the measured rates are much higher than those observed in conventional pilot fixed-bed reactors, which can be explained by the increased local liquid velocities and by the modified Taylor flow regime. Catalytic tests with a very fast model reaction revealed that the external mass transfer performances of the single pellet string reactor are close to those measured in a stirred tank reactor equipped with a catalytic basket. In conclusion, the single pellet string reactor represents a new and efficient alternative to fixed-bed pilot reactors to study shaped catalysts
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Chien, Kuo-Shun, and 簡國順. "Anisotropy of Fluid Flow Through a Single Rock Joint." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/16481525873732656157.
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碩士國立中央大學
土木工程學系
85
Fluid flow through a single rock joint has often been modeled as flow between two parallel plates where the volume flow rate varies as cube of the joint aperture. Recently, synthetic rough surfaces are generated by using a fractal model of surface topography to simulate real joint surfaces that contact each other at discrete points. Then pairs of these surfaces are placed together to form a joint with a random aperture distribution for modeling the flow through rock joints. The seepage flow through the joint is calculated by a finite element computer program. The statistical covariance function demonstrates that the rough surfaces of fractal model display the characteristics of homogeneity and isotropy. Nevertheless, the flow simulations show that the behavior of anisotropy rises with the decrement of mechanical aperture. Since in small aperture the effect of surface roughness controls the distribution of contact area that dominates the stream of the flow path, so flow varies with different directions. Rose-diagrams of flow rate are presented to show the anisotropic flow behavior caused by the variation of aperture. The minimum porous section in the flow path is key factor that blocks the flow across the section.
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McPhail, Stephen John [Verfasser]. "Single phase fluid flow and heat transfer in microtubes / vorgelegt von Stephen John McPhail." 2009. http://d-nb.info/992577039/34.
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Deawwanich, Thana. "Flow and displacement of viscoplastic fluids in eccentric annuli." Thesis, 2013. http://hdl.handle.net/2440/81607.
Повний текст джерелаАнотація:
In the construction of oil and gas well, improper displacement work (primary cementing job) may cause poor zonal isolation, cement channeling, remedial squeeze cementing, and thus lead to a severe problem. The leakage of the wellbore fluids and contamination of sensitive zones resulting from poor primary cementing job such as the Gulf of Mexico's oil spill in April 2010 has been the biggest disaster accidents for mankind history since then.
The experimental flow system was developed for systematic study of both single-fluid flow and two-fluid displacement in eccentric annuli. This flow is relevant to the drilling operation and cementing operation in oil well completions, where drilling fluids are displaced from the annulus between the casing and the well bore by a series of spacer/wash fluids and cement slurries. The design of the system is based on the helical flow geometry, which is a combination of annular axial flow and tangential rotating flow in an annulus. The annular flow apparatus can be operated at various degrees of eccentricity and different angles of inclination to simulate the type of flows in oilfield drilling and cementing operations. A special feature of the flow system is that the inner pipe can be rotated during displacement, allowing the effect of casing rotation on the performance of the annular displacement process to be studied. Single fluid flow with various models of rheological fluids and displacement tests with various models of rheological fluids, especially viscoplastic fluids representing drilling and cementing fluids was conducted at different eccentricities, pipe inclinations, and over a range of flow rates and cylinder rotational speeds.
Regarding the entire results of the displacement experiments, to our knowledge, the images of the moving fluid-fluid interface in annular displacement flow, especially with a rotating cylinder, generated in this work may be considered to be the world leading, since such visual information is not available in the open literature. In addition to flow visualization, the velocity of moving fluidvi-fluid interface in annular displacement flow was studied by measuring the conductivity of tested fluids. The result reveals the dynamics of displacement flow in annuli.
A method was developed for simultaneously determining the displacement efficiency by measuring the conductivity of the mixed fluid phase exiting the annulus. The results obtained are of sufficient accuracy to be useful for assessing the effects of key variables such as pipe standoff, pump rate, pipe rotation and fluid rheology, on the effectiveness of annular displacement process.
The relationship between the pressure gradient and the displacement efficiency has been established for the displacement process. The basic general mixing rule of a binary system occupied in term of pressure gradient may be illustrated. The pressure gradient of the mixture at any specific time of the displacement process may be illustrated by the equation comprising of the pressure gradient of each pure component in the mixture (in mass, mole, or volume fraction) derived from the results of the single-fluid flow experiments. Finally, the graph plots of the model prediction for the friction pressure gradient of the displacement process were shown, illustrating that the results from model equation collapses properly on the experimental result.
To summarize, the results obtained in this work is useful for assessing the effects of fundamental variables such as eccentricity, pipe inclination, flow rate, pipe rotation and fluid rheology, that impact on the effectiveness of the annular displacement process. In particular, the flow visualization data, the velocity of moving fluid-fluid interface, the displacement efficiency, and friction pressure modelling results obtained from this project can be used to compare with, and validate, Halliburton’s 3-D simulation CFD, implemented.Thesis(Ph.D.)--University of Adelaide, School of Chemical Engineering, 2013.
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Kim, Byong-Joo. "Heat transfer and fluid flow aspects of a small-scale single droplet fuel-coolant interaction." 1985. http://catalog.hathitrust.org/api/volumes/oclc/13201274.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1985.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 224-231).
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He, Xiaoliang. "CFD simulation of single-phase and flow boiling in confined jet impingement with in-situ vapor extraction using two kinds of multiphase models." Thesis, 2013. http://hdl.handle.net/1957/36138.
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With continued development of the electronic industry, the demand for highly efficient heat removal solutions requires innovative cooling technologies. A computational fluid dynamic (CFD) study, including heat transfer, is performed for an axisymmetric, confined jet impingement experiencing boiling and coupled with vapor extraction. Boiling occurs at the target surface while extraction occurs at the wall confining the radial flow. The region between the target and confining wall is defined as a confined gap. Extraction is employed to enhance heat transfer and to minimize the potential negative influence of flow instabilities resulting from two-phase flow within a confined region.
A three-dimensional sector of the confined jet is employed in the simulation. A single circular impinging jet with a constant jet diameter (4 mm) and variable gap height (0.5, 1.0 and 1.5 mm), also known as nozzle-to-target spacing, is considered. The effect of mass flux at the confined gap entrance is also investigated (200, 400 and 800 kg/m²-s) for a range of heat flux (5 to 50 W/cm²).
Fluid flow and heat transfer are simulated using the Volume of Fluid (VOF) model and the wall-boiling sub-model within the Multiphase Segregated Flow (MSF) model. The boiling sub-model in the VOF model applies the Rohsenow boiling correlation, while in the MSF model, the Kurul-Podowski boiling sub-model is used. Also, vapor extraction is realized by different mechanisms for these two models. For the VOF model, a specific phase "wall porosity" can be assigned to a wall to make it porous. Over a range of pressure differentials across this porous wall such that the inertial transport influence is negligible, vapor transport should agree with Darcy's law. For the MSF model, a wall can be made permeability to one substance or phase while remaining impermeable to the other substance or phase. However, a portion of the substance or phase reaching the boundary allowed to pass through the surface must be specified. A pressure drop cannot be applied across the wall, thereby prohibiting Darcy flow modeling. The solutions of both models are at steady state.
The boiling curves without vapor extraction from both models are provided and compared to experiments. Simulations matching experimental wall temperatures under-predict theoretical vapor generation and those matching vapor generation over-estimate wall superheat. For cases with no extraction, local temperature and velocity profiles from the VOF model are provided at several radial locations within the confined gap. Scalar temperature and pressure distributions and velocity vectors are presented to explain observations in profiles.Graduation date: 2013
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Duggal, Rajat. "Interplay of micro-scale flow and fluid micro/nanostructure: Solutions of DNA and suspensions of single walled carbon nanotubes." Thesis, 2006. http://hdl.handle.net/1911/18895.
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The dynamics of dilute solutions of DNA flowing in a scaled clown roll-knife free surface coating flow are investigated on multiple scales. The flow is generated between a rotating roll and a stationary glass knife. Extension of fluorescently stained DNA molecules is measured at the minimum gap at low roll speeds. The macroscopic flow is computed and microscopic predictions are obtained by simulating the DNA by Brownian dynamics combined with successive fine-graining (Sunthar and Ravi Prakash 2005). The simulations predict that the DNA should stretch almost to full extension near the roll surface in the region of minimum gap; this does not agree with experimental measurements. The assumption of linear velocity across the chains fails near free surfaces and is the likely cause of the discrepancy.
At high roll speed two separation surfaces arise in the coating bead. The distribution of DNA extension is measured at the separation surface upstream of minimum gap. Slow nodular recirculations are present under the upstream and downstream free surfaces; unexpectedly, DNA molecules are stretched axially in these regions.
Individual single-walled carbon nanotubes (SWNTs) in aqueous suspension are visualized directly by fluorescence video-microscopy. The fluorescent tagging is simple, biocompatible, and allows observation of the dynamics of SWNTs in water. The rotational diffusion coefficient in confinement is measured and the critical concentration at which SWNTs in suspensions start interacting is determined. By analyzing the fluctuating shape of SWNTs, the persistence length of SWNTs is found to range between 32 and 174 mum, in agreement with theoretical estimates; thus, common SWNTs in liquids can be considered as rigid Brownian rods in the absence of imposed external fields.
Drying microscopic drops of a suspension of individual SWNTs in aqueous solution of F68 pluronic surfactant exhibit complex dynamics. The drops dry on glass substrates forming a "crust" at the free surface. The crust is thin (∼ 100 nm) and consists of an entangled mesh of nanotubes and pluronic. The self-assembled crust envelopes the drying drop and leads to a free surface inversion as evaporation proceeds. The convective flow associated with the drying preferentially assembles the micelles into hexagonal arrangement. This technique is promising for developing thin, optically transparent, coatings and films consisting of SWNT's.
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Singhal, Atul. "Single Cavity Trapped Vortex Combustor Dynamics : Experiments & Simulations." Thesis, 2009. http://hdl.handle.net/2005/1123.
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Trapped Vortex Combustor (TVC) is a relatively new concept for potential use in gas turbine engines addressing ever increasing demands of high efficiency, low emissions, low pressure drop, and improved pattern factor. This concept holds promise for future because of its inherent advantages over conventional swirl-stabilized combustors. The main difference between TVC and a conventional gas turbine combustor is in the way combustion is stabilized. In conventional combustors, flame is stabilized because of formation of toroidal flow pattern in the primary zone due to interaction between incoming swirling air and fuel flow. On the other hand, in TVC, there is a physical cavity in the wall of combustor with continuous injection of air and fuel leading to stable and sustained combustion. Past work related to TVC has focussed on use of two cavities in the combustor liner. In the present study, a single cavity combustor concept is evaluated through simulation and experiments for applications requiring compact combustors such as Unmanned Aerial Vehicles (UAVs) and cruise missiles.
In the present work, numerical simulations were initially performed on a planar, rectangular single-cavity geometry to assess sensitivity of various parameters and to design a single-cavity TVC test rig. A water-cooled, modular, atmospheric pressure TVC test rig is designed and fabricated for reacting and non-reacting flow experiments. The unique features of this rig consist of a continuously variable length-to-depth ratio (L/D) of the cavity and optical access through quartz plates provided on three sides for visualization.
Flame stabilization in the single cavity TVC was successfully achieved with methane as fuel, and the range of flow conditions for stable operation were identified. From these, a few cases were selected for detailed experimentation. Reacting flow experiments for the selected cases indicated that reducing L/D ratio and increasing cavity-air velocity favour stable combustion. The pressure drop across the single-cavity TVC is observed to be lower as compared to conventional combustors. Temperatures are measured at the exit using thermocouples and corrected for radiative losses. Species concentrations are measured at the exit using an exhaust gas analyzer. The combustion efficiency is observed to be around 98-99% and the pattern factor is observed to be in the range of 0.08 to 0.13. High-speed imaging made possible by the optical access indicates that the overall combustion is fairly steady, and there is no major vortex shedding downstream. This enabled steady-state simulations to be performed for the selected cases. Insight from simulations has highlighted the importance of air and fuel injection strategies in the cavity. From a mixing and combustion efficiency standpoint, it is desirable to have a cavity vortex that is anti-clockwise. However, the natural tendency for flow over a cavity is to form a vortex that is clockwise. The tendency to blow-out at higher inlet flow velocities is thought to be because of these two opposing effects. This interaction helps improve mixing, however leads to poor flame stability unless cavity-air velocity is strong enough to support a strong anti-clockwise vortex in the cavity. This basic understating of cavity flow dynamics can be used for further design improvements in future to improve flame stability at higher inlet flow velocities and eventually lead to the development of a practical combustor.
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Taher, Dang Koo Reza. "Numerical modelling of single- and multi-phase flow and transport processes in porous media for assessing hydraulic fracturing impacts on groundwater resources." Thesis, 2020. http://hdl.handle.net/21.11130/00-1735-0000-0005-13B9-5.
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Hoque, Mohammad Mainul. "Chacterisation of single and binary phase turbulence in an oscillating grid system." Thesis, 2017. http://hdl.handle.net/1959.13/1335955.
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Research Doctorate - Doctor of Philosophy (PhD)The characteristics of single- and binary-phase turbulence in an oscillating grid system were investigated experimentally by using time-resolved, non-intrusive particle image velocimetry (PIV) technique. Experiments were conducted in three different fields of view (FoV) namely: 10 mm × 10 mm, 30 mm × 30 mm and 60 mm × 60 mm in the center of the tank for grid oscillation frequency 0 to 5 Hz. The grid Reynolds number (Reg) and Taylor Reynolds number (Reλ) ranges were 1080–10800 and 12–60, respectively. Specifically, the focus was on: (i) characterisation of single-phase homogeneous isotropic flow based on specific energy dissipation rate; (ii) modulation of turbulence due to particle-fluid and bubble-fluid interaction; and (iii) quantification of scaling properties of pressure spectrum for single- and binary-phase flow. In order to understand the homogeneous and isotropic turbulence inside the oscillating grid system turbulent length scales, isotropy ratio (IR = vrms/urms), specific energy dissipation rate, and energy spectra were determined from the measured experimental fluctuating velocity field for different grid Reynolds numbers. Fluctuating velocity was found to increase linearly with increasing Reg which was in agreement with the previous reported results. It was found that the turbulence length scale decreased with increase in grid oscillation frequency. The isotropy ratio ranged from 0.77-0.85 which indicated the presence of isotropic homogeneous turbulence in the system. The energy dissipation rate of single-phase flow was determined using the following methodologies: (i) dimensional analysis; (ii) velocity gradient; (iii) structure function; and (iv) energy spectrum. In general, the specific energy dissipation rate increased with increase in grid oscillation frequency. It was found that the specific energy dissipation rates were different for each of the four methodologies. Whilst the analysis identified uncertainties in all four approaches, it was concluded that the energy spectrum methodology was likely to be most reliable since it was able to satisfy the energy balance of the system—this was not possible for other three methods. Moreover, the energy spectra exhibited a slope close to Kolmogorov’s -5/3 in the inertial subrange. White noise was observed in the dissipation range, which was able to be removed by an exponential filter. The modulation of homogeneous and isotropic turbulence was experimentally investigated in the presence of a single stationary particle. The particle diameter varied in the range of 1 to 8 mm (~ 10 to 77 times larger than the flow Kolmogorov length scale). It was found that the fluid-only fluctuating velocity increased by up to 2-25 percent depending upon the particle diameter. The isotropy ratio of the fluid-only phase also increased with the size of the particle; but was much less influenced by the Reynolds number of the grid, Reg. The energy dissipation rate of the fluid-only phase increased with increase in particle size; and followed a power law trend with grid Reynolds number. Longitudinal and transverse integral length scales were determined using the autocorrelation function for both fluid-only and particle-fluid case. The fluid-only phase integral length scales followed a power law dependency with Reg, and decreased when a particle was present. Both longitudinal and transverse energy spectrums in the inertial subrange exhibited a slope less steep than the -5/3 predicted by Kolmogorov when a particle was present. It is thought that the particle presence resulted in the production of turbulence in the inertial region, leading to an energy enhancement in that part of the spectrum. Finally, turbulence intensity was determined as a function of the particle-diameter-to-integral-length-scale ratio, dp/Lx; and it was found that below dp/Lx = 0.41 the turbulence intensity was attenuated, and above this dp/Lx value the turbulence intensity was enhanced. As per the particle-fluid experiments, modulation of homogeneous and isotropic turbulence was also studied due to bubble-fluid interaction. The bubble equivalent spherical diameter was varied in the range 2.7-3.52 mm, that corresponded to approximately 26-34 times larger than the Kolmogorov length scale. In the presence of a bubble, the single-phase fluctuating velocity along the transverse direction was found to be significantly enhanced when compared to that in the longitudinal direction. The presence of the bubble also influenced the isotropy of the fluid flow field; whereby at low grid Reynolds number the isotropy ratio increased with increase in the bubble equivalent spherical diameter, whilst at high Reg the isotropy ratio showed no significant bubble equivalent spherical diameter dependence. The specific energy dissipation rate was found to be influenced by the shape of the bubble, and followed a (positive exponent) power law dependence with the bubble equivalent spherical diameter. Conversely, the integral length scale of the single-phase decreased with increase in the bubble equivalent spherical diameter. It also followed that the spectral slope was less steep than -5/3 in the inertial subrange—corresponding to an enhancement of energy—for both longitudinal and transverse energy spectra. Any effect of bubble size on the energy spectrum in the dissipative region could not be conclusively demonstrated due to the presence of white noise. Finally, the pressure spectrum for both single- and binary-phase flows was obtained by taking the fast Fourier transformation (FFT) of the instantaneous pressure field which was computed from the measured, instantaneous 2D velocity field. It was found that in the inertial subrange the pressure spectra exhibited a -7/3 slope for single-phase flow, whilst that for the binary-phase flow exhibited a less steep slope. The pressure-based integral length scale as well as the Taylor microscale were estimated from autocorrelation function and pressure spectrum, respectively. For single-phase flow, at low grid Reynolds number, the pressure-integral-length-scale-to-velocity-integral-length-scale ratio was found to be constant at around 0.67; whilst the pressure Taylor microscale was approximately 79 percent of the velocity Taylor microscale. Both of these values were consistent with theoretical predictions and published direct numerical simulation results. Finally, a methodology has been proposed whereby the specific energy dissipation rate can be computed from the pressure spectrum. It was found that the values obtained from this approach were approximately 25 percent higher than those calculated directly from velocity spectrum.
45
Shankar, Kumar B. "A Study Of A Vortex Particle Method For Vortex Breakdown Phenomena." Thesis, 2008. http://hdl.handle.net/2005/729.
Повний текст джерелаАнотація:
Vortex breakdown is an important phenomenon observed in swirling flows involving the development of a stagnation point on the axis of the vortex followed by a region of recirculation when the swirl increases beyond a particular level. It has been studied extensively over past 50 years and various theories have been proposed to explain its various aspects. However, a single model explaining all the aspects together is yet to emerge. Numerical simulations of breakdown have been performed using a variety of grid-based as well as vortex methods.
Vortex methods are a Lagrangian alternative to grid-based methods wherein the motion of the vorticity is determined by the local fluid velocity convection, with models for viscous effects when considered. The fluid velocity is obtained from the vorticity field. Only the rotational regions of the flow need to be considered leading to significant economy of computational effort for simulations of vorticity dominated flows, such as vortex breakdown.
The inviscid vortex filament method has been used to simulate several aspects of the vortex breakdown phenomenon. The vortex filament method however, cannot easily simulate viscous effects. To simulate the viscous effects the viscous vortex particle method needs to be used. This work was intended to be a first step towards this end by initially evaluating the effectiveness of the inviscid version of the vortex particle method in simulating the breakdown phenomenon.
The inviscid vortex particle method was found to satisfactorily simulate most qualitative aspects involved in the formation of vortex breakdown such as the retardation of axial velocity along centerline, radial swelling of the vortex core, formation of stagnation points, creation of azimuthal vorticity gradient from axial vorticity gradient and the turning of vortex lines along with the formation of a bubble-like structure with recirculating flow within.
The effect of a wall placed adjacent to the vortex core was simulated by using image vortices. The wall was not found to influence the location of breakdown. However, the initiation of the spiral mode was found to occur earlier when a wall was present.
For a quantitative assessment, a simulation of the experimental results of Faler and Leibovich (1978) was attempted. The simulation managed to predict the location of the breakdown and the extent of the bubble. The shape and height of the bubble obtained however were not in accord with the experimental observations. A single vortical cell was obtained in the interior of the bubble.
46
Owens, Scott Allen 1982. "Advanced analysis of structured packing via computational fluid dynamics simulation." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-12-2410.
Повний текст джерелаАнотація:
This research explored the use of CFD simulations to study single phase flows through structured packing. Flow rates were chosen to approximate those used in the vapor phase of industrial distillation columns. The results were evaluated against experimental results obtained with the same packing model and packed height. Several novel methods were employed to quickly obtain high validity results. A high-fidelity, digital copy of an actual packing element was created in seven hours through CT scanning. The meshing strategy employed adaptive, polyhedral meshing algorithms which resulted in high quality volume meshes with 80 percent less mesh elements than would be required with traditional tetrahedral meshing. Meshing and computation were performed on the TACC clusters. The permitted meshing with up to 57 million volume cells in less than 30 hours while simulations employing a realizable k-[epsilon] model converged in approximately two days using up to 544 processors. Nitrogen simulation predictions were found to be, on average, 7 percent below experimental measurements with water simulations showing considerably more error (~40%). The error is likely attributable a discrepancy between the simulation and experimental geometries. This discrepancy is due to an oversight in sample preparation and not a flaw in the CT scanning process of geometry creation. The volume of data generated in CFD simulation was found to be very valuable for understanding and benchmarking packing performance. Streamlines and contour plots were used to analyze the variation in performance both locally and throughout the packing stack. Significant variation was observed in flow pattern, velocity distribution, and pressure profiles throughout the column. However, the joint regions were found to be most adverse to column energy efficiency.text
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Yelisetti, Subbarao. "Seismic structure, gas hydrate, and slumping studies on the Northern Cascadia margin using multiple migration and full waveform inversion of OBS and MCS data." Thesis, 2014. http://hdl.handle.net/1828/5719.
Повний текст джерелаАнотація:
The primary focus of this thesis is to examine the detailed seismic structure of the
northern Cascadia margin, including the Cascadia basin, the deformation front and
the continental shelf. The results of this study are contributing towards understanding
sediment deformation and tectonics on this margin. They also have important
implications for exploration of hydrocarbons (oil and gas) and natural hazards (submarine landslides, earthquakes, tsunamis, and climate change).
The first part of this thesis focuses on the role of gas hydrate in slope failure observed
from multibeam bathymetry data on a frontal ridge near the deformation front
off Vancouver Island margin using active-source ocean bottom seismometer (OBS)
data collected in 2010. Volume estimates (∼ 0.33 km^3) of the slides observed on this
margin indicate that these are capable of generating large (∼ 1 − 2 m) tsunamis.
Velocity models from travel time inversion of wide angle reflections and refractions
recorded on OBSs and vertical incidence single channel seismic (SCS) data were used
to estimate gas hydrate concentrations using effective medium modeling. Results indicate a shallow high velocity hydrate layer with a velocity of 2.0 − 2.1 km/s that
corresponds to a hydrate concentration of 40% at a depth of 100 m, and a bottom
simulating reflector (BSR) at a depth of 265 − 275 m beneath the seafloor (mbsf).
These are comparable to drilling results on an adjacent frontal ridge. Margin perpendicular normal faults that extend down to BSR depth were also observed on SCS
and bathymetric data, two of which coincide with the sidewalls of the slump indicating
that the lateral extent of the slump is controlled by these faults. Analysis of
bathymetric data indicates, for the first time, that the glide plane occurs at the same
depth as the shallow high velocity layer (100±10 mbsf). In contrast, the glide plane
coincides with the depth of the BSR on an adjacent frontal ridge. In either case, our
results suggest that the contrast in sediments strengthened by hydrates and overlying
or underlying sediments where there is no hydrate is what causing the slope failure
on this margin.
The second part of this dissertation focuses on obtaining the detailed structure
of the Cascadia basin and frontal ridge region using mirror imaging of few widely
spaced OBS data. Using only a small airgun source (120 cu. in.), our results indicate
structures that were previously not observed on the northern Cascadia margin. Specifically, OBS migration results show dual-vergence structure, which could be related to horizontal compression associated with subduction and low basal shear stress resulting from over-pressure. Understanding the physical and mechanical properties of the basal layer has important implications for understanding earthquakes on this margin.
The OBS migrated image also clearly shows the continuity of reflectors which enabled
the identification of thrust faults, and also shows the top of the igneous oceanic crust
at 5−6 km beneath the seafloor, which were not possible to identify in single-channel
and low-fold multi-channel seismic (MCS) data.
The last part of this thesis focuses on obtaining detailed seismic structure of the
Vancouver Island continental shelf from MCS data using frequency domain viscoacoustic
full waveform inversion, which is first of its kind on this margin. Anelastic
velocity and attenuation models, derived in this study to subseafloor depths of ∼ 2
km, are useful in understanding the deformation within the Tofino basin sediments,
the nature of basement structures and their relationship with underlying accreted
terranes such as the Crescent and the Pacific Rim terranes. Specifically, our results
indicate a low-velocity zone (LVZ) with a contrast of 200 m/s within the Tofino basin
sediment section at a depth 600 − 1000 mbsf over a lateral distance of 10 km. This
LVZ is associated with high attenuation values (0.015 − 0.02) and could be a result
of over pressured sediments or lithology changes associated with a high porosity layer
in this potential hydrocarbon environment. Shallow high velocities of 4 − 5 km/s
are observed in the mid-shelf region at depths > 1.5 km, which is interpreted as
the shallowest occurrence of the Eocene volcanic Crescent terrane. The sediment
velocities sharply increase about 10 km west of Vancouver Island, which probably
corresponds to the underlying transition to the Mesozoic marine sedimentary Pacific
Rim terrane. High attenuation values of 0.03 − 0.06 are observed at depths > 1 km,
which probably corresponds to increased clay content and the presence of mineralized
fluids.Graduate
0373
0372
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subbarao@uvic.ca