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1
Franklin, Thomas A. (Thomas Andrew) 1979. "Ferrofluid flow phenomena." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/16937.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 155-158).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
An investigation of ferrofluid experiments and analysis is presented in three parts: a characterization of ferrofluid properties, a study of ferrofluid flow in tubing and channel systems, and a study of ferrofluid free surface sheet flows. The characterization of ferrofluid samples is completed through analysis of magnetization curves measured with a vibrating sample magnetometer. Determination is made of the ferrofluid particle size range, saturation magnetization, low-field magnetic permeability, and magnetic volume fraction. The experimental results are well described by the Langevin theory of paramagnetism. A detailed discussion of the demagnetization factor within the ferrofluid sample is also included. Ferrofluid flow through circular tubing in a laminar regime is examined as a function of the applied magnetic field magnitude, direction, and frequency. Gradients within the applied magnetic field create a magnetic contribution to the pressure drop across a length of tubing. Experiments of ferrofluid flow through a rectangular channel with a free surface when driven by a rotating spatially uniform magnetic field exhibit an anti-symmetric flow profile across the channel width, with a net zero flow rate, consistent with theoretical work of previous research. The first known investigation of ferrofluid free surface sheet flows resulting from a ferrofluid jet impacting a small circular plate is presented. Two distinct magnetic field orientations relative to the incident jet and resulting sheet are examined, producing markedly different results. A magnetic field oriented perpendicular to the jet flow is found to deform the jet cross-section from circular toward an elliptical shape thereby causing the sheet to also change from circular to elliptical, but with the long axis of the sheet oriented perpendicularly to the long axis of the jet cross-section. In the case of a magnetic field applied everywhere perpendicular to the sheet flow a significant decrease in sheet radius is observed. The cause of the decrease in sheet radius is a magnetic field induced decrease in ferrofluid pressure as well as a magnetic field enhanced convective Kelvin-Helmholtz instability. A thorough theoretical development describes the observed phenomena.
by Thomas A. Franklin.
S.M.
2
Watson, Martin James. "Flow regime transitions and associated phenomena." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/8790.
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Alves, Iberê Nascentes. "Slug flow phenomena in inclined pipes /." Access abstract and link to full text, 1991. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9203792.
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Ahmadi, Seyedfarzad. "Dynamical Phase-Change Phenomena." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/99420.
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Matter on earth exists mostly in three different phases of solid, liquid, and gas. With extreme amounts of energy, temperature, or pressure, a matter can be changed between the phases. Six different types of phase-change phenomena are possible: freezing (the substance changes from a liquid to a solid), melting (solid to liquid), condensation (gas to liquid), vaporization (liquid to gas), sublimation (solid to gas), and desublimation (gas to solid). Another form of phase change which will be discussed here is the wetting or dewetting transitions of a superhydrophobic surface, in which the phase residing within the surface structure switches between vapor and liquid. Phase transition phenomena frequently occur in our daily life; examples include: a ``liquid'' to ``solid'' transition when cars decrease their distance at a traffic light, solidification of liquids droplets during winter months, and the dancing of droplets on a non-sticking pan. In this dissertation we will address seven different phase-change problems occurring in nature. We unveil completely new forms of phase-change phenomena that exhibit rich physical behavior. For example, during traffic flow, drivers keep a large distance from the vehicle in front of them to ensure safe driving. When vehicles come to a stop, for example at a red light, drivers voluntarily induce a ``phase transition'' from this ``liquid phase'' to a close-packed ``solid phase''. This phase transition is motivated by the intuition that traveling as far as possible before stopping will minimize the overall travel time. However, we are going to investigate this phase-change process and show that this long standing intuition is wrong. Phase-change of solidification will be discussed for different problems. Moreover, the complex physics of oil as it wicks up sheets of frost and freezing of bubble unveil completely new forms of multiphase flows that exhibit rich physical behavior. Finally, the ``Cassie'' to ``Wenzel'' transition will be investigated for layered nano-textured surfaces. These phenomena will be modeled using thermodynamics and fluid mechanics equations.Doctor of Philosophy
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Ali, Rashid. "Phase Change Phenomena During Fluid Flow in Microchannels." Doctoral thesis, KTH, Tillämpad termodynamik och kylteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26796.
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Phase change phenomena of a fluid flowing in a micro channel may be exploited to make the heat exchangers more compact and energy efficient. Compact heat exchangers offer several advantages such as light weight, low cost, energy efficiency, capability of removing high heat fluxes and charge reduction are a few to mention. Phase change phenomena in macro or conventional channels have been investigated since long but in case of micro channels, fewer studies of phase change have been conducted and underlying phenomena during two-phase flow in micro channels are not yet fully understood. It is clear from the literature that the two-phase flow models developed for conventional channels do not perform well when extrapolated to micro scale. In the current thesis, the experimental flow boiling results for micro channels are reported. Experiments were conducted in circular, stainless steel and quartz tubes in both horizontal and vertical orientations. The internal diameters of steel tubes tested were 1.70 mm, 1.224 mm and the diameter of quartz tube tested was 0.781 mm. The quartz tube was coated with a thin, electrically conductive, transparent layer of Indium-Tin-Oxide (ITO) making simultaneous heating and visualization possible. Test tubes were heated electrically using DC power supply. Two refrigerants R134a and R245fa were used as working fluids during the tests. Experiments were conducted at a wide variety of operating conditions. Flow visualization results obtained with quartz tube clearly showed the presence of confinement effects and consequently an early transition to annular flow for micro channels. Several flow pattern images were captured during flow boiling of R134a in quartz tube. Flow patterns recorded during the experiments were presented in the form of Reynolds number versus vapour quality and superficial liquid velocity versus superficial gas velocity plots. Experimental flow pattern maps so obtained were also compared with the other flow pattern maps available in the literature showing a poor agreement. Flow boiling heat transfer results for quartz and steel tubes indicate that the heat transfer coefficient increases with heat flux and system pressure but is independent on mass flux and vapour quality. Experimental flow boiling heat transfer coefficient results were compared with those obtained using different correlations from the literature. Heat transfer experiments with steel tubes were continued up to dryout condition and it was observed that dryout conditions always started close to the exit of the tube. The dryout heat flux increased with mass flux and decreased with exit vapour quality. The dryout data were compared with some well known CHF correlations available in the literature. Two-phase frictional pressure drop for the quartz tube was also obtained under different operating conditions. As expected, two-phase frictional pressure drop increased with mass flux and exit vapour quality.QC 20101206
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Kuang, Pei Qiong. "Surface phenomena in capillary flow of polymer solutions." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7597.
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Evaluations of apparent slip and surface effects characterizing polymer adsorption are reported for laminar capillary flow of dilute aqueous solutions of three homologous compounds of Polyox, denoted by WSR 301, Coagulant and FRA. Measurements were carried out using very dilute solutions in the polymer concentration range 5 to 200 ppm and very fine glass capillary tubes with diameters varying from 0.0054 to 0.047 cm. Results were obtained for glass capillary tubes coated with a silane compound (dimethyldiethoxysilane) as well as for the untreated glass tubes to provide a comparison between wall effects observed with a hydrophilic surface and a chemically modified surface. The results indicate that flow enhancement characterized by a positive effective velocity at the wall is dominant at the very low polymer concentrations and flow retardation characterized by a negative effective velocity at the wall is dominant at the higher concentrations comprising the polymer concentration range investigated. In general, it was found that the magnitude of the effective velocity at the wall increases with increasing wall shear stress and the contribution to the total flow rate becomes more significant in the tubes of smaller diameter. A transition from a positive to a negative effective velocity at the wall was observed with increasing polymer concentration. The critical concentration marking the transition was found to be higher for the silane-treated tubes than for the untreated tubes. The effective hydrodynamic thickness of the adsorbed polymer layer corresponding to zero shear was evaluated directly from the capillary flow data. The thickness in the plateau region at higher polymer concentrations was found to be greater than two times the root mean square radius of gyration of the polymer molecule for solutions of the three polymers in the untreated tubes while lower value was obtained for the same solutions in the treated tubes. A new analysis was applied to separate the contributions of polymer adsorption and slip in the evaluation of the effective velocity at the wall. In the analysis, the flow was modeled by postulating an adsorption isotherm for representation of the variation of the adsorbed layer thickness at zero shear with polymer concentration and assuming a linear dependence of the effective slip velocity on the wall shear stress. Effective hydrodynamic thicknesses of the adsorbed layers are presented as a function of the polymer concentration and wall shear stress for the three Polyox homologues investigated in the chemically treated and untreated glass tubes. The variation of the slip coefficients with polymer concentration of the solutions was also evaluated. End effect corrections based on flow measurements obtained by varying the tube lengths of the capillaries in the L/D range 750 to 2000 were applied to the data using a modification of the Bagley plot.
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Fearn, R. M. "Fundamental flow phenomena in a sudden symmetric expansion." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235187.
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Shim, K. C. "Fluctuating phenomena in tube banks in cross-flow." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355078.
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Tehrani, Ali A. K. "Gulping phenomena in transient countercurrent two-phase flow." Thesis, University of Exeter, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341194.
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Crook, Andrew James. "Numerical investigation of endwall/casing treatment flow phenomena." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/41316.
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Rolfe, Daniel James. "Accretion flow and precession phenomena in cataclysmic variables." Thesis, n.p, 2001. http://library7.open.ac.uk/abstracts/page.php?thesisid=52.
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Matthews, Jason E. "Thermoelectric and Heat Flow Phenomena in Mesoscopic Systems." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/12108.
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xvii, 189 p. ： ill. (some col.)Low-dimensional electronic systems, systems that are restricted to single energy levels in at least one of the three spatial dimensions, have attracted considerable interest in the field of thermoelectric materials. At these scales, the ability to manipulate electronic energy levels offers a great deal of control over a device's thermopower, that is, its ability to generate a voltage due to a thermal gradient. In addition, low-dimensional devices offer increased control over phononic heat flow. Mesoscale geometry can also have a large impact on both electron and phonon dynamics. Effects such as ballistic transport in a two-dimensional electron gas structure can lead to the enhancement or attenuation of electron transmission probabilities in multi-terminal junctions. The first half of this dissertation investigates the transverse thermoelectric properties of a four-terminal ballistic junction containing a central symmetry-breaking scatterer. It is believed that the combined symmetry of the scatterer and junction is the key component to understanding non-linear and thermoelectric transport in these junctions. To this end, experimental investigations on this type of junction were carried out to demonstrate its ability to generate a transverse thermovoltage. To aid in interpreting the results, a multi-terminal scattering-matrix theory was developed that relates the junction's non-linear electronic properties to its thermoelectric properties. The possibility of a transverse thermoelectric device also motivated the first derivation of the transverse thermoelectric efficiency. This second half of this dissertation focuses on heat flow phenomena in InAs/InP heterostructure nanowires. In thermoelectric research, a phononic heat flow between thermal reservoirs is considered parasitic due to its minimal contribution to the electrical output. Recent experiments involving heterostructure nanowires have shown an unexpectedly large heat flow, which is attributed in this dissertation to an interplay between electron-phonon interaction and phononic heat flow. Using finite element modeling, the recent experimental findings have provided a means to probe the electron-phonon interaction in InAs nanowires. In the end, it is found that electron-phonon interaction is an important component in understanding heat flow at the nanoscale. This dissertation includes previously unpublished co-authored material.
Committee in charge: Dr. Richard Taylor， Chair； Dr. Heiner Linke， Advisor； Dr. David Cohen， Member； Dr. John Toner， Member； Dr. David Johnson， Outside Member
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Quinn, Mark Kenneth. "Shock diffraction phenomena and their measurement." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/shock-diffraction-phenomena-and-their-measurement(4c41f25a-2ba2-4a4b-aa9c-cdb8bb9ba921).html.
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The motion of shock waves is important in many fields of engineering and increasingly so with medical applications and applications to inertial confinement fusion technologies. The flow structures that moving shock waves create when they encounter a change in area is complex and can be difficult to understand. Previousresearchers have carried out experimental studies and many numerical studies looking at this problem in more detail. There has been a discrepancy between numerical and experimental work which had remained unanswered. One of the aims of this project is to try and resolve the discrepancy between numerical and experimental work and try to investigate what experimental techniques are suitable for work of this type and the exact way in which they should be applied. Most previous work has focused on sharp changes in geometry which induce immediate flow separation. In this project rounded corners will also be investigated and the complex flow features will be analyzed.Two geometries, namely a sharp 172 degree knife-edge and a 2.8 mm radius rounded corner will be investigated at three experimental pressure ratios of 4, 8 and 12 using air as the driver gas. This yields experimental shock Mach numbers of 1.28, 1.46 and 1.55. High-speed schlieren and shadowgraph photography with varying levels of sensitivity were used to qualitatively investigate the wave structures. Particle image velocimetry (PIV), pressure-sensitive paint (PSP) and traditional pressure transducers were used to quantify the flow field. Numerical simulations were performed using the commercial package Fluent to investigate the effect of numerical schemes on the flow field produced and for comparison with the experimental results. The sharp geometry was simulated successfully using an inviscid simulation while the rounded geometry required the addition of laminar viscosity. Reynolds number effects will be only sparsely referred to in this project as the flows under investigation show largely inviscid characteristics. As the flow is developing in time rather than in space, quotation of a distance-based Reynolds number is not entirely appropriate; however, Reynolds number based on the same spatial location but varying in time will be mentioned. The density-based diagnostics in this project were designed to have a depth of field appropriate to the test under consideration. This approach has been used relatively few times despite its easy setup and significant impact on the results. This project contains the first quantative use of PIV and PSP to shock wave diffraction. Previous studies have almost exclusively used density-based diagnostics which, although give the best impression of the flow field, do not allow for complete analysis and explanation of all of the flow features present. PIV measurements showed a maximum uncertainty of 5% while the PSP measurements showed an uncertainty of approximately 10%.The shock wave diffraction process, vortex formation, shear layer structure, secondary and even tertiary expansions and the shock vortex interaction were investigate. The experimental results have shown that using one experimental technique in isolation can give misleading results. Only by using a combination of experimental techniques can we achieve a complete understanding of the flow field and draw conclusions on the validity of the numerical results. Expanding the range of the experimental techniques currently in use is vital for experimental aerodynamic testing to remain relevant in an industry increasingly dominated by numerical research. To this end, significant research work has been carried out on extending the range of the PSP technique to allow for the capture of shock wave diffraction, one of the fastest transient fluid processes, and for applications to low-speed flow (< 20 ms−1).
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Legono, D. "Behaviour of flow in open channel bends." Thesis, City University London, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375820.
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Stockdale, Richard-James. "Developing GPS river flow tracers (GRiFTers) to investigate large scale river flow phenomena." Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:5802.
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Existing flow measurement methods in natural gravel rivers are largely based on a series of point measurements detached from the dynamic nature of river flow. Traditional measurement methods are limited in many environments and locations due to an inability to access directly the channel; this situation is further complicated at high discharges where entry into the channel becomes impossible. The inadequacy of currently utilised flow measurement methods is highlighted in the study of riffle-pool sequences where limited data has produced gaps in the understanding of these fundamentally important bedform structures. Within the study of riffle-pool sequences the most prominent debates concern the precise means of sequence development and maintenance, the existence/operation of the velocity reversal hypothesis and the spatial compositions and periodicity of these quasi-regular bedform features. The expanding usage of remote sensor monitoring techniques, the incorporation of GPS receivers into drifters to provide improved positioning, and the adaptation of drifters for use in the surf zone and in estuaries and lakes have combined to highlight the potential of producing a GPS river flow tracer (GRiFTer). The development of a GRiFTer suitable for deployment in a natural gravel bed river system is described whilst the logistics of performing a field based GRiFTer investigation, data acquisition and analysis methods and the achievable accuracy of the approach are also considered. The development of a GPS River Flow Tracer provides an innovative approach to the acquisition of surface velocity measurements through the development of a series of GRiFTer based analysis tools and techniques. The suite of tools developed to date includes; the ability to measure a single primary flowline through a reach, a means of independently measuring the effective width of channel flow, the identification of low velocity zones (and the direction of flow within these areas), three different methods for the measurement of surface flow velocity (primary flowline, cross-sectional averaged and reach scale) and a means of defining riffles and pools from the relationship between depth and surface flow velocities. The study ultimately concludes with a conceptual model for the development and maintenance of riffle-pool sequences based on an adaptation of the flow convergence routing hypothesis.
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Whitehurst, R. "Mass flow in binary stars." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379895.
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Suñol, Galofré Francesc. "Bubble and droplet flow phenomena at different gravity levels." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/32305.
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Two-phase flows are encountered in a wide range of applications both on-ground and in space. The dynamics of such flows in the absence of gravity is completely different from that in normal gravity due to the absence of buoyancy forces. A deeper understanding of the behavior of multiphase flows is essential in order to improve the operation of devices which require the use of two-phase systems. Analytical and experimental work is still needed for enhancing the control of two-phase flows, due to the theoretical complexity and the lack of experimental data for certain configurations.
In this work, the behavior of two-phase flows has been studied experimentally in normal gravity and in microgravity conditions. In particular, the single-jet configuration has been investigated for bubbly jets and droplet jets. Dynamics of individual bubbles and droplets as well as the global structure of the jets has been considered. The opposed-jet configuration has been investigated for bubbly flows. Different separation between jets and orientation angles have been studied in normal gravity, and the obtained results have been compared to the microgravity case. A numerical model has been implemented to study single-phase jet impingement and opposed bubbly jets at different gravity levels. Good qualitative agreement between the simulations and the experiments has been obtained. The bubble bouncing process, prior to coalescence, after collision with a flat free surface has been also studied experimentally in normal gravity conditions.
The results presented in this work will help to improve the general understanding of two-phase flows in normal gravity and in microgravity conditions, with general applications on mixing devices, environmental and propulsion systems.
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Belibagli, Kadir Bulent. "Flow phenomena in horizontal axially rotated partially filled cylinders." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq39319.pdf.
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Kolb, William Blake. "The coating of monolithic structures analysis of flow phenomena /." Access abstract and link to full text, 1993. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9318176.
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Herescu, Alexandru. "Two-Phase Flow In Microchannels| Morphology And Interface Phenomena." Thesis, Michigan Technological University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3565323.
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The existence and morphology, as well as the dynamics of micro-scale gas-liquid interfaces is investigated numerically and experimentally. These studies can be used to assess liquid management issues in microsystems such as PEMFC gas flow channels, and are meant to open new research perspectives in two-phase flow, particularly in film deposition on non-wetting surfaces. For example the critical plug volume data can be used to deliver desired length plugs, or to determine the plug formation frequency. The dynamics of gas-liquid interfaces, of interest for applications involving small passages (e.g. heat exchangers, phase separators and filtration systems), was investigated using high-speed microscopy - a method that also proved useful for the study of film deposition processes.
The existence limit for a liquid plug forming in a mixed wetting channel is determined by numerical simulations using Surface Evolver. The plug model simulate actual conditions in the gas flow channels of PEM fuel cells, the wetting of the gas diffusion layer (GDL) side of the channel being different from the wetting of the bipolar plate walls. The minimum plug volume, denoted as critical volume is computed for a series of GDL and bipolar plate wetting properties. Critical volume data is meant to assist in the water management of PEMFC, when corroborated with experimental data. The effect of cross section geometry is assessed by computing the critical volume in square and trapezoidal channels. Droplet simulations show that water can be passively removed from the GDL surface towards the bipolar plate if we take advantage on differing wetting properties between the two surfaces, to possibly avoid the gas transport blockage through the GDL.
High speed microscopy was employed in two-phase and film deposition experiments with water in round and square capillary tubes. Periodic interface destabilization was observed and the existence of compression waves in the gas phase is discussed by taking into consideration a naturally occurring convergent-divergent nozzle formed by the flowing liquid phase. The effect of channel geometry and wetting properties was investigated through two-phase water-air flow in square and round microchannels, having three static contact angles of 20, 80 and 105 degrees. Four different flow regimes are observed for a fixed flow rate, this being thought to be caused by the wetting behavior of liquid flowing in the corners as well as the liquid film stability. Film deposition experiments in wetting and non-wetting round microchannels show that a thicker film is deposited for wetting conditions departing from the ideal 0 degrees contact angle. A film thickness dependence with the contact angle theta as well as the Capillary number, in the form hR ≈ Ca(2/3 )/cos(&thetas;) is inferred from scaling arguments, for contact angles smaller than 36 degrees. Non-wetting film deposition experiments reveal that a film significantly thicker than the wetting Bretherton film is deposited. A hydraulic jump occurs if critical conditions are met, as given by a proposed nondimensional parameter similar to the Froude number. Film thickness correlations are also found by matching the measured and the proposed velocity derived in the shock theory. The surface wetting as well as the presence of the shock cause morphological changes in the Taylor bubble flow.
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White, Samuel Scott. "Visualization of flow phenomena in a vascular graft model." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/16887.
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Eccles, Errol R. A. (Errol Ray Antonio). "Flow and heat transfer phenomena in aerated vibrated beds." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74281.
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Flow characteristics including resonance phenomena, bubble phenomena, particle circulation and mixing patterns as well as surface-to-bed heat transfer in aerated vibrated beds were studied experimentally. Beds of various model particles were vibrated in the vertical direction with a frequency varying from 0-25 Hz and half-amplitude from 0-4 mm. Alumina, glass beads and molecular sieve particles of sizes ranging from 6 $ mu$m to 3600 $ mu$m were used as the model particles. Air flow rates through holes in the bottom plates varied from 0 to 4 times the minimum fluidizing velocity with one, five or a multiplicity of holes. The resonance phenomenon was characterized by a sudden bed expansion and intense surface agitation; this phenomenon was generally observed only in beds of small particles (d$ sb{ rm p}$ $<$ 250 $ mu$m). Bubble sizes increased while the bubble rise velocities decreased with increasing vibration frequency. An analytical model was developed to predict the resonant frequency assuming that the aerated vibrated bed behaves as a porous piston undergoing reciprocating motion at the applied frequency. Contact heat transfer between an immersed circular cylinder and the vibrated bed was found to be a function of particle circulation which, in turn, depends on the vibration parameters. Particle circulation is maximal at the point at which the bed displayed resonant behaviour. The cylinder-to-bed heat transfer coefficient is also maximal at resonance. A correlation is proposed for the surface-to-bed heat transfer based on these features.
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Blake, Malcolm Owen. "Flow erosion phenomena with invert emulsions in hydraulic equipment." Thesis, Coventry University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386514.
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Fink, David Allan. "Surge dynamics and unsteady flow phenomena in centrifugal compressors." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14569.
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Ruslim, Franky. "Flow phenomena in cake washing driven by mass forces." Göttingen Cuvillier, 2008. http://d-nb.info/99160492X/04.
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Lazo-Martinez, Israel Esteban. "Liquid Crystal Enabled Electrokinetic Phenomena." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1397725003.
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Akbar, Muhammad Khalid. "Transport Phenomena in Complex Two and Three-Phase Flow Systems." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4897.
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Two and three-phase flow processes involving gas, liquid and solid, are common in nature and industry, and include some of the most complex and poorly-understood transport problems. In this research hydrodynamics, heat and mass transfer processes in complex two and three-phase flows were investigated. The interfacial surface area concentration in a short vertical column subject to the through flow of fiber-liquid-gas slurry was experimentally measured using the gas absorption technique. The experimental data were statistically analyzed for parametric effects, and were empirically correlated. The absorption of a gaseous species by a slurry droplet with internal circulation and containing reactive micro-particles was simulated, and parametrically studied. The micro-particles were found to enhance the absorption rate. The absorption rate was sensitive to droplet recirculation, and shrinkage of particles with time resulted in declining absorption rates. The transport of soot particles, suspended in laminar hot gas flowing in a tube, was modeled and parametrically studied. Due to coupled thermal radiation and thermophoresis, a radially-nonuniform temperature profile develops, leading to sharp, non-uniform radial soot-concentration profiles. The assumption of monodisperse particles leads to over-prediction of thermophoresis. The transport and removal of particles suspended in bubbles rising in a stagnant liquid pool were modeled based on a Eulerian – Monte Carlo method. The bubble hydrodynamics were treated in Eulerian frame, using the Volume-of-Fluid (VOF) technique, while particle equations of motion were numerically solved in Lagrangian frame. The bubbles undergo shape change, and have complex internal circulation, all of which influence the particle removal. Model predictions were also compared with experimental data. Using a resemblance between two-phase flow in microchannels, and in large channels at microgravity, a simple Weber number-based two-phase flow regime map was developed for microchannels. Based on the available air-water experimental data, a criterion for the prediction of conditions that lead to flow regime transition out of the stratified-wavy flow pattern in horizontal annular channels was proposed. The thermocapillary effects on liquid-vapor interface shape during heterogeneous bubble ebullition in microchannels were analytically studied.
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Rhodes, Scott E. (Scott Edward) 1981. "Magnetic fluid flow phenomena in DC and rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17670.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 299-301).
An investigation of magnetic fluid experiments and analysis is presented in three parts: a study of magnetic field induced torques in magnetorheological fluids, a characterization and quantitative measurement of properties relating to the transition of a ferrofluid drop from a continuous phase into a discrete phase and also into a spiral flow, and a study of magnetic field induced ferrofluid flow reversals. The torque exerted on a spindle filled with magnetorheological fluid (MR fluid) and placed inside a uniform rotating magnetic field is measured with varying rotating magnetic field amplitude and frequency, total fluid volume, and MR fluid volume ratio. When compared to similar ferrofluid torque measurements where the torque increased with rotating magnetic field frequency, the torque frequency dependence of the MR fluid decreases with increasing magnetic field frequency. A simple analysis determines the dependence of the magnetic body torque on particle size to describe the different behavior between the ferrofluid and MR fluid. When a fluorocarbon based ferrofluid is contained between two glass plates separated by a small gap (Hele-Shaw cell) and excited by an applied uniform rotating magnetic field first and then a DC axial magnetic field, a phase like transition occurs that transforms the ferrofluid drop from a continuous phase to a discrete phase. Considering the dominant energy in the configuration to be contributed from the magnetostatic energy of the DC magnetic field and interfacial surface energy, a calculus of minimization of free energy is performed to determine the number of smaller ferrofluid drops that will result from the transition and the threshold axial magnetic field for the transition to occur.
(cont.) When the order of the applied magnetic fields is reversed, the DC axial magnetic field is applied first causing the ferrofluid droplet to form the labyrinth instability. The rotating magnetic field is then applied creating a spiral formation. Experiments are conducted for varying Hele-Shaw cell separation gap, and rotating magnetic field amplitude and frequency. Measurements were consistent with our model. A cylindrical vessel is filled with a water-based ferrofluid and excited by a uniform rotating magnetic field that induces a counter-rotating circular flow in the vessel. A DC axial magnetic field is slowly raised to change the curvature of the fluid surface and results in a change in the ferrofluid flow direction to co-rotating with the applied magnetic field. Measurements are taken of the threshold axial magnetic field that results in the change of flow direction for varying rotating magnetic field direction, amplitude, and frequency. An analysis is included that describes the change in flow direction due to surface curvature.
by Scott E. Rhodes.
S.M.
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Pearson, Natalie Clare. "Mathematical modelling of flow and transport phenomena in tissue engineering." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:43688cc7-b523-4676-8c41-72db7fc07814.
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Tissue engineering has great potential as a method for replacing or repairing lost or damaged tissue. However, progress in the field to date has been limited, with only a few clinical successes despite active research covering a wide range of cell types and experimental approaches. Mathematical modelling can complement experiments and help improve understanding of the inherently complex tissue engineering systems, providing an alternative perspective in a more cost- and time-efficient manner. This thesis focusses on one particular experimental setup, a hollow fibre membrane bioreactor (HFMB). We develop a suite of mathematical models which consider the fluid flow, solute transport, and cell yield and distribution within a HFMB, each relevant to a different setup which could be implemented experimentally. In each case, the governing equations are obtained by taking the appropriate limit of a generalised multiphase model, based on porous flow mixture theory. These equations are then reduced as far as possible, through exploitation of the small aspect ratio of the bioreactor and by considering suitable parameter limits in the subsequent asymptotic analysis. The reduced systems are then either solved numerically or, if possible, analytically. In this way we not only aim to illustrate typical behaviours of each system in turn, but also highlight the dependence of results on key experimentally controllable parameter values in an analytically tractable and transparent manner. Due to the flexibility of the modelling approach, the models we present can readily be adapted to specific experimental conditions given appropriate data and, once validated, be used to inform and direct future experiments.
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Raeisi, Dehkordi Amir Hooshang. "Investigation of flow boiling phenomena in small-scale complex geometries." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2531.
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This study concerns measurement and prediction of single-phase and flow boiling heat transfer coefficients and pressure drops in mini multi-channel geometries with and without interconnecting passages, including plate channel; parallel channel; in-line pin-fin and in-line off-set pin-fin surfaces. Experiments were performed with refrigerant R113 and deionised water at atmospheric pressure. Single-phase and flow boiling heat transfer coefficients and pressure drops were obtained over a range of effective heat fluxes and mass fluxes. For the plate and parallel channel surfaces, the results obtained have been compared with several published macro- and micro-channels correlations. For the in-line and in-line off-set pin fin surfaces, as the geometries have some similarities with tube bundles, the results obtained have been predicted using the standard correlations for tube bundles. The results also have been compared with several existing correlations developed based on macro-scale tube bundles and micro-pin-fin surfaces data. The saturated flow boiling heat transfer coefficients for the parallel channel and pin-fin surfaces were similar to within the experimental uncertainty, and considerably higher than the plate channel values, all dependent on heat flux and reasonably independent of mass flux and vapour mass fraction. This indicated that the dominant heat-transfer mechanism in the saturated boiling flow regime was nucleate boiling for all surfaces. The parallel channel, in-line and off-set pin-fin surfaces improved heat transfer by increasing the surface area and the heat transfer coefficient in comparison with the plate channel surface. The two-phase pressure drops in the parallel channel and pin-fin surfaces were considerably larger than that for the plate channel surface. Thus, the reduction in wall temperature is achieved by a significant pressure drop penalty. For the pin-fin surfaces, at low vapour qualities the heat transfer coefficients were in reasonable agreement with the conventional scale tube bundles correlations however as the vapour quality increases, the correlations were not able to predict the heat transfer coefficient as unlike the conventionally-sized tube bundles, the convective enhancement does not happen in the mini-pin-fin surfaces tested. The nucleate pool boiling correlation of Cooper (1984) provided a good agreement with the data for all surfaces tests with R113 and deionised water. The measured two-phase pressure drops for both pin-fin surfaces tests with R113 and deionised water were in a good agreement with the predicted values obtained from standard correlations for tube bundles, indicating pressure drop methods maybe transferable.
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Almeida, Hugo Stefanio de. "Nonlinear turbulent transonic flow phenomena influence on aeroelastic stability analysis." Instituto Tecnológico de Aeronáutica, 2010. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1123.
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The present work is aimed at studying the influence of viscous effects in transonic aeroelastic analyses. To achieve this goal, a two-dimensional and viscous aeroelastic computational solver, for CAE analysis, is developed, which uses unstructured computational meshes and which is able to capture the main aeroelastic phenomena relevant in the transonic regime of flight. The aeroelastic system considered to test the present methodology is the classical typical section model. The system has two structural degrees of freedom. These are pitching and plunging, or heaving. The structural degrees of freedom can be treated within solver in a coupled manner or separately, in a loosely coupled fashion. The typical section model is an approximation to the treatment of a full wing, in which the airfoil at 75% of the semi-span is analyzed. The structural response is obtained by solving a set of a second order ordinary differential equations in time, with aerodynamic forcing. The coupling of the structural degrees of freedom occurs primarily through the aerodynamic forcing terms. The unsteady aerodynamic problem is treated through the numerical solution of the Reynolds-averaged Navier-Stokes equations. These equations are solved using a finite volume method for unstructured computational grids, which uses a second-order centered spatial discretization and a second order time marching scheme. Turbulence closure is achieved through the Spalart-Allmaras one-equation eddy viscosity turbulence model. A reduction of the computational time for the unsteady aerodynamic simulations is obtained through the implmentation of a few convergence acceleration methods, which include the use of a constant CFL number, implicit residual smoothing and unsteady multigrid methods. The aeroelastic problem is solved through the coupling of the aerodynamic and structural formulations. In the present case, the structural equations are cast in a modal formulation and the unsteady aerodynamic responses are represented by aerodynamic states obtained by rational interpolating polynomials. The complete system of equations is written in state space format in the Laplace domain. The aeroelastic stability condition can, then, be determined by standard eigenvalue analyses of the system dynamic matrix.
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Naraidoo, Marcus. "Investigation of horizontal co-current two-phase slug flow phenomena." Thesis, University of Bristol, 1989. http://hdl.handle.net/1983/460a5ab0-b98e-49c9-bce5-f657d2d3f19b.
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Kapur, Nikil. "Flow phenomena in fixed-gap and gravure roll coating systems." Thesis, University of Leeds, 1999. http://etheses.whiterose.ac.uk/929/.
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This thesis describes investigations into a number of coating processes using experimental, analytical and computational techniques. The first problem, considered experimentally, is that of reverse roll coating with a liquid reservoir positioned directly above horizontally aligned rollers. Measurements of the film thickness as a function of the height of fluid in the reservoir and speed ratio are presented. When the wetting line is located downstream of the nip, either a decrease in the height of the associated hydrostatic head or an increase in the speed ratio causes a reduction in the thickness of the outgoing film. However, when the wetting line is located upstream of the nip the opposite is found to be true. The bead-break instability in forward meniscus coating is considered both experimentally and analytically. Agreement between predictions from a simple mathematical model of the stable bead and experimentally determined meniscus positions is seen to be excellent. A perturbation hypothesis is used to predict the onset of the bead-break instability, at which the upstream meniscus accelerates rapidly towards the downstream one, so the two collide and the bead collapses. The results from the model compare well with experiments. An outline of a method for using the bead-break instability as a design criterion is also presented. Typically in a slot, blade or knife coater the downstream meniscus is assumed to pin at a corner of the coating device. In chapter 5, a series of experiments and a corresponding computational study, are presented which illustrate that the meniscus can advance up the face of such coating devices (in this case a roll-flat plate system). Reducing the corner angle is seen to reduce the size of the climb region and the associated recirculation at this point at the downstream meniscus. It is also shown that the meniscus can detach from the corner and retreat into the gap, which can in turn give rise to the ribbing instability. An offset gravure coating arrangement is considered in chapter 6. The coating arrangement is split into two areas of study - the offset gravure nip and the kiss coating bead. An experimental investigation of the offset nip with the two rolls vertically aligned and running at the same speed in forward mode reveals two ways in which the metered film thickness can be influenced. Either increasing the nip force by pressing the two rolls together or decreasing the roll speeds causes a reduction in the metered film thickness. At higher speeds the metered film thickness is observed to asymptote to a limiting value, the value of which depends on the gravure pattern. The reverse mode kiss coating bead operating at speed ratios greater than one is also investigated. Experiments reveal that under these conditions, all the fluid is transferred from the roll surface to the web and the two make contact due to the generation of a sub-ambient pressure field within the bead. Two models based on lubrication theory are derived, one assuming an infinitely tensioned web and a second that incorporates the effect of web flexibility. The latter is found to give much better agreement with the experimental data. Finally a perturbation hypothesis is applied to these to models in order to predict the onset of the ribbing instability, both of which are found to give reasonable agreement with the experimental data. Finally, the results of a systematic experimental investigation of reverse mode direct gravure coating is reported, where the web runs directly over a gravure roll surface. This wide ranging parametric study illustrates the effect of the operating parameters on the final film thickness. Key findings are that speed ratio, fluid properties and cell shape and size can significantly influence the final film thickness. For a fixed roll speed it is observed that as the web speed is increased the gravure bead becomes unstable. This results in streaking on the web, and gives an upper limit to the speed ratio.
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Mitchell, William James. "Transport phenomena in viscous flow and particle motion in fluidized beds /." Title page, table of contents and abstract only, 1988. http://web4.library.adelaide.edu.au/theses/09ENS/09ensm682.pdf.
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Rogers, D. A. Philip. "Flow phenomena and splitting techniques in horizontal pneumatic conveying pipe-lines." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490827.
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This work documents the research, design and implementation of devices to improve the balance of junction splits in the pneumatic conveying systems of conventional coal fired power stations. The organisation of the thesis follows the design process chronologically, culminating in the installation of the prototype designs in operational pneumatic conveying systems.
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LIU, WEN. "TRANSPORT PHENOMENA ASSOCIATED WITH LIQUID METAL FLOW OVER TOPOGRAPHICALLY MODIFIED SURFACES." UKnowledge, 2012. http://uknowledge.uky.edu/me_etds/16.
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Brazing and soldering, as advanced manufacturing processes, are of significant importance to industrial applications. It is widely accepted that joining by brazing or soldering is possible if a liquid metal wets the solids to be joined. Wetting, hence spreading and capillary action of liquid metal (often called filler) is of significant importance. Good wetting is required to distribute liquid metal over/between the substrate materials for a successful bonding.
Topographically altered surfaces have been used to exploit novel wetting phenomena and associated capillary actions, such as imbibitions (a penetration of a liquid front over/through a rough, patterned surface). Modification of surface roughness may be considered as a venue to tune and control the spreading behavior of the liquids. Modeling of spreading of liquids on rough surface, in particular liquid metals is to a large extent unexplored and constitutes a cutting edge research topic.
In this dissertation the imbibitions of liquid metal has been considered as pertained to the metal bonding processes involving brazing and soldering fillers. First, a detailed review of fundamentals and the recent progress in studies of non-reactive and reactive wetting/capillary phenomena has been provided. An imbibition phenomenon has been experimentally achieved for organic liquids and molten metals during spreading over topographically modified intermetallic surfaces. It is demonstrated that the kinetics of such an imbibition over rough surfaces follows the Washburn-type law during the main spreading stage. The Washburn-type theoretical modeling framework has been established for both isotropic and anisotropic non-reactive imbibition of liquid systems over rough surfaces. The rough surface domain is considered as a porous-like medium and the associated surface topographical features have been characterized either theoretically or experimentally through corresponding permeability, porosity and tortuosity. Phenomenological records and empirical data have been utilized to verify the constructed model. The agreement between predictions and empirical evidence appears to be good. Moreover, a reactive wetting in a high temperature brazing process has been studied for both polished and rough surfaces. A linear relation between the propagating triple line and the time has been established, with spreading dominated by a strong chemical reaction.
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Hoogenboezem, Teunis Adrianus. "Heat transfer phenomena in flow through packed beds / Teunis Adrianus Hoogenboezem." Thesis, North-West University, 2006. http://hdl.handle.net/10394/4300.
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In order to simulate the thermal-fluid performance of a pebble bed reactor such as the PBMR, heat transfer phenomena in packed beds must be characterized. In the pseudo-heterogeneous simulation approach that is often employed, the bed is not modeled as a single lumped entity but rather is discretized into control volumes, each with a given homogeneous porosity. Therefore, the Nusselt number characteristics for pebble-to-fluid heat transfer must be investigated for homogeneous porosity packed beds.
The purpose of this study is to measure the heat transfer coefficient (Nusselt number) for pebble-to-fluid convection heat transfer for a given set of discrete homogeneous porosities and then compare it with existing correlations.
A literature study was conducted and it was found that several heat transfer phenomena exist in a packed bed and that in order to obtain useful results it is necessary to isolate connective heat transfer from conduction and radiation heat transfer. Convective heat transfer for packed beds can be divided into the following two divisions, namely:
• Pebble-to-fluid heat transfer;
• Wall-to-fluid heat transfer;
In this study the heat transfer coefficient (Nusselt number) for pebble-to-fluid convection heat transfer is measured for three discrete homogeneous porosity test sections ( 0.36; 0.39; 0.45) that form part of the PBMR High Pressure Test Unit (HPTU). As part of the experimental procedure the standard uncertainty due to the instrument inaccuracies were determined. Data from the physical tests was systematically processed to obtain results of Nusselt number as a function of Reynolds number. From the processed data the relevant non-dimensional parameters could be plotted along with the standard uncertainty in each data point. Repeatability of the data as well as the comparison of the data with correlations from the literature survey is also done and graphically illustrated.
From the results it can be concluded that the HPTU test facility provides good quality results with high repeatability and relatively low uncertainty. The maximum standard uncertainty of 10.88% implies that the data measured on the HPTU is reliable. However, significant differences were found in the values measured for the homogeneous porosity test sections versus that of randomly packed beds that were employed in studies by other authors.Thesis (M.Ing. (Mechanical Engineering)--North-West University, Potchefstroom Campus, 2007.
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Robinson, Andrew. "Use of methods to investigate transport phenomena of multiphase turbulent flow." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6116/.
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The mixing of multiphase turbulent flow within a column is investigated using Positron-Emission Particle-Tracking (PEPT) to understand the controlling phenomena of convection of heat towards the inside surface of its wall in the measurement of the inside-wall heat transfer coefficient by inverse analysis. This is part of a design options study initiated by Rolls-Royce for a key process in the reclamation of uranium from uranium bearing materials. The column contains water and electrolyte and loose metallic swarf. Compressed air is distributed into the column from a perforated plate and hence the multiphase flow is gravity driven. A dynamic assessment of mixing is provided through the framework of the Reynolds-Avergaed Navier-Stokes (RANS) equation in the evaluation of stresses within the multiphase flow. Inverse analysis of heat conduction across the wall of the column provides measurement of the inside-wall heat transfer coefficient. The mixing of swarf coincides with the convergence of the stationary dynamics of the multiphase turbulent flow measured using PEPT. Tikhonov regularisation affords the resolution of the inside-wall heat transfer coefficient of the inverse analysis. A common global gas hold-up between different flows segregates the controlling phenomena of momentum transfer and convection of heat towards the inside surface of the column wall.
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Little, Adrienne Blair. "An understanding of ejector flow phenomena for waste heat driven cooling." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54373.
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In an attempt to reduce the dependence on fossil fuels, a variety of research initiatives has focused on increasing the efficiency of conventional energy systems. One such approach is to use waste heat recovery to reclaim energy that is typically lost in the form of dissipative heat. An example of such reclamation is the use of waste heat recovery systems that take low-temperature heat and deliver cooling in space-conditioning applications. In this work, an ejector-based chiller driven by waste heat will be studied from the system to component to sub-component levels, with a specific focus on the ejector. The ejector is a passive device used to compress refrigerants in waste heat driven heat pumps without the use of high grade electricity or wear-prone complex moving parts. With such ejectors, the electrical input for the overall system can be reduced or eliminated entirely under certain conditions, and package sizes can be significantly reduced, allowing for a cooling system that can operate in off-grid, mobile, or remote applications. The performance of this system, measured typically as a coefficient of performance, is primarily dependent on the performance of the ejector pump. This work uses analytical and numerical modeling techniques combined with flow visualization to determine the exact mechanisms of ejector operation, and makes suggestions for ejector performance improvement. Specifically, forcing the presence of two-phase flow has been suggested as a potential tool for performance enhancement. This study determines the effect of two-phase flow on momentum transfer characteristics inside the ejector while operating with refrigerants R134a and R245fa. It is found that reducing the superheat at motive nozzle inlet results in a 12-13% increase in COP with a 14-16 K decrease in driving waste heat temperature. The mechanisms of this improvement are found to be a combination of two effects: the choice of operating fluid (wet vs. dry) and the effect of two-phase flow on the effectiveness of momentum transfer. It is recommended that ejector-based chillers be operated such that the motive nozzle inlet is near saturation, and environmentally friendly dry fluids such as R245fa be used to improve performance. This work provides critical methods for ejector modeling and validation through visualization, as well as guidance on measures to improve ejector design with commensurate beneficial effects on cooling system COP.
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Huang, Chao-Ming. "Experimental study of pressure difference phenomena in rarefied gases /." free to MU campus, to others for purchase, 1996. http://wwwlib.umi.com/cr/mo/fullcit?p9812957.
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Mielke, Eric. "Study on the Transport Phenomena in Complex Micro-Reactors." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36040.
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Continuous processing in the pharmaceutical and fine chemical industries, particularly in micro/milli-scale reactors, has been a topic of interest in literature in recent years due to the advantages offered over batch reactions. One such advantage is the enhanced transport properties of operating at smaller scales, although the quantification of the transport phenomena is not straightforward when wall and entrance effects cannot be neglected.
In the first study presented, various micro-mixer geometries and scales were considered to increase the mixing efficiency in liquid-liquid systems of diverse interfacial tensions for fast reactions. The conditions were varied over different flow regimes; including slug flow, parallel flow, and drop flow. A mass-transfer-limited test reaction was used to evaluate the overall volumetric mass transfer coefficients (Korga) as a function of the average rate of energy dissipation (ε) for each mixer design. The onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers for low interfacial-tension systems (i.e., n-butanol-water). In the drop flow regime for energy dissipation rates of around 20 to 500 W/kg, Korga values ranged from approximatively 0.14 to 0.35 s-1 and 0.004 to 0.015 s-1 for the relatively low and high interfacial-tension (i.e., toluene-water) systems, respectively.
The second investigation explored the heat transfer properties of a FlowPlate® system by Ehrfeld Mikrotechnik BTS. First, in a non-reactive system with rectangular serpentine channels (d_h<1mm, 400
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Yuhua, Yan. "Cavitation phenomena and the admittance of air in the flow through an orifice." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257548.
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Rivera-Cedeno, Carlos J. "Numerical simulation of dynamic stall phenomena in axial flow compressor blade rows." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12405.
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Okada, Yasuhiko. "A STUDY ON THE POTENTIAL FOR RAPID FLOW PHENOMENA IN GRANULAR SOILS." 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149983.
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Chapman, Emily May. "Microfluidic visualisation and analysis of multiphase flow phenomena at the pore scale." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/46169.
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Micro-fluidic devices have been designed and used to investigate immiscible fluid-fluid displacement processes. Due to their optically transparent nature, such devices allow direct visualisation of pore scale events using light microscopy. In this thesis, we focus on imaging multiphase flow phenomena at the pore scale within specifically designed micro-models using optical and Raman microscopy. The flow channel designs have been selected to investigate fundamental questions relating to fluid displacement mechanisms. The Lucas-Washburn equation predicts that the distance a meniscus travels within a smooth cylindrical capillary is proportional to the square root of time. However, it is poorly understood how surface roughness of the capillary influences the rate of imbibition. This is of great importance for flow in real porous media. Therefore, the displacement dynamics within a series of single capillaries of increasing surface roughness was investigated. It was found that as the roughness increased, the rate of penetration decreased. The rate of decrease with increasing roughness was observed to be different from recent computer simulation studies. Using specifically designed single-junction micro-models, the role of pore geometry on fluid displacement during drainage and imbibition processes is investigated via quasi-static and spontaneous experiments under ambient conditions. The experimental results are directly compared to theory and Lattice Boltzmann Model (LBM) simulations. The experimental critical pore filling pressures observed for the quasi-static experiments agree well to those predicted by the Young-Laplace equation and follow the expected filling sequence. However, the experimental spontaneous imbibition results were found to be different from those predicted by the Young-Laplace equation: instead of entering the narrowest available downstream throat, the wetting phase enters an adjacent throat first. Thus, pore geometry plays a vital role as it becomes the main deciding factor in the displacement sequence. This observation may have serious implications for the prediction of displacement processes at the Darcy scale: current Pore Network Models (PNMs) adopt the Young-Laplace displacement sequence for spontaneous imbibition processes and may therefore need to be revised. To further consider these observations, more complex models consisting of multiple connected junctions, are being investigated. Finally, experiments have been conducted to investigate Raman spectroscopy to understand surfactant enhanced oil recovery (EOR) processes within micro-models. This may prove particularly useful for EOR as micro-emulsion formation is difficult to discern optically. The work presented demonstrates that Raman spectroscopy is an effective technique in visualising pore scale fluid flow processes and distributions.
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Nguyen, Minh Chau. "Hydrodynamic transport phenomena in suspension of microalgae : particle separation using pulsatile flow." Thesis, Université Paris Cité, 2021. http://www.theses.fr/2021UNIP7174.
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La séparation des particules est nécessaire dans de nombreuses applications en chimie, physique, biologie, domaines médicaux et biotechnologie. Par exemple, la récolte de biomasse, qui est l'une des étapes clés de la production de biocarburants à partir des microalgues et des cyanobactéries, est un processus complexe et coûteux (20-30 % du coût total) en raison de la petite taille et aussi de la faible différence entre la densité des micro-organismes et celle de leurs milieux de culture. Ainsi, de nouvelles techniques peu coûteuses sont nécessaires pour remplacer ou améliorer le processus de la séparation. Tandis que plusieurs méthodes passives et actives ont été proposées pour la séparation des particules en écoulement stationnaire, l'écoulement pulsé a reçu moins d'attention. Le but de cette étude est de déterminer les effets de la pulsation d'écoulement sur la séparation des particules dans un microcanal du type « double Y». Seulement l'un des deux écoulements entrants contient des particules et l'efficacité de la séparation est définie comme le rapport entre le nombre des particules s'échappant de la sortie opposée et le nombre total des particules. Les cellules mortes et motiles de Chlamydomonas reinhardtii sont respectivement utilisées comme particules passives et actives. Des expériences microfluidiques et des simulations sont réalisées pour chaque partie de l'étude et les principaux résultats sont résumés ci-dessous: Pour les particules passives: - Lorsque les écoulements entrants dans le microcanal sont stationnaires, le seul paramètre qui permet de contrôler la séparation des particules est le rapport entre les débits aux entrées. L'efficacité de la séparation augmente avec l'augmentation de ce rapport. Pour approcher l'efficacité maximale (0,5), ce rapport doit être supérieur à 20, ce qui n'est pas toujours pratique. - Lorsque les écoulements entrants sont pulsés avec un déphasage, le réglage de ce déphasage peut contrôler l'efficacité de la séparation. - Lorsque 0,5 < amplitude de pulsation < 2 et 1 s < période de pulsation < 10 s, l'efficacité de la séparation augmente avec le déphasage de sorte qu'un déphasage de 180° aboutit à une efficacité maximale. Une tendance similaire est observée pour des valeurs plus élevées de l'amplitude (comme beta = 5) uniquement si la période de pulsation est suffisamment petite. Pour les particules actives: - Les particules actives (cellules motile) n'obéissent pas au protocole de contrôle imposé par la pulsation à l'entrée du système. Comme les particules actives choisissent aléatoirement leur sortie du microcanal, l'efficacité de la séparation reste toujours proche de 0,5. Par conséquent, la pulsation de l'écoulement (seule) ne présente aucun avantage par rapport à un écoulement stationnaire pour la séparation des particules actives. - Cependant, lorsque le comportement phototactique des algues est activé, l'avantage de la pulsation devient évident. En présence d'une stimulation lumineuse, l'efficacité de la séparation augmente respectivement jusqu'à 65 % et 75 % dans les écoulements stationnaires et pulsés. Bien que nos expériences soient menées sur une algue modèle (Chlamydomonas reinhardtii), une simulation numérique a démontré que l'idée d'utiliser un écoulement pulsé peut être étendue à la séparation de toutes autres particules actives stimulées par un champ externe attractif ou répulsif. Ainsi, les applications potentielles peuvent aller au-delà de la récolte des algues pour le control et l'amélioration des processus de séparation, de sélection ou d'accumulation sans avoir besoin de composants mécaniques ou de substances chimiquesParticle separation is an important requirement in chemistry, physics, biology, medical domains and biotechnology. For instance, the conventional biomass harvesting which is one of the key steps in production of biofuels from non-feed stocks such as microalgae and cyanobacteria, is a complex and costly process (20-30% of total cost) due to the small size and low-density difference of the photosynthesis microorganisms and their growth media. Thus, novel low-cost techniques are required to substitute or improve the downstream separation process. While a variety of active and passive techniques have been proposed for the separation process in steady flows, pulsatile flow has received much less attention. The purpose of this study is to determine the effects of flow pulsation on the separation of particles in a double Y-microchannel. Only one of the two entering flows contains the particles and the separation efficiency is defined as the ratio of the particles escaping from the opposite outlet to the total number of particles. Dead and motile cells of Chlamydomonas reinhardtii are used as passive and active particles, respectively. Both experiments and simulations are carried out for each part of the study. The key results can be summarized as follows: For passive particles: - When the inlet flows are in a steady regime, the only parameter that allows controlling the particle separation/distribution is the ratio between the flow rates at the inlets. The separation efficiency increases with increasing this ratio. To approach the maximum efficiency (0.5), this ratio should be more than 20, which is not always practical. - When the inlet flows are pulsating with a phase shift, adjusting the phase shift between the inlet flows can control the separation efficiency. - When 0.5 < pulsation amplitude < 2 and 1 s < pulsation period < 10 s, the separation efficiency increases with the phase shift such that phi = 180° gives the highest efficiency. A similar trend can be observed for higher values of amplitude (like beta = 5) only if the pulsation period is small enough. For active particles: - Active particles (motile cells) do not obey the control protocol imposed at the inlet of the system. The separation efficiency remains around 0.5 implying that active particles choose their exit from the microchannel randomly. Therefore, pulsation (alone) shows no advantage for separation of the active particles compared to a steady flow. - However, when the phototactic behavior of the algae is coupled with pulsatile flow features, the advantage of pulsation becomes clear. In the presence of light stimulation, the separation efficiency increases to 65% and 75% in steady and pulsatile flows respectively. Although the experiments are conducted on the well-known model alga, Chlamydomonas reinhardtii, a simplified numerical simulation demonstrated that the idea can be extended to any other active particle stimulated by an attractive or repulsive external field. Thus, the potential applications of pulsatile flow can go beyond algae harvesting to control and improve separation, selection or accumulation processes without using any mechanical component or chemical substance
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Hussein, Sheik Abdulkadir. "Electrokinetic phenomena in aqueous suspended films and foams." Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/33718.
Full textAbstract:
Electrokinetic phenomena in liquid foams is at a junction between two areas. On one side is the investigation of liquid foam drainage, and on the other side is electrokinetics of surface driven flow on solid-liquid interfaces. However, the electrokinetic phenomena in liquid foam films significantly lack understanding. Therefore, the novelty of the thesis is to address the mentioned gap in three stages. The outcome has potential applications in a novel separation approaches of biological molecules such as proteins and DNA. In the first stage, the electrokinetic flow of a sufficiently thick (180 μm) free liquid film was investigated using cationic and anionic surfactants by confocal micron-resolution particle image velocimetry (μ-PIV). The reverse of the surface charge resulted in a shift in charge of the electrical double layer at the free liquid film interface, which caused the direction of the electroosmotic velocity to reverse. In each surfactant type used, the fluid velocity profiles were measured at different depths of the free liquid film (different z-planes). It was found how the fluid velocity varied with depth. Numerical simulations of the electroosmotic flow in the same system were also performed using Finite Element Method to understand the flow dynamics. A reasonably good agreement was found between the numerical simulations and the experimental results validating the model. In the second stage, instead of flow visualisation particles, rhodamine B (RB) and fluorescein isocyanate (FICT) dye were added to the free liquid film. Under the initial conditions of pH 7.2, RB is a neutral dye, and FICT has a -2 charge. Under an imposed electric field pH variations were detected and an interesting flow profile was observed. The CFD model developed earlier (stage one) was modified to include the local pH variation. The behaviour of the simulated pH had a good agreement with the behaviour of the FICT. Further confirmation of local pH variation was undertaken using extra new experiments which also showed a good agreed with the simulation. In the third stage, a liquid foam electrokinetic separation chamber was designed to extend the study to include practical applications. The first challenge was to achieve a stable foam under external electric field. A polymer-surfactant mixture can solve the stability problem. However, the mixture of polymers required an alkaline pH (>9) condition for the polymer mixture to be soluble in the aqueous system. Lectin and tetramethylrhodamine goat anti-rabbit (IgG) protein mixture with different molecular mass to charge ratio (50 kDa and 150 kDa) were injected near the anode. The system was monitored in three location: (a) in a vicinity of the injection region, (b) between the two electrodes and (c) in a vicinity of the cathode. In the region (a), a decay of the luminescence intensity of the fluorescein of the two proteins was noted with varying rate. In region (b), an increase followed by a decrease in fluorescein intensity of the proteins was observed again at a varying rate. In region (c), an increase of the dye concentration was observed and again at a different rate. The observed difference was caused by difference of the electrophoretic velocity of the two proteins. The setup proved that proteins could be separated based on their electrophoretic mobility inside a liquid foam. The findings from the thesis show the ability to manipulate fluid flow within a free liquid film, and inside a liquid foam system by an external DC electric field, is not only interesting academically but has potential application in a novel separation approach of biological molecules and beyond. The result show, with the correct surfactant formulation, it possible to make a stable foam under an electric field which can be set up for separation of proteins using foam electrokinetics.
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Crippa, Simone. "Accurate physical and numerical modeling of complex vortex phenomena over delta wings." Licentiate thesis, Stockholm : School of engineering sciences, Royal Institute of Technology, 2006. http://www.diva-portal.org/kth/theses/abstract.xsql?dbid=4164.
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Yuan, Tao. "Reduced order modeling for transport phenomena based on proper orthogonal decomposition." Texas A&M University, 2003. http://hdl.handle.net/1969.1/1470.
Full textAbstract:
In this thesis, a reduced order model (ROM) based on the proper orthogonal decomposition (POD) for the transport phenomena in fluidized beds has been developed. The reduced order model is tested first on a gas-only flow. Two different strategies and implementations are described for this case. Next, a ROM for a two-dimensional gas-solids fluidized bed is presented. A ROM is developed for a range of diameters of the solids particles. The reconstructed solution is calculated and compared against the full order solution. The differences between the ROM and the full order solution are
smaller than 3.2% if the diameters of the solids particles are in the range of diameters used for POD database generation. Otherwise, the errors
increase up to 10% for the cases presented herein. The computational time of the ROM varied between 25% and 33% of the computational time of the full order solution. The computational speed-up depended on the complexity of the transport phenomena, ROM methodology and reconstruction error. In this thesis, we also investigated the accuracy of the reduced order model based on the POD. When analyzing the accuracy, we used two simple sets of governing partial differential equations: a non-homogeneous Burgers' equation and a system of two coupled Burgers' equations.
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Katterwe, Sven-Olof. "Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena." Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-62583.
Full textAbstract:
In this thesis, intrinsic Josephson junctions, naturally formed in the strongly anisotropic high-temperature superconductor Bi2Sr2CaCu2O8 (Bi-2212), are studied experimentally. For this purpose, small mesa structures are fabricated on the surface of single crystals using micro- and nano-fabrication tools, focused ion beam is used to reduce the area of the mesa-structures down to ≈ 1 × 1 μm2. The properties of charge transport across copper-oxide layers inside the mesas are studied by intrinsic tunneling spectroscopy. Temperature, bias and magnetic field dependences of current-voltage characteristics are examined. In the main part of the thesis, the behavior of intrinsic Josephson junctions in magnetic fields B parallel to the copper-oxide planes is studied. Parallel magnetic fields penetrate the junctions in the form of Josephson vortices (fluxons). At high magnetic fields, fluxons are arranged in a regular lattice and are accelerated by a sufficient high transport current. As the fluxon lattice is moving through the mesa, it emits electromagnetic waves in the important THz frequency range. Properties of Bi-2212 mesas in this flux-flow regime are studied in this thesis. The following new observations were made during the course of this work: a crossover from thermal activation above Tc to quantum tunneling below Tc is seen in the interlayer transport-mechanism, the Fraunhofer pattern of Ic(B) is observed clearly in Bi-2212, superluminal electromagnetic cavity resonances and phonon-polaritons are observed in Bi-2212. It is argued that the employed technique for miniaturization of mesas and the obtained results can be useful for a better understanding of fundamental properties of high-temperature superconductors and for the realizations of coherent flux-flow oscillators and coherent phonon-polariton generators in the important THz frequency range.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript.