Dissertations / Theses on the topic 'Field transfer'
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1
Hart, David Marvin. "Light-Field Style Transfer." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7763.
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For many years, light fields have been a unique way of capturing a scene. By using a particular set of optics, a light field camera is able to, in a single moment, take images of the same scene from multiple perspectives. These perspectives can be used to calculate the scene geometry and allow for effects not possible with standard photographs, such as refocus and the creation of novel views.Neural style transfer is the process of training a neural network to render photographs in the style of a particular painting or piece of art. This is a simple process for a single photograph, but naively applying style transfer to each view in a light field generates inconsistencies in coloring between views. Because of these inconsistencies, common light field effects break down.We propose a style transfer method for light fields that maintains consistencies between different views of the scene. This is done by using warping techniques based on the depth estimation of the scene. These warped images are then used to compare areas of similarity between views and incorporate differences into the loss function of the style transfer network. Additionally, this is done in a post-training fashion, which removes the need for a light field training set.
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Basu, Soumyadipta. "Near-field radiative energy transfer at nanometer distances." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31777.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Zhang, Zhuomin; Committee Member: Citrin, David; Committee Member: Hesketh, Peter; Committee Member: Joshi, Yogendra; Committee Member: Peterson, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Rein, Gordon J. "Transfer of training in organizations, a field study." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24229.pdf.
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Dai, Jin. "Near-Field Radiative Heat Transfer between Plasmonic Nanostructures." Doctoral thesis, KTH, Optik och Fotonik, OFO, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-195653.
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Radiative heat transfer (RHT) due to coupled electromagnetic near field scan significantly exceed that dictated by Planck’s law. Understanding such phenomenon is not only of fundamental scientific interest, but also relevant to a broad range of applications especially connected to nanotechnologies.This dissertation elaborates, through a scattering approach based on the rigorous coupled wave analysis method, how plasmonic nanostructures can tame the near-field RHT between two bodies. The transmission-factor spectra are corroborated by photonic band diagrams computed using a finite element method. The main work begins by showing that the phenomenon of spoofsurface plasmon polariton (SSPP) guided on grooved metal surfaces can play a similar role as surface phonon polariton in enhancing the RHT between two closely placed plates. Since dispersions of SSPPs especially their resonance frequencies can be engineered through geometrical surface profiling,one has great freedom in tailoring spectral properties of near-field RHT. Further enhancement of RHT can be achieved through techniques like filling of dielectrics in grooves or deploying supercells. A thorough study of RHT betweentwo 1D or 2D grooved metal plates confirms super-Planckian RHT at near-field limit, with 2D grooved metal plates exhibiting a superior frequency selectivity. We also present RHT with a more exotic type of plasmonic nanostructures consisting of profile-patterned hyperbolic metamaterial arrays, and show that with such plasmonic nanostructures one can achieve an ultrabroadband super-Planckian RHT.QC 20161111
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Shah, Simon Michael. "Magnetisation transfer effects at ultra high field MRI." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/39398/.
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Increased signal to noise ratio in ultra high field Magnetic Resonance Imaging (MRI) has allowed the development of quantitative imaging techniques and new contrast mechanisms, such as Chemical Exchange Saturation Transfer (CEST) to be probed. The development of CEST contrast imaging has involved overcoming a number of technical challenges associated with ultra high field MRI. The B1 transmit field was, and still is, a major challenge. Presented in this thesis, the B1 transmit field in regions of low B1 are improved with the use of dielectric pads and a simulation study shows that the overall B1 transmit field homogeneity is significantly improved when multi-transmit slice-selective RF spokes pulse sequences are used. Multiple methods have been developed to quantify the chemical exchange from slow exchanging proton pools seen in CEST contrast imaging. However, magnetisation transfer (MT) from the macromolecular bound pool contaminates current quantification methods, and presented in this thesis is a method whereby the CEST and MT are simultaneously saturated using dual frequency saturation pulses, allowing the CEST contrast in z-spectra to be separated from the MT and to enhance visualisation of the CEST effects. Despite the considerable interest in CEST, only one study has probed the CEST effects in blood, and interestingly high levels of CEST signals can be observed from the superior sagittal sinus. To investigate these effects, z-spectra from ex vivo blood samples considering the effects of oxygenation, haematocrit levels and cell structure were quantified. Quantification shows that the main source of the CEST signals was from the cells within the blood.
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Prussing, Keith F. "An investigation of surface shape effects on near-field radiative transfer." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54321.
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It has been shown that the energy exchange between two objects can be
greatly enhanced when the separation between the objects is on the order
of the wavelength of thermal emission. The earliest theoretical and
computational work focused on simple planar and spherical geometries, or
they resorted to approximations that separated the object to outside of
the thermal wavelength \(\lambda_T = hc/(k_BT)\). Since those original
works, the study of near-field energy exchange has expanded to object
shapes that can be described by a separable coordinate system using a
spectral expansion of the dyadic Green function of the system. The
boundary element method has also been used to study arbitrary shapes in
thermal equilibrium. Application of these new expansion methods to
general shapes out of thermal equilibrium will facilitate in the
optimization of nanoscale structures.
A three step process is used to investigate the effects of object shape
on the total and directionality of the energy exchange between objects.
First, a general expression for the energy flux between the objects will
be formulated. Second, a computational method to evaluate the
expression will be implemented. Finally, the effects of varying the
surface geometry will be explored.
The computational results demonstrate that the total energy exchange
between two bodies is influenced by the surface shape of the objects
even when the surface areas are held constant. While the primary
increase over the classical blackbody energy exchange \(\sigma T^4 A\)
is primarily governed by separation of the surfaces, we show that the
view factors from classical far-field radiative transfer can be used to
predict the change in the total energy exchange from a reference
configuration at the same separation when the surface area of the two
objects is comparable. Additionally, we demonstrate that the spatial
distribution of the energy exchange can be localized into small spatial
region with a peak value increased over \SI{30}{\percent} by using two
objects with dramatically different projected areas.
7
Huang, Yi Ph D. Massachusetts Institute of Technology. "Electrically-tunable near-field heat transfer with ferroelectric materials." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92139.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 75-80).
Radiative heat transfer at small separations can be enhanced by orders of magnitude via the use of surface phonon polariton or plasmon polariton waves. This enhancement has potential applications in different devices, such as thermal emitters, thermal rectifiers, thermophotovoltaic and thermoelectric energy conversion systems. In this thesis, the author explores the tunable optical properties of ferroelectric materials to manipulate the near-field radiative heat transfer between two surfaces, aiming at the active control of near-field radiation heat transfer. Soft mode hardening of ferroelectric thin films induced by environmental changes, such as temperature and electric field, is widely used as a basis for tunable and switchable electrical and optical devices. However, this mechanism has not yet been examined for heat transfer applications. Using the fluctuation-dissipation theorem and the Dyadic Green's function method, the author shows via simulation that the magnitude and spectral characteristics of radiative heat transfer can be tuned via an externally applied electric field and temperature. Ways are explored to maximize the tuning contrast and discuss the trade-off between maximizing tunability and heat transfer. Our simulation results suggest that ferroelectrics can be used to develop new types of tunable nano-scale devices for thermal and energy conversion applications.
by Yi Huang.
S.M.
8
Meyer, Antoine. "Active control of heat transfer by an electric field." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMLH13/document.
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La stabilité d’un fluide Newtonien diélectrique confiné dans un anneau cylindrique et soumis à un gradient radial de température et à un champ électrique est étudiée. Le gradient de température induit une stratification de la permittivité électrique du fluide et de sa masse volumique. Trois poussées thermiques rentrent alors en jeu : la gravité terrestre créée la poussée d’Archimède, la rotation des cylindres engendre la poussée centrifuge, et le champ électrique induit la poussée diélectrophorétique. L’effet de ces poussées est étudié dans différentes combinaisons, principalement à travers l’étude de la stabilité linéaire, mais également par la simulation numérique directeThe stability of a Newtonian dielectric fluid confined in a cylindrical annulus and submitted to a radial temperature gradient and an electric field is studied. The temperature gradient induces a stratification of the electric permittivity and of the density. Thus three thermal buoyancies intervene: the Earth gravity creates the Archimedean buoyancy, the rotation of the cylinders generates the centrifugal buoyancy, and the electric field induces the dielectrophoretic buoyancy. The effect of these buoyancies is studied in different combination, principally through the linear stability analysis, but also by direct numerical simulation
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Carpenter, Joanna Katharine Hicks. "Magnetic field effects on electron transfer reactions in photosynthetic bacteria." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390466.
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Tong, Jonathan Kien-Kwok. "Photonic engineering of near- and far-field radiative heat transfer." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104127.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 181-195).
Radiative heat transfer is the process by which two objects exchange thermal energy through the emission and absorption of electromagnetic waves. It is one of nature's key fundamental processes and is ubiquitous in all facets of daily life from the light we receive from the Sun to the heat we feel when we place our hands near a fire. Fundamentally, radiative heat transfer is governed by the photonic dispersion, which describes all the electromagnetic states that can exist within a system. It can be modified by the material, the shape, and the environment. In this thesis, morphological effects are used to modify the photonic dispersion in order to explore alternative methods to spectrally shape, tune, and enhance radiative heat transfer from the near-field to the far-field regimes. We start by investigating the application of thin-film morphologies to different types of materials in the near-field regime using a rigorous fluctuational electrodynamics formalism. For thin-film semiconductors, trapped waveguide modes are formed, which simultaneously enhance radiative transfer at high frequencies where these modes are resonant and suppress radiative transfer at low frequencies where no modes are supported. This spectrally selective behavior is applied to a theoretical thermophotovoltaics (TPV) system where it is predicted the energy conversion efficiency can be improved. In contrast, thin-films of metals supporting surface plasmon polariton (SPP) modes will exhibit the opposite effect where the hybridization of SPP modes on both sides of the film will lead to a spectrally broadened resonant mode that can enhance near-field radiative transfer by over an order of magnitude across the infrared wavelength range. In order to observe these morphological spectral effects, suitable experimental techniques are needed that are capable of characterizing the spectral properties of near-field radiative heat transfer. To this end, we developed an experimental technique that consists of using a high index prism in an inverse Otto configuration to bridge the momentum mismatch between evanescent near-field radiative modes and propagation in free space in conjunction with a Fourier transform infrared (FTIR) spectrometer. Preliminary experimental results indicate that this method can be used to measure quantitative, gap-dependent near-field radiative heat transfer spectrally. While utilizing near-field radiative transfer remains a technologically challenging regime for practical application, morphological effects can still be used to modify the optical properties of materials in the far-field regime. As an example, we use polyethylene fibers to design an infrared transparent, visibly opaque fabric (ITVOF), which can provide personal cooling by allowing thermal radiation emitted by the human body to directly transmit to the surrounding environments while remaining visible opaque to the human eye.
by Jonathan Kien-Kwok Tong.
Ph. D.
11
Lu, Ming. "Synergetic Attenuation of Stray Magnetic Field in Inductive Power Transfer." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78621.
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Significant stray magnetic field exists around the coils when charging the electric vehicles (EVs) with inductive power transfer (IPT), owning to the large air gap between the transmitter and receiver. The methods for field attenuation usually introduce extra losses and reduce the efficiency. This study focuses on the synergetic attenuation of stray magnetic field which is optimized simultaneously with the efficiency. The optimization is realized with Pareto front.
In this dissertation, three methods are discussed for the field attenuation. The first method is to tune the physical parameters of the winding, such as the inner radii, outer radii, distribution of the turns, and types of the litz wires. The second method is to add metal shields around the IPT coils, in which litz wires are used as shields to reduce the shielding losses. The third method is to control the phases of winding currents, which avoids increasing the size and weight of the IPT coils.
To attenuate the stray magnetic field by tuning the physical parameters, the conventional method is to sweep all the physical parameters in finite-element simulation. This takes thousands of simulations to derive the Pareto front, and it's especially time-consuming for three-dimensional simulations. This dissertation demonstrates a faster method to derive the Pareto front. The windings are replaced by the lumped loops. As long as the number of turns for each loop is known, the efficiency and magnetic field are calculated directly from the permeance matrices and current-to-field matrices. The sweep of physical parameters in finite-element simulation is replaced by the sweep of the turns numbers for the lumped loops in calculation. Only tens of simulations are required in the entire procedure, which are used to derive the matrices. An exemplary set of coils was built and tested. The efficiency from the matrix calculation is the same as the experimental measurement. The difference for stray magnetic field is less than 12.5%.
Metal shields attenuate the stray magnetic field effectively, but generates significant losses owning to the uneven distribution of shield currents. This dissertation uses litz wires to replace the conventional plate shield or ring shield. Skin effect is eliminated so the shield currents are uniformly distributed and the losses are reduced. The litz shields are categorized to two types: shorted litz shield and driven litz shield. Circuit models are derived to analyze their behaviors. The concept of lumped-loop model is applied to derive the Pareto front of efficiency versus stray magnetic field for the coils with litz shield. In an exemplary IPT system, coils without metal shield and with metal shields are optimized for the same efficiency. Both the simulation and experimental measurement verify that the shorted litz shield has the best performance. The stray magnetic field is attenuated by 65% compared to the coils without shield.
This dissertation also introduces the method to attenuate the stray magnetic field by controlling the phases of winding currents. The magnetic field around the coils is decomposed to the component in the axial direction and the component in the radial direction. The axial component decreases with smaller phase difference between windings' currents, while the radial component exhibits the opposite property. Because the axial component is dominant around the IPT coils, decreasing the phase difference is preferred. The dual-side-controlled converter is applied for the circuit realization. Bridges with active switches are used for both the inverter on the transmitter side and the rectifier on the receiver side. The effectiveness of this method was verified both in simulation and experiment. Compared to the conventional series-series IPT with 90° phase difference between winding currents, stray magnetic field was attenuated by up to 30% and 40% when the phase differences of winding currents are 50° and 40°, respectively.
Furthermore, an analytical method is investigated to calculate the proximity-effect resistance of the planar coils with ferrite plate. The objective of this method is to work together with the fast optimization which uses the lumped-loop model. The existence of the ferrite plate complicates the calculation of the magnetic field across each turn which is critical to derive the proximity-effect resistance. In this dissertation, the ferrite plate is replaced by the mirrored turns according to the method of image. The magnetic fields are then obtained from Ampere's Law and Biot-Savart Law. Up to 200 kHz, the difference of the proximity-effect resistance is less than 15% between calculation and measurement.Ph. D.
12
Subramanian, Rajkumar. "Heat Transfer to a Droplet Translating in an Electric Field." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1108851150.
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Cattò, Silvia <1990>. "Thermochronometric evidence of far-field stress transfer in continental collisions." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8653/1/SC_Tesi_SilviaCatto%CC%80.pdf.
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In this dissertation, two low-temperature thermochronometers [fission-track analysis on apatite and (U-Th)/He analyses on zircons] are applied on various tectonostratigraphic units from three collisional settings: (i) the Bitlis-Pütürge Massif (SE Turkey), (ii) the Lesser Caucasus (Georgia, Armenia, Azerbaijan), and (iii) the Strandja Massif (SE Bulgaria and NW Turkey). The aim of the study is to better understand the syn- and post-collisional thermochronological evolution of collisional orogens, thus elucidating the dynamics of stress partitioning and transmission during continental collisions. Another focal point of this study is to constrain better the timing of the Arabia-Eurasia collision in the area of its maximum indentation and clarify the overall evolution of the area. From a general viewpoint, our dataset for the Eurasian foreland north of the Arabia-Eurasia collision (the Bitlis-Pütürge Massif and the Lesser Caucasus region) suggest that the tectonic stresses related to the collision during mid-Miocene time were transmitted efficiently over large distances, focusing preferentially at rheological discontinuities located as far as the Lesser Caucasus and the Eastern Pontides. Since the late Middle Miocene a new tectonic regime is active as the westward translation of Anatolia is accommodating most of the Arabia-Eurasia convergence, thus decoupling the foreland from the orogenic wedge and precluding efficient northward stress transfer. In the Strandja Massif the mechanism of stress transmission was very different. The bulk of the massif has escaped significant Alpine-age deformation, which is recorded only in the northern sector. We argue that in the Strandja orogen the stress mostly bypassed the orogenic prism and focused on the Srednogorie rift basin to the north, rheologically weakened by previous Late Cretaceous back-arc extension.
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Muñiz, García Claudia. "Rapid Energy Transfer to an Energy Buffer." Thesis, KTH, Kommunikationssystem, CoS, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91941.
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This master thesis introduces a new technology applicable to nearly all mobile and portable electrical devices since all of them need energy to operate. This thesis attempts to cut the last wire - this one the wire to the primary power source. In other words, fast and efficient wireless energy transference through a strong, focused near magnetic field whose fast attenuation will avoid interference with surrounding communication systems or human harm. This energy is transferred to and will be stored inside the mobile device where nothing but a small and simple secondary circuit has been placed. The thesis project began by creating an initial SPICE computer model, providing an easy and rapid way of testing both convergence and feasibility of the topology as the design evolved from the well-known and widely used Switch Model Power Supply technology through to the detailed design and implementation of the prototype, including supporting the iterative process of testing and optimizing, all stages are carefully described in the document. The thesis shows both theoretically and practically that this idea is feasible and capable of power transmission.Detta examensarbete introducerar en ny teknologi som är applicerbar till de flesta mobila och portabla elektriska apparater då dessa behöver energi för att fungera. Detta arbete försöker klippa den sista ledningen den som leder till den primära kraftkällan. Med andra ord, är denna teknik en snabb och effektiv trådlös energiöverföring genom ett starkt, fokuserat närbeläget magnetfält. Tack vare magnetfältets kraftiga dämpning undviks interferens med intilliggande kommunikationssystem eller personskador. Denna energi är överförd till, och lagras inuti en bärbar apparat där endast en liten och enkel sekundärkrets har placerats. Examensarbetsprojektet påbörjades med skapandet av en inledande SPICE datormodell. Modellen möjliggjorde ett enkelt och snabbt sätt att testa både konvergens och genomförbarhet av topologin samtidigt som designen utvecklades från den välkända och vitt använda Switch Power Supply-teknologin till den detaljerade designen och implementationen av prototypen. Modellen stöttade samtidigt den iterativa processen av test och optimering. Alla faser är utförligt beskrivna i rapporten och arbetet visar både teoretiskt och praktiskt att denna idé är genomförbar och möjliggör kraftöverföring.
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Harder, Donald R. "Convective heat transfer from a cylinder in a strong acoustic field." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305867.
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Thesis (M.S. in Mechanical Engineering and M.S. in Astronautical Engineering) Naval Postgraduate School, December 1995.Thesis advisor(s): Ashok Gopinath, Oscar Biblarz. "December 1995." Bibliography: p. 103-104. Also available online.
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Yaghi, Abdulfattah. "Training transfer in human resources management a field study on supervisors /." Diss., Mississippi State : Mississippi State University, 2006. http://library.msstate.edu/etd/show.asp?etd=etd-11292005-235221.
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Singer, Farah. "Influence of the nonlocal effects on the near-field radiative heat transfer." Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2338.
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Dans ce mémoire de thèse, nous étudions la validité de quelques modèles non locaux de la permittivité diélectrique (PD) dans le calcul du coefficient de transfert de chaleur par rayonnement (CTCR) entre deux matériaux diélectriques, semi- infinies, plans et parallèles, et séparés par un espace vide de largeur d.Dans les études théoriques antérieures, il a été montré que lorsque l'on considère un modèle local de la PD, le transfert de chaleur par rayonnement en champ proche (TCRCP) suit une loi 1/d² quand d devient de l'ordre ou inférieure à quelques centaines de nanomètres. Cette divergence non physique constitue la faille majeure du modèle local. Plusieurs efforts ont été fournis afin de développer un nouveau modèle de la PD qui tient compte des effets nonlocaux. Aucune correction non locale pour le TCRCP n’a été abordée dans le passé dans le cas des diélectriques. Cependant dans le cas des métaux, un travail complet a été effectué en utilisant le modèle non local de Lindhard-Mermin de la PD.Nos travaux portent sur l'étude de quatre modèles différents de la PD nonlocale. Nous exploitons ces modèles pour le calcul du CTCR entre deux plans de 6H-SiC. Nous montrons que le CTCR sature quand d tend vers zéro. La distance du début de saturation dépend grandement des paramètres clés de chaque modèleIn this thesis, we study the validity of few nonlocal models of the dielectric permittivity in the calculation of the radiative heat transfer coefficient (RHTC) between two semi-infinite parallel dielectric planes separated by a vacuum gap of width d.In past theoretical studies, it has been shown that upon considering a local model of the dielectric permittivity, near field radiative heat transfer (NFRHT) between two dielectric materials follows a 1/d2 law when d is of the order or less than few hundreds of nanometers. This nonphysical diverging increase has been the bottleneck of the local model. Overwhelming efforts have been deployed in order to come up with a new model in which the nonlocal effects of the dielectric permittivity are taken into account. To the best of our knowledge, no nonlocal correction to the NFRHT has been addressed in the past in the case of dielectrics. In the case of metals however, an important and complete work has been performed using the Lindhard-Mermin nonlocal dielectric permittivity model.Our work focuses on studying four different nonlocal models of the dielectric permittivity and on using them in the calculation of the RHTC between two solid semi-infinite parallel planes of 6H-SiC. We show that the RHTC saturates as the separation distance d tend to zero. The distance at which saturation starts to take place depends on key parameters involved in each model
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Mayo, Yague Ignacio. "Flow field and heat transfer in a rotating rib-roughened cooling passage." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19529/1/MayoYague_Ignacio.pdf.
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A great effort has been carried out over the recent years in the understanding of the flow field and heat transfer in the internal cooling channels present in turbine blades. Indeed, advanced cooling schemes have not only lead to the increase of the gas turbine efficiency by increasing the Turbine Inlet Temperature above the material melting temperature, but also the increase of the turbine lifespan. To allow such progresses, modern experimental and numerical techniques have been widely applied in order to interpret and optimize the aerodynamics and heat transfer in internal cooling channels. However, the available data is limited in the case of internal cooling channels in turbine rotor blades. Rotation and temperature gradients introduce Coriolis and centripetal buoyancy forces in the rotating frame of reference, modifying significantly the aerothermodynamics from that of the stationary passages. In the case of turbine rotor blades, most of the investigations are either based on point-wise measurements or are constraint to low rotational regimes. The main objective of this work is to study the detailed flow and heat transfer of an internal cooling channel at representative engine dimensionless operating conditions. This work introduces a laboratory test section that operates ribbed channels over a wide range of Reynolds, Rotation and Buoyancy numbers. In the present work, the Reynolds number ranges from 15,000 to 55,000, the maximum Rotation number is equal to 0.77, and the maximum Buoyancy number is equal to 0.77. The new experimental facility consists in a versatile design that allows the interchangeability of the tested geometry, so that channels of different aspect ratios and rib geometries can be easily fitted. Particle Image Velocimetry and Liquid Crystal Thermography are performed to provide accurate velocity and heat transfer measurements under the same operating conditions, which lead to a unique experimental data set. Moreover, Large Eddy Simulations are carried out to give a picture of the entire flow field and complement the experimental observations. Additionally, the numerical approach intends to provide a robust methodology that is able to provide high fidelity predictions of the performance of internal cooling channels.
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Artvin, Zafer. "Fabrication Of Nanostructured Samples For The Investigation Of Near Field Radiation Transfer." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614826/index.pdf.
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Radiative heat transfer in nanostructures with sub-wavelength dimensions can exceed that predicted by Planck's blackbody distribution. This increased effect is due to the tunneling of infrared radiation between nanogaps, and can allow the eventual development of nano-thermo-photo-voltaic (Nano-TPV) cells for energy generation from low temperature heat sources. Although near field radiation effects have been discussed for many years, experimental verification of these effects is very limited so far. In this study, silica coated silicon wafer sample chips have been manufactured by using MEMS fabrication methods for testing the near field radiation effects. A variety of samples with 1×
1, 2×
2 and 5×
5 mm2 area, and with 25 nm, 50 nm, 100 nm and 200 nm (nano-gap) separations have been prepared. 3D structures with vacuum gaps have been obtained by bonding of the silica coated wafers. The samples have been tested in an experimental setup by a collaborative group at Ö
zyegin University, Istanbul. An increase in the net radiation heat transfer with decreasing nano-gap size has been reported by the Ö
zyegin group who used these samples in a parallel study. The thesis outlines the micro-fabrication techniques used for the sample preparation. Also, the manufacturing problems we have faced during this research program are discussed.
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Provan, Gabrielle. "Coherent scatter radar observations of field line resonances and flux transfer events." Thesis, University of Leicester, 1998. http://hdl.handle.net/2381/30613.
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The Earth's magnetosphere is constantly being perturbed by its interaction with the solar wind and the interplanetary magnetic field (IMF). This thesis involves a study of the ionospheric signatures of two separate processes which arise in the magnetosphere through these interactions, namely field line resonances and flux transfer events. Field line resonances - standing magnetohydrodynamic waves - have previously been observed as a periodic modulation of the plasma drift velocity by the Goose Bay HF and SABRE VHF coherent scatter radars. They produce latitudinally-structured spectral peaks at ultra low frequencies (1 to 6 mHz) observed predominantly during the night and early morning (0000 to 0600 MLT). A comparison of the spectra observed by the Goose Bay and SABRE radars demonstrates that the frequencies of the field line resonances are, on average, almost identical despite the different latitudinal ranges covered by the two radars. Possible explanations for the similarity of the signatures on the two radar systems are discussed. The CUTLASS Finland HF coherent radar has been run in a two-beam special scan mode, which offered excellent temporal and spatial information on the plasma convection flow in the high-latitude ionosphere. A detailed study of one day of this data revealed a number of pulsed drift enhancements, seemingly moving away from the radar. These transients are identified here as the ionospheric signature of flux transfer events (FTEs), transient reconnection between the IMF and magnetosphere. The transient signatures are used to produce an average mapping of newly reconnected field lines, calculated by analysing two years of both high-time resolution and normal scan data from the CUTLASS Finland radar. It is shown that the coherent scatter observations are consistent with the precipitation regimes observed by low-altitude satellites and the cusp signature predictions of the Lockwood (1997) and Onsager and Lockwood (1997) model of dayside reconnection phenomena.
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Kaharabata, Samuel K. "Moisture transfer behind windbreaks : laboratory simulations and conditional sampling in the field." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60535.
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The spatial distribution of local evaporation from ground-based sources behind solid and porous windbreaks was studied in laboratory models for steady state and intermittent flows. Field observations of wind and turbulence characteristics (turbulence intensity, power spectra and integral length scale L) over surfaces whose zero displacement (d) and roughness length (z$ sb0$) had also been determined, were used to scale the laboratory simulations. Scaling parameters were z/z$ sb0$, $ sigma$/U, L/z$ sb0$ and Uz$ sb{0}$/K, where z, U, $ sigma$ and K are height, wind speed, standard deviation of velocity fluctuations and turbulent diffusivity, respectively. The 50% porosity barrier was found to be the most effective single-barrier set-up for the reduction of moisture loss.Conditional sampling of fluctuations w' and q' of the wind and moisture, respectively, with sonic anemometer and fast-response Krypton hygrometer behind solid and porous windbreaks in the field, revealed frequency of occurrence, duration and intensity of those turbulent structures primarily responsible for moisture transfer.
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Choi, Chang-Hoon. "Fast field-cycling magnetism transfer contrast magnetic resonance imaging (FFC MTC MRI)." Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=158558.
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Magnetisation Transfer Contrast (MTC) is a well-established magnetic resonance imaging (MRI) contrast-generating mechanism, and is widely used for clarifying MR-invisible macromolecular information indirectly via MR-detectable free protons using an offresonance pre-saturation radiofrequency (RF) pulse (or MT pulse). As a result of MT pulse irradiation, magnetisation between both proton pools is exchanged and the signal intensity of mobile protons is decreased in relation to the amount of macromolecules. MTC MRI is normally implemented at a fixed magnetic field; however, it may be useful to evaluate changes of the MT effect as a function of magnetic field (B0). In order to explore fielddependent MTC experiments using a single MR instrument, two techniques are required, which enable simultaneously shifting both B0 and the resonance frequency of an RF coil (f0) during MT pulse irradiation and returning them to the original condition during MR data acquisition. Switching of B0 is achieved by fast field-cycling (FFC). FFC is a novel technique allowing B0 to shift between levels rapidly during the pulse sequence. This makes it possible to perform a number of beneficial field-dependent studies and/or to provide new MR contrast mechanisms. Switching of f0 requires an actively frequencyswitchable RF coil. This coil was designed and constructed for frequencies at and below 2.5 MHz proton Larmor frequency. The design employed PIN diodes, and enabled switching f0 between five different values. Using these techniques and tools, fielddependent MTC experiments were carried out with a control sample and samples with different concentrations of agarose gel. Due to the absence of macromolecules in the control, the MT effect was almost zero, whereas the MT effect observed in agarose samples increased with increasing concentration of macromolecules. Furthermore, MT effects ((for a given set of MT pulse conditions) were larger at higher B0.
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Francoeur, Mathieu. "NEAR-FIELD RADIATIVE TRANSFER: THERMAL RADIATION, THERMOPHOTOVOLTAIC POWER GENERATION AND OPTICAL CHARACTERIZATION." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/58.
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This dissertation focuses on near-field radiative transfer, which can be defined as the discipline concerned with energy transfer via electromagnetic waves at sub-wavelength distances. Three specific subjects related to this discipline are investigated, namely nearfield thermal radiation, nanoscale-gap thermophotovoltaic (nano-TPV) power generation and optical characterization. An algorithm for the solution of near-field thermal radiation problems in one-dimensional layered media is developed, and several tests are performed showing the accuracy, consistency and versatility of the procedure. The possibility of tuning near-field radiative heat transfer via thin films supporting surface phononpolaritons (SPhPs) in the infrared is afterwards investigated via the computation of the local density of electromagnetic states and the radiative heat flux between two films. Results reveal that due to SPhP coupling, fine tuning of near-field radiative heat transfer is possible by solely varying the structure of the system, the structure being the film thicknesses and their distance of separation. The coexistence of two regimes of near-field thermal radiation between two thin films of silicon carbide is demonstrated via numerical simulations and an asymptotic analysis of the radiative heat transfer coefficient. The impacts of thermal effects on the performances of nano-TPV power generators are investigated via the solution of the coupled near-field thermal radiation, charge and heat transport problem. The viability of nano-TPV devices proposed so far in the literature, based on a tungsten radiator at 2000 K and indium gallium antimonide cell, is questioned due to excessive heating of the junction converting thermal radiation into electricity. Using a convective thermal management system, a heat transfer coefficient as high as 105 Wm-2K-1 is required to maintain the junction at room temperature. The possibility of characterizing non-intrusively, and potentially in real-time, nanoparticles from 5 nm to 100 nm in size via scattered surface wave is explored. The feasibility of the characterization framework is theoretically demonstrated via a sensitivity analysis of the scattering matrix elements. Measurements of the scattering matrix elements for 200 nm and 50 nm gold spherical particles show the great sensitivity of the characterization tool, although an ultimate calibration is difficult with the current version of the experimental set-up.
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Cercignani, M. "Quantitative MRI of the human brain : magnetisation transfer and magnetic field mapping." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445353/.
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The ultimate goal of this thesis was to identify ways of combining the parametric maps produced by the use of multiple quantitative Magnetic Resonance Imaging (MRI) techniques. As a first stage towards this goal, this thesis focuses on magnetisation transfer (MT) imaging, and on the use of field mapping techniques to improve the reliability of other quantitative techniques such as functional MRI (fMRI) and diffusion tensor (DT) MRI. After summarising the basic principles of MRI, the MT phenomenon is described and a quantitative MT model is reviewed. A set of experiments is then described aiming at optimising the acquisition parameters for the measurement of the MT ratio (MTR). The interaction between T and MT is investigated, confirming that MTR acquisition protocols should be designed to minimize T -weighting. Next, the quantitative model of MT is used to optimise the white-to-grey matter contrast to noise ratio of a pulse sequence for MTR measurement, at both 1.5 T and 3.0 T. The following chapter is focused on the optimisation of quantitative MT for in vivo applications. First, the sensitivity to noise of the technique is investigated using simulations. Second, the implementation of a 3D pulse sequence for quantitative MT is described. The sequence is used at 1.5 T and at 3.0 T to collect data from healthy volunteers, providing normative values. Finally, the set of sampling points used to measure MT parameters is optimised using the Cramer-Rao lower bound, showing dramatic improvements in both precision and accuracy. Next, after a review of static field inhomogeneities and field mapping, the consequences of field inhomogeneities on quantitative MT are evaluated. The use of novel acquisition sequences for field mapping is investigated, the application of field-map based correction for fMRI and DT MRI data is considered, and its effects are discussed. Finally, an attempt to combine different parameters through multivariate analysis is presented, by using principal component analysis to identify patterns of association between MT parameters. Finally, an attempt to combine different tialysis is presented, by using principal componen ssociation between MT parameters.
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Siegrist, Florian [Verfasser], and Ferenc [Akademischer Betreuer] Krausz. "Light-field driven charge and spin transfer / Florian Siegrist ; Betreuer: Ferenc Krausz." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1206096403/34.
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蔡慶銘 and Hing-ming Michael Chua. "Transition intensities and energy transfer of lanthanide ions in crystals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1994. http://hub.hku.hk/bib/B31211409.
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Chua, Hing-ming Michael. "Transition intensities and energy transfer of lanthanide ions in crystals /." [Hong Kong : University of Hong Kong], 1994. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13692689.
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Ahmad, Syed Waqas. "Combined effect of electric field and surface modification on pool boiling of R-123." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/6600.
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The effect of surface modification and high intensity electric field (uniform and non – uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non – uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high – resolution camera.
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Thorkildsen, Kenneth J. "Numerical field model simulation of fire and heat transfer in a rectangular compartment." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23995.
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Approved for public release; distribution is unlimitedShipboard fires have been the bane of mariners since man's earliest attempts to sail the sea. Understanding the behavior of fire in an enclosed space such as those found on today's modern seagoing vessels will greatly enhance the mariner's ability to combat or prevent them. In a joint effort between the Naval Postgraduate School and the University of Notre Dame a computer code has been developed to model a full scale fire in a closed compartment. The code uses finite volume formulation to obtain numerical solutions to the unsteady, three-dimensional conservation equations of mass, momentum and energy. Included are the effects of turbulence, strong buoyancy, surface radiation and wall conduction. The code gives velocities, pressure, temperatures and densities throughout the field. This thesis applies that computer code to the U.S. Navy's full scale fire test chamber at Naval Air Warfare Center, China Lake, California. Advance computer graphics techniques, including color contouring and three dimensional vector field plotting have been applied to make output more informative. It is hoped that someday this model could provide a useful tool for naval architects in the design of a fire safe ship, and a cost effective means for developing/evaluation of new firefighting equipment and techniques.
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Fan, Philex Ming-Yan. "Power management and power conditioning integrated circuits for near-field wireless power transfer." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290143.
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Near-field wireless power transfer (WPT) technology facilitates the energy autonomy of heterogeneous systems, significantly augmenting complementary metal-oxide-semiconductor field-effect-transistor (CMOS) technology. In low-power wearable devices, existing power conditioning integrated circuits do not maximize the power factor (PF) for rectification and power conversion efficiency (PCE) due to multiple conversion. Additionally, there is no core power management for the entire power flow. The majority of the research focuses on active rectifiers, which reduce the turn-on voltage for rectification. Certain studies target the output voltage regulation via feedback to the transmitter or direct battery charging without power maximization. Firstly, this study investigates a high-power factor WPT front-end circuit that is namely the mono-periodic switching rectifier (MPSR) and implemented in a 0.18µm 1.8V/5V CMOS process. Integrated phase synchronizers are used to align the waveshape of a wirelessly-coupled sinusoidal voltage source in a receiving coil to the corresponding conducting current. Using this approach, the PF can be increased from roughly 0.6 to unity without requiring any wireless or wired feedback to the transmitter. The proposed MPSR can also provide AC-DC rectification, and step up and down the sinusoidal voltage source's peak amplitude using a pulse-width modulator. Measured voltage conversion ratios range between 0.73X and 2X, and the PF can be boosted up to unity. Secondly, the wireless power system-on-chip (WPower-SoC) is proposed and implemented in a 0.18µm 1.8V/3.3V CMOS process. The WPower-SoC integrating power management can provide rectification, output voltage regulation, and battery charging. Additionally, the implementation of feedforward envelope detection (FED) can reduce the variation in a wireless power link and improve load transient responses. Simulated results demonstrate that 5% of the output voltage regulation is improved when an output load changes. Moreover, the FED reduces approximately 40% of the transient response time. Overshoot and undershoot voltages are decreased by 23% and 26.5%, respectively. The measured output voltage regulates at 3.42V and can supply output power up to 342mW. A temperature sensor as part of the power management core remains active when the WPT receivers enter sleep mode to prolong the battery usage time. In the final part of this study, a nano-watt high-accuracy temperature sensing core is implemented in a 0.18µm 1.8V/3.3V CMOS process that can self-compensate the temperature shift without the need for additional compensating techniques that consume extra power.
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Williams, Devin Wells. "Optimization of Near Field Coupling for Efficient Power Transfer Utilizing Multiple Coupling Structures." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32933.
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A rise in the need for dynamic energy allocation has been associated with the saturation of available portable wireless electronic devices. Currently, the methods for transmitting this energy efficiently have been limited to a number of options, including near field resonant magnetic coupling. Previous research with mid-range (dâ 4r) wireless power transfer has resulted in coupling efficiencies of close to 40%. In order to increase efficiency in transfer a more directive transmission system was developed using a phased array. Coupling networks were used to shift the resonance of the coupling device, leading to a tightly coupled network by array phasing. Coupling networks for the phased array were optimized using a hybrid combination of a full wave Method of Moments simulation with circuit simulation. Results were validated in a full wave simulator, and field results were shown during resonance. S-parameter results show simulated transfer efficiencies of 70% (-1.5dB) for a phased array structure and 62.3% (-2.4dB) for a single feed structure. Single feed prototyping S-parameter results show coupling efficiencies of 25% (-5.9dB). All coupling measurements are at a distance 4r with reference to the largest transmitting coupler.Master of Science
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Abdelaal, Mohamed Riad Mohamed. "Electric Field Driven Enhancement of Heat and Mass Transfer to a Liquid Drop." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1321968954.
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Colban, William Frederick IV. "Effects of Realistic Combustor Exit Profiles on a Turbine Vane Endwall." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/31013.
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Engine designers continually push the combustor exit temperature higher to produce more power from gas turbine engines. These high turbine inlet temperatures, coupled with high turbulence levels and flow field non-uniformities, make turbine vane and endwall cooling a very critical issue in engine design. To appropriately cool these surfaces, knowledge of the passage flow field and endwall temperature distribution at representative engine conditions is necessary.
A combustor test section was used to simulate realistic turbine inlet profiles of turbulence, normalized temperature, normalized total pressure, and normalized streamwise velocity to study the flow field in a turbine vane passage and the adiabatic temperature distribution on the endwall. The combustor liner film-cooling and exit slot flows were varied independently to determine their relative effect on endwall cooling in the downstream turbine vane.
Flow field measurements revealed the presence of a previously unmeasured third vortex in the vane passage. The tertiary vortex was located above the passage vortex and had rotation opposite to the passage vortex. Increasing the amount of slot flow reduced the size and strength of the nearwall vortices, while increasing the size and strength of the tertiary vortex. Adiabatic endwall temperature measurements revealed higher temperatures surrounding the base of the vane. The endwall measurements also showed that the exit slot flow was effective at cooling only a region of the endwall near the vane leading edge on the suction side. Increasing slot flow was found to have a larger thermal benefit to the endwall relative to increasing combustor liner film-cooling.
Master of Science
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Li, Yichen. "Phase-field Modeling of Phase Change Phenomena." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99148.
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The phase-field method has become a popular numerical tool for moving boundary problems in recent years. In this method, the interface is intrinsically diffuse and stores a mixing energy that is equivalent to surface tension. The major advantage of this method is its energy formulation which makes it easy to incorporate different physics. Meanwhile, the energy decay property can be used to guide the design of energy stable numerical schemes.
In this dissertation, we investigate the application of the Allen-Cahn model, a member of the phase-field family, in the simulation of phase change problems. Because phase change is usually accompanied with latent heat, heat transfer also needs to be considered. Firstly, we go through different theoretical aspects of the Allen-Cahn model for nonconserved interfacial dynamics. We derive the equilibrium interface profile and the connection between surface tension and mixing energy. We also discuss the well-known convex splitting algorithm, which is linear and unconditionally energy stable. Secondly, by modifying the free energy functional, we give the Allen-Cahn model for isothermal phase transformation. In particular, we explain how the Gibbs-Thomson effect and the kinetic effect are recovered. Thirdly, we couple the Allen-Chan and heat transfer equations in a way that the whole system has the energy decay property. We also propose a convex-splitting-based numerical scheme that satisfies a similar discrete energy law. The equations are solved by a finite-element method using the deal.ii library. Finally, we present numerical results on the evolution of a liquid drop in isothermal and non-isothermal settings. The numerical results agree well with theoretical analysis.Master of Science
Phase change phenomena, such as freezing and melting, are ubiquitous in our everyday life. Mathematically, this is a moving boundary problem where the phase front evolves based on the local temperature. The phase change is usually accompanied with the release or absorption of latent heat, which in turn affects the temperature. In this work, we develop a phase-field model, where the phase front is treated as a diffuse interface, to simulate the liquid-solid transition. This model is consistent with the second law of thermodynamics. Our finite-element simulations successfully capture the solidification and melting processes including the interesting phenomenon of recalescence.
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Yang, Shuai. "Alternative power transfer for passive RFID systems in challenging applications." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/270885.
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This dissertation presents a case study which attempts to implement a passive Ultra High Frequency Radio Frequency Identification (UHF RFID) system on aircraft landing gear (LG) to permit component configuration management. It is shown that a monostatic RFID system with two reader antennas, one on the LG main fitting and one in the wing bay allows up to 64 kbits of data to be associated with each LG component. A 7 dB system margin allows data on each LG component to be updated wirelessly and will also enable a passive UHF RFID-based LG health and usage monitoring system when tags with required sensors become available. Results from an electromagnetic simulation show that when a metal is illuminated by a nearby antenna the E-field distribution close to its surface is stronger than in free space. To explore if the stronger E-field can be used to enhance the performance of a conventional passive tag, a 5 cm × 6 mm × 3.02 m aluminium bar has been selected as the tagging object and connected to the reader via an RF feed. It is shown that a conventional metal tag which has a maximum free space range of 1.3 m when mounted on a metal plate can be detected up to 30 m along the aluminium bar from the RF feed. When orientated with the long axis normal to the metal surface a conventional passive tag with a dipole antenna can efficiently harvest the E- field and can be read at least 50 m away from the antenna feed. The proposed use of metal objects as a nearfield antenna is well suited to some applications, but in others a significant wireless path is still required. In such a case, a semi-passive tag can be used. It is demonstrated that a semi-passive tag only requires 14.4 ̧œ‡̧‘Š to be read over 42 m in a bistatic RFID system. Such a power consumption can be easily achieved by most energy harvesting techniques. It is demonstrated that a solar-powered semi-passive tag can be read at a range of 22 m, but its performance is still limited by multipath effects. A distributed antenna system (DAS) can be used to overcome these effects by using frequency and phase hopping techniques. It is demonstrated that 50 solar-powered semi-passive tags can be read with no missed detections over a 10 m × 20 m office area with 4 dB system margin.
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Cooke, Jason Randolph. "Light front field theory calculation of deuteron properties /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9662.
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Bridenstine, Mark. "Convective heat transfer from a vertical cylinder in a high amplitude resonant sound field." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA320233.
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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, September 1996.Thesis advisor(s): Ashok Gopinath. "September 1996." Includes bibliographical references (p. 95-96). Also available online.
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Wojtas, David Heinrich. "Suppressing Discretization Error in Langevin Simulations of (2+1)-dimensional Field Theories." Thesis, University of Canterbury. Physics and Astronomy, 2006. http://hdl.handle.net/10092/1294.
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Lattice simulations are a popular tool for studying the non-perturbative physics of nonlinear field theories. To perform accurate lattice simulations, a careful account of the discretization error is necessary. Spatial discretization error as a result of lattice spacing dependence in Langevin simulations of anisotropic (2 + 1)-dimensional classical scalar field theories is studied. A transfer integral operator (TIO) method and a one-loop renormalization (1LR) procedure are used to formulate effective potentials. The effective potentials contain counterterms which are intended to suppress the lattice spacing dependence. The two effective potentials were tested numerically in the case of a phi-4 model. A high accuracy modified Euler method was used to evolve a phenomenological Langevin equation. Large scale Langevin simulations were performed in parameter ranges determined to be appropriate. Attempts at extracting correlation lengths as a means of determining effectiveness of each method were not successful. Lattice sizes used in this study were not of a sufficient size to obtain an accurate representation of thermal equilibrium. As an alternative, the initial behaviour of the ensemble field average was observed. Results for the TIO method showed that it was successful at suppressing lattice spacing dependence in a mean field limit. Results for the 1LR method showed that it performed poorly.
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Luo, Yuxia. "The study of energy transfer and local field effect in lanthanide complexes with high and low symmetry." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/696.
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There are lots of important applications for lanthanides (Ln) because of their unique properties. The properties are closely linked to the environment of the crystal field. Thus, two kind of crystals Cs2NaLn(NO2)6 with high Th point-group symmetry and LnPO4 with monoclinic symmetry were chosen to study quantum cutting and Stokes shift. Quantum cutting is a kind of down-conversion energy transfer in which one excitation ultraviolet photon is transformed into multiple near infrared photons. This phenomenon has been studied in Cs2NaY0.96Yb0.04(NO2)6. The emission from Yb3+ can be excited via the NO2- antenna. The electronic transition of NO2- is situated at more than twice the energy of the Yb3+. At room temperature, one photon absorbed at 470 nm in the triplet state produced no more than one photon emitted. Some degree of quantum cutting was observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into singlet and triplet state. The quantum efficiency was about 10% at 25 K. In Chapter 3, Stokes shift which is the energy shift between the peak maxima in absorption and emission was studied. Stokes shift is related to the flexibility of the lattice and the coordination environment. Cs2NaCe(NO2)6 with 12-coordinated Ce3+ situated at a site of Th symmetry demonstrated the largest Ce-O Stokes shift of 8715 cm−1. The 4f1 ground state and 5d1 potential surfaces have displaced so much along the configuration coordinate that overlap takes place above the 5d1 minimum, leading to thermal quenching of emission at 53 K. A comparison of Stokes shifts with other Ce-O systems with different coordination number demonstrated larger Stokes shifts for Ce3+ ions with higher coordination number. Systematic research about the energy transfer (ET) and energy migration phenomenon is still scarce, although they exist extensively among lanthanide ions. The energy migration in highly doped materials has been stated as very fast or slow, but no experimental proof was reported. In Chapter 4, the ET between Tb3+ and Eu3+ was investigated experimentally and compared with available theoretical models in the regime of high Tb3+ concentrations in 30 nm LaPO4 nanoparticles at room temperature. The ET efficiency approached 100% even for lightly Eu3+-doped materials. The use of pulsed laser excitation and switched-off continuous wave laser diode excitation demonstrated that the energy migration between Tb3+ ions, situated on La3+ sites with a 4 Å separation was not fast. The quenching of Tb3+ emission in singly doped LaPO4 only reduced the luminescence lifetime by about 50% in heavily doped samples. Various theoretical models have been applied to simulate the luminescence decays of Tb3+ and Eu3+-doped LaPO4 samples of various concentrations. The transfer mechanism has been identified as forced electric dipole at each ion. The control of energy transfer rate and efficiency is also an important issue. There are many chemical and geometrical factors that affect energy transfer, including the spectra overlap, the dipole orientation and the distance between the donor and acceptor. The local field of the emission center is another factor that affect the energy transfer by changing the photonic environment. In Chapter 5, the local field effect on the energy transfer between Tb3+ and Eu3+ doped in LaPO4 dispersed in different solvents and solids with a wide range of refractive indexes was studied. The effects of local field (reflected by refractive index) on the ET efficiency and ET rates were clarified that the ET efficiency would decrease with increasing refractive index, while ET rates were independent of the refractive index
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Augello, Elisa. "Precise Near-Field Focusing exploiting Bessel Beam Launchers for Wireless Power Transfer at millimeter waves." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25774/.
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Wireless Power Transfer has become a promising technology to overcome the limits of wired solutions. Within this framework, the objective of this thesis is to study a WPT link at millimeter waves involving a particular type of antenna working in the radiative near-field, known as Bessel Beam (BB) Launcher. This antenna has been chosen for its peculiarity of generating a Bessel Beam which is by nature non-diffractive, showing good focusing and self-healing capabilities. In particular, a Bull-Eye Leaky Wave Antenna is designed and analysed, fed by a loop antenna and resonating at approximately 30 GHz. The structure excites a Hybrid-TE mode showing zeroth-order Bessel function over the z-component of the magnetic field. The same antenna is designed with two different dimensions, showing good wireless power transport properties. The link budgets obtained for different configurations are reported. With the aim of exploiting BB Launchers in wearable applications, a further analysis on the receiving part is conducted. For WPT wearable or implantable devices a reduced dimension of the receiver system must be considered. Therefore, an electrically large loop antenna in planar technology is modified, inserting phase shifters in order to increase the intensity of the magnetic field in its interrogation zone. This is fundamental when a BB Launcher is involved as transmitter. The loop antenna, in reception, shows a further miniaturization level since it is built such that its interrogation zone corresponds to the main beam dimension of transmitting BB Launcher. The link budget is evaluated with the new receiver showing comparable results with respect to previous configurations, showing an efficient WPT link for near-field focusing. Finally, a matching network and a full-wave rectifying circuit are attached to two of the different receiving systems considered. Further analysis will be carried out about the robustness of the square loop over biological tissues.
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Feng, Junjie. "6.78MHz Omnidirectional Wireless Power Transfer System for Portable Devices Application." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/101839.
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Wireless power transfer (WPT) with loosely coupled coils is a promising solution to deliver power to a battery in a variety of applications. Due to its convenience, wireless power transfer technology has become popular in consumer electronics. Thus far, the majority of the coupled coils in these systems are planar structure, and the magnetic field induced by the transmitter coil is in one direction, meaning that the energy power transfer capability degrades greatly when there is some angle misalignment between the coupled coils.
To improve the charging flexibility, a three–dimensional (3D) coils structure is proposed to transfer energy in different directions. With appropriate modulation current flowing through each transmitter coil, the magnetic field rotates in different directions and covers all the directions in 3D space. With omnidirectional magnetic field, the charging platform can provide energy transfer in any direction; therefore, the angle alignment between the transmitter coil and receiver coil is no longer needed.
Compensation networks are normally used to improve the power transfer capability of a WPT system with loosely coupled coils. The resonant circuits, formed by the loosely coupled coils and external compensation inductors or capacitors, are crucial in the converter design. In WPT system, the coupling coefficient between the transmitting coil and the receiving coil is subject to the receiver's positioning. The variable coupling condition is a big challenge to the resonant topology selection. The detailed requirements of the resonant converter in an omnidirectional WPT system are identified as follows: 1). coupling independent resonant frequency; 2). load independent output voltage; 3). load independent transmitter coil current; 4). maximum efficiency power transfer; 5). soft switching of active devices. A LCCL-LC resonant converter is derived to satisfy all of the five requirements.
In consumer electronics applications, Megahertz (MHz) WPT systems are used to improve the charging spatial freedom. 6.78 MHz is selected as the system operation in AirFuel standard, a wireless charging standard for commercial electronics. The zero voltage switching (ZVS) operation of the switching devices is essential in reducing the switching loss and the switching related electromagnetic interference (EMI) issue in a MHz system; therefore, a comprehensive evaluation of ZVS condition in an omnidirectional WPT system is performed. And a design methodology of the LCCL-LC converter to achieve ZVS operation is proposed.
The big hurdle of the WPT technology is the safety issue related to human exposure of electromagnetic fields (EMF). A double layer shield structure, including a magnetic layer and a conductive layer, is proposed in a three dimensional charging setup to reduce the stray magnetic field level. A parametric analysis of the double shield structure is conducted to improve the attenuation capability of the shielding structure.
In an omnidirectional WPT system, the energy can be transferred in any direction; however the receiving devices has its preferred field direction based on its positioning and orientation. To focus power transfer towards targeted loads, a smart detection algorithm for identifying the positioning and orientation of receiver devices based on the input power information is presented. The system efficiency is further improved by a maximum efficiency point tracking function. A novel power flow control with a load combination strategy to charge multiple loads simultaneously is explained. The charging speed of the omnidirectional WPT system is greatly improved with proposed power flow control.Doctor of Philosophy
Wireless power transfer (WPT) is a promising solution to deliver power to a battery in a variety of applications. Due to its convenience, wireless power transfer technology with loosely coupled coils has become popular in consumer electronics. In such system, the receiving coil embedded in the receiving device picks up magnetic field induced by the transmitter coil; therefore, energy is transferred through the magnetic field and contactless charging is achieved. Thus far, the majority of the coupled coils in these systems are planar structure, and the magnetic field induced by the transmitter coil is in one direction, meaning that the energy power transfer capability degrades greatly when there is some angle misalignment between the coupled coils. To improve the charging flexibility, a three–dimensional (3D) coils structure is proposed to transfer energy in different directions, also known as in omnidirectional manner. With omnidirectional magnetic field, the charging platform can provide energy transfer in any direction; therefore, the angle alignment between the transmitter coil and receiver coil is no longer needed. In a WPT system with loosely coupled coils, the energy transfer capability suffers from weak coupling condition. To improve the power transfer capability, the electrical resonance concept between the inductor and capacitor at the power transfer frequency is adopted. A novel compensation network is proposed to form a resonant tank with the loosely coupled coils and maximize the power transfer at the operating frequency. As for the WPT system with loosely coupled coils, the energy transfer capability is also proportional to the operating frequency. Therefore, Megahertz (MHz) WPT systems are used to improve the charging spatial freedom. 6.78 MHz is selected as the system operation in AirFuel standard, a wireless charging standard for commercial electronics. The zero voltage switching (ZVS) operation of the switching devices is essential in reducing the switching loss and the switching related electromagnetic interference (EMI) issue in a MHz system; therefore, a comprehensive evaluation of ZVS condition in an omnidirectional WPT system is performed. The big hurdle of the WPT technology is the safety concern related to human exposure of electromagnetic fields (EMF). Therefore, a double layer shield structure is first applied in a three dimensional charging setup to confine the electromagnetic fields effectively. The stray field level in our charging platform is well below the safety level required by the regulation agent. Although the energy can be transferred in an omnidirectional manner in the proposed charging platform, the energy should be directed to the target loads to avoid unnecessary energy waste. Therefore, a smart detection method is proposed to detect the receiver coil's orientation and focus the energy transfer to certain direction preferred by the receiver in the setup. The energy beaming strategy greatly improves the charging speed of the charging setup.
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Yanik, Erim. "Magnetic Field and Heat Transfer Analysis of Magnetic Refrigeration Systems with Different Magnet Array Geometries." Thesis, Southern Illinois University at Edwardsville, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10808213.
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Magnetic refrigeration is one of the alternative cooling technologies that is environmental friendly and has high theoretical coefficient of performance values. This thesis study focuses on magnetic field and heat transfer enhancement of a reciprocating-type magnetic refrigeration system. A set of NdFeB 52 MGOe permanent magnets were employed to form a Halbach magnet array. Gadolinium (Gd) was used as the magnetocaloric material. It was placed concentrically within the Halbach array aperture with the working fluid running through the gap in between the magnet assembly and Gd yielding annular flow. Three different annular flow geometries namely; circular, octagonal and hexagonal cross-sections were studied. Magnetization process was analyzed theoretically, numerically and experimentally for k = 4 configuration. Numerical analysis was done by Finite Element Method Magnetics (FEMM), theoretical analysis was conducted by a mathematical model, and experimental analysis was performed on a Halbach magnet array. Obtained magnetic field results were used to calculate corresponding entropy changes and heat flux values. These values were compared to numerical heat transfer results from ANSYS and a close agreement between results were observed.
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Pratik, Ujjwal. "Design of Capacitive Wireless Power Transfer Systems with Enhanced Power Density and Stray Field Shielding." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7598.
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Wireless power transfer is becoming relevant today because of its effectiveness and convenience. It has been employed into consumer electronics such as cellular charging and electric vehicle charging. In general, inductive wireless power transfer (IPT) is mostly used for WPT. IPT requires coils and power transfer enhancing material such as ferrite to transfer power. However, Capacitive wireless Power Transfer (CPT) appears as an alternative because it requires cost effective and light metal plate couplers. Among CPT couplers, Vertical (stacked) Four-Plate Coupler (V4PC) structure offers the advantage of higher input and output self-capacitances, rotational misalignment.
Safety is one of the most important aspect of wireless power transfer. This thesis proposes a solution to minimize the leakage electric field of Vertical 4-Plate Couplers (V4PCs). It does so by finding the optimum value of circuit parameters. The effectiveness of the proposed solution is shown by experimental results.
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Cole, Matthew Thomas. "Dry-transfer of chemical vapour deposited nanocarbon thin films." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/241515.
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This thesis presents the development of chemical vapour deposited (CVD) graphene and multi-walled carbon nanotubes (MWCNTs) as enabling technologies for flexible transparent conductors offering enhanced functionality. The technologies developed could be employed as thin film field emission sources, optical sensors and substrate-free wideband optical polarisers. Detailed studies were performed on CVD Fe and Ni catalysed carbon nanotubes and nanofibres on indium tin oxide, aluminium and alumina diffusion barriers. Activations energies of 0.5 and 1.5 eV were extracted supporting surface diffusion limited catalysis forCNTs and CNFs. For the first time an activation energy of 2.4 eV has been determined for Cu-catalysed growth of CVD graphene. Graphene was shown to deviate significantly from the more traditional rate-limited surface diffusion and suggests carbon-atom-lattice integration limited catalysis. An aligned dry-transferred MWCNT thin film fabrication technique was developed using MWCNTs of varied lengths to control the optical transparency and conductivity. A process based on the hot-press lamination of bilayer CVD graphene (HPLG) was also developed. Transport studies revealed that these thin films behave, in a macroscopic sense, similar to traditional c-axis conductive graphite and deviate toward tunnel dominated conduction with increasing degrees of network disorder. Various MWCNT-based thin film field emitters were considered. Solution processing was shown to augment the surface work function of the MWCNTs resulting in reduced turn-on electric fields. Integrated zinc oxide nanowires were investigated and were shown to ballast the emission, thereby preventing tip burn out, and offered lower than expected turn-on fields due to the excitation of a hot electron population. To obviate nearest neighbour electrostatic shielding effects an electrochemical catalyst activation procedure was developed to directly deposit highly aligned sparse carbon nanofibres on stainless steel mesh. Highly-aligned free-standing MWCNT membranes were fabricated through a solid-state peeling technique. Membranes were spanned across large distances thereby offering an ideal platform to investigate the unambiguous photoresponse of MWCNTs by removing all extraneous substrate interfaces, charge traps and nanotube-electrode Shottky barriers as well as using pure, chemically untreated material. Oxygen physisorbtion was repeatedly implicated through in-situ lasing and in-situ heated EDX measurements, FT-IR and low temperature transport and transfer measurements. A MWCNT membrane absorptive polariser was fabricated. Polarisers showed wideband operation from 400 nm to 1.1 μm and offered operation over greater spectral windows than commercially available polymer and glass-support dichroic films. Ab-initio simulations showed excellent agreement with the measured polarisation attributing the effect to long-axis selective absorption.
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McConnell, Brian Gregory. "A Coupled Heat Transfer and Electromagnetic Model for Simulating Microwave Heating of Thin Dielectric Materials in a Resonant Cavity." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/36179.
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Microwave heating is an emerging but still underutilized tool in modern industrial applications. The task of designing microwave applicators for heating industrial materials with temperature-dependent properties is challenging, and trial-and-error system prototyping is an expensive and wasteful means to accomplish this goal. The purpose of this work is to combine existing heat transfer and electromagnetic models to provide a complete simulation for heating dielectric materials in a resonant microwave cavity. The numerical simulation is validated by comparison to several independent sets of experimental data. The ultimate goal is to provide a research tool that will facilitate the industrial microwave applicator design process. With a complete, accurate, and user-friendly numerical simulation, parameters affecting the temperature distribution in stationary and moving process materials can be studied to optimize the results before the first prototype is made. This work also explores the sources of power loss in a microwave system and develops means for quantifying these power losses.Master of Science
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Gorchon, Jon. "Current and field induced magnetization reversal in Pt/Co/Pt and (Ga, Mn)(As, P) ferromagnetic films." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112143.
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La manipulation de l’état magnétique d’un système ferromagnétique présente un grand intérêt en raison de possibles applications technologiques. Comprendre les mécanismes fondamentaux qui contrôlent l’aimantation est donc particulièrement important. La compréhension de certains mécanismes peut également avoir un impact dans d’autres domaines de la physique. C’est le cas par exemple de la dynamique de déplacement de parois de domaines sous champ magnétique dans le régime de reptation (creep) qui peut être assimilé à celui d’une interface élastique et qui présente un caractère universel. Cette thèse présente tout d’abord, à travers un travail expérimental sur des couches ultra-minces de Pt/Co/Pt, une description complète de la dynamique de déplacement de parois de domaines sous champ magnétique. Une analyse auto-cohérente permet d’extraire tous les paramètres de contrôle, des exposants universels sont confirmés et un nouveau régime dynamique (le TAFF) est identifié. Une deuxième étude porte sur le déplacement de parois sous courant électrique en géométrie étendue dans un film de (Ga,Mn)(As,P). Cette étude met en évidence des instabilités de forme des parois de domaines soumises à un gradient de courant électrique. Les limites de stabilités sont analytiquement prédites et présentent un bon accord avec les expériences. Un troisième travail porte sur le renversement de l’aimantation à l’interface entre un film de (Ga,Mn)(As,P) et une électrode non ferromagnétique. Un renversement stochastique de l’aimantation sous courant continu est mis en évidence. Son origine réside dans l’accumulation de spin à l’interface qui diminue fortement l’aimantation locale. Un modèle simplifié permet de décrire la probabilité de retournement de l’aimantation et d’extraire les temps caractéristiques associésEffectively manipulating the magnetic state of a ferromagnet has a great interest for possible technological applications. Understanding the underlying fundamental mechanisms is thus particularly important. In some cases, the understanding of some mechanisms may even importantly impact other areas of physics. This is the case for example with field induced magnetic domain walls motion in the creep regime, where the wall can be assimilated to an elastic interface and follows an universal behavior. This thesis presents through an experimental work on Pt/Co/Pt ultra-thin samples, a complete description of the temperature and field dependent domain wall dynamics. A self-consistent analysis allows the extraction of all control parameters, identifying the new Thermally Activated Flux Flow regime, and confirming universal thermal scaling exponents. A second study focuses on current induced domain wall motion in an extended geometry of a (Ga,Mn)(As,P) ferromagnetic film. This study unveils domain wall shape instabilities under a gradient of current. The instability limits are analytically predicted in agreement with the experimental observations. A third work concerns the magnetization reversal mechanism evidenced at the interface between a (Ga,Mn)(As,P) film and a non-ferromagnetic electrode under a current flow. The reversal is shown to be stochastic and mainly governed by the spin accumulation at the interface, which reduces importantly the local magnetization. A simplified model allows the description of the reversal probability and the time scales involved in the mechanism of reversal are accessed and discussed
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Ianiro, Andrea. "Flow field and heat transfer in swirling impinging jets." Tesi di dottorato, 2011. http://www.fedoa.unina.it/8822/1/Ianiro_2011.pdf.
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The high heat transfer rate obtainable with impinging jets is widely recognized and explained in scientific literature and the use of jets is very popular in many industrial applications like paper drying, glass tempering and turbine blades cooling. A huge quantity of data is available for single, rows and arrays of jets with also correlations for heat and mass transfer.
A major disadvantage of impinging isothermal and flame jets, however, is that the local heat flux can be highly non-uniform (Viskanta, 1993). For some applications, like electronic cooling or chemical vapour deposition, high values of heat and mass transfer with radial uniformity are requested. The swirling impinging jets, characterized by tangential velocity components that cause a spiral-shaped motion and the broadening of the jet, could be a possible solution to achieve both high heat transfer and radial uniformity.
The purpose of this work is to study the flow field and the heat transfer in swirling impinging jets. For the present study the swirling jets are obtained with helical inserts based on the concept of the cross swirling strips inside the nozzle and two experimental techniques are used: Tomographic Particle Image Velocimetry (Elsinga et al., 2006) for the three-dimensional three-components flow field measurements and IR thermography along with the “heated thin foil” heat transfer sensor (Carlomagno and Cardone, 2010) for the heat transfer measurements.
In chapter one the literature about free and impinging jets is reviewed in attempt to explain how the flow field influences the heat transfer distribution on the wall and to describe the state of the art in the field of swirling impinging jets and swirl flows. This literature review motivates the study of swirling impinging jets in order to understand both the fluid mechanics characteristics and the heat transfer performances. So far, has not yet been formulated a comprehensive framework where all the results about vortex dynamics in swirl flows can be satisfactorily explained, and the modelling of rotating and swirling flows is still considered a perpetual challenge (Jakirlic et al. 2002). Most of the quantitative experimental studies on swirling flows have been limited to examining flow details using single-point measurement techniques, such as Laser Doppler Velocimetry (LDV), or planar techniques, such as PIV in particular. The inability to make instantaneous volumetric measurements often leads to ambiguities in the interpretation of the data, which necessitates various assumptions to link these reduced dimensional representations to the three-dimensional instantaneous structure of the flow. At the same time, while numerical simulation such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) in particular, has been instrumental in elucidating the three-dimensional dynamical features of swirling flows (see e.g. García-Villalba et al. 2006, Ranga Dinesh and Kirkpatrick 2009), they have to face with the difficulty of obtain reliable velocity profiles at the nozzle exit as boundary conditions (Ortega-Casanova et al. 2010). On the heat transfer side, almost all data related to swirling impinging jets reported in literature are presented as radial distribution even though, to assess the behavior of the flow field on the wall, two dimensional measurements are required. Furthermore, is not available in literature a quantitative analysis for the concept of heat transfer uniformity.
In chapter two, the basic working principles and the state of art of research about Tomographic PIV are described in order to understand the main parameters involved in the design of the experiments for the flow field measurements.
In chapter three, the basic working principles and the state of art of research on IR thermography for convective heat transfer measurements are described in order to understand the main parameters involved in the design of the experiments for the heat transfer measurements.
In chapter four, the flow field measurements are presented. A first study is performed by means of time resolved tomographic PIV on the three dimensional flow field of free swirling jets (at Reynolds number equal to 1,000) in order to analyze the main features of this complex flow. The development of the jets, the effect of swirl and the growth and interactions of coherent structures is discussed describing flow topology in swirling jets. Swirling impinging jets (at Reynolds number equal to 10,000) are then studied at low nozzle to plate distance analyzing both instantaneous measurements and flow statistics. This study allows to understand how the impinged plate influences the development of the jets and the lifetime of its coherent structures; a special attention is put on the development of the jet in the “wall jet” region.
In chapter six, are presented experimental two-dimensional measurements of convective heat transfer between a flat plate and a swirling air jet impinging on it. This work is performed at a fixed Reynolds number (Re = 28,000) for different nozzle-to-plate distances and for different Swirl numbers. The heat transfer performances of swirling jets are also compared with those of a circular jet in order to account for both effects of the swirl and of the cross strips in the nozzle. Data are reported as Nusselt number surface maps, surface averaged Nusselt number and surface standard deviation percentage of the Nusselt number, in the attempt to quantify heat transfer rate and uniformity. In particular, this work represents the first effort to quantify non-uniformity in convective heat transfer coefficients in case of swirling, multichannel and circular jets. Moreover, the author proposes the use of the standard deviation percentage of the Nusselt number as a quantitative estimator for the heat transfer uniformity.
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Greco, Carlo Salvatore. "Investigation of Synthetic Jets Heat Transfer and Flow Field." Tesi di dottorato, 2015. http://www.fedoa.unina.it/10418/1/Greco_Carlo_Salvatore_27.pdf.
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The present thesis deals with the investigation of synthetic jets heat transfer and flow field behaviour. Synthetic jets are devices used mainly for flow control and heat transfer. Such devices are able to "synthetize" a jet from the ambient in which they are embedded through a simple membrane oscillation inside a cavity with an orifice. Such features make them high reliable, silent and easy to be miniaturized. For these reasons, they are widely investigated also as electronic cooling devices. State of art literature shows that the heat transfer performance of these devices are promising. Under these considerations, the present research is focused on the design and analysis of a different type of synthetic jet device with respect to its classical configuration. Such a device is experimentally characterized through the study of its free and impinging flow field. Furthermore the heat transfer rate has been evaluated. The novel configurations are compared to the performance of a classical synthetic jet device.
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Wu, Chia-Chu, and 吳家駒. "Electro-Magnetic Analysis of Near Field Wireless Power Transfer Modules." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/8k4ztw.
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碩士國立臺北科技大學
冷凍空調工程系所
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Since mobile phones, electric vehicles and related applications vigorously emerge, wireless charging become an attractive technology for more convenient usage.Therefore, wireless power transmission league and protocol also appeared to promote this technology. The two main league are known as Wireless Power Consortium (WLC) and Alliance for Wireless Power (A4WP). The research of this article used the wireless power transmission module which developed by the ferrite vendor. We designed for inductors for differentleagues, combo inductors for Near Field Communication (NFC) and Wireless Power Consortium (WLC) in order to compare thesimulated and measured results. At first, we confirmed the accuracy of the simulation by comparing simulated data with experimental data and then built a simulation design guide.Secondly, due to the restriction of inductor configuration and matching circuit of each league, the quality factor of inductors becomes the primary issue of this technique. To solve the problem, we added ferrite materials as the substrate of the inductor and changed the structure of the substrate. Reducing proximity effects of the inductor occur in high frequency could lead to the decrease of resistance and increase the inductance value as well as the quality factor. The charging efficiency could also be improved. The errors between measurement and the simulation were under 5%; in other words, the inductor design can be optimized in the simulation environment instead of the time-consuming methodology by trial-and-error; hence, the manufacturing costs decreased. In this study, A4WP inductor was simulated through one-to-one characteristics. Based on the results, we expected to develop one-to-many in the near future.
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Crispo, Cuono Massimo. "Investigation of chevron synthetic jets flow field and heat transfer." Tesi di dottorato, 2017. http://www.fedoa.unina.it/12095/1/Crispo_cuonomassimo_30.pdf.
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The present thesis analyses the effect of a saw-tooth exit pattern, called chevron exit, on the flow field and heat transfer of a synthetic jet. The chevron exits are generally applied at the trailing edge of jet engine nozzles for acoustic noise reduction and mixing enhancement. For the present study, the synthetic jet is obtained by a loudspeaker as oscillating element and a contoured nozzle as inlet/outlet aperture. Two experimental techniques are used: Stereoscopic Particle Image Velocimetry for the two-dimensional three-component flow field measurements and Infrared thermography in conjunction with the heated thin foil heat transfer sensor for the heat transfer measurements.
Owing to the peculiar features of synthetic jets and the effect of the chevron elements on the coherent structures organisation, the chevron exit could lead to a heat transfer enhancement. It is shown that this kind of nozzle can produce an increase of turbulence intensity levels in some regions of the field and entrainment and mixing enhancement by introducing streamwise coherent structures.