Дисертації з теми "Dispersion à changement de phase"
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O'Neill, Poppy. "Phase change dispersions as high performance heat transfer fluids." Electronic Thesis or Diss., Lyon, INSA, 2022. http://www.theses.fr/2022ISAL0073.
Повний текст джерелаThis thesis focuses on the heat transfer, transport, and rheological behaviour of novel two-phase fluids, named phase change dispersions. Phase change dispersions consist of phase change material dispersed into a continuous phase with the aid of surfactants. The optimal formulation procedure for phase change dispersions with high stabilities, low supercooling degrees and high apparent specific heat capacities is discussed and an innovative approach in fine-tuning the thermophysical properties of phase change dispersions with the use of cosurfactants is defined. Two of the developed formulations were then chosen for a heat transfer and rheological behaviour comparison to observe the effect that surfactants have on the transport and heat transfer properties during heating. This was performed using a test-rig to measure the bulk fluid and inner wall temperatures of the phase change dispersions flowing through a cylindrical tube under the constant heat flux boundary condition. The crystallisation heat transfer and rheological behaviour of a phase change dispersion was also examined through calculation of heat balances in a rectangular duct. During melting and crystallisation, an interesting phenomenon was discovered, that the transition from laminar to turbulent with phase change dispersions was much lower than those predicted for Newtonian fluids. By regression of the experimental results, correlations for the average Nusselt numbers for laminar and turbulent flow are presented, using a modified Reynolds number and a Prandtl number correction factor. A numerical model for the thermal behaviour studies of a phase change dispersion during its cooling in laminar flow through a rectangular duct was developed and is based on the quasi-homogeneous single fluid approach. The evolution of the experimental and theoretical values shows good agreement and the model satisfactorily predicts the behaviour, with variations of less than 5%
Ben, Ettouil Fadhel. "Modélisation rapide du traitement de poudres en projection par plasma d'arc." Phd thesis, Université de Limoges, 2008. http://tel.archives-ouvertes.fr/tel-00345752.
Повний текст джерелаLe procédé de projection par plasma d'arc soufflé et les principaux phénomènes qui régissent la formation du jet de plasma, les échanges thermiques et dynamiques entre la particule et l'écoulement du jet gazeux et la construction du dépôt sont examinés. Nous avons fait une étude bibliographique des modèles développées par ailleurs pour simuler les différentes fonctionnalités du procédé.
Les fondements et les caractéristiques du logiciel « Jets&Poudres » sont exposés, avant de présenter le modèle du transfert plasma-particule qui prend en compte la conduction interne à la particule et les déplacements des fronts de changement de phase. Dans ce modèle le calcul de l'évaporation de la particule est découplé du problème de la dynamique du gaz dans le jet et nous exploitons les résultats de J. C. Knight et le modèle de « Pression en retour » (Back Pressure) qu'il a développé. Une étude qualitative est consacrée à l'effet des paramètres de dispersion de la poudre en sortie de l'injecteur sur le traitement d'une particule isolée et sur la construction du dépôt. Ces effets mis en évidences, nous exposons un modèle de transport d'un lot de particules représentatif d'une poudre dans l'injecteur afin d'évaluer la dispersion en masse, taille et vitesse avant l'entrée dans le jet. Ce modèle complexe prend ent compte les collisions particule-parois et les colisions binaires particule- particule.
Les résultats de ces deux modèles sont discutés. Le traitement dynamique et thermique de la particule isolée est en bon accord avec ceux de la littérature. Ce qui autorise l'étude des conditions opératoires et des paramètres des différentes composantes fonctionnelles du procédé (torche, gaz plasmagène, injecteur, poudre...) sur le traitement des particules et leurs histoires thermique et dynamique.
Le modèle a été utilisé pour évaluer la quantité de matière nanostructurée conservée en fin de traitement et avant impact sur le substrat. Nous avons également exploité le modèle de dispersion de poudre pour la simuler la tache-dépôt formée par la projection ‘statique' de poudres de différents matériaux et de différentes granulométries.
Galambos, Paul C. "Two-phase dispersion in micro-channels /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/7100.
Повний текст джерелаSin, Vai Kuong. "Particle dispersion in two-phase turbulent flows." Thesis, University of Macau, 2000. http://umaclib3.umac.mo/record=b1637076.
Повний текст джерелаChahine, Rebecca. "Ingénierie aux échelles nanométriques de matériaux chalcogénures à changement de phase pour les mémoires à changement de phase du futur." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY058.
Повний текст джерелаIn terms of performance, cost and functional speed, phase-change memories are playing a key role in data storage technologies. Leveraging the properties of some chalcogenide materials, phase-change materials (PCMs) present unique features, mainly: fast and reversible switching between amorphous and crystalline states with significant optical and electrical contrasts between the both states. However, for an improved performance, the elevated power consumption due to the high programming current must be reduced, and the crystallization temperature also has to be increased. In this context, we have developed new multilayer systems of [GeTe/C]n and [Ge2Sb2Te5/C]n. The aim is to obtain, in a controlled and reproducible manner, a thin layer of nanostructured PCM with dimensions less than 10 nm. The multilayers were produced by the magnetron sputtering deposition technique in a 200 mm industrial equipment with a multi-cathode chamber. The multilayers are amorphous after deposition. Ion beam techniques permitted to check periodicity and composition of the multilayers. The sheet resistance and reflectivity as a function of temperature were measured in situ. The crystallization temperature of PCM in the multilayer structure increases and is dependent on the thickness of the PCM layer and that of the carbon films. The kinetics and magnitude of the amorphous-crystal transition of PCM in the multilayers are also significantly affected. The impact of the multilayer structure on the crystallization of GeTe versus Ge2Sb2Te5 is then compared and discussed with respect to their crystallization mechanism. We show that the initially amorphous multilayer structure is retained even after PCM crystallization during an annealing that is identical to the one used for the manufacture of memory devices (300 °C for 15 min). Thus, it is possible to obtain nanocrystalline grains of PCM in amorphous C on the order of 4 nm vertically and 20-30 nm in the layer plane. These results are compared with the microstructure of C-doped GeTe and Ge2Sb2Te5 films. Finally, by using X-ray diffraction measurements in the laboratory and by in situ experiments at the SOLEIL synchrotron, we were able to follow the evolution of the structure of these multilayers during annealing. For example, we reported that a local percolation effect of the GeTe grains between the layers of C occurs above a certain temperature
Deshpande, Kiran B. "Studies On Phase Inversion." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/285.
Повний текст джерелаErcan, Cemal. "Gas phase dispersion in mobile bed and spray contacting." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74224.
Повний текст джерелаThe ADPF model was found to represent well the residence time distribution curves for all experiments with both gas-liquid contactors. Comprehensive correlations were obtained as axial dispersion number, D/u$ sb{ rm G}$d$ sb{ rm p}$, for MBC; as dispersion length, D/u$ sb{ rm G}$, for spray contacting.
For spray contacting, gas dispersion length increases strongly with liquid flow rate but varies little with gas flow rate and column height.
For MBC, axial dispersion number is very sensitive to packing size and to liquid flow rate, but has low dependence on static bed height and gas flow rate. Axial dispersion number is linearly proportional to liquid holdup, with this proportionality a weak function of only static bed height. The trends in axial dispersion number with operating variables for MBC parallel those for countercurrent gas-liquid flow in fixed bed contacting (FBC), but with the much higher throughputs possible with MBC than in FBC, axial dispersion number is typically about one order of magnitude higher.
In both contactors the effect of axial dispersion on mass transfer is demonstrated to be very important at high recovery level. A comprehensive analysis of hydrodynamics and mass transfer in MBC is presented.
For the model of transient response of mass transfer between two fluid phases, both in axially dispersed countercurrent flow, moment equations were derived for the general case and for one special case. These moment derivations provide the needed theoretical framework for future experimental investigation of the degree of interaction between coefficients of mass transfer and of axial dispersion.
Avramopoulos, Hercules. "Phase effects in dispersion compensated passively mode-locked lasers." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47342.
Повний текст джерелаSoupart-Caron, Adèle. "Stockage de chaleur dans les matériaux à changement de phase." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI078/document.
Повний текст джерелаThis PhD thesis deals with the understanding of the heat transfer mechanisms and with the development of thermal energy storage system for the industrial waste heat recovery application. The use of Phase Change Materials (PCM) is attractive for its high storage density and its possibility to deliver heat at constant temperature. However, the PCM low thermal conductivity leads to develop heat transfer improvement methods, such as heat exchangers with increased heat transfer surface. The goal is to characterize the behavior of such heat exchangers An experimental study, where four several heat exchangers have been tested with different orientations (horizontal/vertical) and injection types (upward/downward), highlighted the impact of natural convection during the melting process and the volume contraction one during the solidification. These results have been validated through a 3D numerical model. A performance comparison method based on an energy calculation through an experimental mesh is proposed and enables to select a heat exchanger on criteria such as the storage density, the characteristic time and the cost. Three PCM, adapted to our application, have been tested at the intended temperature (100-200 °C) by integrating them into a storage system made of a stainless steel tube with aluminum circular fins. Their ability to resist to repeated cycles has been assessed and their behavior has been compared. The salts mixture, H105 (Tmelting = 122 °C), is not selected for the application because of it low storage density (≈ 56 kWh/m3) and its large melting area. The sebacic acid (Tmelting = 132 °C) has a repeatable behavior with cycles and a higher storage density (≈ 66 kWh/m3) and is appropriate as storage material. The sugar alcohol, erythritol (Tmelting = 118 °C), has good thermo-physical properties (128 kWh/m3) but the crystallization control is a key point to use it as a PCM
Valance, Stéphane. "Aspects mécaniques du changement de phase allotropique à l'échelle mésoscopique." Lyon, INSA, 2007. http://theses.insa-lyon.fr/publication/2007ISAL0101/these.pdf.
Повний текст джерелаThe prediction of the mechanical state of steel structures submit to thermo-mechanical loading must take into account consequences of allotropic phase change. Indeed, phase change induce, at least for steels, a mechanism of TRansformation Induced Plasticity (TRIP) leading to irreversible deformation even for loading less than elastic yield limit. Homogeneized analytical models generally fail to achieve a correct prediction for complex loading. In order to overcome these difficulties, we present a model achieving a sharper description of the phenomenon. The mesoscopic working scale we adopt here is the grain scale size. Hence, we consider that the behaviour of each phase is homogenous in the sense of continuous media mechanic, whereas the front is explicitly described. We work both experimentally and numerically. Experimentally, we designed a test facility enabling thermo mechanical loading of the sample under partial vacuum. Acquisition of sample surface while martensitic transformation is happening leads, under some hypothesis and thanks to Digital Image Correlation, to the partial identification of area affected by transformation. Numerically, the eXtended Finite ElementMethod is applied for weakly discontinuous displacement fields. Used of this method needs to numerically track the transformation front -discontinuity support. In that goal, based on level set method, we develop FEM numerical scheme enabling recognition and propagation of discontinuity support. Finally, this work is complete by an approach of driving forces introduced through Eshelbian mechanics which are dual of front velocity. Keywords : allotropic phase change, TRansformation Induced Plasticity, eXtended Finite Element Method (X-FEM), Level set method
Valance, Stéphane Borst René de. "Aspects mécaniques du changement de phase allotropique à l'échelle mésoscopique." Villeurbanne : Doc'INSA, 2008. http://docinsa.insa-lyon.fr/these/pont.php?id=valance.
Повний текст джерелаRakotondrandisa, Aina. "Modélisation et simulation numérique de matériaux à changement de phase." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR051/document.
Повний текст джерелаIn this thesis we develop a numerical simulation tool for computing two and three-dimensional liquid-solid phase-change systems involving natural convection. It consists of solving the incompressible Navier-Stokes equations with Boussinesq approximation for thermal effects combined with an enthalpy-porosity method for the phase-change modeling, using a finite elements method with mesh adaptivity. A single-domain approach is applied by solving the same set of equations over the whole domain. A Carman-Kozeny-type penalty term is added to the momentum equation to bring to zero the velocity in the solid phase through an artificial mushy region. Model equations are discretized using Galerkin triangular finite elements. Piecewise quadratic (P2) finite-elements are used for the velocity and piecewise linear (P1) for the pressure. The coupled system of equations is integrated in time using a second-order Gear scheme. Non-linearities are treated implicitly and the resulting discrete equations are solved using a Newton algorithm. The numerical method is implemented with the finite elements software FreeFem++ (www.freefem.org), available for all existing operating systems. The programs are written and distributed as an easy-to-use open-source toolbox, allowing the user to code new numerical algorithms for similar problems with phase-change. We present several validations, by simulating classical benchmark cases of increasing difficulty: natural convection of air, melting of a phase-change material, a melting-solidification cycle, a basal melting of a phase-change material, and finally, a water freezing case
Krishnardula, Venu Gopal. "Transient liquid phase bonding of ferritic oxide dispersion strengthened alloys." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Fall/Dissertation/KRISHNARDULA_VENU_19.pdf.
Повний текст джерелаBaker, S. A. "Liquid dispersion in two-phase flow in a packed column." Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636015.
Повний текст джерелаEisele, Andreas. "PHASE AND AMPLITUDE MODULATED OFDM FOR DISPERSION MANAGED WDM SYSTEMS." Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4178.
Повний текст джерелаM.S.
Optics and Photonics
Optics and Photonics
Optics MS
Wei, Suwan. "Transient liquid phase bonding of an oxide dispersion strengthened superalloy." Thesis, Brunel University, 2002. http://bura.brunel.ac.uk/handle/2438/7861.
Повний текст джерелаAhn, Andrew In-Kyun 1979. "Fast Phase Dispersion Microscope : a new instrument for cellular biology." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/87867.
Повний текст джерелаIncludes bibliographical references (p. 143-144).
by Andrew In-Kyun Ahn.
M.Eng.
Zaepffel, Didier. "Modélisation des écoulements bouillants à bulles polydispersées." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00682899.
Повний текст джерелаSaw, Lin K. "Phase inversion in polyurethane prepolymer-water dispersions." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/15350.
Повний текст джерелаFurfaro, Damien. "Simulation numérique d'écoulements multiphasiques, problèmes à interfaces et changement de phase." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4751/document.
Повний текст джерелаThis work deals with the numerical simulation of compressible multiphase flows in velocity disequilibrium. A HLLC-type two-phase Riemann solver is developed and validated against exact solutions and experimental data. This solver is robust, simple, accurate and entropy preserving. The numerical method is then implemented in 3D unstructured meshes. Furthermore, a numerical technique consisting in enforcing the correct energy partition at a discrete level in agreement with the multiphase shock relations is built. The multiphase extension of the HLLC-type Riemann solver is realized and allows the simulation of a wide range of applications. Finally, a droplet heat and mass transfer model with large range of validity is derived. It is valid in any situation: evaporation, flashing and condensation. It accounts for coupled heat and mass diffusion in the gas phase, thermodynamics of the multi-component gas mixture and heat diffusion inside the liquid droplet, enabling in this way consideration of both droplets heating and cooling phenomena
Pigot, Corentin. "Caractérisation électrique et modélisation compacte de mémoires à changement de phase." Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0185.
Повний текст джерелаPhase-change memory (PCM) is arguably the most mature emerging nonvolatile memory, foreseen for the replacement of the mainstream NOR-Flash memory for the future embedded applications. To allow the design of new PCM-based products, SPICE simulations, thus compact models, are needed. Those models need to be fast, robust and accurate; nowadays, no published model is able to fill all these requirements.The goal of this thesis is to propose a new compact model of PCM, enabling PCM-based circuit design. The model that we have developed is entirely continuous, and is validated on a wide range of voltage, current, time and temperature. Built on physical insights of the device, a thermal runaway in the Poole-Frenkel mechanism is used to model the threshold switching of the amorphous phase. Besides, the introduction of a new variable representing the melted fraction, depending only on the internal temperature, along with a crystallization speed depending on the amorphous fraction, allow the accurate modeling of all the temporal dynamics of the phase transitions. Moreover, an optimized model card extraction flow is proposed following the model validation, relying on a sensibility analysis of the model card parameters and a simple set of electrical characterizations. It enables the adjustment of the model to any process variation, and thus ensures its accuracy for the design modeling at every step of the technology development
LIU, HONG GEN. "Resolution numerique de problemes a changement de phase en regime diffusif." Paris 11, 1995. http://www.theses.fr/1995PA112285.
Повний текст джерелаDucros, Delphine. "La dispersion dans un monde changeant : variations des coûts de la dispersion chez le chevreuil, et leurs effets sur l'évolution de la dispersion." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30294.
Повний текст джерелаNatal dispersal is a process by which individuals move from their natal to reproductive ranges which is fundamental for population dynamics and persistence. Through for example the limitation of inbreeding or the capacity it provides to reach and colonize new habitats containing resources or mates, it can be highly beneficial to dispersing individuals. However, dispersal can also be costly for the individuals, through increased mortality or attrition, energy expenditure, or lost habitat opportunities and time. Its expression at the population level thus depends on the balance between costs and benefits, and theory states that dispersal may become counter-selected if costs outweigh benefits. In the current context of global change, we may expect (1) dispersal costs to increase with the degradation of environments and (2) increased dispersal costs to decrease dispersal success and geographical reach through evolutionary mechanisms. Moreover, because dispersal costs may vary with actual dispersal movement, we may wonder what are the discrete alternative tactics roe deer may use in contrasting environments (3). In this PhD, I aimed to address these three perspectives using two roe deer datasets from two geographically distinct populations (GPS data in Haute-Garonne and Capture-Mark-Recapture data in Deux-Sèvres, France), as well as a modelling approach. First, I show that, despite having a good body condition, dispersers incur costs in terms of mortality, reproduction and growth, and that climate change may increase mortality costs. Concomitant to these variations in costs, I also found that realised dispersal has diminished over the past 30 years by more than 30% in both sexes. Second, I identified at least six alternative dispersal tactics in roe deer, characterised by different movement timing, amplitude and duration, which may imply different outcomes in terms of costs and population dynamics. Lastly, my analyses suggest that dispersal might evolve towards tortuous and short distance movements when mortality costs increase, limiting the geographical reach of dispersal. Overall, these results highlight the concerning effects global changes may have on dispersal costs and dispersal evolution. Because dispersal is a species and context dependent process, more studies addressing the impacts of global changes on dispersal costs, ideally incorporating alternative dispersal tactics, will provide valuable information to better predict how species may cope with environmental changes
Shane, Janelle. "Optical micromanipulation using dispersion-compensated and phase-shaped ultrashort pulsed lasers /." St Andrews, 2009. http://hdl.handle.net/10023/730.
Повний текст джерелаCHEN, DONGSHENG. "Iron/Chromium Phase Decomposition Behavior in Oxide Dispersion Strengthened Ferritic Steels." Kyoto University, 2015. http://hdl.handle.net/2433/199417.
Повний текст джерелаMerlin, Kevin. "Caractérisation thermique d'un matériau à changement de phase dans une structure conductrice." Thesis, Nantes, 2016. http://www.theses.fr/2016NANT4004/document.
Повний текст джерелаWaste heat recovery is a challenge for the improvement of energy efficiency. Latent heat storage is a solution that addresses this issue. We focus on industrial processes with high energy on power ratios. One of the identified processes is the sterilization of food products. However, phase change materials, which have low thermal conductivities, do not provide sufficient thermal powers for these applications. The improvement of the heat exchange surface or the increase in thermal conductivity of the material are then necessary. A first experimental thermal storage comparing various heat transfer intensification techniques was achieved. The concept based on paraffin and Expanded Natural Graphite (ENG) has proven to be the most efficient compared to solutions using fins or graphite powder. The thermal characterization of the selected composite material ENG/paraffin was performed by several methods. Effective thermal conductivities values of about 20 W.m-1.K-1 were obtained. In a second step, a 100kW/6kW.h demonstrator is designed and realized. This device tested on an existing sterilization process provides an energy saving of 15%, as expected. The identification of the planar thermal conductivity of the composite material and the influence of the thermal contact resistance are carried out using an experimental device, coupled to a numerical model. Finally, an aging device is used to study the thermal stability of this material
Martinelli, Matthieu. "Stockage d’énergie thermique par changement de phase – Application aux réseaux de chaleur." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI084/document.
Повний текст джерелаThis study is about a shell and tubes latent heat thermal energy storage system. This system is expected to be integrated in a district heating network substation. Heat transfers inside the PCM as well as convection flow regime inside the heat transfer fluid are investigated.A first experimental study aims at demonstrating the necessity of internal insert inside the tubes in order to avoid mixed convection flow regime. Two highly finned tubes as well as two inserts are tested. Inserts are either cylindrical or helical. Better thermal performances are obtained with the helical one. Besides, it is shown that free convection, between the fins is negligible. Effective thermal conductivities are estimated with an experimental and analytical approach at 7.4 and 10.9 W/m/K for the 7 fpi and the 10 fpi tube.A second test campaign is carried out with metallic foams. The first one is stochastic and in copper while the second one is regular and in alumina. Effective thermal conductivities are around 13.4 and 39.4 W/m/K respectively. The copper foam heat exchanger is shown to be better than a copper finned tube in terms of stored energy and thermal power, whereas only half the mass of the fins is used in the foam.Eventually a CFD numerical model is experimentally validated. This model shows that free convection inside the PCM is negligible on the overall thermal performances even though it modifies the solid/liquid interface shape locally
Figus, Christophe. "Changement de phase en milieu poreux : application à l'étude d'un évaporateur capillaire." Toulouse, INPT, 1996. http://www.theses.fr/1996INPT101H.
Повний текст джерелаGENDRE, DIDIER. "Transferts thermiques dans certains materiaux presentant un changement de phase solide/solide." Paris, ENMP, 1993. http://www.theses.fr/1993ENMP0466.
Повний текст джерелаCamassel, Bruno. "Contribution à l'étude du changement de phase liquide-vapeur en milieu poreux." Toulouse 3, 2003. http://www.theses.fr/2003TOU30157.
Повний текст джерелаBruneau, Jean Michel. "Étude et réalisation de disques optiques ré-inscriptibles à changement de phase." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10050.
Повний текст джерелаDauvergne, Jean-Luc. "Réduction et inversion de modèles de conduction thermique avec changement de phase." Bordeaux 1, 2008. http://www.theses.fr/2008BOR13616.
Повний текст джерелаAguirre-Puente, Jaime. "Problemes de changement de phase dans les milieux disperses contenant de l'eau." Paris 6, 1988. http://www.theses.fr/1988PA066623.
Повний текст джерелаAguirre-Puente, Jaime. "Problèmes de changement de phase dans des milieux dispersés contenant de l'eau." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37611215d.
Повний текст джерелаViglieno, Emmanuel. "Changement catégoriel et transition de phase : les catégories perceptives comme des attracteurs." Phd thesis, Université Paul Valéry - Montpellier III, 2013. http://tel.archives-ouvertes.fr/tel-00958335.
Повний текст джерелаImbach, Pablo. "Impacts du changement climatique sur les services des écosystèmes en Méso-Amérique." Paris 6, 2011. http://www.theses.fr/2011PA066318.
Повний текст джерелаBayle, Raphaël. "Simulation des mécanismes de changement de phase dans des mémoires PCM avec la méthode multi-champ de phase." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX035.
Повний текст джерелаPhase change memories (PCM) exploit the variation of resistance of a small volume of phase change material: the binary information is coded through the amorphous or crystalline phase of the material. The phase change is induced by an electrical current, which heats the material by the Joule effect. Because of its fast and congruent crystallization, theGe2Sb2Te5 alloy is widely used for PCM. Nevertheless, to get a better reliability at high temperatures, which is required e.g. for automotive applications, STMicroelectronics uses a Ge-rich GeSbTe alloy. In this alloy, chemical segregation and appearance of a new crystalline phase occur during crystallization. The distribution of phases and alloy components are critical for the proper functioning of the memory cell; thus, predictive simulations would be extremely useful. Phase field models are used for tracking interfaces between areas occupied by different phases. In this work, a multi-phase field model allowing simulating the distribution of phases and species in Ge-rich GeSbTe has been developed. The parameters of the model have been determined using available data on this alloy. Two types of simulations have been carried out, firstly to describe crystallization during annealing of initially amorphous deposited thin layer; secondly to follow the evolution of phase distribution during memory operation using temperature fields that are typical for those operations. Comparisons between simulations and experiments show that they both exhibit the same features
Patra, Abhirup. "Surface properties, adsorption, and phase transitions with a dispersion-corrected density functional." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/516784.
Повний текст джерелаPh.D.
Understanding the “incomprehensible” world of materials is the biggest challenge to the materials science community. To access the properties of the materials and to utilize them for positive changes in the world are of great interest. Often scientists use approximate theories to get legitimate answers to the problems. Density functional theory (DFT) has emerged as one of the successful and powerful predictive methods in this regard. The accuracy of DFT relies on the approximate form of the exchange-correlation (EXC) functional. The most complicated form of this functional can be as accurate as more complicated and computationally robust method like Quantum Monte Carlo (QMC), Random Phase Approximation (RPA). Two newest meta-GGAs, SCAN and SCAN+rVV10 are among those functionals. Instantaneous charge fluctuation between any two objects gives rise to the van der Waals (vdW) interactions (often termed as dispersion interactions). It is a purely correlation effect of the interacting electrons and thus non-local in nature. Despite its small magnitude it plays a very important role in many systems such as weakly bound rare-gas dimers, molecular crystals, and molecule-surface interaction. The traditional semi-local functionals can not describe the non-local of vdW interactions; only short- and intermediate-range of the vdW are accounted for in these functionals. In this thesis we investigate the effect of the weak vdW interactions in surface properties, rare-gas dimers and how it can be captured seamlessly within the semi-local density functional approximation. We have used summed-up vdW series within the spherical-shell approximation to develop a new vdW correction to the meta-GGA-MS2 functional. This method has been utilized to calculate binding energy and equilibrium binding distance of different homo- and hetero-dimers and we found that this method systematically improves the MGGA-MS2 results with a very good agreement with the experimental data. The binding energy curves are plotted using this MGGA-MS2, MGGA-MS2-vdW and two other popular vdW-corrected functionals PBE-D2, vdW-DF2. From these plots it is clear that our summed-up vdW series captures the long-range part of the binding energy curve via C6, C8, and, C10 coefficients. The clean metallic surface properties such as surface energy, work functions are important and often play a crucial role in many catalytic reactions. The weak dispersion interactions present between the surfaces has significant effect on these properties. We used LDA, PBE, PBSEsol, SCAN and SCAN+rVV10 to compute the clean metallic surface properties. The SCAN+rVV10 seamlessly captures different ranges of the vdW interactions at the surface and predicts very accurate values of surface energy ( ) , and work function (𝞥) and inter-layer relaxations (𝞭%). Our conclusion is adding non-local vdW correction to a good semi-local density functional such as SCAN is necessary in order to predict the weak attractive vdW forces at the metallic surface. The SCAN+rVV10 has also been employed to study the hydrogen evolution reaction (HER) on 1T-MoS2. We have chosen as a descriptor differential Gibbs free energy (𝚫 GH ) to understand the underlying mechanism of this catalytic reaction. Density functional theory calculations agree with the experimental findings. In the case of layered materials like 1T-MoS2, vdW interactions play an important role in hydrogen binding, that SCAN+rVV10 calculation was able to describe precisely. We have also used SCAN and SCAN+rVV10 functionals to understand bonding of CO on (111) metal surfaces, where many approximations to DFT fail to predict correct adsorption site and adsorption energy. In this case SCAN and SCAN+rVV10 do not show systematic improvements compared to LDA or PBE, rather, both SCAN and SCAN+rVV10 overbind CO more compared to PBE but less compared to the LDA. This overbinding of CO is associated with the incorrect charge transfer from metal to molecule and presumably comes from the density-driven self-interaction error of the functionals. In this thesis we assessed different semi-local functionals to investigate molecule surface systems of 𝞹-conjugated molecules (thiophene, pyridine) adsorbed on Cu(111), Cu(110), Cu(100) surfaces. We find the binding mechanism of these molecules on the metallic surface is mediated by short and intermediate range vdW interactions. Calculated values of binding energies and adsorbed geometries imply that this kind of adsorption falls in the weak chemisorption regime. Structural phase transitions due to applied pressure are very important in materials science. However, pressure induced structural phase transition in early lanthanide elements such as Ce are considered as abnormal first order phase transition. The Ce 𝝰-to-𝝲 isostructural phase transition is one of them. The volume collapse and change of magnetic properties associated with this transition are mediated by the localized f-electron. Semi-local density functionals like LDA, GGA delocalize this f-electron due to the inherent self-interaction error (SIE) of these functionals. We have tested the SCAN functional for this particular problem, and, it was found that the spin-orbit coupling calculations with SCAN not only predicts the correct magnetic ordering of the two phases, but also gives a correct minima for the high-pressure 𝝰-Ce phase and a shoulder for the low-pressure 𝝲-Ce phase.
Temple University--Theses
Balandraud, Xavier. "Changement de phase et changements d'échelle dans les alliages à mémoire de forme." Montpellier 2, 2000. http://www.theses.fr/2000MON20013.
Повний текст джерелаHyot, Bérangère. "Etude physique et théorique des matériaux à changement de phase pour disques optiques." Grenoble INPG, 2001. http://www.theses.fr/2001INPG0087.
Повний текст джерелаKiouseloglou, Athanasios. "Caractérisation et conception d' architectures basées sur des mémoires à changement de phase." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT128/document.
Повний текст джерелаSemiconductor memory has always been an indispensable component of modern electronic systems. The increasing demand for highly scaled memory devices has led to the development of reliable non-volatile memories that are used in computing systems for permanent data storage and are capable of achieving high data rates, with the same or lower power dissipation levels as those of current advanced memory solutions.Among the emerging non-volatile memory technologies, Phase Change Memory (PCM) is the most promising candidate to replace conventional Flash memory technology. PCM offers a wide variety of features, such as fast read and write access, excellent scalability potential, baseline CMOS compatibility and exceptional high-temperature data retention and endurance performances, and can therefore pave the way for applications not only in memory devices, but also in energy demanding, high-performance computer systems. However, some reliability issues still need to be addressed in order for PCM to establish itself as a competitive Flash memory replacement.This work focuses on the study of embedded Phase Change Memory in order to optimize device performance and propose solutions to overcome the key bottlenecks of the technology, targeting high-temperature applications. In order to enhance the reliability of the technology, the stoichiometry of the phase change material was appropriately engineered and dopants were added, resulting in an optimized thermal stability of the device. A decrease in the programming speed of the memory technology was also reported, along with a residual resistivity drift of the low resistance state towards higher resistance values over time.A novel programming technique was introduced, thanks to which the programming speed of the devices was improved and, at the same time, the resistance drift phenomenon could be successfully addressed. Moreover, an algorithm for programming PCM devices to multiple bits per cell using a single-pulse procedure was also presented. A pulse generator dedicated to provide the desired voltage pulses at its output was designed and experimentally tested, fitting the programming demands of a wide variety of materials under study and enabling accurate programming targeting the performance optimization of the technology
Mint, brahim Maimouna. "Méthodes d'éléments finis pour le problème de changement de phase en milieux composites." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0157/document.
Повний текст джерелаIn this thesis we aim to develop a numerical tool that allow to solve the unsteady heatconduction problem in a composite media with a graphite foam matrix infiltrated witha phase change material such as salt, in the framework of latent heat thermal energystorage.In chapter 1, we start by explaining the model that we are studying which is separated in three sub-parts : a heat conduction problem in the foam, a phase change problem in the pores of the foam which are filled with salt and a contact resistance condition at the interface between both materials which results in a jump in the temperature field.In chapter 2, we study the steady heat conduction problem in a composite media withcontact resistance. This allow to focus on the main difficulty here which is the treatment of the thermal contact resistance at the interface between the carbon foam and the salt. Two Finite element methods are proposed in order to solve this problem : a finite element method based on Lagrange P1 and a hybrid dual finite element method using the lowest order Raviart-Thomas elements for the heat flux and P0 for the temperature. The numerical analysis of both methods is conducted and numerical examples are given to assert the analytic results. The work presented in this chapter has been published in the Journal of Scientific Computing [10].The phase change materials that we study here are mainly pure materials and as a consequence the change in phase occurs at a single point, the melting temperature. This introduces a jump in the liquid fraction and consequently in the enthalpy. This discontinuity represents an additional numerical difficulty that we propose to overcome by introducing a smoothing interval around the melting temperature. This is explained in chapter 3 where an analytical and numerical study shows that the error on the temperature behaves like " outside of the mushy zone, where _ is the width of the smoothing interval. However, inside the error behaves like p " and we prove that this estimation is optimal due to the energy trapped in the mushy zone. This chapter has been published in Communications in Mathematical Sciences [58].The next step is to determine a suitable time discretization scheme that allow to handle the non-linearity introduced by the phase change. For this purpose we present in chapter 4 four of the most used numerical schemes to solve the non-linear phase change problem : the update source method, the enthalpy linearization method, the apparent heat capacity method and the Chernoff method. Various numerical tests are conducted in order to test and compare these methods for various types of problems. Results show that the enthalpy linearization is the most accurate at each time step while the apparent heat capacity gives better results after a given time. This indicates that if we are interestedin the transitory states the first scheme is the best choice. However, if we are interested in the asymptotic thermal behavior of the material the second scheme is better. Results also show that the Chernoff scheme is the fastest in term of calculation time and gives comparable results to the one given by the first two methods.Finally, in chapter 5 we use the Chernoff method combined with the hybrid-dual finiteelement method with P0 and the lowest order Raviart-Thomas elements to solve thenon-linear heat conduction problem in a realistic composite media with a phase change material. Numerical simulations are realised using 2D-cuts of X-ray images of two real graphite matrix foams infiltrated with a salt. The aim of these simulations is to determine if the studied composite materials could be assimilated to an equivalent homogeneous phase change material with equivalent thermo-physical properties. For all simulationsconducted in this work we used the free finite element software FreeFem++ [41]
Belot, Malik. "Stockage de la chaleur dans un lit de particules à changement de phase." Thesis, Perpignan, 2018. http://www.theses.fr/2018PERP0065.
Повний текст джерелаThis work intends to characterize heat transfer in fluid-particle flows, specifically when phase change occurs inside the particles. The proposed model takes into account the external heat resistance (heat transfer at the particle-fluid interface) and the internal heat resistance (conduction inside and at the wall of the particle, natural convection in the liquid phase of the particle, phase change). External transfer with the surrounding fluid is described by correlations linking an external Nusselt number to Reynolds and Prandtl numbers related to the surrounding fluid. Internal conduction is calculated thanks to analytical solutions. The influence of natural convection was studied on an isolated sphere for different combinations of Rayleigh and Prandtl numbers. A correlation between an internal Nusselt number, and particle Rayleigh and Prandtl numbers was established using these simulations. This correlation allows calculating the transient evolution of the average temperature of the particle when natural convection occurs. Phase change is taken into account by a Phase Field model averaged over the particle and validated by comparison with experimental and numerical studies from the literature. Finally, the whole model and the effects of the different phenomena it describes are tested on a fixed bed of particles at mesoscopic scale using a Discrete Element Method–Computional Fluids Dynamics (DEM-CFD) model. Internal conduction and natural convection gives similar quantities of total energy stored for the same Biot number, however heat transfer distribution is modified. Phase change greatly reduces the volume of storage. Increasing the Biot number leads to a greater amount of energy stored. Finally, heat transfer greatly depends on porosity distribution
Khalloufi, Mehdi. "Ecoulements multiphasiques avec changement de phase et ébullition dans les procédés de trempe." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM014/document.
Повний текст джерелаQuenching processes of metals are widely adopted procedures in the industry, in particular automotive, nuclear and aerospace industries, since they have direct impacts on changing mechanical properties, controlling microstructure and releasing residual stresses of critical parts. Quenching is a highly nonlinear process because of the strong coupling between the fluid mechanics, heat transfer at the interface solid-fluid, phase transformation in the metal and boiling. In spite of the maturity and the popularity of numerical formulations, several involved mechanisms are still not well resolved.Therefore we propose a Direct Numerical Simulation of quenching processes at the industrial scale dealing with these phenomena. The fluid mechanics is simulated using a Finite Element Method adapted for high convective flows allowing the use of high stirring velocity in the quenching bath. Heat transfers are computed directly without the use of heat transfer coefficients but using the strong coupling between the fluid and the solid. We use a phase change model for the water that models all boiling regimes. A unified formulation of the Navier-Stokes equations, taking into account a compressible gas and an incompressible liquid is developed to model more accurately the vapor-water dynamics. A dynamic mesh adaptation procedure is used, increasing the resolution in the description of the interfaces and capturing more accurately the features of the flows.We assess the behavior and the accuracy of the proposed formulation in the simulation of time-dependent challenging numerical examples and experimental results.These recent developments enable the optimization of the process in terms of operating conditions, resources consumed and products conception
Hariri, Ahmad. "Etude de commutateurs hyperfréquences bistables à base des matériaux à changement de phase (PCM)." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0013/document.
Повний текст джерелаThe work presented in this manuscript focuses on the design, simulation and realization of new microwave switches structures based on the integration of thin layers of innovative functional materials such as phase change materials (PCM) and phase transition materials. (PTM). The operating principle of these components is based on the change of resistivity present by these materials. We exploited the reversible resistivity change of GeTe of phase change materials family between the two states: amorphous with high resistivity and crystalline with low resistivity to realize a new structure of SPST switch. Then, we have integrated this switch structure on a new structure of DPDT (Double Port Double Throw) switch matrix based on phase change materials for application in satellite payload. We have used the insulatingmetal transition presented by the vanadium dioxide (VO2) of phase transition materials family to realize a new two terminals simple switch structure on a very wide frequency band (100 MHz–220 GHz)
Covaci, A., JG Mashiya, I. Molope, I. Tshiame, R. Molatlhegi, and P. Ngobeni. "Miniaturized method based on matrix solid-phase dispersion for the rapid screening of 36 pesticides in Agricultural food commodities." Taylor & Francis, 2010. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001435.
Повний текст джерелаMaréchal, William. "Utilisation de méthodes inverses pour la caractérisation de matériaux à changement de phase (MCP)." Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3014/document.
Повний текст джерелаWith the development of intermittent sources of energy and the depletion of fossil fuels, the subject of energy storage is becoming an important topic. One of the studied options is tthe latent hermal storage using of phase change materials (PCM). One application for this type of energy storage is to improve the thermal insulation in buildings. To make the best use of these materials it is necessary to be able to predict their energy behavior. This requires a precise knowledge of their thermophysical properties, first of all of the specific enthalpy function of the material . Currently, it is often suggested to approximate the enthalpy by the direct integration of the thermograms obtained through calorimetry experiments (notion of "equivalent" calorific capacity). This approach is false because thermograms are only a time related representation of complex phenomena where thermal transfers arise in the cell of the calorimeter acting with the thermophysical properties. As a result, for example, the shape of thermograms depends on the heating rate and on the mass of the sample, which is not the case for the enthalpy of the PCM, which depends, at constant pressure, only on the temperature or on the concentration (for the solutions). We propose to compare the results given by a of a numerical direct model with experimental thermograms. The main objective in this thesis is then to use this direct model in an inverse method in order to identify the parameters of the equation of state, which enables us to calculate the specific enthalpy . First of all, the detail of an enthalpy model is presented, and then validated by comparison with experiments, allowing us to reconstruct the thermograms of pure substances or of salt solutions, of which the enthalpies are known. A study of the influence of the various parameters ( , , , .,..) on the shape of thermograms is also undertaken in order to deduce their sensibilities. A reduced model is then developed in order to reduce the calculating time of the direct model. This optimized model allows the use of inverse methods with acceptable durations. Several inverses algorithms are then presented: Levenberg-Marquardt, evolutionary and Simplex which has proved to be the fastest). We shall then apply this algorithm to identify, from calorimetric experiments, the enthalpy function of pure substances or of salt solutions. The results that we obtain show that it is possible to identify a function independent of the heating rate and of the mass, which validates the method. An analysis of the various sources of errors in the identification process and of their influences on the result allows us to estimate the quality of the enthalpy function that we identify
Saluel, Didier. "Enregistrement ultra haute densité sur un média à changement de phase par micropointes conductrices." Grenoble INPG, 1999. http://www.theses.fr/1999INPG0186.
Повний текст джерелаGagou, Yaovi Agbeko. "Etude du changement de phase dans le composé PbK2LiNb5O15 de la famille des TTB." Toulon, 2002. http://www.theses.fr/2002TOUL0005.
Повний текст джерелаTrigui, Abdelwaheb. "Analyse du transfert de chaleur dans les matériaux composites à changement de phase (MCP)." Thesis, Paris Est, 2013. http://www.theses.fr/2013PEST1040.
Повний текст джерелаPas de résumé en anglais