Dissertations / Theses on the topic 'Precipitators'
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1
Ramamoorthy, Thiagarajan. "Mechanical Behavior of Membranes in Electrostatic Precipitators." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1125868299.
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Parasram, Navin Tarun. "Particle motion in electrostatic precipitators." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247076.
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Barnes, Kathryn L. "Mechanisms of particle migration in electrostatic precipitators." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/7505.
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Electrostatic precipitators are high efficiency gas cleaning devices widely used in industry for removing particulates from process gases. A major factor affecting their performance is particle migration, which is governed by the complex interaction of electrical and hydrodynamic phenomena. A fuller understanding of these fundamental mechanisms is therefore essential to the development of realistic mathematical models. The work described in this thesis concentrates on the fluid-particle interactions in a wire-plate-system. A pilot-scale rig was built using actual components from an industrial precipitator, allowing realistic conditions to be simulated in the laboratory. Hot-wire anemometry and laser-Doppler photon correlation techniques were employed to study the time-averaged velocity field. Several designs of wall strengthener were considered, and in each case the effect on the surrounding flow field was investigated using helium bubble visualisation. The turbulent nature of the fluid was characterised by local dispersion coefficient values and fluctuating velocity components. Alumina test dust in the size range 1-10 pm was used in the precipitator under a variety of operating conditions, and a technique was established for extracting representative dust samples. The samples allowed simultaneous measurement of concentration and size distribution, from which concentration profile development and collection efficiency information was obtained. Two alternative numerical models of the precipitator were developed, both incorporating the results from the fluid flow field experimentation. The first approach was based on the finite difference solution of the convective-diffusion equation, using appropriate boundary conditions. In the second approach, the transport of dust down the precipitator duct was simulated by the step-wise progression of a series of vertical line-sources, whose motion was governed by electrical migration and lateral diffusive spread. The validity of the models was tested by comparison of the predicted concentration profiles with corresponding experimental results.
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Veluthen, Vijayagopal. "Plasma enhanced mercury capture in wet electrostatic precipitators." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1177527557.
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Lutfullaeva, Anbara. "Wet Electrostatic Precipitator, Increasing the Efficiency of Collecting Dust Particlesthrough Vibrating Precipitator Analysis." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1584444404824906.
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Majid, Muhammad [Verfasser]. "Dust Resistivity and Re-circulation in Electrostatic Precipitators / Muhammad Majid." München : Verlag Dr. Hut, 2012. http://d-nb.info/1026652235/34.
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Ivanenko, Yevhen. "Modelling and Simulation of Electrostatic Precipitators with a Dust Layer." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-44773.
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A dust layer, especially based on high-resistivity dust, at the collecting electrodes may cause a back corona discharge in electrostatic precipitators (ESP). It can significantly reduce the ESP efficiency and as a result cause ecological damages. To study the dust layer influence inside ESPs, it is necessary to derive an adequate model of the ESP precipitation process with a dust layer at the collecting electrode. The research of the present thesis is focused on stationary studies of the precipitation process with a dust layer at the collecting electrode in ESPs. Three mathematical models are proposed as a description of the precipitation process with a dust layer at the collecting electrode. The models are based on Maxwell’s equations and the finite element method (FEM). COMSOL Multiphysics software is used for their implementation. In all models the dust layer has constant conductivity and the air region has constant ion mobility. In the first model there are no coupling conditions, which is required in mathematics, are given between the two regions. The solution found by COMSOL Multiphysics does not provide physically acceptable coupling conditions. In the second model, a continuous transition zone is introduced between the two regions so that no coupling conditions are required. With the large derivatives in the transition zone, the nonlinear solver in COMSOL Multiphysics does not converge. Finally, in the third model, the dust layer and the grounded collecting electrode are replaced with a boundary condition for the air region. The properties of the third model are investigated, and these models can be used to study the influence of the dust layer. The results of these investigations are reported and discussed.
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Telenta, Marijo. "AEROSOL CALCULATION AND PRESSURE DROP SIMULATION FOR SIEVING ELECTROSTATIC PRECIPITATORS." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1172857667.
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Yuen, Albert Wai Ling Materials Science & Engineering Faculty of Science UNSW. "Collector current density and dust collection in wire-plate electrostatic precipitators." Awarded by:University of New South Wales. Materials Science and Engineering, 2006. http://handle.unsw.edu.au/1959.4/28274.
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Even minimal improvements in particle collection efficiency of electrostatic precipitators significantly reduce dust emission from fossil-fuelled power stations and reduce pollution. Yet current designs rely on the Deutsch collection theory, which was developed for tubular precipitators and has been applied to wire-plate precipitators on the assumption that the inter-electrode electric fields at the same discharge distance in both were similar. Differences in geometry and associated collector electric fields and current density non-uniformity have not been taken into account, although the collector electric field and current density of the wire-plate precipitator are not uniform. And observations show that precipitated dust patterns and the distribution of collector current density are interrelated. Investigations revealed a simple square law relationship between the collector electric field and the collector current density in the space charge dominated coronas. Applying this relationship to the Deutsch collection theory led to a current-density-based collection formula that takes into account the non-uniform collector current density distribution. The current-density-based collection formula is then used to assess the impact of collector current density on collection efficiency, the results closely following published measurements. Applying the current-density-based collection formula to estimate the dust accumulation shows that most of the dust accumulates at collector locations facing the corona wires. The effect of the non-uniform precipitated dust layer on collection performance is assessed using the distributed corona impedance - the ratio of the inter-electrode voltage and the non-uniform collector current. Re-distribution of the collector current profile as dust builds up is also compatible with published measurements. Finally this is applied to optimize the wire-plate precipitator collection performance. This shows that optimal collection performance is obtained with the wire-wire spacing less than the wire-plate distance, once again confirming published experimental results. This is the first analytical approach to show better collection performance can be achieved at the ratio of wire-wire spacing/wire-plate distance not equal to unity, which has been the standard industry practice since 1960.
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Potrymai, Eduard, and Ivan Perstnov. "Time Dependent Modelling and Simulation of the Corona Discharge in Electrostatic Precipitators." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-33293.
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Corona discharge is one of the crucial problems related with high-voltage equipment. This paper focuses on the physical and numerical modelling of corona discharge in an Electrostatic precipitator (ESP). The model is based on Maxwells equations and the Finite element method (FEM) and is implemented with the COMSOL Multiphysics software.The simulation allows studying the electric charge distribution and the behaviour of the electric field inside the ESP. The work is focused primarily on time-dependent studies of the corona discharge.
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Devine, Phillip John. "A controllable, variable waveform, high voltage, switched mode power supply for electrostatic precipitators." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/30176.
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Increased awareness of the effects of atmospheric pollution has meant that electrostatic precipitators, which have been used since the early part of this century to separate particulate matter from process gas streams, are now required to achieve particulate collection efficiencies in excess of 99.7% for a number of processes. Increasingly stringent legislation concerning industrial particulate emissions has challenged the precipitation industry to consider how equipment can be improved to reduce, in particular, heavy metal and respirable size particulate discharges. Electrostatic precipitators charge dust particles in a gas stream by corona-producing electrodes, and remove the charged particles by electrostatic attraction under high electric fields. This thesis details the development of a prototype high frequency (20KHz), high voltage (50kV), high power (25 kW) switched mode precipitator power supply with technological advances over conventional units. A high frequency, high voltage, high power precipitator supply using high frequency inverter technology coupled to a novel ferrite cored, high voltage transformer-rectifier unit has been designed and built. It is capable of delivering in a controlled and responsive way 25kW at 50kV into a load that may suffer from sparking and flashover. The developmental stages of the prototype from initial concept through to field trials of the supply at a power station in the UK are detailed.
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Bennett, Fiona. "Electrostatic charge phenomena in powder processes for dry powder inhalers." Thesis, University of Sunderland, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365417.
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Kunapareddy, Naveen. "A Proof-of-Concept Test for Seperation Efficiency of an Electro-Cyclone." Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1237569168.
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Bromley, Kay. "A three dimensional simulation of the ion-drift problem in electrostatic precipitators using an analytical finite element approach appropriate to a wide variety of geometries." Thesis, University of Leicester, 1996. http://hdl.handle.net/2381/34748.
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A computer simulation of the ion drift problem in air has been developed to predict the potential, electric field and space charge density in various geometries applicable to wire-duct electrostatic precipitators. The development of the design of the model is explained and its implementation in a fourth generation language is described. The generality of the overall design allows new features to be included. The model uses existing analytical expressions derived using the variational functionals for Poisson's equation and the Galerkin residual for current continuity which are solved iteratively. The resulting system of simultaneous equations are represented in a matrix formulation. Routines in the program: construct the matrices; set the boundary conditions; identify 'Known' and 'unknown' node parameters; iteratively solve the system of equations; test for convergence and output the solution. The Galerkin residual using a field dependent mobility has been derived and a one dimensional simulation for cylindrical geometry has been developed. Predictions are compared for linear relationships between field magnitude and ion mobility. The feasibility of extending this to other relationships is considered. The design and implementation of a three dimensional model with constant mobility is described. The grid can be fitted to a variety of geometries, with plane and curved electrodes, using a functional for equipotential surfaces. No further adaptations to the model are required to make predictions for these different geometries. Charge injection is modelled using a fixed field injection law. Predictions for plane-plane and cylindrical geometries are compared to analytical solutions. The need to improve the efficiency of the program is identified. Possible options to achieve this are discussed so that the model may be developed as a design tool for novel discharge electrodes in electrostatic precipitators.
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Haynes, Nicholas. "The sieving electrostatic precipitator." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1176404052.
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Gottipati, Pranitha. "The dry sieving electrostatic precipitator." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1176320016.
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Khan, Wajahat. "Moving-membrane-based electrostatic precipitator." Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1173975992.
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Gunenc, Mehmet V. "Enhanced Charging Sieving Electrostatic Precipitator." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1195594122.
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Lancereau, Quentin. "Modélisation d'un collecteur électrostatique compact en régime laminaire pour la capture de bio-particules submicroniques aéroportées." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENI111/document.
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La détection d'agents biologiques dans l'air ambiant est devenue un enjeu majeur notamment en environnement hospitalier et dans la protection contre le bioterrorisme. Dans ce contexte, la miniaturisation des dispositifs d'analyse permet d'envisager leur utilisation directement sur la zone d'étude. Afin d'obtenir un échantillon concentré et représentatif, la filtration de l'air reste cependant un point délicat. Parmi les différents principes exploitables pour la collecte de particules aéroportées, l'emploi des forces électriques semble être prometteur pour améliorer les performances des dispositifs qui se trouvent généralement fondés sur des forces inertielles. Dans cette étude, une modélisation fine des collecteurs électrostatiques a été conduite pour une géométrie fil / cylindre. Elle décrit tout d'abord les champs hydrodynamiques d'un écoulement charriant des inclusions dans lequel est imposée une décharge couronne. Une injection éventuelle de vapeur dans la chambre de collecte a nécessité ensuite la détermination des champs de température et concentration de la vapeur. Une analyse dimensionnelle inspectionnelle a montré que ces champs possèdent deux termes de couplage fort dont on a justifié l'omission dans cette étude ; les phénomènes physiques mis en jeu ont alors pu être classés selon une cascade d'influences non réciproques et la résolution numérique du modèle s'en est trouvée facilitée. Quatre configurations d'écoulement différentes, caractérisées par des recirculations d'origine électro hydrodynamiques, ont été identifiées et leurs impacts sur les rendements de collecte quantifiés. De plus, une procédure de dimensionnement des filtres électrostatiques fondée sur un nombre de Deutsch représentatif des rendements a été mise en place. Son exploitation a montré l'intérêt de la mise en parallèle de petits collecteurs pour filtrer des débits d'air importants. Cette étude s'est achevée par l'analyse des effets engendrés par l'injection de vapeur dans la chambre de collecte. Elle a jeté les bases d'une explication pour l'augmentation des rendements de collecte résultant de cette injectionDetection of airborne biological agents has become a major challenge especially in hospitals and the protection against bioterrorism. In this context, the miniaturization of analytical devices allows to consider their direct use in the field. To obtain a representative and concentrated sample, air filtration remains a delicate point. Among the various principles used to collect airborne particles, the use of electrical forces seems to be promising to improve performance beyond these of devices that are based on inertial forces.In this study, a detailed model of electrostatic collectors was developed in the wire/cylinder geometry. It first describes the hydrodynamic flow fields carring inclusions in which a corona discharge is imposed. Afterwards, the possible injection of steam into the collection chamber required the determination of the temperature and vapor concentration fields. An inspectionnal dimensional analysis justified the omission of two strong coupling terms. Therefore, in this study, the involved physical phenomena could be classified according to a non-reciprocal influences cascade and the numerical model is become simpler. Four different flow patterns, characterized by their electrohydrodynamic secondary flows, were identified and their impact on the collection efficiencies was quantified. In addition a design procedure of electrostatic filters, based on a representative efficiency Deutsch number, has been developed. This procedure shows the interest of parallelizing small collectors to filter important airflows. This study was completed by the analysis of the effects of steam into the collection chamber. It provides the basis for an explanation of the collection efficiencies increase related to this injection
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Morosko, Jason M. "Composite Discharge Electrode for Electrostatic Precipitator." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1173374043.
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Bahner, Mark A. "A reduced-turbulence, reduced-entrainment electrostatic precipitator." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040702/.
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Bharmal, Huzefa A. "Performance Evaluation of Wet Metal Plate Electrostatic Precipitator." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1133462252.
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Khan, Zahirul Hasan. "Bench- and Pilot-Testing of Sieving Electrostatic Precipitator." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1177721692.
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Al-Majali, Yahya T. "Novel Hybrid Composite Discharge Electrode for Electrostatic Precipitator." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1492188040079733.
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Broďák, Kamil. "Napájecí zdroj elektrostatického odlučovače." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221177.
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The diploma thesis focuses on the problems of electric power precipitators. Due to their current dominant position, the work concentrates on the sources of single phase transformers operating at the frequency of 50 Hz controlled by thyristors. The first part describes the electrostatic precipitator and its principle. This is followed by a brief insight into the proposal for an electrostatic precipitator. The work also explains the high voltage source that is divided into a transformer with a rectifier and into a control box with power circuits and control circuits that provide the power supplied by a transformer. The work also offers an explanation of the HV source system that operates at different conditions. The last part suggests a proposal for cooling cabinet including thyristors, for power line control box resources, for a supply line and a line to the transformer.
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Eboreime, Ohioma. "Numerical Modeling of the Novel Cross-Flow Electrostatic Precipitator." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1575646113189561.
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Ong, Chun Hoe. "Electrostatic precipitator to collect large quantities of particulate matter." Thesis, University of Iowa, 2017. https://ir.uiowa.edu/etd/5976.
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Traditional aerosol samplers are limited in their abilities to collect large quantities of particulate matter due to their low flow rates, high pressure drops, and are noise intrusiveness. The goal of this study was to develop an alternate aerosol sampler using electrostatic precipitation technology that was safe and not noise intrusive to be deployed in homes. The O-Ion B-1000 was selected as the most suitable electrostatic precipitator (ESP) for achieving the goal of this study because of its affordability, the design of its collection electrode and its high flow rate. The collection efficiency of the ESP was assessed for three aerosols; Arizona Road Dust (ARD), NaCl and diesel fumes. ARD was found to have the highest average collection efficiency (65%) followed by NaCl (43%) and lastly diesel fumes (41%).
A method for recovering the particulate matter deposited on the collection electrode was developed. The dust collected on the electrode was recovered onto polyvinyl chloride (PVC) filters moistened with deionized water. Additionally, the recovery of the three test aerosols, ARD, NaCl, and diesel fumes, from the collection electrode was assessed. A gravimetric analysis was done to determine the amount of dust recovered. The collection efficiency was used to calculate the amount of mass expected on the filter for a particular aerosol. NaCl had the highest recovery at 95% recovery, followed by ARD (73%) and lastly diesel fumes (50%). Two identical ESPs were also deployed in an office and in a bedroom, 104.47 mg and 9.64 mg of particulate matter (PM) was recovered respectively.
The noise and ozone level produced by the ESP was evaluated to determine the ESP’s viability as a household aerosol sampler. The ESP’s high setting had a noise level of 45.8 dB and ozone generation rate of 0.036 mg/min. The results of the calculation showed that in an averaged size unventilated room (6.10 m × 6.10 m × 2.44 m), it would take 6 hours and 53 minutes for the ozone levels to reach the recommended maximum exposure limits per National Ambient Air Quality Standards (NAAQS). Additionally, a ventilation of 230 L/min is needed in order to prevent the ozone levels generated by the ESP from exceeding maximum exposure limits per NAAQS.
Overall, the O-Ion B-1000 met the criteria of collecting 1 mg of PM in a 24 hour sampling for ARD and NaCl. Diesel fumes however, required 30 hours to collect 1 mg of PM. The noise levels generated by the ESP set on high was one dB above the Environmental Protection Agency (EPA) standards for indoor noise limit. However, the noise is proportional to inverse distance squared; the ESP should not pose a problem during household deployment. Ozone generated by the ESP was also found to be below 0.07 ppm as set by the EPA with an average ventilation of 230 L/min. The average ventilation of a household is 1500 L/min, thus the ozone generated by the ESP would not surpass 0.07 ppm. However, the ESP should not be deployed in unventilated rooms for a period of more than 6 hours and 53 minutes.
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Leguen, Claire. "Prior Austenite Grain Size Controlled by Precipitates." Phd thesis, INSA de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00511322.
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During this study, the correlation between the evolution of the prior austenitic grain size and of the precipitation state during thermal treatment performed on steels is presented. To do this, the precipitation state has been finely characterized. Precipitate volume fractions were measured by plasma spectroscopy. Transmission Electron Microscopy (TEM) was used to determine the precipitate size distributions (HAADF images) and the precipitate chemical composition (EDX, EELS for carbon and nitrogen). In order to treat ELLS spectra obtained on complex carbonitrides (V,Nb,Ti)(C,N), a routine based on the Least Mean square Fitting have been developed. Results obtained with this method are in gopd agreement with those obtained by EDX analysis for metallic elements (Nb, V, Ti, ...). Then, grain size distributions were determined using a special etching called "Bechet-Beaujard", which reveals the prior austenite grain boundaries. Two alloys have been characterized in this study. (i) A model alloy, the FeVNbCN, which presents two precipitate types, NbC and VCN. This alloy was chosen to study the role of nitrogen on the precipitation state during reversion treatments. A model predicting the precipitation kinetics, coupled with a model for grain growth, give a good agreement with experimental results on grain sizes, precipitate sizes and on precipitate volume fraction. (ii) An industrial steel, the 16MnCr5+Nb was also studied. This alloy exhibits the presence of AlN and NbC precipitates. The correlation obtained between the Prior Austenite Grain Size and the evolution of the precipitation state shows that a large volume fraction of small precipitates allows a great pinning of grain boundaries. Finally, during thermo-mechanical treatments performed in the industry, some large grains may grow faster than smaller grains, leading to the so-called abnormal grain growth. This kind of growth can lead to undesirable mechanical instabilities. We have developed a criterium for abnormal grain growth which predicts the risk of such growth for a given precipitation state. This model presents a good agreement with all experimental results for both studied alloys.
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Toh, Shoichi. "Interface structure of augite precipitates in orthopyroxene." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150842.
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Franklin, Guy Sinclair. "Novel iron precipitates for drinking water treatment." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/8351.
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She, Minggang. "Phase field model for precipitates in crystals." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46020.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2008.Includes bibliographical references (p. 261-270).
Oxygen precipitate caused by oxygen supersaturation is the most common and important defects in Czochralski (CZ) silicon. The presence of oxygen precipitate in silicon wafer has both harmful and beneficial effects on the microelectronic device production. Oxygen precipitates are useful for gathering metallic contaminants away from the device regions and for increasing the mechanical strength of the wafer [Borghesi, 1995], but they also can destroy the electrical and mechanical characteristics of the semiconductor and microelectronic devices [Abe, 1985; Kolbesen, 1985]. The understanding of the mechanism of the formation and growth of the oxygen precipitates in CZ silicon is a key to improve the quality of silicon wafer. The goal of this thesis is to provide a full understanding of the growth of an isolated oxygen precipitate in CZ silicon and its morphological evolution by means of phase-field method, and to gain the insight of the morphological transition of the oxygen precipitate and the distribution of oxygen, vacancy, and self-interstitial around the single oxygen precipitate. The traditional approach to simulate multiphase system is the sharp interface model. Sharp interface model requires tracking the interface between phases, which make the simulation much difficult and complicate. Phase-field model offers an alternative approach for predicting mesoscale morphological and microstructure evolution of inhomogeneous multiphase system. The most significant computational advantage of a phase-field model is that explicit tracking of the interface is unnecessary. In this thesis, the phase-field model is applied to simulate the evolution of oxygen precipitates in CZ silicon. A phase-field model for a two-component inhomogeneous system was first derived to set up the framework of phase-field method and a dynamically adaptive finite element method also was built to specifically solve phase-field equations. This model was used to investigate the effects of interfacial and elastic properties on the growth of a single precipitate, coarsening of two precipitates, and competitive growth of multiple precipitates. For an isolated precipitate growth, both elastic energy and interfacial energy affect the precipitate morphological evolution.
(cont.) Numerical results show the shape of the precipitate is determined by the relative contributions of elastic energy and interfacial energy, the degree of elastic anisotropy, and the degree of interfacial anisotropy. A dimensionless length scale LS3 was defined to represent the relative contributions of the interfacial energy and elastic energy. For large LS3 (LS3 > 5), the anisotropic elasticity plays a dominant role and precipitate evolves to held the elastic anisotropy even if the interfacial anisotropy is very strong. However, if LS3 ~1 or elasticity is isotropic, the strong anisotropy ([epsilon]4 =/> 0.05 ) of the interface will be the dominant factor to determine the precipitate shape. The growth rate of an isolated precipitate follows the diffusion-controlled power law. The elasticity significantly decreases the precipitate growth rate, while the anisotropy of the interface does not. Coarsening of two precipitates was also explored with different interfacial and elastic properties. The results also show that both elasticity and interfacial anisotropy enhance the coarsening rate. For competitive growth of multiple precipitates, a gap was found to be developed between the precipitates because of the precipitate screening, but this gap could be destroyed by increasing the interfacial energy or introducing elastic energy. Based on the framework of the previous phase-field model, another phase-field model coupling CALPHAD thermodynamic assessment was developed to simulate the growth of the oxygen precipitate in CZ isilicon. An asymptotic analysis was performed to understand the phase-field model at the sharp interface limit and all physical principles of the solid precipitate growth problem were recovered. a Cristobalite and amorphous oxygen precipitates were calculated at different orientations and temperatures. Disk-like shape, square, ellipse, a slightly deformed sphere are reproduced for oxygen precipitates, which agrees with the experimental observations very well. In addition, the growth rates of amorphous precipitates and a cristobalite precipitates at different temperatures show that at high temperature 1100 °C, amorphous precipitate has the largest growth rate, while at low temperature 900 °C, a cristobalite precipitate grows faster.
(cont.) This qualitatively explained why different polymorphs and shapes of the oxygen precipitate were observed in experiments at different annealing temperatures.
by Minggang She.
Ph.D.
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Yuan, Gaihuan. "Microstructures characterization of precipitates in zirconium alloys." Thesis, University of Bolton, 2016. http://ubir.bolton.ac.uk/1137/.
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Zirconium alloys are used as the fuel cladding materials in nuclear power reactors. Corrosion resistance is one of the most important factors for the application of zirconium alloys, which involves the lifetime of fuel assembles, and the safety and reliability of the operation for nuclear power reactors. According to the current research, the characterizations of precipitates in zirconium alloys affect the corrosion resistance significantly. However, the investigation results about the precipitates in zirconium alloys are variable. Zr-4 (Zr-1.2Sn-0.2Fe-0.1Cr), E110 (Zr-1Nb) and Zirlo (Zr-1Sn-1Nb-0.1Fe) are commercial alloys to be widely applied for pressurized water reactors(PWRs). Zr-4, E110 and Zirlo, as the representatives of Zr-Sn, Zr-Nb and Zr-Sn-Nb alloys, are widely applied for PWRs. Three alloys were developed in the early time, and there are many data and experience for the performance in reactors As the references. Three alloys are studied and the precipitates and microstructures are systematically analyzed. The transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and High-resolution transmission electron microscopy (HRTEM) have been used to study the composition, structure, defects and orientation relationship of the precipitates in commercially available Zr-based alloys.
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Shah, Hardikkumar G. "PERFORMANCE EVALUATION OF WET PLATE ESP FOR SUB-MICRON PARTICLES." Ohio University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1141954317.
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Li, Ke. "Experimental and theoretical study of sub-micron aerosol collection efficiency by Laminar Wet-Membrane electrostatic precipitator." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1177439835.
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Mannella, Nikolas E. "Design, Manufacturing, and Testing of a Pilot Wet Electrostatic Precipitator." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1492558871480272.
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Williams, Charles D. H. "Some magnetic effects of clustering in iron doped magnesium oxide." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6606/.
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The growth of a magnesioferrite precipitate in iron doped (˜lOOOOppm wt.) magnesium oxide crystals, heat treated at 973K in oxygen, is studied with torque, magnetisation and magnetic resonance measurements. The torque and magnetisation results are in agreement with a model which assumes that the precipitate grows by diffusion limited Ostwald ripening.The effects of the particle size distribution and cubic magnetocrystalline anisotropy of the orientated octahedral precipitate particles on the magnetisation and torque curves are calculated. A magnetometrie demagnetisation tensor is defined for assemblies of orientated dipoles, its variation with the assembly size is investigated and used to calculate the longitudinal demagnetisation factors of octahedra. The ferromagnetic resonance spectra obtained were not in agreement with the generally used theory of de Biasi and Devezas (J. Appl. Phys. (1978)49, 2466). A new theory, based on a spin Hamiltonian, of the FMR response of an anisotropic superparamagnet is proposed and compared with some of the experimental spectra.
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Mesnard, Frédéric. "L'approche probabiliste de l'estimation des precipitations par radar." Toulouse 3, 1998. http://www.theses.fr/1998TOU30192.
Full textAbstract:
L'estimation des precipitations par radar a partir de methodes probabilistes constitue le theme commun d'articles, presentes dans la these, que l'auteur a prepares ou auxquels il a participe. Les deux premieres contributions sont etroitement liees ; elles sont le resultat d'une combinaison entre une modelisation statistique des cellules de pluie et une methode d'estimation de l'intensite moyenne de precipitation a partir de la mesure de la fraction d'aire couverte par la pluie. La contribution suivante est l'etude de la crue-eclair de biescas (7 aout 1996), dans les pyrenees aragonaises. On montre que l'activite des cellules orageuses, en terme d'intensite de pluie, est intimement liee a leur activite electrique ; il existe une correlation forte entre l'intensite de pluie et la densite d'eclair nuage-sol. L'utilisation des radars meteorologiques se generalise dans les services de prevision des crues. Une experimentation, toujours en cours, dans le bassin superieur de la garonne, a pour but de montrer l'efficacite d'une utilisation en temps reel de donnees radar. Nous en presentons ici quelques resultats. La contribution suivante traite d'une methode d'ajustement probabiliste de donnees radar basee sur la comparaison des distributions de probabilite des reflectivites et des intensites de pluie. Elle permet un etalonnage de mesures radar a partir de mesures effectuees au sol, non necessairement simultanees, a l'aide de pluviometres a intensite. La derniere contribution presente les resultats de l'application d'une technique d'estimation des precipitations a partir de mesures effectuees par un radar polarimetrique travaillant a une longueur d'onde attenuee. Les points d'originalite de cette methode sont d'une part qu'elle est independante de l'etalonnage du radar et d'autre part qu'elle permet la correction d'attenuations importantes.
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Ibasco, Suzette. "Magnesium phosphate precipitates and coatings for biomedical applications." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40691.
Full textAbstract:
Metals are extensively used materials in orthopaedics and oral implants and several research studies have reported that coating the surface improves the osteoconduction and bone bonding ability of the metal. Low temperature aqueous precipitation techniques are advantageous over other coating processes as they allow the incorporation of thermally unstable compounds. Although some magnesium phosphates have been shown to be well tolerated in bone tissue [Zimmermann 2006], they are relatively unstudied as bioceramics. The first part of this research project was to determine the precipitation conditions at which different magnesium phosphate phases form. Ultimately, the primarily goal of this study was to investigate a new low temperature route to produce magnesium phosphate coatings by reacting substrates sputter coated with magnesium metal in an aqueous phosphate solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersion spectroscopy (EDS) were used to characterize and identify the magnesium phosphate precipitates. SEM revealed that coatings formed by the reaction of magnesium metal with ammonium dihydrogen phosphate formed a continuous coating of struvite crystals. Importantly, this coating was durable enough to withstand the peel test (ASTM D 3359). Furthermore, this coating was also useful as a reactive surface to form hydroxyapatite coating. Biocompatibility assays, showed that magnesium phosphates precipitates and coatings were non-toxic and sustained cell viability. This study shows the possibility of forming a number of potentially biocompatible surface coatings on a metal model through a low temperature in situ process. This process shows good promise in producing enhanced coatings with many advantages over currently used techniques.Les métaux sont largement utilisés comme matériaux dans la conception d’implants orthopédiques et dentaires et plusieurs études ont montré qu’un revêtement de leurs surfaces améliore leur propriété d’ostéoconduction et leur capacité de liaison au tissu osseux. Les techniques de précipitation aqueuse à basse température sont plus élaborées comparées aux autres techniques de revêtement car elles permettent l’incorporation de composés thermiquement instables. Bien que certains phosphates de magnésium soient bien tolérés au sein du tissu osseux [Zimmermann 2006], ils sont relativement peu étudiés comme biocéramiques. La première partie de ce projet de recherche était de déterminer les conditions de précipitations auxquelles les différentes phases des phosphates de magnésium se forment. L’objectif majeur de cette étude était d’explorer une nouvelle méthode, à basse température, pour produire des revêtements de phosphate de magnésium par la réaction de substrats revêtus par pulvérisation avec des métaux magnésiens, dans une solution aqueuse de phosphate.La diffraction des rayons X et la microscopie électronique à balayage, couplée à la spectrométrie par dispersion d’énergie, furent utilisées pour caractériser et identifier les précipités de phosphates de magnésium. La microscopie électronique à balayage a révélé que les revêtements produits par la réaction d’un métal magnésiun avec un phosphate diacide d’ammonium forment un revêtement continu de cristaux de struvite. Ce revêtement présentait également la caractéristique majeure de résister au test d’arrachage. Les tests de biocompatibilité ont montré que les précipités de phosphates de magnésium ainsi que les revêtements de surface étaient non toxiques et amélioraient la viabilité cellulaire. Cette étude démontre la possibilité de former un éventail de revêtements potentiellement biocompatibles à la surface d’un$
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Rozdilsky, Ian. "3-D atomic scale characterisation of growing precipitates." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301389.
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Furdanowicz, Waldemar. "Effects of diffraction on microanalysis of embedded precipitates." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/86253.
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Van, Eeden Gert Christian. "The numerical modelling of a flue gas precipitator / G.C. van Eeden." Thesis, North-West University, 2003. http://hdl.handle.net/10394/359.
Full textAbstract:
Suspended fly-ash particles in industrial emission gasses have a major
degrading effect on the whole environment. Electrostatic precipitation is one
of the oldest and most effective gas-cleaning processes used today.
Electrostatic precipitators use electrostatic forces to clean the flue gas of ash
particles. Stricter emission control laws force industries (like SASOL) to
improve their electrostatic precipitators.
This study consists of a comprehensive literature survey and the development
of a numerical fluid flow model. The proper flow of the gas through an
electrostatic precipitator is one of the most important factors to ensure high
collection efficiencies. The gas flow must be distributed over the whole flow
domain in order to utilize the entire collecting area. The three-dimensional
numerical model only considers the fluid dynamics of a precipitator. The finite
volume method together with the SIMPLE algorithm is used to solve the fluid
dynamic equations.
The computer resources available are not sufficient to simulate the full detail
of the structures inside a full-scale precipitator. Thus the precipitator flow
domain was simplified by making certain assumptions and approximations.
The distribution plates in the precipitator inlet ensure good gas distribution
through the entire precipitator. Porous baffles are used to approximate the
distribution plates and the electrical fields are approximated by porous
mediums.
The effect of the distribution plates and the electrical fields on the gas flow
through the precipitator was investigated. The results have shown that the
gas flow was expanded over the whole flow domain and the maximum
velocity inside the precipitator was significantly reduced because of the effect
of the distribution plates. The simulated gas flow velocity profiles are in
relative good agreement with measured velocity profiles. The methodology
followed in this study can be used to predict gas flow patterns inside a
precipitator but further research is necessary.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.
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Jaffrezo, Jean-Luc. "Etude du lessivage des aerosols atmospheriques par les precipitations." Paris 7, 1987. http://www.theses.fr/1987PA077211.
Full textAbstract:
Identification sur le terrain des facteurs de variation des concentrations des especes minerales non reactives dans les precipitations; etude des mecanismes de transfert entre phases pluie et aerosols
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Marsan, David. "Multifractals espace-temps, dynamique et predicibilite ; application aux precipitations." Paris 6, 1998. http://www.theses.fr/1998PA066228.
Full textAbstract:
Il est observe pour de nombreux champs geophysiques des proprietes d'invariance d'echelle, a la fois dans le domaine spatial et dans le domaine temporel. Cependant, a l'exception d'un nombre tres limite d'etudes, ces deux domaines de description ont systematiquement ete distingues, alors qu'une approche spatio-temporelle parait tout a fait pertinente. C'est precisement cette approche qui est etudiee dans ce travail de these. L'unification des deux domaines, en un modele de cascade multiplicative invariante d'echelle, generatrice de distributions multifractales, requiert l'examen attentif de plusieurs caracteristiques ; en particulier, l'anisotropie espace-temps de la symetrie d'echelle, ainsi que l'invariance par changement de repere galileen des champs decrits, necessite le developpement du cadre de l'invariance d'echelle generalisee dans ce domaine spatio-temporel. De plus, la fleche du temps, ou causalite, est une propriete a assurer lors de la construction numerique de telles distributions. Cette approche permet un traitement tout a fait original de questions propres aux systemes dynamiques non-lineaires, en ce sens qu'elle prend pleinement en compte le caractere fortement intermittent des processus etudies. Ainsi, les limites de predicibilite intrinseques et la possibilite de prevoir le futur statistique d'un processus geophysique connu jusqu'a un temps donne sont etudiees. Il est alors possible de montrer que l'information exploitable pour la prevision diminue a toute echelle, suivant un taux possedant lui aussi une invariance d'echelle. Des methodes concretes sont developpees afin d'exploiter optimalement, dans ces limites strictes de predicibilite, cette information, a toute echelle. Le cas des champs de precipitation est examine. L'acces a des donnees de reflectivite radar permet de tester et valider ce modele sur des bases de donnees volumineuses. Il est de plus possible de profiter du modele introduit dans cette these afin d'expliquer des comportements dynamiques jusque la mal compris, entre autre comment la fractalite du support actif du champ de reflectivite depend du niveau d'activite pluvieuse local.
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Dogan, Omer Nihat. "Interactions between austenite grain boundaries and aluminum nitride precipitates." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054927506.
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Sankarasubramanian, R. "Symmetry-Breaking Transitions In Equilibrium Shapes Of Coherent Precipitates." Thesis, Indian Institute of Science, 2000. https://etd.iisc.ac.in/handle/2005/191.
Full textAbstract:
We present a general approach for determining the equilibrium shape of isolated, coherent, misfitting particles by minimizing the sum of elastic and interfacial energies using a synthesis of finite element and optimization techniques. The generality derives from the fact that there is no restriction on the initial or final shape, or on the elastic moduli of the particle and matrix, or on the nature of misfit. The particle shape is parameterized using a set of design variables which are the magnitudes of vectors from a reference point inside the particle to points on the particle/matrix interface. We use a sequential quadratic programming approach to carry out the optimization. Although this approach can be used to find equilibrium shapes of particles in three dimensional systems, we have presented the details of our formulation for two dimensional systems under plane strain conditions.
Using our formulation, we have studied the equilibrium shapes in two dimensional systems with cubic anisotropy; the precipitate and matrix phases may have different elastic moduli, and the misfit may be dilatational or non-dilatational. The equilibrium shapes and their size dependence are analysed within the framework of symmetry-breaking shape transitions. These transitions are further characterized in terms their dependence on the cubic elastic anisotropy parameter, defined by A = 2C44/(C11 – C12), and on the modulus mismatch, defined by δ=μp/μm, where /μp and μm are the effective shear moduli of the precipitate and matrix phases, respectively. Depending on the type of misfit, the systems may be classified into the following four cases:
Case A: For dilatational misfit, the equilibrium shapes in isotropic systems are circular (with an isotropic or I symmetry) at small sizes and undergo a transition at a critical size to become ellipse-like (with an orthorhombic or O symmetry). This I --O transition is continuous and is obtained only when the precipitate phase is softer than the matrix. These results are in good agreement with the analytical results of Johnson and Cahn.
In cubic systems with dilatational misfit, the particles exhibit a transition from square-like shapes (with a tetragonal or T symmetry) at small sizes to rectangle-like shapes (with an O symmetry) at large sizes. This T -- O transition is continuous. It occurs even in systems with stiffer precipitates; however, it is forbidden for systems with δ >δC, where δ C represents a critical modulus mismatch. The critical size decreases with increasing cubic anisotropy (i.e., with increasing values of (A-1)/(A+1). The sides of the square-like and rectangle-like shapes are along the elastically soft directions.
Case B: In these systems, the principal misfits e*xx and e*yy differ in magnitude but have the same sign. The precipitates at small sizes become elongated along the direction of lower misfit; this shape has an O symmetry. In systems with A > 1, they continue to become more elongated along the same direction, exhibiting no symmetry-breaking transition. However, in systems with A < 1, particles at large sizes are elongated along an intermediate direction between the direction of lower misfit and one of the elastically soft <11> directions; this shape has only a monoclinic or M symmetry. This O - M transition, in which the mirror symmetries normal to the x and y axes are lost, may be discontinuous or continuous. The critical size increases with δ (in the range 0.8 < δ <1.25), indicating that this transition would also be forbidden for systems with δ > δC. In systems with A < 1, the critical size decreases with increasing values of A-1/ A+1
Case C: In these systems, the principal misfits differ in both magnitude and sign, and the misfit strain tensor allows an invariant line along which the normal strain is zero. The precipitates at small sizes are elongated along the direction of lower absolute misfit, and possess an 0 symmetry. At large sizes, the mirror symmetries normal to the x and y axes are broken to yield shapes which are elongated along a direction between that of lower misfit and the invariant line. This 0 -> M transition is continuous and occurs in all the systems irrespective of the value of A The critical size increases with A and decreases with δ.
Case D; The misfit in this case is a special form of that in Case C; the principal misfits have the same magnitude but opposite signs. The precipitates at small sizes have a square-like shape with its sides normal to the < 11 > axes, irrespective of the type of cubic anisotropy. At large sizes, they become rectangle-like with the long axis oriented along one of the <11> directions. Similar to Case C, this T - 0 transition is continuous and occurs in all the systems irrespective of the values of A. The critical size increases with A and decreases with δ.
Thus, we have identified all the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two dimensional systems. We have identified their origin and nature, and characterized them in terms of their dependence on the anisotropy parameter and modulus mismatch.
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Sankarasubramanian, R. "Symmetry-Breaking Transitions In Equilibrium Shapes Of Coherent Precipitates." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/191.
Full textAbstract:
We present a general approach for determining the equilibrium shape of isolated, coherent, misfitting particles by minimizing the sum of elastic and interfacial energies using a synthesis of finite element and optimization techniques. The generality derives from the fact that there is no restriction on the initial or final shape, or on the elastic moduli of the particle and matrix, or on the nature of misfit. The particle shape is parameterized using a set of design variables which are the magnitudes of vectors from a reference point inside the particle to points on the particle/matrix interface. We use a sequential quadratic programming approach to carry out the optimization. Although this approach can be used to find equilibrium shapes of particles in three dimensional systems, we have presented the details of our formulation for two dimensional systems under plane strain conditions.
Using our formulation, we have studied the equilibrium shapes in two dimensional systems with cubic anisotropy; the precipitate and matrix phases may have different elastic moduli, and the misfit may be dilatational or non-dilatational. The equilibrium shapes and their size dependence are analysed within the framework of symmetry-breaking shape transitions. These transitions are further characterized in terms their dependence on the cubic elastic anisotropy parameter, defined by A = 2C44/(C11 – C12), and on the modulus mismatch, defined by δ=μp/μm, where /μp and μm are the effective shear moduli of the precipitate and matrix phases, respectively. Depending on the type of misfit, the systems may be classified into the following four cases:
Case A: For dilatational misfit, the equilibrium shapes in isotropic systems are circular (with an isotropic or I symmetry) at small sizes and undergo a transition at a critical size to become ellipse-like (with an orthorhombic or O symmetry). This I --O transition is continuous and is obtained only when the precipitate phase is softer than the matrix. These results are in good agreement with the analytical results of Johnson and Cahn.
In cubic systems with dilatational misfit, the particles exhibit a transition from square-like shapes (with a tetragonal or T symmetry) at small sizes to rectangle-like shapes (with an O symmetry) at large sizes. This T -- O transition is continuous. It occurs even in systems with stiffer precipitates; however, it is forbidden for systems with δ >δC, where δ C represents a critical modulus mismatch. The critical size decreases with increasing cubic anisotropy (i.e., with increasing values of (A-1)/(A+1). The sides of the square-like and rectangle-like shapes are along the elastically soft directions.
Case B: In these systems, the principal misfits e*xx and e*yy differ in magnitude but have the same sign. The precipitates at small sizes become elongated along the direction of lower misfit; this shape has an O symmetry. In systems with A > 1, they continue to become more elongated along the same direction, exhibiting no symmetry-breaking transition. However, in systems with A < 1, particles at large sizes are elongated along an intermediate direction between the direction of lower misfit and one of the elastically soft <11> directions; this shape has only a monoclinic or M symmetry. This O - M transition, in which the mirror symmetries normal to the x and y axes are lost, may be discontinuous or continuous. The critical size increases with δ (in the range 0.8 < δ <1.25), indicating that this transition would also be forbidden for systems with δ > δC. In systems with A < 1, the critical size decreases with increasing values of A-1/ A+1
Case C: In these systems, the principal misfits differ in both magnitude and sign, and the misfit strain tensor allows an invariant line along which the normal strain is zero. The precipitates at small sizes are elongated along the direction of lower absolute misfit, and possess an 0 symmetry. At large sizes, the mirror symmetries normal to the x and y axes are broken to yield shapes which are elongated along a direction between that of lower misfit and the invariant line. This 0 -> M transition is continuous and occurs in all the systems irrespective of the value of A The critical size increases with A and decreases with δ.
Case D; The misfit in this case is a special form of that in Case C; the principal misfits have the same magnitude but opposite signs. The precipitates at small sizes have a square-like shape with its sides normal to the < 11 > axes, irrespective of the type of cubic anisotropy. At large sizes, they become rectangle-like with the long axis oriented along one of the <11> directions. Similar to Case C, this T - 0 transition is continuous and occurs in all the systems irrespective of the values of A. The critical size increases with A and decreases with δ.
Thus, we have identified all the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two dimensional systems. We have identified their origin and nature, and characterized them in terms of their dependence on the anisotropy parameter and modulus mismatch.
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Ettori, Maxime Philippe. "A new electrostatic precipitator for breath-borne aerosol: preliminary study and tests." Thesis, KTH, Mikro- och nanosystemteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-117737.
Full textAbstract:
The goal of this master thesis was to preliminary study, design and test a new electrostatic precipitator (ESP) for the capture of human breath-borne aerosol. This system needs to collect aerosolized bacteria/viruses in exhaled droplets, while being compatible with an open interface micro-fluidic system, in which an integrated bio-sensor will detect their presence. The final system may constitute an efficient point-of-care test for lower respiratory tract infection diagnoses. The number of exhaled droplets and the amount of pathogenic material being extremely low, the system needs to provide a high collection efficiency, while being compatible with the technologies used in a point-of-care test.In this work, a thorough study of the state-of-the-art in particle collection systems is presented, as well as theories needed for the conception of an ESP. Based on this knowledge, the main features and solutions were chosen and integrated in a conceptual design of a novel ESP. COMSOL simulations were performed to guide the design of the collection system. A specific simulation code was written to simulate the droplets motion inside a highly simplified ESPmodel. Thereafter, an experimental setup was build, and several configurations of ESP were tested. The efficiency of each configuration was assessed by quantifying the amount of dye, initially dissolved in the dispensed liquid, collected by the ESP. An impinger, placed at the setup outlet, is used to quantify the losses inside the system.Three configurations of ESP were tested, and their collection efficiency analyzed. The best experiment has shown a very promising net collection efficiency of 45%. Conclusions were drawn from the three systems. Even though the ESP system has not met all the specifications, this preliminary study was successful.Finally, guidelines for the creation of a more efficient ESP, and for tests with pathogenic material, could be proposed.
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Ouloum, Ahmed. "Recherches sur les precipitations dans le haut atlas central (maroc)." Paris 4, 1989. http://www.theses.fr/1989PA040071.
Full textAbstract:
L'etude par des methodes statistiques des precipitations et leur repartition dans le temps et dans l'espace montagnard met en evidence le role de l'orientation des versants aux vents dominants. Les precipitations aux altitudes inferieures a mille cinq cent metres sont plus elevees sur le versant "sous le vent"; par contre, sur le versant "au vent", c'est l' inverse. Le resultat montre une heterogeneite plus grande dans la repartition des precipitations face aux vents d'ouest. Une des explications est que le haut atlas central, par son altitude considerable, constitue une barriere suffisante pour developper un climat d'abri dont l'apport des precipitations orographiques est l'un de ses propres aspectsResearch carried out through statistical methods on precipitations and how they are periodically distributed over mounta in areas shows the importance of orientation of mountain sides in relation to the prevailing winds. Below one thousand five hundred meters, precipitations are higher on the leeward side. However, it is just the opposite on the windward sid e. The results point to a greater heterogeneity in the distribution of precipitations on sides facing westerly winds. One of the explanation lies in the fact that the very height of the high atlas central range acts as a natural barrier helping to develop a sheltered climate. One of the distinctive characteristics of such a climate is precisely to bring u p orographical precipitations
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Obligis, Estelle. "Estimation des precipitations par radiometrie hyperfrequence pendant l'experience toga-coare." Paris 7, 1996. http://www.theses.fr/1996PA077106.
Full textAbstract:
On connait aujourd'hui le role enorme joue par les precipitations tropicales dans la circulation generale. Les tropiques etant couverts a 75% par les oceans, seules des etudes a partir de donnees satellitaires peuvent fournir une estimation globale des precipitations. La methode que nous proposons pour restituer les precipitations par radiometrie hyperfrequence satellitaire est basee sur un modele de transfert radiatif et sur une methode d'inversion simples. Elle presente donc l'avantage de tenir compte au mieux de l'ensemble des processus physiques intervenant dans le transfert radiatif atmospherique tout en conservant un temps calcul raisonnable. Cette methode a tout d'abord ete testee sur des donnees radiometriques aeroportees. Nous avons montre qu'il etait possible de restituer les principales structures de precipitations (air clair, precipitations convectives ou stratiformes). Nous l'avons ensuite appliquee a des donnees radiometriques satellitaires provenant du radiometre ssm/i. Malgre la grande difficulte que presente l'estimation des precipitations depuis l'espace, les champs de precipitations obtenus sont tout a fait coherents et ont pu etre valides a l'aide d'une methode de classification nuageuse. Enfin, une partie importante et originale de ce travail a consiste a ameliorer la physique du transfert radiatif du modele en etudiant l'influence de particules heterogenes et non spheriques sur les coefficients volumiques atmospheriques. Nous avons ainsi pu tester l'influence de la presence de la couche de fonte sur les temperatures de brillance issues du modele
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Roux, Frank. "Les lignes de grains de copt81 : environnement, precipitations, cinematique, thermodynamique." Paris 7, 1987. http://www.theses.fr/1987PA077154.
Full textAbstract:
Dans cette these sont etudiees 11 lignes de grains, ensembles de nuages convectifs alignes se deplacant sur l'afrique de l'ouest, observees au cours de l'experience copt81, conduite en mai/juin 1981 a korhogo dans le nord de la cote d'ivoire, et dont une caracteristique etait la presence des deux radars meteorologiques doppler ronsard. Le chapitre 1 est consacre aux methodologies radar. Apres une rapide revue des principes de la mesure et des procedures de traitement des donnees de vitesse, un developpement plus detaille est donne pour des methodes originales de restitutions thermodynamiques et de quantification des interactions avec l'environnement. Dans le chapitre 2, l'experience copt81 est replacee dans le cadre de la meteorologie tropicale et plus particulierement de l'afrique de l'ouest, ainsi que par rapport aux etudes anterieures d'observation et de modelisation des systemes convectifs mesoechelle. Les resultats de copt81 sont detailles dans le chapitre 3 par l'etude de l'environnement thermodynamique et cinematique, des caracteristiques communes et des particularites des 11 lignes de grains qui ont ete observees. Cet ensemble de resultats et les elements nouveaux qui ont pu etre deduits sont ensuite discutes, et des perspectives de developpements futurs sont evoques dans la conclusion