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Matthias, John Robert. "Quantum evaporation from superfluid helium." Thesis, University of Exeter, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390167.
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Beverley, Katharine Jane. "Evaporation of liquids from structured and non-structured mixtures." Thesis, University of Hull, 2004. http://hydra.hull.ac.uk/resources/hull:7039.
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The work presented in this thesis describes the evaporation rates of a wide variety of samples obtained under a controlled gas flow using a gravimetric technique. Evaporation rates for pure liquids with vapour pressures ranging from 0.1 to 500 Torr, water contained in silica particles, alkane/squalane mixtures, hexane gelled with silica particles, surfactant/water mixtures, immiscible layered liquid mixtures and emulsions have been determined. For pure liquids and simple unstructured liquid mixtures, the evaporation rate is limited by diffusion through a stagnant vapour layer at the liquid surface. As the degree of structure within the liquid mixture increases, the time taken for concentration gradients developing in the evaporation process to relax becomes longer relative to the time taken for diffusion through the stagnant vapour layer. For highly structured liquid mixtures, the rate limiting process switches to diffusion and convection within the liquid mixture. In the case of creamed oil-in-water emulsions, evaporation of the continuous water phase is limited by diffusion through the stagnant vapour layer, whilst the evaporation rate of the emulsified oil is consistent with a mechanism in which the oil drops remain separated from the vapour phase by a thin water film. Oil transport from the drops to the vapour occurs by diffusion of dissolved oil across this film.
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Thomas, Angeli Elizabeth. "Mathematical modelling of evaporation mechanisms and instabilities in cryogenic liquids." Thesis, University of Southampton, 1999. https://eprints.soton.ac.uk/50640/.
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In this thesis we propose a model for laminar natural convection within a mixture of two cryogenic fluids with preferential evaporation. This full model was developed after a number of smaller models of the behaviour of the surface of the fluid had been examined. Throughout we make careful comparison between our analytical and computational work and existing experimental and theoretical results. The coupled differential equations for the main model were solved using an explicit upwind scheme for the vorticity-transport, temperature and concentration equations and the multigrid method for the Poisson equation. From plots of the evolution of the system, it is found that convection becomes stronger when preferential evaporation is included. This new model demonstrates how to include preferential evaporation, and can be applied to other fluid systems.
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Coffman, Chase Spenser. "Electrically-assisted evaporation of charged fluids : fundamental modeling and studies on ionic liquids." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103421.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 243-250).
Electrosprays of the pure-ion variety embody a unique collection of attributes that have compelled interest in derivative technologies across a spectrum of applications ranging from Focused Ion Beams (FIB) to microrocketry. Unlike conventional colloid sources (i.e., so-called cone-jets or others sources from which droplets typically emanate), pure ion sprays are commonly characterized by narrow distributions of high specific charge and nominal energy deficits as a result of their evaporative mechanisms. Among other properties of the spray, these are known to enable well-behaved optics (e.g. for nanometric patterning with FIB) and low power overhead (e.g. for efficient electrical-to-kinetic energy transduction in microrocketry) while also providing for innate simplicity and spatial compactness. In spite of their potential for paradigm-shifting impact, the practicality of contemporary pure-ion sources has been tempered by issues relating to reliability and predictability. In contrast to droplet emission, for example, empirical studies strongly suggest that pure-ion modes are only permissible under special sets of circumstances and that important beam qualities (namely the stability but also the current) are sensitive functions of the meniscus configuration. The difficulty in controlling these modes is somewhat abated through the use of fluids like ionic liquids (IL), particularly in connection with several heuristics that have emerged, but the process remains substantially fickle. This is believed to owe most directly to an undeveloped physical understanding. While the physics that govern conventional colloid sources are at least functionally understood at this point, an analogous grasp of their ion relatives has proven elusive. The purpose of this thesis is to begin addressing this issue by way of rigorous theoretical investigations, with the ultimate aim of offering deeper fundamental insight and additional recourse to future design initiatives beyond the existing set of over-simplified heuristics. In this thesis we first conduct a survey of potential contributors to the very multi-physical phenomenon of charge evaporation and identify key influences through basic order-of-magnitude analyses. These are used to inform the formulation of a detailed mathematical framework that is subsequently leveraged in the exploration of evaporation behaviors for a prototypical ionic liquid meniscus across a range of field, media, and hydraulic conditions. The results uncover a previously uncharted family of highly-stressed but ostensibly stable solutions for the problem of a volumetrically-unconstrained source. These appear to be confined to a particular subregion of the global parameter space that emphasizes thoughtful sizing of the meniscus and architecting of the feeding system. The impedance aspect of the latter, in particular, is believed to play a critical role in steady emission when large scale disparities, which are common in practical settings, exist across the parent meniscus. Additional influences that are often neglected in the literature, such as that of the liquid permittivity, are also elucidated and shown to play meaningful roles in evaporation. We conclude by outlining a reasonably comprehensive set of conditions that should be met for steady emission and substantiate these with tangible evidence from our studies.
by Chase Coffman.
Ph. D.
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Tsoumpas, Ioannis. "Experimental study of the evaporation of sessile droplets of perfectly-wetting pure liquids." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209196.
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The study presented in this dissertation concerns the evaporation, in normal ambient conditions, of sessile droplets (pinned and freely receding) of various HFE liquids (instead of the widely used water), which are considered so far as environmentally friendly and are often used as heat-transfer fluids in thermal management applications. They are pure perfectly-wetting and volatile liquids with low thermal conductivity and high vapor density. These properties affect in their own way many aspects concerning droplet evaporation such as the evaporation-induced contact angles, evaporation rate of a droplet, contact line pinning and Marangoni flow, all of which are treated in the present dissertation.In general, the thesis starts with a general introduction including but not limited to sessile droplets (Chapter 1). In Chapter 2 we provide a general overview of capillarity-related concepts. Then, in Chapter 3 we present the interferometric setup, along with the liquids and the substrate that is used in the experiments, and also explain the reasons why this particular method is chosen. In Chapter 4 we address, among others, the issue of evaporation-induced contact angles under complete wetting conditions. The behavior of the global evaporation rate is also examined here, whereas in Chapter 5 we discuss the influence of thermocapillary stresses on the shape of strongly evaporating droplets. Finally, before concluding in Chapter 7, we address in Chapter 6 the still open question of the influence of non-equilibrium effects, such as evaporation, on the contact-line pinning at a sharp edge, a phenomenon usually described in the framework of equilibrium thermodynamics. The experimental results obtained are also compared with the predictions of existing theoretical models giving rise to interesting conclusions and promising perspectives for future research.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Todorova, Desislava V. "Modelling of dynamical effects related to the wettability and capillarity of simple and complex liquids." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13740.
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This Thesis explores physical phenomena characteristic for thin liquid films and small droplets of simple and complex liquids on solid substrates for which wettability and capillarity control their statical and dynamical properties. We start by discussing the general concepts of wettability and capillarity and introduce the common mathematical framework of the lubrication approximation for studies of thin liquid films and small contact angle drops. We demonstrate the derivation of the generic equation describing the evolution of a film of simple liquid from the Navier-Stokes equations. We show how this model can be further extended to incorporate various effects relevant to the case of complex liquids. The results described in the Thesis comprise three projects with the common main theme of the influence of wettability and capillarity on the statics and dynamics of the studied systems, namely (i) Evaporating sessile droplets fed through the solid substrate - a geometry that allows us to discuss steady states of the system and their role in the time evolution of freely evaporating droplets without influx in an isothermal case; (ii) The influence of a solute--dependent wettability on the stability, static and dynamical properties of thin films and drops of non-volatile mixtures, suspensions and solutions; (iii) A parameter-passing scheme between particle-based Molecular Dynamics simulations and the continuum lubrication model which allows us to discuss equilibrium properties of small polymeric droplets. We present the physical questions arising in the three systems and discuss approaches and results as well as possible extensions.
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Heinert, Carter J. "Hidden Involvement of Liquids and Gases in Electrostatic Charging." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case162312024539738.
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Down, Edward M. "Enhancement of plate heat exchanger performance using electric fields." Thesis, City University London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339994.
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Galvagno, Mariano. "Modelling of driven free surface liquid films." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/16574.
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In several types of coating processes a solid substrate is removed at a controlled velocity U from a liquid bath. The shape of the liquid meniscus and the thickness of the coating layer depend on U. These dependencies have to be understood in detail for non-volatile liquids to control the deposition of such a liquid and to lay the basis for the control in more complicated cases (volatile pure liquid, solution with volatile solvent). We study the case of non-volatile liquids employing a precursor film model that describes partial wettability with a Derjaguin (or disjoining) pressure. In particular, we focus on the relation of the deposition of (i) an ultrathin precursor film at small velocities and (ii) a macroscopic film of thickness h ∝ U^(2/3) (corresponding to the classical Landau Levich film). Depending on the plate inclination, four regimes are found for the change from case (i) to (ii). The different regimes and the transitions between them are analysed employing numerical continuation of steady states and saddle-node bifurcations and simulations in time. We discuss the relation of our results to results obtained with a slip model. In connection with evaporative processes, we will study the pinning of a droplet due to a sharp corner. The approach employs an evolution equation for the height profile of an evaporating thin film (small contact angle droplet) on a substrate with a rounded edge, and enables one to predict the dependence of the apparent contact angle on the position of the contact line. The calculations confirm experimental observations, namely that there exists a dynamically produced critical angle for depinning that increases with the evaporation rate. This suggests that one may introduce a simple modification of the Gibbs criterion for pinning that accounts for the non-equilibrium effect of evaporation.
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Forestier, Serge. "Etude de l’évaporation d’un liquide répandu au sol suite à la rupture d’un stockage industriel." Thesis, Saint-Etienne, EMSE, 2011. http://www.theses.fr/2011EMSE0625/document.
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Ce travail de thèse s'inscrit dans le cadre d'un projet de recherche entre le CEA et ARMINES (Centre LGEI/ Ecole des Mines d'Alès). Il vise à améliorer la connaissance des mécanismes physiques se produisant lorsque qu’une nappe de liquide (inflammable et/ou toxique stocké à pression atmosphérique) s’évapore suite à la rupture de son stockage. La démarche expérimentale employée consiste à réaliser un plan d'expériences visant à exprimer le débit d'évaporation initial d’une nappe sous différentes conditions initiales de température de liquide et de sol, sous différentes vitesse d’écoulement, de température d’air et selon différentes épaisseurs initiales de liquide. Les différents flux thermiques échangés entre la nappe et son environnement, la température de la nappe et le débit d'évaporation sont mesurés et quantifiés.Les débits d'évaporation expérimentaux sont confrontés à ceux prédits par les différentes corrélations disponibles dans la littérature. Deux analyses de sensibilité sont également réalisées sur ces corrélations et les résultats confrontés à ceux du plan d'expériences afin de vérifier si les corrélations attribuent le même poids aux différents paramètres expérimentaux que le phénomène en lui-même.Les relevés de température dans l'épaisseur de la nappe mettant en évidence la présence de cellules de convection naturelle est également étudiée. Par ailleurs, la température moyenne de la surface est déterminée à partir des différents flux thermiques échangés entre la nappe et son environnement.A l'aide des résultats obtenus, l'étude de plusieurs éléments a été réalisée: l’écart de prédiction sur les résultats des équations bilan thermique et massique selon la température employée pour les incrémenter, la nette différence de température entre la surface et le coeur du liquide, rarement prise en compte dans les modèles théoriques, le rôle prépondérant de la convection naturelle dans le phénomène d'évaporation.Un dernier chapitre étudie la dispersion de la température de surface (phénomène peu étudié dans la littérature) à l'aide d'une caméra thermique. Des zones de températures homogènes apparaissent alors dans le cas de l'essai mettant en oeuvre un écoulement de cavité au-dessus du liquide. La présence de différentes zones de température implique que la cinétique d’évaporation n’est pas uniforme sur la surface de la nappe. A partir de ces résultats, le coefficient de transfert de matière est étudié en fonction de la régression du niveau de liquide dans le bac et conclut à une diminution non modélisée par les corrélations existantesThis work belongs to a research project between CEA and ARMINE (LGEI center/ Ecole des Mines d’Alès). It aims at increasing comprehension of physical mechanism generating when a liquid pool (either flammable or toxic parked under atmospheric pressure) evaporates after loss of containment. An experimental design is realized in order to express some characteristics of evaporation phenomena (initial evaporation rate, steady evaporation rate and duration of unsteady evaporation rate) as a function of initial liquid and soil temperature, wind velocity, air temperature and initial liquid thickness. Heat fluxes exchanged between the pool and its environment are either measure or computed.Experimental evaporation rates are compared to those predicted by correlations available in the literature. Two sensitivity analyses are performed and their results are confronted to those from experimental design. It allows determining if the importance of the different experimental parameters is the same from the correlations to the phenomena itself.Temperature measurements in liquid thickness highlight the presence of natural convection cells. Besides, mean surface temperature is computed from measurements of heat fluxes exchanged between the pool and its environment. From the different results, several points are investigated: the shift between heat and mass balance equations according to the temperature employed to compute them the difference between the liquid bulk and liquid surface temperature, barely taken into account in correlations the noteworthy role of natural convection in the evaporation phenomena.A last chapter studies the surface temperature distribution thanks to an infrared thermometer. Homogeneous temperatures areas appear in the case of cavity flows. The presence of different temperature areas implies that evaporation kinematic in not uniform in the whole surface. From these result the mass transfer coefficient is studied as a function of the step height between the top of the cavity and the liquid surface. It concludes to a mass transfer coefficient decrease non modeled by the different correlations in the literature
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Frauendorf, Stefan. "Evaporation Rates for Liquid Clusters." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-32079.
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Mujahid, Raqibul I. "Evaporation of liquid fuel droplet." abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1460767.
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Frauendorf, Stefan. "Evaporation Rates for Liquid Clusters." Forschungszentrum Rossendorf, 1995. https://hzdr.qucosa.de/id/qucosa%3A22035.
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Saenz, Pedro Javier. "Evaporation of liquid layers and drops." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/9980.
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This thesis focuses on investigating the stability, dynamics and physical mechanisms of thermocapillary flows undergoing phase change by means of direct numerical simulations and experiments. The novelty of the general approach developed in this work lies in the fact that the problems under consideration are addressed with novel fully-coupled transient two-phase flow models in 3D. Traditional simplifications are avoided by accounting for deformable interfaces and by addressing advection-diffusion mechanisms not only in the liquid but also in the gas. This strategy enables a realistic investigation of the interface energy and mass transfer at a local scale for the first time. Thorough validations of the models against theory and experiments are presented. The thesis encompasses three situations in detail: liquid layers in saturated environments, liquid layers in unsaturated environments and evaporation of liquid droplets. Firstly, a model grounded in the volume-of-fluid method is developed to study the stability of laterally-heated liquid layers under saturated environments. In this configuration, the planar layer is naturally vulnerable to the formation of an oscillatory regime characterized by a myriad of thermal wave-like patterns propagating along the gas-liquid interface, i.e. hydrothermal waves. The nonlinear growth of the instabilities is discussed extensively along with the final bulk flow for both the liquid and gas phases. Previously unknown interface deformations, i.e. physical waves, induced by, and enslaved to, the hydrothermal waves are reported. The mechanism of heat transfer across the interface is found to contradict previous single-phase studies since the travelling nature of the hydrothermal waves leads to maximum heat fluxes not at the points of extreme temperatures but somewhere in between. The model for saturated environments is extended in a second stage to assess the effect of phase change in the hydrothermal waves for the first time. New numerical results reveal that evaporation affects the thermocapillary instabilities in two ways: the latent energy required during the process tends to inhibit the hydrothermal waves while the accompanying level reduction enhances the physical waves by minimizing the role of gravity. Interestingly, the hydrothermal-wave-induced convective patterns in the gas decouple the interface vapour concentration with that in the bulk of the gas leading to the formation of high (low) concentrations of vapour at a certain distance above interface cold (hot) spots. At the interface the behavior is the opposite. The phase-change mechanism for stable layers is also discussed. The Marangoni effect plays a major role in the vapour distribution and local evaporation flux and can lead to the inversion of phase-change process, i.e. the thermocapillary flow can result into local condensation in an otherwise evaporating liquid layer. The third problem discussed in this thesis concerns with the analysis of evaporating sessile droplets by means of both experiments and 3D numerical modeling. An experimental apparatus is designed to study the evaporation process of water droplets on superheated substrates in controlled nitrogen environments. The droplets are simultaneously recorded with a CCD camera from the side and with an infrared camera from top. It is found that the contact line initially remains pinned for at least 70% of the time, period after which its behaviour changes to that of the stick-slip mode and the drop dries undergoing contact line jumps. For lower temperatures an intermediate stage has been observed wherein the drop evaporates according to a combined mode. The experimental work is complemented with numerical simulations. A new model implementing the diffuse-interface method has been developed to solve the more complex problems of this configuration, especially those associated with the intricate contact-line dynamics. Further insights into the two-phase flow dynamics have been provided as well as into the initial transient stage, in which the Marangoni effect has been found to play a major role in the droplet heating. For the first time, a fully-coupled two-phase direct numerical simulations of sessile drops with a moving contact line has been performed. The last part of this work has been devoted to the investigation of three-dimensional phenomena on drops with irregular contact area. Non-sphericity leads to complex three-dimensional drop shapes with intricate contract angle distributions along the triple line. The evaporation rate is found to be affected by 3D features as well as the bulk flow, which become completely non-axisymmetric. To the best of our knowledge, this work is the first time that three-dimensional two-phase direct numerical simulations of evaporating sessile drops have been undertaken.
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Shukla, Pranav. "Inducing Liquid Evaporation with Hygroscopic Gels." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/101555.
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Mammals secrete fluids from the sweat glands known as perspiration which helps in thermoregulation. However, sweat can interfere with vision, comfort, grip, and results in malodor due to bacterial action. To combat the aforementioned issues, antiperspirants are widely used personal hygiene products to stop the sweat by blocking the sweat glands. Typically, aluminum salts present in the antiperspirants dissolve in the sweat and create a temporary plug to cut the flow of sweat. However, there has been a long debate going on the safety concerns of aluminum-based antiperspirants. Although there is no concrete evidence to prove the carcinogenicity of aluminum, various studies have also shown that long exposure to aluminum can lead to breast cancer in women. Hence there is a potential need to find aluminum-free alternatives for antiperspirants. Consumers are also showing an increased demand for more natural cosmetic products. The current study presents a novel aluminum-free the hygroscopic gel which can potentially serve as an antiperspirant. A synthetic sweat duct has been developed to mimic the sweating behavior of humans and to test the synthesized gels. Hygroscopic materials readily absorb and/or adsorb water from a humid environment. The hygroscopic gel can cause long-range evaporation of water from the sweat leading to
crystallization of minerals which can ultimately clog the sweat duct and prevent sweating.Master of Science
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Goedecke, Nils. "Evaporation-driven liquid flow in micro channels." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417369.
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Sutter, Benjamin. "Étude de l'évaporation d'aérosols liquides semi-volatils collectés sur médias fibreux." Thesis, Vandoeuvre-les-Nancy, INPL, 2009. http://www.theses.fr/2009INPL067N/document.
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Cette étude s’inscrit dans le cadre de l’amélioration des connaissances liées à l’évaporation d’aérosols liquides semi-volatils collectés sur des filtres à fibres. Le phénomène d’évaporation d’aérosols collectés sur médias fibreux induit des problèmes de sécurité avec notamment une surexposition des salariés aux vapeurs, à l’aval des systèmes généraux de filtration de l’air. De plus, lors des contrôles des concentrations atmosphériques des aérosols, l’évaporation induit une sous-estimation de la phase particulaire de l’aérosol prélevé qui est problématique en termes de prévention de l’exposition. L’objectif de ces travaux a donc été de produire de nombreux résultats expérimentaux afin, d’une part, de compléter les rares présents dans la littérature et, d’autre part, d’améliorer les modèles théoriques développés précédemment. Deux approches expérimentales ont été menées afin d’identifier le processus d’évaporation d’un aérosol collecté. La première, nommée approche globale, permet de suivre l’évaporation de l’aérosol par la quantification des vapeurs à l’aval du filtre, au cours du temps. La seconde, nommée approche microscopique, étudie l’évaporation de gouttes collectées sur les fibres d’une fibre à l’échelle microscopique. Les deux approches réalisées lors de ces travaux s’accordent sur le fait que l’évaporation d’un aérosol liquide semi-volatil ne peut être modélisée par les modèles proposés par la littérature. Des hypothèses ont été avancées afin d’expliquer la divergence de cinétique d’évaporation entre la théorie et les expérimentationsThis study falls within the scope of improving knowledge concerning evaporation of semi-volatile liquid aerosols collected on fibrous filters. Under these conditions, the aerosol evaporation phenomenon causes problems of safety, in particular over-exposure of employees to vapours downstream of general air filtering systems. Furthermore, when controlling aerosol atmospheric concentrations, evaporation results in under-estimation of the sampled aerosol particle phase and this is clearly problematic in exposure prevention terms. The aim of this work was therefore to record a large number of experimental data, both to make up for their scarcity in the literature and to improve previously developed theoretical models. Two experimental approaches were implemented to identify the evaporation process for a collected aerosol. The first, termed the global approach, allowed us to monitor aerosol evaporation by measuring vapour quantity downstream of the filter with respect to time. The second, microscopic, approach considers evaporation of droplets collected on the filter fibres on a microscopic scale. The two approaches implemented during this research lead to agreement on the fact that evaporation of a liquid semi-volatile aerosol cannot be satisfactorily represented by the theoretical models proposed in the literature. Hypotheses are advanced to explain the divergence in evaporation kinetics between theoretical and experimental work
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Fang, Gang. "Rate of liquid evaporation, statistical rate theory approach." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0001/NQ35153.pdf.
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Howell, Aaron W. "Evaporation and disintegration of heated thin liquid sheets." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53861.
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In this study, a numerical model is used to investigate the evaporation and flow characteristics of heated liquid sheets and films. The liquid is modeled as water and as black liquor, a byproduct produced by paper mills. In the pulping process, black liquor is concentrated in an evaporator as a falling film. The effectiveness of the evaporator is reduced due to fouling on heat transfer surfaces.
Two flow arrangements are studied: falling films, where the liquor and steam are separated by a heat transfer surface; and liquid curtains, which is a thin sheet of liquid falling due to gravity surrounded by steam. For the liquid curtain, the liquid and gas come into direct contact, therefore there is no place for fouling to occur allowing for a more consistent operation of the evaporator. This type of arrangement is not currently used in paper mills but is being investigated in this work to determine its feasibility.
The fluid system is simulated using the finite volume method with a single-fluid field to capture the liquid-gas interface. This study investigates how the breakup of a liquid curtain is affected by flow parameters and how the breakup into droplets influences the evaporation characteristics of the liquid curtain.
It is found that the falling film evaporator has a much higher liquid evaporation rate than evaporating as a liquid curtain. However the falling film evaporator has an entrance length with no evaporation, and liquid curtains allow for evaporation to start occurring very near the inlet. If reducing length of the evaporator is a priority, liquid curtain evaporators can obtain a higher evaporation rate than falling films within the same distance.
Falling film evaporation has a higher steam efficiency than a liquid curtain evaporator. However, for short evaporator lengths the rate at which water is removed from a liquid curtain evaporator is much greater, but at the cost of a higher steam consumption rate.
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Doro, Emmanuel O. "Computational modeling of falling liquid film free surface evaporation." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44812.
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A computational model is developed to investigate fundamental flow physics and transport phenomena of evaporating wavy-laminar falling liquid films of water and black liquor. The computational model is formulated from first principles based on the conservation laws for mass, momentum, energy and species in addition to a phase transport equation for capturing interface deformation and evolution. Free surface waves are generated by monochromatic perturbation of velocity. Continuum models for interfacial evaporation define source terms for liquid vaporization and species enrichment in the conservation laws. A phenomenological crystallization model is derived to account for species depletion due to salt precipitation during black liquor falling film evaporation. Using highly resolved numerical grids on parallel computers, the computational model is implemented to analyze the dynamics of capillary separation eddies in low Reynolds number falling films, investigate the dominant mechanisms of heat transfer enhancement in falling films at moderately high Reynolds numbers and study the fundamental wave structures and wave induced transport in black liquor falling films on flat and cylindrical walls. From simulation results, a theory based on the dynamics of wavefront streamwise pressure gradient is proposed to explain interfacial waves interaction that give rise to multiple backflow regions in films dominated by solitary-capillary waves. The study shows that the mechanism of heat transfer enhancement in moderately high Reynolds number films follows from relatively lower conduction thermal resistance and higher crosswise convective transport at newly formed intermediate wavefronts. Interfacial phenomena such as wave-breaking and vapor entrainment observed in black liquor falling films is explained in terms of a mechanistic theory based on evolution of secondary instabilities and large amplitude wave force imbalances.
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Crafton, Elyssa Farah. "Measurements of the evaporation rates of heated liquid droplets." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17589.
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Brown, Mark Gregory. "The boundary conditions for quantum evaporation in liquid '4He." Thesis, University of Exeter, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277101.
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Booth, Alexander John. "A novel, biomimetically inspired, flash evaporation liquid atomization system." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.713482.
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The increasing demands placed on conventional methods of liquid atomization, in terms of spray quality, now mean that there is a need for a new, disruptive, liquid atomization technology which can rapidly improve spray performance to meet the growing sophistication required of modern liquid spray systems. This thesis details an investigation into the mode of action of a liquid atomization system (pMISTe) which shows promise to be able to provide this disruptive new spray technology. Influenced by the defence mechanism of the bombardier beetle, this atomization method produces a large amount of volumetric shear in a body of liquid, by inducing a flash evaporation of a proportion of the total liquid mass in an enclosed chamber. The flash evaporation is created firstly by heating the liquid far above its saturation temperature at an ambient external pressure - in a chamber cavity sealed by an electronically controlled ejection valve. This valve is released very rapidly, causing the liquid in the chamber to suddenly `see' the ambient external pressure. It is this sudden exposure of a superheated liquid to the low external ambient pressure that drives the flash evaporation and the atomisation. The atomization system was investigated using a staged experimental method, including a mixture of Taguchi Design of Experiment (DoE) and full factorial techniques. From these investigations the main characteristics of the mode of action of the system were identified. These were that, in general, increases in chamber liquid temperature caused decreasing average droplet size, and that increases in refill flow rate caused increasing droplet size; due to the primary flash evaporation mechanism. In addition more complex secondary behaviours, attributed to the fluid dynamic properties of the system, were discovered. The performance of the system is also discussed with reference to its suitability for a range of spray applications
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Tolonen, Erik. "Evaporation Characteristics of a Liquid Bio-Fuel from Chicken Litter." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26060.
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Alternative fuels are becoming more important as fossil fuels become more expensive. This thesis describes the production and properties of a bio-oil produced from waste biomass, in this case chicken litter. A higher quality fuel was produced through thermal and chemical upgrading of the raw bio-oil; this fuel is similar in some respects to fossil fuels, as it has a high hydrocarbon content and energy density comparable to gasoline.
Combustion of liquid fuels commonly occurs in clouds of droplets, and studying the evaporation of single liquid drops provides information on the evaporation characteristics of the fuel as a whole. Droplet evaporation tests on the chicken litter fuel were carried out using the suspended droplet/moving furnace technique. For some tests, a fine wire thermocouple was used as the droplet suspension in order to measure the distillation characteristics of the fuel. An existing computational model based on continuous ther- modynamics was used to model the evaporation of the fuel. The modelled composition of the fuel was based on an existing pyrolysis field ionization mass spectrometry (Py-FIMS) analysis and used five major groups of compounds. The properties for these groups re- quired for the model were determined using several prediction methods and the values then used in a numerical model.
Model predictions of droplet temperatures calculated for the fuel showed good agree- ment with the measured temperatures, indicating that the modelled composition gave an accurate picture of the fuel. Droplet evaporation histories also agreed well with mea- surements, but were not capable of reproducing the observed disruption of the droplet produced by internal boiling at higher temperatures, nor the formation of a solid residue at the end of evaporation. Further enhancements to the model should allow the prediction of residue formation.Model predictions of droplet temperatures calculated for the fuel showed good agree- ment with the measured temperatures, indicating that the modelled composition gave an accurate picture of the fuel. Droplet evaporation histories also agreed well with mea- surements, but were not capable of reproducing the observed disruption of the droplet produced by internal boiling at higher temperatures, nor the formation of a solid residue at the end of evaporation. Further enhancements to the model should allow the prediction of residue formation.
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Gajcowski, Edward J. "Transient model for liquid droplets evaporating from heated solid surfaces." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/17383.
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Semenov, Sergey. "Computer simulations of evaporation of sessile liquid droplets on solid substrates." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10277.
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Present work is focused on the numerical study of evaporation of sessile liquid droplets on top of smooth solid substrates. The process of evaporation of a sessile liquid droplet has lots of different applications both in industry and research area. This process has been under study for many years, and still it is an actual problem, solution of which can give answers on some fundamental and practical questions. Instantaneous distribution of mass and heat fluxes inside and outside of an evaporating sessile droplet is studied in this research using computer simulations. The deduced dependences of instantaneous fluxes are applied for self-consistent calculations of time evolution of evaporating sessile droplets. The proposed theory of evaporating sessile droplets of liquid has been validated against available experimental data, and has shown a good agreement. Evaporation of surfactant solution droplets is studied experimentally. The theory, proposed for two stages of evaporation, fits experimental data well. An additional evaporation stage, specific for surfactant solutions, is observed and described. Mathematical modelling of this stage requires further research on surfactant adsorption and its influence on the value of receding contact angle. Numerical study of the evaporation of microdroplets is conducted in order to evaluate the significance of different evaporation mechanisms (diffusive and kinetic models of evaporation) and different physical phenomena (Kelvin s equation, latent heat of vaporization, thermal Marangoni convection, Stefan flow).
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Chen, Chen. "Evaporation au sein de systèmes microfluidiques : des structures capillaires à gradient d'ouverture aux spirales phyllotaxiques." Thesis, Toulouse, INSA, 2016. http://www.theses.fr/2016ISAT0020/document.
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Les effets capillaires sont très courant dans la Nature. Dans le contexte du séchage de milieux poreux dont la taille de pore est dans la gamme micromètre-millimètre, ils jouent un effet dominant en contrôlant la répartition des phases (liquide-vapeur) dans l’espace poral, au fur et a` mesure que le séchage se produit. L’idée du présent travail est d’étudier le séchage d’un fluide pur et mouillant dans des micromodèles, c’est-à-dire des milieux poreux modèles quasi-2D et micro-fabriqués. Nous présentons des résultats obtenus pour différentes géométries. Typiquement, les micromodèles utilisés sont constitués de réseaux de cylindres pris en sandwich entre deux plaques. La distribution des phases et le taux d’évaporation dans de tels micromodèles peuvent être aisément mesurés par visualisation directe puis traitement d’images.En jouant sur l’arrangement spatial des cylindres, on obtient dans un premier temps des micromodèles pour lesquels le taux de séchage est quasi-constant, depuis le début de l’expérience de séchage jusqu’à l’évaporation totale du liquide saturant initialement le système. Typiquement, cette situation est obtenue quand la taille des pores décroît en allant du centre du micromodèle vers sa périphérie (les micromodèles sont axisymmétriques). Au contraire, quand la taille des pores croît du centre vers la périphérie, l’invasion d’un front de séchage stable est observée, d’ou` un temps de séchage total bien supérieur.Nous avons aussi réalisé un autre type de microsystèmes, au sein duquel les cylindres sont arrangés en spirale de Fibonacci, en nous inspirant de motifs observés en phillotaxie. Dans de tels systèmes, des films liquides épais se développent le long des spirales, au cours du séchage, et jouent un rôle crucial dans la cinétique d’évaporation. Cette situation rappelle celle déjà étudiée par Chauvet dans des tubes capillaires de section carrée. Cependant, elle est plus complexe, de par la nature poreuse du micromodèle (alors qu’un tube capillaire, tel qu’étudié par Chauvet, peut être vu comme un pore unique) et parce que les films liquides y ont une forme plus complexe. Pour de tels systèmes, nous présentons des résultats expérimentaux quantifiant l’effet des films liquides sur la cinétique de séchage, en lien avec des prédictions théoriques issues d’un modèle de séchage visco-capillaire. Un tel modèle nécessite l’utilisation du logiciel Surface Evolver pour modéliser la forme des films liquides, couplée avec des simulations directes de l’écoulement de Stokes dans les films liquides, pour y calculer la résistance visqueuse a` l’écoulement induit par l’évaporation.Enfin, dans un dernier chapitre, plusieurs expériences d’évaporation sont conduites sur des micromodèles déformables. Des effets élasto-capillaires peuvent en effet induire des changements de géométrie de l’espace poral en cours d’évaporation, ce qui, comme vu précédemment, peut affecter la distribution des phases et la cinétique de séchageCapillarity is a common phenomenon encountered in Nature. In the context of the drying of porous media with pore size in the micrometer-millimeter size range, capillary effects play a dominant role in controlling the phases (liquid or vapor) distribution in the pore space as drying occurs. The basic idea of the present work is to study the drying of pure, wetting fluids in micro-fabricated, quasi-2D, model porous media (hereafter called micromodels). We present results obtained for different micromodel geometries. Typically, the micromodels used consist of arrangements of cylinders sandwiched between a top and bottom plate. Phases distribution and evaporation rates in such micromodels can easily be measured by direct visualizations and subsequent image processing.By tuning the cylinders pattern, one can first obtain micromodels for which the drying rate is almost constant, from the beginning of the drying experiment to the total evaporation of the liquid initially filling the system. Typically, this situation is obtained when the pores size decreases from the micromodel center to the periphery (the micromodels are axisymmetric). On the contrary, when the pores size increases from the center to the periphery, invasion of a stable drying front is observed, resulting in a much longer total drying time.We also designed another type of micromodel where the cylinders are arranged in a Fibonacci spiral pattern, a design inspired by phyllotaxic structure. In such systems, thick liquid films develop along the spirals during drying and play a key role in the drying kinetics. This situation is reminiscent of that already studied by Chauvet in capillary tubes with square cross-sections. However, it is more complex because of the porous nature of the micromodel (whereas a single capillary tube, as studied by Chauvet, can be viewed as a unique pore), and because of the much more complex liquid films shapes. For such systems, we present some experimental results on the liquid films effects on the drying kinetics, together with theoretical prediction, based on a visco-capillary drying model. Such a modelling requires the use of the Surface Evolver software to model the film shape, coupled with DNS simulations of the Stokes flow within the liquid films to compute the viscous resistance to the evaporation-induced flow.Finally, as a last part of this thesis, several evaporation experiments performed on deformable micromodels are presented. This preliminary work aims at reaching a situation where elasto-capillary effects modify the pore space geometry during evaporation. This, as seen above, should in turn alter the phase distribution during evaporation and the drying kinetics
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Naillon, Antoine. "Écoulements liquide-gaz, évaporation, cristallisation dans les milieux micro et nanoporeux : études à partir de systèmes modèles micro et nanofluidiques." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17681/1/Naillon.pdf.
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Les écoulements en milieux poreux sont omniprésents tant dans la nature que dans l'industrie. Les travaux menés dans cette thèse ont pour objectif d’étudier ces écoulements en présence de liquide et de gaz. Cela correspond aux situations d'imbibition (ou invasion capillaire), de drainage (ou déplacement d'un fluide mouillant par la mise en pression d'un fluide non mouillant), et d'évaporation (ou de séchage). L'étude se base sur l'utilisation de systèmes modèles artificiels. Une première partie de ce travail se concentre sur les écoulements liquide-gaz dans les milieux dont la taille des pores est inférieure à 100 nm. Ces milieux sont dits nanoporeux. A cette échelle, différents phénomènes sont susceptibles de modifier les écoulements liquide-gaz par rapport à ce qui est observé à l’échelle micrométrique : accrochage de la ligne de contact, pression fortement négative en phase liquide ou cavitation par exemple. Des expériences sont donc nécessaires pour mieux caractériser ces écoulements. En parallèle, les récents progrès en nanofabrication permettent d’obtenir des systèmes dont la profondeur peut descendre jusqu’à quelques nanomètres. Cette approche, désormais classique à plus grande échelle, nous fournit un outil innovant pour étudier les écoulements dans des milieux nanoporeux modèles, en deux dimensions. Un atout évident de ce type de modèles est qu'ils permettent une visualisation directe des deux phases, liquide et gaz. Des dispositifs nanofluidiques en silicium-verre et à profondeur constante ont été réalisés dans la gamme 20-500 nm. Un nouveau procédé de nanofabrication basé sur une lithographie laser à niveau de gris a été développé afin d’obtenir des dispositifs à profondeurs variables en une seule étape. Les expériences d'imbibition et un modèle théorique ont mis en avant que la pressurisation du gaz accélère son transport dans le liquide. Ensuite, des expériences de drainage ont été réalisées dans des dispositifs nanofluidiques avec des pressions de l’ordre de 20 bars. Des simulations sur réseau de pores utilisant l’algorithme de percolation d'invasion ont montré que les motifs d'invasion expérimentaux correspondaient à ce qui était attendu à l’échelle micrométrique pour des écoulements à faible nombre capillaire. Enfin, l'évaporation en nanocanaux a révélé des cinétiques intéressantes d'apparition et de croissance de bulles dans le liquide. Une ouverture est faite sur l'intérêt de poursuivre ces études dans des systèmes déformables. La deuxième partie de cette thèse s'est focalisée sur la cristallisation du chlorure de sodium à l'échelle d’un pore micrométrique. Dans le cas particulier du séchage d'une solution de sel, l'évaporation amène à la cristallisation des espèces dissoutes. Ce phénomène est largement impliqué dans la problématique de la conservation des oeuvres d'arts ou de la détérioration précoce des édifices. Les mécanismes qui conduisent à la génération de contraintes par un cristal sur une paroi, appelée pression de cristallisation, ne sont pas encore admis tant à l’échelle macro que microscopique. Des déformations induites par la cristallisation du sel ont été observées dans des dispositifs microfluidiques verre-polymère (PDMS). La vitesse de croissance d’un cristal a été mesurée à haute cadence d'acquisition, aboutissant à une nouvelle valeur de la constante de cinétique de réaction, supérieure d'un à deux ordres de grandeur aux données de la littérature. Un modèle numérique prédit l'évolution du champ de concentration en sel dissous lors de la croissance du cristal. Complété par une analyse théorique qui a mis en avant un nombre de Damkhöler prenant en compte les propriétés de transport et la taille du pore, il a permis de construire un diagramme de phase qui traduit les conditions favorables à la génération de contraintes par un cristal sur une paroi. Enfin, un mécanisme de génération de contraintes négatives entraînant la fermeture du pore a été observé.
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Borgetto, Nicolas. "Étude expérimentale du comportement et de l’évaporation d’un film liquide combustible en présence d’une flamme." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0106/document.
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L'évolution des stratégies d'injection du combustible dans les moteurs automobiles a fait apparaître de nouvelles problématiques. Parmi celles-ci, l'existence d'un dépôt de carburant sur les parois de la chambre de combustion a un impact sur les performances environnementales du moteur. En effet, l'évaporation de ce film liquide en proche paroi ne peut qu'influencer de manière sensible la phase de combustion. L'objectif de ce travail était de mettre en place une configuration académique maîtrisée et les diagnostics nécessaires à une première analyse phénoménologique du comportement et de l'évaporation d'un film liquide combustible déposé sur une paroi interagissant avec la combustion en phase gazeuse. L'approche expérimentale choisie a permis de générer un dépôt d'heptane liquide contrôlé sur une paroi verticale. Celle-ci est positionnée dans un écoulement ascendant de prémélange air/méthane dans lequel une flamme oblique est stabilisée sur un barreau. En parallèle, un diagnostic de mesure a été développé pour étudier les propriétés du film. Ce système d'interférométrie à faible cohérence a permis de réaliser une mesure locale simultanée de la température de paroi et de l'épaisseur du film en présence de l'écoulement réactif. Dans un premier temps, l'étude de configurations non réactives a permis de préciser les caractéristiques du film et de son évaporation, lorsque celui-ci s'écoule à contre-courant de l'écoulement gazeux. Plusieurs comportements types ont été mis en évidence et analysés. En présence de la flamme, une première approche a été consacrée à l'évolution des mécanismes qui influencent l'évaporation du film et son comportement par rapport au cas non réactif. Enfin, une analyse phénoménologique de l'impact de l'évaporation au sein de la couche limite sur les caractéristiques du front de flamme a été menée. Celle-ci a permis de mettre en évidence l'effet rétroactif de ce dernier sur le mélange des vapeurs, et une forte diversité des zones réactionnelles dans l'espaceThe evolution of fuel injection strategies in automobile engines has brought about new problem sets in their design and optimization. Among these, is the deposition of liquid fuel on the inner walls of the combustion chamber, impacting the environmental performance of the engine. Indeed, evaporation of the liquid film near the wall can significantly influence combustion. The aim of this work was to develop a controllable experimental configuration along with the necessary diagnostics for a first phenomenological analysis of the behaviour and evaporation of a liquid fuel film deposited on a wall as it interacts with gas phase combustion. The chosen experimental approach allowed the generation a liquid film of heptane on a vertical wall that is positioned within an upward flowing lean premixed methane/air mixture with a rod stabilised oblique V-flame. In parallel, a low coherence interferometry diagnostic system was developed to study the properties of the heptane film, permitting simultaneous measurements of the local wall temperature and film thickness in the presence of a reacting flow. Initially, the properties of the film and its evaporation were studied under non reacting conditions in a counter-current gas flow configuration. Several typical trends were identified and analyzed. In the presence of the flame, the change in physical mechanisms that influence the evaporation and behaviour of the film was evaluated by comparing results to the non reacting case. Phenomenological analysis was then conducted on the impact of film evaporation within the velocity boundary layer on the properties of the flame front. A retroactive effect of the flame front on the mass transfer of heptane gas was observed and a significant spatial variation of reaction zones reported
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Sellers, Sally M. "Heat transfer resulting from the evaporation of liquid droplets on a horizontal heated surface." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17993.
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Chauvet, Fabien. "Effet des films liquides en évaporation." Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT062H/document.
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Ce travail est axé sur l'étude de l'évaporation lente d'un liquide confiné dans un tube capillaire de section carrée, en lien avec l'étude du phénomène de séchage. Dans un tel capillaire, si le liquide est suffisamment mouillant, des films liquides se forment par capillarité le long des coins internes. L'évaporation du liquide en sommet de film engendre un pompage capillaire et l'espèce volatile est alors transportée, sous phase liquide, au plus près du sommet du capillaire. Ce mode de transport dépend de la compétition entre les effets capillaires et les effets visqueux et de gravité qui s'opposent tous deux au mouvement du liquide vers le sommet du capillaire. Ces films liquides sont étudiés en adoptant une approche expérimentale. Le principe des expériences est de laisser un liquide volatil s'évaporer dans un tube capillaire carré. Plusieurs expériences d'évaporation sont réalisées en faisant varier la nature du liquide, la taille du capillaire et son orientation (horizontale et verticale). Une méthode de thermographie infra-rouge permet de mesurer le profil de température le long du capillaire. Le refroidissement induit par le changement de phase liquide-vapeur ainsi que sa position sont alors mesurables. A partir d'une méthode de visualisation par ombroscopie, plusieurs grandeurs sont mesurées : position du ménisque principal, taux d'évaporation et épaisseur relative des films. En s'appuyant sur une analyse simple du transfert de masse, on montre alors que les cinétiques d'évaporation obtenues expérimentalement se divisent en trois principales phases caractéristiques, ressemblant fortement aux trois périodes de la cinétique classique de séchage des milieux poreux capillaires. L'analyse de l'hydrodynamique des films montre qu'il est indispensable de prendre en compte l'arrondi interne des coins des capillaires dans la modélisation de l'écoulement au sein des films. On montre notamment que le phénomène étudié est très sensible à ce paramètre, qui limite l'extension des films. Ce travail expérimental a permis de développer une modélisation du transfert de masse dans la configuration étudiée, couplée à une modélisation de l'écoulement des films, et finalement de proposer un modèle de séchage d'un capillaire carré quantitativement satisfaisantIn connection with the study of the phenomenon of drying, this work focuses on the study of slow evaporation of a liquid confined in a capillary of square cross section. In such a capillary, if the liquid wetting contact angle is low enough, liquid films are trapped by capillary forces along the capillary inside corners. Evaporation of the liquid at the film top creates a capillary pumping. The volatile species is then transported in liquid phase to the top of the capillary. This efficient mode of transport depends on the competition between the effects of capillarity and the effects of viscosity and gravity both opposing to the liquid flow towards the top of the capillary. In this work, the liquid films are studied experimentally.The principle of the experiments is to leave a volatile liquid evaporate in a square capillary tube. Several evaporation experiments are conducted, varying the liquid, the capillary tube size and its orientation (horizontal and vertical). An infrared thermography method allows to measure the temperature profile along the capillary. The cooling induced by the liquid-vapor phase change and its location is then measured. Owing to an ombroscopy visualization method, the location of the bulk meniscus, the evaporation rate and the relative thickness of the films can be measured. The experimental results show that the evaporation kinetics is similar to the drying kinetics of capillary porous media. This finding allows to study evaporation in a square capillary by analogy with the study of drying of capillary porous media. Based on a simple analysis of mass transfer in the system, it is then shown that the evaporation kinetics obtained experimentally can be divided into three main characteristic phases. The analysis of the hydrodynamic of the films shows that it is essential to take into account the roundeness of the capillary tube inside corners in the modelling of the flow in the films. We show that the phenomenon studied is very sensitive to the degree of roundedness of the tube internal corners, which limits the extension of the films. Modelling of the mass transfer coupled with modelling the film flow lead to a quantitatively satisfactory model of the drying of a square capillary tube
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Cline, Donna MacGrath. "Chemical and evaporative behaviors of synthetic liquid nuclear waste." FIU Digital Commons, 1991. http://digitalcommons.fiu.edu/etd/2390.
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In the 1960's the Department of Energy at Oak Ridge National Laboratory designed eight 50,000 gallon storage tanks for the liquid nuclear waste. Each tank was designed with its own ventilation system to purge radiolytic hydrogen and oxygen from the tank. This design induced water removal and necessitated the additional requirement of entraining radioactivity from the exiting system by the use of demisters and HEPA filters.
Up until the 1980's this was a sufficient method, via the hydrofracture process, of disposing the liquid nuclear waste. However since then, this method has been terminated and the tanks are nearing capacity. In the transfer of the liquid waste to the holding tanks, large amounts of water are used to prevent line clogging and solid build up in the pipes. Utilizing the existing system, this thesis proposes the idea of sparging air into the liquid waste and increasing the tank temperature in order to eliminate excess water. Parameters such as increasing the sparging air temperature, and dehumidifying and eliminating carbon dioxide from the sparging air, are investigated theoretically and experimentally in small scale experiments. In addition, the effects of vapor pressure lowering and its simultaneous effect on the evaporation rate are investigated through the activity coefficient of sodium nitrate, the major component of the liquid waste. Precipitate blockage formations in the sparging tube have also been addressed.
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Senoner, Jean-Mathieu. "Simulations aux grandes échelles de l’écoulement diphasique dans un brûleur aéronautique par une approche Euler-Lagrange." Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0024/document.
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Les turbines à gaz aéronautiques doivent satisfaire des normes d'émissions polluantes toujours en baisse. La formation de polluants est directement liée à la qualité du mélange d’air et de carburant en amont du front de flamme. Ainsi, leur réduction implique une meilleure prédiction de la formation du spray et de son interaction avec l'écoulement turbulent gazeux. La simulation aux grandes échelles (SGE) semble un outil numérique approprié pour étudier ces mécanismes. Le but de cette thèse est d’évaluer l'impact de modèles d'injection simplifiés sur la SGE de l'écoulement diphasique évaporant d’une configuration complexe. La configuration cible choisie est un brûleur aéronautique installé sur le banc expérimental MERCATO. Le banc expérimental est equipé d’un système d’injection d'air vrillé et d’un système d'injection liquide avec un atomiseur pressurisé swirlé représentatif de foyers aéronautiques réels. Dans un premier temps, un modèle d'injection simplifié pour atomiseurs pressurisés swirlés négligeant les effets de l'atomisation sur la dynamique du spray est présenté. L'objectif principal de ce modèle réside dans la reproduction de conditions d’injection similaires pour des traitements Eulériens et Lagrangiens de la phase particulaire. Dans un second temps, la composante Lagrangienne de ce modèle d'injection est combinée à un modèle d'atomisation secondaire de la litérature pour permettre une prise en compte partielle des phénomènes de pulvérisation liquide. Les SGE de l'écoulement diphasique évaporant de la configuration MERCATO présentées comportent deux aspects. Premièrement, différents modèles d’injection sont évalués pour quantifier leur impact sur la dynamique de la phase particulaire. Deuxièmement, une comparaison de simulations Euler-Euler et Euler-Lagrange reposant sur un modèle d'injection unifié est effectuéeAeroautical gas turbines need to satisfy growingly stringent demands on pollutant emission. Pollutant emissions are directly related to the quality of fuel air mixing prior to combustion. Therefore, their reduction relies on a more accurate prediction of spray formation and interaction of the spray with the gaseous turbulent flowfield. Large-Eddy Simulation (LES) seems an adequate numerical tool to predict these mechanisms. The objective of this thesis is to evaluate the impact of simplified injection methods on the LES of the evaporating two-phase flow inside a complex geometry. The chosen target configuration is an aeronautical combustor installed on the MERCATO test-rig. The experimental setup includes an air-swirler injection system and a pressureswirl atomizer typical of realistic aeronautic combustors. In a first step, a simplified injection model for pressure swirl atomizers neglecting the impact of liquid disintegration on spray dynamics is presented. The main objective of this model lies in the reproduction of similar injection conditions for Eulerian and Lagrangian representations of the dispersed phase. In a second step, the Lagrangian injection method is combined to a secondary breakup model of the literature to partly account for the liquid disintegration process. The presented LES’s of the evaporating two-phase flow inside the MERCATO geometry consider two different aspects. First, the impact of injection modeling on spray dynamics is assessed. Second, Euler-Euler and Euler-Lagrange simulations relying on the common simplified injection model are compared
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Raghunathan, Vijay. "Consequence analysis of aqueous ammonia spills using an improved liquid pool evaporation model." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1440.
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Source term modeling is the key feature in predicting the consequences of releases from
hazardous fluids. Aqueous ammonia serves the purpose of a reducing medium and is
replacing anhydrous ammonia in most of the Selective catalytic reduction (SCR) units.
This newly developed model can estimate the vaporization rate and net mass evaporating
into the air from a multicomponent non- ideal chemical spill. The work has been divided
into two parts. In the first step a generic, dynamic source term model was developed that
can handle multicomponent non-ideal mixtures. The applicability of this improved pool
model for aqueous ammonia spills was then checked to aid in the offsite consequence
analysis of aqueous ammonia spills.
The behavior of the chemical released depends on its various inherent properties,
ambient conditions and the spill scenario. The different heat transfer mechanisms
associated with the pool will strongly depend on the temperature of the liquid pool
system at different times. The model accounts for all the temperature gradients within
the contained pool and hence helps us establish better estimation techniques for source
terms of chemical mixtures. This research work will help obtain more accurate and
reliable liquid evaporation rates that become the critical input for dispersion modeling
studies.
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Prat, Olivier. "Etude de l'Evaporation de Précurseurs Liquides Intervenant dans la Fabrication de Fibres Optiques." Montpellier 2, 2003. http://www.theses.fr/2003MON20002.
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Cobb, Zoe. "Development of evaporative light scattering detection for coupling with capillary LC." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273107.
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Magdelaine-Guillot, de Suduiraut Quentin. "Hydrodynamique des films liquides hétérogènes." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS531.
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Revêtir une surface d’un film mince permet de lui conférer de nouvelles propriétés, comme en réduire les reflets ou améliorer sa résistance aux rayures. Une méthode pour produire ces revêtements est le dépôt par voie liquide : elle consiste à couvrir la surface avec un matériau dispersé dans un liquide puis à le sécher. Cette méthode permet de fonctionnaliser efficacement et rapidement de grandes surfaces. Bien qu'attrayante pour l’industrie verrière, la perspective d'une fonctionnalisation par voie liquide se heurte actuellement à l'apparition de défauts dans le film lors de son séchage, notamment des variations d'épaisseurs sur de grandes distances. Ces imperfections détériorent l'esthétique et les propriétés optiques de la surface. Dans cette thèse, nous apportons un éclairage sur l’apparition de ces défauts, en étudiant les écoulements générés lors du séchage de films liquides de mélanges binaires. En effet, l'évaporation du solvant peut induire des variations de composition qui génèrent en retour des gradients de tension à la surface du film qui le déstabilisent. La combinaison d'expériences modèles, de modélisations théoriques et de simulations numériques ont permis de mettre en évidence et de décrire quantitativement plusieurs régimes, qui correspondent aux différents effets limitant l’instabilité : la pesanteur, la pression de Laplace, l’homogénéisation latérale par diffusion des composées dans le film ou au contraire la stratification verticale de ces composés, causée par l’évaporation. Une étude indépendante a été menée sur la génération de trains de bulles lorsque de l’air est lentement injecté dans un bainCoating processes allow functionalizing a surface to obtain new properties, as anti-glare or anti-scratch. Amongst the various methods, wet coating, the process of spreading then drying a liquid layer containing a material of interest, is particularly appealing because of its efficiency and low cost. One key hurdle, however, is the possible apparition of defects in the film during the drying process, notably, thickness variations over large areas. These imperfections degrade the aspect and the optical properties of the surface. In this Ph.D. thesis, we shed light on the apparition of these defects, by studying the flows triggered by the evaporation in liquid films of binary mixtures. Indeed, the evaporation of the solvent can induce variations of composition which generate in return gradients of tension at the film surface which destabilize it. The combination of model experiments, theoretical modeling and numerical simulations allowed us to reveal and describe quantitatively several regimes, which correspond to the factor limiting the instability: gravity, Laplace pressure, lateral homogenization by diffusion of the compounds or by their vertical stratification due to the evaporation. An independent study has been lead on the generation of bubble trains when air is slowly injected in a bath
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Gong, Shengjie. "An Experimental Study on Micro-Hydrodynamics of Evaporating/Boiling Liquid Film." Doctoral thesis, KTH, Kärnkraftsäkerhet, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-50216.
Full textAbstract:
Study of liquid film dynamics is of significant importance to the understanding and control of various industrial processes that involve spray cooling (condensation), heating (boiling), coating, cleaning and lubrication. For instance, the critical heat flux (CHF) of boiling heat transfer is one of the key parameters ensuring the efficiency and safety of nuclear power plants under both operational and accident conditions, which occurs as the liquid layers (microlayer and macrolayer) near the heater wall lose their integrity. However, an experimental quantification of thin liquid film dynamics is not straightforward, since the measurement at micro-scale is a challenge, and further complicated by the chaotic nature of boiling process. The object of present study is to develop experimental methods for the diagnosis of liquid film dynamics, and to obtain data for the film instability under various conditions. A dedicated test facility was designed and constructed where micro conductive probes and confocal optical sensors were used to measure the thickness and dynamic characteristics of a thin liquid film on various heater surfaces, while a high speed camera was used to get visual observation. Extensive tests were performed to calibrate and verify the two thickness measuring systems. The micro conductive measuring system was proven to have a high reliability and repeatability with maximum system error less than 5µm, while the optical measuring system is capable of recording the film dynamics with spatial resolution of less than 1 mm. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz, which are more suitable for rapid process. The confocal optical sensors were therefore employed to measure the dynamic thickness of liquid films (ethanol, hexane and water) evaporating on various horizontal heater surfaces (aluminum, copper, silicon, stainless steel and titanium) to investigate the influences of heat flux, the surface and liquid properties on the film instability and the critical thickness. The critical thickness of water film evaporating on various surfaces was measured in the range of 60-150 mm, increasing with the increased contact angle or increased heat flux (evaporating rate) and also with the decreased thermal conductivity of the heater material. The data suggest the conjugate heat transfer nature of the evaporating liquid film dynamics at higher heat fluxes of interest to boiling and burnout. In the case of hexane on the aged titanium surface with contact angle of ~3o, the liquid film is found resilient to rupture, with film oscillations at relatively large amplitude ensuing as the averaged film thickness decreases below 15 µm. To interpret our experimental findings on liquid film evolution and its critical thickness at rupture, a theoretical analysis is also performed to analyze the dynamics of liquid films evaporating on heater surfaces. While the influences of liquid properties, heat flux, and thermal conductivity of heater surface are captured by the simulation of the lubrication theory, influence of the wettability is considered via a minimum free energy criterion. The thinning processes of the liquid films are generally captured by the simulation of the lubrication theory. For the case with ideally uniform heat flux over the heater surface, the instability of the liquid film occurs at the thickness level of tens micro meters, while for the case of non-uniform heating, the critical thicknesses for the film rupture are closer to the experimental data but still underestimated by the lubrication theory simulation. By introducing the minimum free energy criterion to considering the influence of surface wettability, the obtained critical thicknesses have a good agreement with the experimental ones for both titanium and copper surfaces, with a maximum deviation less than ±10%. The simulations also explain why the critical thickness on a copper surface is thinner than that on a titanium surface. It is because the good thermal conductivity of copper surface leads to uniform temperature distribution on the heat surface, which is responsible for the resilience of the liquid film to rupture. A silicon wafer with an artificial cavity fabricated by Micro Electronic Mechanical System (MEMS) technology was used as a heater to investigate the dynamics of a single bubble in both a thick and thin liquid layer under low heat flux (<60 kW/m2). The maximum departure diameter of an isolated bubble in a thick liquid film was measured to be 3.2 mm which is well predicted by the Fritz equation. However, in a thin liquid layer with its thickness less than the bubble departure diameter, the bubble was stuck on the heater surface with a dry spot beneath. A threshold thickness of the liquid film which enables the dry spot rewettable was obtained, and its value linearly increases with increasing heat flux. In addition, another test section was designed to achieve a constant liquid film flow on a titanium nano-heater surface which helps to successfully carry boiling in the liquid film from low heat flux until CHF. Again, the confocal optical sensor was employed to measure the dynamics of the liquid film on the heater surface under varied heat flux conditions. A statistical analysis of the measured thickness signals that emerge in a certain period indicates three distinct liquid film thickness ranges: 0~50 µm as microlayer, 50~500 µm as macrolayer, 500~2500 µm as bulk layer. With increasing heat flux, the bulk layer disappears, and then the macrolayer gradually decreases to ~105 µm, beyond which instability of the liquid film may lose its integrity and CHF occurs. In addition, the high-speed camera was applied to directly visualize and record the bubbles dynamics and liquid film evolution. Dry spots were observed under some bubbles occasionally from 313 kW/m2 until CHF with the maximum occupation fraction within 5%. A dry spot was rewetted either by liquid receding after the rupture of a bubble or by the liquid spreading from bubbles’ growth in the vicinity. This implies that the bubbles’ behavior (growth and rupture) and their interactions in particular are of paramount importance to the integrity of liquid film under nucleate boiling regime.QC 20111205
VR-2005-5729, MSWI
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Ebrahimian, Shiadeh Seyed Vahid. "Développement de modèles d'évaporation multi-composants et modélisation 3D des systèmes de réduction de NOx (SCR)." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0029/document.
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L'objectif de cette thèse est de développer un ensemble de modèles numériques afin de simuler les processus physico-chimiques dans la chambre de combustion ainsi que dans le système de post-traitement des gaz d'échappement des moteurs à combustion interne. Dans la première partie de cette thèse, deux nouveaux modèles d'évaporation de gouttelettes et de film liquide multi-composants sont proposés. Dans le modèle d'évaporation des gouttelettes, une nouvelle expression du débit d'évaporation a été proposée. Il a été montré que la prise en compte du flux de chaleur dû à la diffusion d'enthalpie des espèces est primordiale dans le bilan d'énergie à l'interface de la goutte. De plus, les investigations numériques ont montré l'importance de la prise en compte d'une équation d'état de gaz réel dans les conditions de hautes pressions et / ou de basses températures ambiantes. Un modèle d'évaporation multi-composant de film liquide a ensuite été développé sur la base du modèle d'évaporation de film mono-composant déjà mis en oeuvre dans le code industriel IFP-C3D. En particulier, les lois de paroi ont été généralisées pour l'évaporation du film multi-composant de manière similaire au modèle de l'évaporation des gouttelettes. Il a été montré l'importance de la température de la paroi dans le processus d'évaporation d'un film liquide. Contrairement à l'évaporation des gouttes, les investigations numériques effectuées ont montré que l'utilisation d'une équation d'état de gaz parfait conduit à des résultats proches de ceux qui sont obtenus en utilisant une équation d'état de gaz réel. Ceci se traduit par un gain en temps de calculs important. La deuxième partie de la thèse utilise les modèles d'évaporation, développés dans la première partie de la thèse, avec un nouveau modèle de thermolyse développé afin de produire de l'ammoniac nécessaire pour le système SCR. Dans la présente étude, l'ammoniac est produit à partir de la solution aqueuse d'urée injectée dans la ligne de tuyau d'échappement. L'eau s'évapore et l'urée se décompose en ammoniac nécessaire pour le système SCR. L'évaporation de l'eau est modélisée avec les modèles d'évaporation proposés dans la première partie de cette thèse, avec quelques modifications afin de prendre en compte l'influence de l'urée sur l'évaporation de l'eau. Un nouveau modèle de thermolyse multi-étape pour l'urée a été ensuite implanté dans IFP- 3D afin de simuler la distribution de l'ammoniac gazeux à l'entrée de système de dépollution SCR. Ce modèle est également capable de simuler la formation de sous- roduits (dépôt solide) de la thermolyse d'urée. Les résultats numériques des modèles développés ont permis de montrer le potentiel des développements réalisés au cours de ce travail dans le cadre d'applications industriellesThe aim of the present thesis is to develop a set of numerical models in order to simulate the physical and chemical processes in combustion chamber as well as in exhaust gas after-treatment system of internal combustion engines. In the first part of the thesis, two new multi- omponent evaporation models for droplet and liquid film are proposed. In the droplet evaporation model, a new expression of the evaporation rate has been proposed. It has been shown that taking into account the heat flux due to the enthalpy diffusion of species is of primary significance in the energy balance at the droplet surface. In addition, numerical investigations have shown the importance of considering a real gas equation of state in the high pressure and/or low temperature conditions. A multi-component liquid film evaporation model has then been developed based on the single-component film evaporation model already implemented in IFP-C3D code. Particularly, the wall laws have been generalized for the multi-component film evaporation taking into account the mentioned features applied to the droplet evaporation model. The importance of surface temperature in the evaporation of liquid film has also been shown. Contrary to the droplet evaporation, the numerical investigations on film evaporation have shown that using an ideal mixture equation of state leads to results similar to those obtained using a real gas equation of state. The second part of the thesis uses the evaporation models, developed in the first part of the thesis, along with a new developed thermolysis model in order to produce the ammonia needed for the SCR system. In the present study, ammonia is produced from the urea-water solution injected into the exhaust pipe line. Water evaporates and urea decomposes to ammonia needed for SCR system. The evaporation of water is modeled with the proposed evaporation models in the first part of the present thesis with some modifications in order to take into account the influence of urea on the water evaporation. New multi-step thermolysis model for urea is then implemented in the IFP-C3D code in order to simulate the distribution of gaseous ammonia at the entrance of SCR system. The present model is also able to simulate the formation of solid by-products from urea thermolysis. The numerical results of the developed models allow us to assess the contribution of the developments made during this work in the context of industrial applications
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Ladam, Yves. "Atomisation et évaporation d'un jet mixte hélium liquide/Hélium gazeux." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10042.
Full textAbstract:
Ce travail experimental est une contribution a l'etude du fractionnement et evaporation d'un liquide par un gaz en geometrie de jets turbulents coaxiaux. Ce phenomene est notamment rencontre dans les moteurs cryotechniques de fusee. L'utilisation de l'helium liquide et gazeux permet de realiser des ecoulements a grands nombres de reynolds r e 10 5 et grands nombres de weber w e 10 3. De plus la faible chaleur latente de l'helium liquide (20 j/g) permet de faire varier l'importance du phenomene de vaporisation dans de grandes proportions. Une premiere etude a l'aide de micro thermometres a isole les roles respectifs du fractionnement et de l'evaporation du liquide par le cocourant gazeux. Pour des jets a fort nombre de weber, nous avons montre que le fractionnement du liquide est tres efficace et fournit l'accroissement de surface d'echange necessaire a l'evaporation rapide. Une seconde etude par diffusion de la lumiere dans l'aerosol d'helium a permi de quantifier la disparition d'interface liquide/gaz par vaporisation. Dans nos conditions experimentales (w e 10 3), nous avons montre que la quantite d'interface au dela du cone potentiel du jet liquide decroit exponentiellement avec l'exces d'enthalpie transporte par le gaz. L'utilisation de fluides cryogeniques pour des experiences d'hydrodymique a donne lieu a un important devellopement instrumental qui est presente dans ce memoire.
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Mouret, Quentin. "Etude expérimentale des mécanismes d’évaporation d’un film liquide combustible et de la stratification induite." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI022/document.
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Durant les régimes de fonctionnement transitoires à froid des technologies d’Injection Directe Essence, des films liquides peuvent se former sur les parois du cylindre moteur. L’interaction entre le gradient de fraction de vapeur, résultant de l’évaporation de ces films avec le front de flamme, est responsable de la majorité des émissions d’hydrocarbures imbrulés (HC). Dans ces travaux, une configuration expérimentale simplifiée a été développée de façon à générer un gradient de fraction de vapeur par évaporation, dans un contexte d’écoulement réactif confiné, mais préservé des complexités inhérentes aux configurations industrielles. L’étude porte sur les influences de la vitesse de l’écoulement et de la température de l’interface de changement de phase sur les intensités des transferts de masse et de chaleur ainsi que sur l’établissement de la stratification de vapeur. Dans un premier temps, les flux de vapeur et de chaleur provenant d’une paroi poreuse saturée en liquide volatil ont été mesurés et évalués. Dans un second temps, le gradient de fraction de vapeur à proximité de la paroi poreuse a été caractérisé par un diagnostic de Fluorescence Induite par Laser (FIL). L’approche globale a confirmé que le flux de chaleur consommé par le changement de phase représente une part importante du flux de chaleur total échangé. De plus, les résultats de mesures de FIL ont montré l’existence de différents types de distributions et comportements provenant du lien étroit entre la forte densité du mélange gazeux et la formation de la couche de vapeurDuring cold start and warm up engine regimes for Gasoline Direct Injection (GDI) technology, fuel liquid films may accumulate on the cylinder walls. The interaction between the mass fraction gradient, witch is resulting from its evaporation, and the front flame, manages to produce the majority of Unburnt HydroCarbon (UHC) emissions. In order to reproduce the conditions found in internal combustion without the industrial setup complexity, an academic experimental configuration has been developed to generate a mass fraction gradient by evaporation. This study focuses on the influence of the air stream velocity and the influence of the phase change interface temperature. First, mass and heat fluxes from the phase change surface have been measured and calculated near a porous wall saturated with volatile liquid. Then, the mass fraction gradient near the porous wall has been characterised by a Laser Induced Fluorescence (LIF) diagnostic. The global approach has confirmed that latent heat flux represents a major part of the total heat transfer flux exchange. Moreover, LIF results have shown different global behaviours that link the high density of the gas mixture to the vapour layer formation
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Yun, Thomas. "Fuel reformation and hydrogen generation in variable volume membrane batch reactors with dynamic liquid fuel introduction." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53550.
Full textAbstract:
In recent years, the need for high performance power sources has increased dramatically with the proliferation of ultra-compact electronic systems for mobile communication, man-portable and versatile military equipment, and electric vehicles. Volume- and mass- based power density are two of the most important performance metrics for portable power sources, including hydrogen generating fuel reforming systems (onboard) for hydrogen fuel cells. Two innovative multifunctional reactor concepts, CO2/H2 Active Membrane Piston (CHAMP) and Direct Droplet Impingement Reactor (DDIR), are combined for the purpose of hydrogen generating fuel reforming system (onboard) for fuel cells. In CHAMP-DDIR, a liquid fuel mixture is pulse-injected onto the heated catalyst surface for rapid flash volatilization and on-the-spot reaction, and a hydrogen selective membrane is collocated with the catalyst to reduce the diffusion distance for hydrogen transport from the reaction zone to the separation site. CHAMP-DDIR allows dynamic variation of the reactor volume to optimally control the residence time and reactor conditions, such as pressure and temperature, thus improving both the reaction and separation processes.
A comprehensive CHAMP-DDIR model, which couples key physical processes including 1) catalytic chemical reactions, 2) hydrogen separation/permeation at membrane, 3) liquid fuel evaporation, and 4) heat and mass transport, has been developed to investigate the behavior of this novel reactor system, aiming at maximizing the volumetric power density of hydrogen generation from methanol/water liquid fuel. The relationships between system design parameters and the rate-limiting process(es), i.e., reaction, permeation, and transport, which govern reactor output, have identified. Experimental characterization of the prototype reactor has been performed for laboratory demonstration of the concept and model validation. Both model predictions and experiments successfully demonstrate the unique practical performance improvements of CHAMP-DDIR through combining time-modulated fuel introduction and the active change of reactor volume/pressure.
This work has led to a number of fundamental insights and development of engineering guidelines for design and operation of CHAMP-DDIR class of reactors, which can be extended to a broad range of fuels and diverse practical applications.
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Vieira, Marcelo Mendes. "Estudo experimental de jatos evaporativos." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-11042002-132126/.
Full textAbstract:
Foi construído um arranjo experimental para estudar o comportamento dos jatos evaporativos. Um injetor foi projetado para controlar e manter constantes a pressão e temperatura de reservatório durante a injeção. Um bocal cônico convergente de seção reta com diâmetro de saída de 0,30 mm e ângulo entre sua geratriz e seu eixo simetria igual à 10º forma o elemento principal do injetor. O jato é descarregado em uma câmara de baixa pressão de dimensões suficientemente grandes para manter a pressão constante durante o curto período de ensaio, igual à 1 s. Quando injetado, o líquido sofre uma repentina queda de pressão ocasionando sua evaporação. Os fluidos utilizados são os combustíveis querosene e óleo diesel, e a substância n-dodecano, os quais se caracterizam pela possibilidade de uma evaporação completa, de forma adiabática. Utilizou-se o método \"schlieren\" para a visualização do escoamento. A análise dos jatos é feita de forma qualitativa através dos registros fotográficos. Foram observados os seguintes tipos de jato: (1) contínuo, (2) pulverizante e (3) evaporação na superfície. O primeiro jato não implica em imediata mudança de fase tornando o jato de líquido emergente intacto. Com o aumento da temperatura de injeção, existe o espalhamento e a evaporação do jato, formando o segundo tipo de jato, onde é possível visualizar o campo do gradiente de densidade do escoamento e a formação de ondas de evaporação e de choque que pode ocorrer a uma distância proporcional a vários diâmetros à jusante. Em jatos com evaporação completa, foram constadas a formação de ondas de choque tanto de formas elipsóide como de esferóide para elevadas temperaturas. As fotografias digitais são submetidas à filtragem e processamento matemático para melhor destacar tais fenômenos do escoamento.An experimental apparatus has been built to study the behaviour of flashing jets. An injector was designed to control and maintain the jet pressure and temperature at constant values during the injection process. A conical convergent nozzle whose main dimensions are 0,30 mm of exit diameter, 8 mm long, and a convergence half-angle of 10º is the central component of the injection system. The jet is discharged into a low-pressure chamber large enough to keep the reservoir pressure constant during the short test period of about 1 s. As the testing liquid expands in the nozzle it undergoes a sudden pressure drop causing its evaporation. The fluids are usual fuels, such as kerosene and diesel oil, and the substance ndodecane, which are distinguishable by the possibility of a complete evaporation in an isoentropic expansion process. The photographic method \"schlieren\" is used for flow visualisation. A qualitative analysis is made of the photographic documentation of the images obtained using a CCD camera. The images can be grouped into three categories of jets: (1) continuous, (2) shattering, and (3) with surface evaporation. The first regime has an undisturbed a liquid column, which remains more or less intact during the injection process. In the second type, the existing liquid jet is shattered by vapour nucleation and, in some cases, shock waves are clearly visible. It happens at higher temperature than the preceding evaporation mode. Finally, in special situations, the jet undergoes an evaporation at its surface and the two-phase mixture expands at a high speed followed by a shock wave before the mixture attains the pressure reservoir.
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Munier, Laurent. "Simulations expérimentale et numérique des effets retardés d'une explosion en milieu clos et en présence de produits liquides." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10091/document.
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Peut-on modéliser de manière fiable les effets collatéraux (en termes de quantité ou concentration de produits éjectés) et les conséquences d’une explosion en milieu clos, et en présence de produits chimiques liquides ? Pour répondre à cette vaste question, qui soulève spontanément de nombreux sous-problèmes, les travaux de thèse se sont déroulés en trois temps : 1/une étude qualitative et semi-quantitative du scénario général, afin de comprendre le déroulement chronologique des évènements, et d’émettre les hypothèses nécessaires à une modélisation, 2 /L’étude systématique des effets d’une explosion en milieu clos, en présence ou non de produits liquides. Avant de modéliser la dégradation du produit liquide soumis à une température et à une pression élevées, les expérimentations préliminaires ont en effet fait apparaître la nécessité de quantifier dans le temps et dans l’espace, les effets thermiques et mécaniques d’une explosion à volume constant, 3/L’élaboration de modèles 0D(t) à partir des conclusions précédentes afin, d’une part, d’estimer la durée de vie d’une phase liquide dans un environnement thermodynamique contraint et, d’autre part, de démontrer la possibilité de modéliser le problème global de manière réduite. En effet, le terme source d’un tel évènement ne peut être modélisé par une libération ponctuelle de produit : il s’agit d’une libération étendue dans le temps, par le biais d’un écoulement chaud a priori diphasique et de débit variable. Les couplages des phénomènes, observés expérimentalement, rendent nécessaires : 1 - Une modélisation instationnaire de l’évolution de la pression et une estimation du niveau de température atteint dans le volume d’étude, après détonation d’une charge explosive, 2 - Une modélisation de la libération de la phase liquide dans l’enceinte, sous forme de gouttes millimétriques ou de gouttelettes microniques 3 - Une modélisation instationnaire des transferts couplés de masse et d’énergie entre la phase liquide et la phase gazeuse en présence et prise en compte d’éventuelles réactions chimiques à haute pression et haute température 4 - Et enfin, une modélisation instationnaire des rejets à la brèche. L’étude d’une explosion à volume constant a montré qu’il est possible de modéliser de manière simple la montée continue en pression de l’enceinte par une fonction exponentielle croissante. Pour une configuration de référence donnée – explosion d’une sphère d’explosif dans un parallélépipède – la valeur maximale de pression est directement proportionnelle au taux de chargement en explosif, sur l’intervalle [0,01 – 0,6] kg/m3. Le passage à une géométrie différente ou plus complexe demande l’introduction d’un coefficient correctif pour traduire l’amplification (ou l’atténuation) de la combustion turbulente des produits de détonation avec l’air ambiant. En ce qui concerne le champ de température par contre, notre analyse a montré qu’il coexiste des zones chaudes et des zones dites « froides » et que la valeur de température homogène finale calculée à partir d’un code thermochimique ne peut constituer qu’une simple indication. Seule une estimation du volume respectif de ces zones a été proposée ici. Nous avons établi que les propriétés physico-chimiques des produits stockés sont un point clef du problème et on suppose ces données connues pour une gamme de produits chimiques liquides à pression ambiante, communément utilisés dans l’industrie. Seul le phénomène d’évaporation a été développé dans ce mémoire. L’introduction de réactions chimiques entre constituants se traduirait dans les modèles par des termes sources supplémentaires liés à l’apparition ou la disparition d’espècesIs it possible to model collateral effects due to an explosion (on a chemical facility for instance) occuring in a closed volume containing liquid chemical products storage units ?This thesis deals with a zerodimensionnal modelisation of such a 3D complex problem to asses the final thermodynamic state of chemical products released in the atmosphere. Developped sub-models take into account:- the unsteady time histories of the internal overpressure and temperature,- the unsteady liquid ejection (droplets sizes)- the unsteady modelisation of the local heat and mass transfers between the gas phase and the liquid phase- the unsteady ejection process of the resulting multiphase mixture in the environment.Models and sub-models are validated thanks to many experimental results
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Abdel-Qader, Zainab. "The role of liquid mixing in evaporation of complex multi-component mixtures, modelling using continuous thermodynamics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0017/MQ58435.pdf.
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Guion, Alexandre Nicolas. "Modeling and simulation of liquid microlayer formation and evaporation in nucleate boiling using computational fluid dynamics." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112380.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 243-252).
The transport of latent heat makes boiling one of the most efficient modes of heat transfer, allowing a wide range of systems to improve their thermal performance, from microelectronic devices to nuclear power plants. In particular, Boiling Water Reactors (BWR) use boiling as the primary mode of heat transfer in the reactor core to accommodate very high heat fluxes. In Pressurized Water Reactors (PWR) subcooled flow boiling can occur in hot sub-channels. As a bubble grows outside of a surface imperfection during nucleate boiling, viscous stresses at the wall can be strong enough to impede liquid motion and trap a thin liquid layer - referred to as microlayer, underneath the growing bubble. The contribution of microlayer evaporation to overall heat transfer and bubble growth can be large, in particular in the case of water1. In practice, numerical simulations of nucleate boiling resolve the macroscopic interface of the bubble and resort to subgrid models to account for the evaporation of the microlayer at the microscopic scale. The applicability of this subgrid modeling approach relies on the capacity to initialize the microlayer shape and extension, prior to its evaporation. However, existing models of microlayer formation are either physically incomplete2 or purely empirical3. In this work, we first confirm through a sensitivity study the need for accurate modeling of microlayer formation to initialize boiling simulations and to reproduce physical boiling dynamics (a). Then, we build the first generally applicable model for microlayer formation through direct computations of the hydrodynamics of bubble growth at the wall for a wide range of conditions and fluids, including water at 0.101MPa (lab experiments) and 15.5MPa (PWR), capillary numbers Ca [is element of] [0.001; 0.1], and contact angles [theta] [is element of] [10°; 90°] (b). In addition, we modify an existing experimental pool boiling setup to measure with unprecedented accuracy initial bubble growth rates needed to predict microlayer formation (c). Lastly, we develop a numerical procedure based on hydrodynamics theories to obtain mesh-independent results in moving contact line simulations for a wide range of contact angles and viscosity ratios (d). In particular, we use direct computations of the transition to a Landau-Levich-Derjaguin film in forced dewetting to inform the onset of microlayer formation in nucleate boiling. These contributions(a) (b) (c) (d) bridge a significant gap in our understanding of how boiling works and can be modeled at the microscopic scale, which represents a first step in designing surfaces with higher heat transfer performance and in building safer and more efficient energy systems.
by Alexandre Nicolas Guion.
Ph. D.
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Lench, Martyn John. "Direct contact heat transfer between an evaporating fluid and an immiscible liquid." Thesis, University of South Wales, 1991. https://pure.southwales.ac.uk/en/studentthesis/direct-contact-heat-transfer-between-an-evaporating-fluid-and-an-immiscible-liquid(972548ab-c177-40e4-8800-4c24d6021f67).html.
Full textAbstract:
An investigation has been conducted into the process of cooling water by the evaporation of droplets of isopentane in direct contact. The research has potential industrial application to a pickling acid recovery crystalliser. In order to minimise industrial equipment size a counter current flowing apparatus was developed and studied. Studies of optimum column height were carried out over a wide range of flow and drop size values. Several computer-based models have been developed to predict optimum column height. The results of initial models were used to modify experimental work and gave rise to the measurement of initial drop size using a high speed video camera technique. A more sophisticated version of the computer based model has been developed and is the major product of this research. This included the development of a dimensionless correlation for instantaneous heat transfer to an evaporating droplet. This is based on existing correlations which are compared and modified empirically. The correlation produced is: Nu= 2 + 0.76 Re 1/3 Pr 1/2 The computer model with this correlation is accurate to within 22%. The model assumes an average vapour half opening angle (β) of 135° based on published work. Drop velocities are based on terminal values and rigid sphere behaviour of 2-phase droplets is assumed. The final model assumes that the vapour and liquid dispersed phase remain attached as they rise through the column. Reynolds number of the continuous phase is found to have no independent effect on minimum evaporative height. The pinch temperature difference in the temperature profiles through the evaporative column is found to be significant in determination of minimum evaporative height. An approximate relationship of the form: Minimum evaporative height α ΔTpinch-0.5 is proposed.
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Novak, Vladimir. "Experimental and Numerical Studies of Mist Cooling with Thin Evaporating Subcooled Liquid Films." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10528.
Full textAbstract:
An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness.
A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters.
Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.
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Schlesinger, Daniel. "Molecular structure and dynamics of liquid water : Simulations complementing experiments." Doctoral thesis, Stockholms universitet, Fysikum, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-120808.
Full textAbstract:
Water is abundant on earth and in the atmosphere and the most crucial liquid for life as we know it. It has been subject to rather intense research since more than a century and still holds secrets about its molecular structure and dynamics, particularly in the supercooled state, i. e. the metastable liquid below its melting point. This thesis is concerned with different aspects of water and is written from a theoretical perspective. Simulation techniques are used to study structures and processes on the molecular level and to interpret experimental results. The evaporation kinetics of tiny water droplets is investigated in simulations with focus on the cooling process associated with evaporation. The temperature evolution of nanometer-sized droplets evaporating in vacuum is well described by the Knudsen theory of evaporation. The principle of evaporative cooling is used in experiments to rapidly cool water droplets to extremely low temperatures where water transforms into a highly structured low-density liquid in a continuous and accelerated fashion. For water at ambient conditions, a structural standard is established in form of a high precision radial distribution function as a result of x-ray diffraction experiments and simulations. Recent data even reveal intermediate range molecular correlations to distances of up to 17 Å in the bulk liquid. The barium fluoride (111) crystal surface has been suggested to be a template for ice formation because its surface lattice parameter almost coincides with that of the basal plane of hexagonal ice. Instead, water at the interface shows structural signatures of a high-density liquid at ambient and even at supercooled conditions. Inelastic neutron scattering experiments have shown a feature in the vibrational spectra of supercooled confined and protein hydration water which is connected to the so-called Boson peak of amorphous materials. We find a similar feature in simulations of bulk supercooled water and its emergence is associated with the transformation into a low-density liquid upon cooling.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript.
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Maréchal, Anne. "Etude de la déformation et des instabilités pouvant apparaître à la surface libre d'un liquide soumis localement à une évaporation intense." Grenoble 1, 1993. http://www.theses.fr/1993GRE10030.
Full textAbstract:
L'interface liquide-vapeur d'un fluide chauffe par bombardement electronique, dans une enceinte sous vide, est etudiee. Dans un premier temps, on determine la deformation de l'interface du systeme stationnaire. Dans un deuxieme temps, on effectue une etude de stabilite lineaire de cette interface. On s'interesse principalement au mecanisme destabilisant lie a l'evaporation intense. On analyse deux systemes classiques de la litterature, fluide chauffe par le bas, que l'on compare a un systeme chauffe par le haut. On etudie, ensuite, un systeme plus proche du procede d'enrichissement de l'uranium par separation isotopique par laser sur vapeur atomique