Quelques aspects de la physique des transferts en milieu poreux lors d'un processus d'humidification par condensation PDF Download

Author: Salah Larbi
Publisher:
ISBN:
Category :
Languages : fr
Pages : 97

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Book Description
LE TRAVAIL PRESENTE DANS CE MEMOIRE CONCERNE L'ETUDE DE L'HUMIDIFICATION PAR CONDENSATION DE MATERIAUX CAPILLARO-POREUX. DEUX OBJECTIFS SONT PRINCIPALEMENT VISES: L'ANALYSE DES MECANISMES D'ENVAHISSEMENT DU MILIEU PAR LA PHASE CONDENSEE ET L'EVALUATION DES POSSIBILITES OFFERTES PAR LES MODELES CONTINUS DE DESCRIPTION DES TRANSFERTS COUPLES DE CHALEUR ET DE MASSE POUR PREVOIR CES PHENOMENES. OUTRE LA COMPLEXITE DES INTERACTIONS ENTRE LES PROCESSUS DE VAPORISATION-CONDENSATION SUR LES INTERFACES GAZ-LIQUIDE, LA COMPARAISON ENTRE RESULTATS D'EXPERIENCES ET SIMULATION NUMERIQUE A PERMIS DE DEGAGER LE ROLE ET L'IMPORTANCE RELATIVE DES MECANISMES DE TRANSFERT DE MASSE: VAPEUR-LIQUIDE, ET D'ENERGIE: CONDUCTION-CHANGEMENT DE PHASE. LES COMPOSANTES DE CES DIFFERENTS MECANISMES, RESPECTIVEMENT ASSOCIEES AUX GRADIENTS DE SATURATION ET DE TEMPERATURE ONT ETE EXPLICITEES ET LEUR INFLUENCE SUR LA CINETIQUE DE CONDENSATION PRECISEE. CETTE ANALYSE A EGALEMENT PERMIS DE COMPRENDRE LES DEFAILLANCES DES MODELES THEORIQUES SIMPLIFIES ET DE JUSTIFIER, AU MOINS PARTIELLEMENT, L'USAGE DU MODELE DE PHILIP DE VRIES EN TANT QUE MODELE DE PREDICTION

Author: Karl Stephan
Publisher: Springer Science & Business Media
ISBN: 3642524575
Category : Technology & Engineering
Languages : en
Pages : 342

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Book Description
I welcome the opportunity to have my book translated, because of the great emphasis on two-phase flow and heat transfer in the English-speaking world, as related to research, university education, and industrial practice. The 1988 Springer-Verlag edition of "Warmeiibergang beim Kondensieren und beim Sieden" has been enlarged to include additional material on falling film evaporation (Chapter 12) and pressure drop in two-phase flow (Chapter 13). Minor errors in the original text have also been corrected. I would like to express my sincere appreciation to Professor Green, Asso ciate Professor of German at Rensselaer, for his excellent translation and co operation. My thanks go also to Professor Bergles for his close attention to technical and linguistic details. He carefully read the typescript and made many comments and suggestions that helped to improve the manuscript. I hope that the English edition will meet with' a favorable reception and contribute to better understanding and to progress in the field of heat transfer in condensation and boiling. February 1992 K. Stephan Preface to the German-Language Edition This book is a continuation of the series "Heat and Mass Transfer" edited by U. Grigull, in which three volumes have already been published. Its aim is to acquaint students and practicing engineers with heat transfer during condensa tion and boiling, and is intended primarily for students and engineers in mechanical, chemical, electrical, and industrial processing engineering.

Author: Marziye Mirbagheri
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"Cette thèse de doctorat porte sur le transfert de masse dans des milieux poreux incluant la diffusion de surface et des phases interactives. Le transport massique au travers des matériaux poreux est un phénomène essentiel pour de nombreux processus technologiques et naturels. Les plantes et les légumes absorbent l'eau et les nutriments, puis les stockent dans un espace poreux à travers leurs capillaires. Les humains respirent en partie à travers les pores de leur peau. La diffusion de produit ou de réactif dans des catalyseurs poreux, qui sont utilisés pour augmenter la vitesse de réaction et de production, est contrôlée par la diffusion moléculaire à travers l'espace vide. La diffusion et l'adsorption de surface sont particulièrement importantes dans les déshumidificateurs, où l'humidité est contrôlée par l'adsorption de l'eau par des adsorbants, tel que le gel de silice. La diffusion contrôle la cinétique de presque toutes les réactions chimiques à l'état solide telles que le métamorphisme géologique, le traitement thermique de l'acier et la fabrication de semi-conducteurs et de supraconducteurs. Par conséquent, il est crucial de comprendre les bases fondamentales de la diffusion et sa dépendance à diverses propriétés physiques et structurelles. Dans cette dissertation, une revue de littérature liée à la recherche actuelle est d'abord fournie. Le développement d'un modèle analytique, calculant la diffusivité effective dans un milieu poreux anisotrope bidimensionnel est ensuite présenté. Une vérification détaillée du modèle à l'aide de théorie et d'une méthode de calcul numérique est réalisé. Ensuite, des calculs réalisés dans un environnement tridimensionnel ont été entrepris afin d'étudier l'effet de la porosité, de la taille des pores (particule), de la morphologie des pores, de la surface spécifique et de l'anisotropie sur les gaz et la diffusion superficielle dans des réseaux de sphères solides, de cavités sphériques et de pores et de fibres se chevauchant de façon aléatoire. Les calculs numériques ont établi les contributions relatives du gaz et de la surface au processus global de transport massique. La diffusion de surface est explorée comme mécanisme sélectif pour la déshumidification de divers gaz dans des réseaux de pores cylindriques et de fibres, où les structures des pores capillaires sont plus sélectives. La dernière section est une étude expérimentale de la diffusion et de la sorption de la vapeur d'eau dans des nanocomposites de polyacrylamide-silice afin d'identifier de nouvelles stratégies de conception pour les membranes à perméabilité sélective. Puisque la capacité d'adsorption et la diffusivité de surface des nanoparticules de silice peuvent être manipulées par l'adsorption du polymère sur la silice, un choix judicieux de la fraction volumique du polymère est nécessaire afin d'améliorer la perméabilité sélective. Similairement, la capacité d'absorption de l'eau par le polymère peut être contrôlée par des nanoparticules, puisqu'en présence d'un pénétrant (i.e. : eau), lorsque le polymère est lié à la surface des nanoparticules, celles-ci ont moins de mobilité. Finalement, des conclusions et des recommandations pour des travaux futurs sont fournies." --

Author: V. G. Rifert
Publisher: WIT Press (UK)
ISBN:
Category : Science
Languages : en
Pages : 402

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Book Description
In processes with condensation of steam-to-gas compositions or refrigerative agents an intensification of condensation is often required because thermal resistance on the condensation side can be greater than the thermal resistance of the heat transfer wall on the cooling side. In this work, a pair of researchers from the National Technical U. of Ukraine and the State Academy of Refrigeration (Ukraine) provide information about the enhancement of condensation, including research results from the former USSR they feel deserves wider dissemination as well as discussion of different theoretical models of the condensation process. The US office of WIT Press is Computational Mechanics. Annotation : 2004 Book News, Inc., Portland, OR (booknews.com).

Author: Sameer Khandekar
Publisher: Springer
ISBN: 9783030484637
Category : Science
Languages : en
Pages : 0

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Book Description
This book is an expanded form of the monograph, Dropwise Condensation on Inclined Textured Surfaces, Springer, 2013, published earlier by the authors, wherein a mathematical model for dropwise condensation of pure vapor over inclined textured surfaces was presented, followed by simulations and comparison with experiments. The model factored in several details of the overall quasi-cyclic process but approximated those at the scale of individual drops. In the last five years, drop level dynamics over hydrophobic surfaces have been extensively studied. These results can now be incorporated in the dropwise condensation model. Dropwise condensation is an efficient route to heat transfer and is often encountered in major power generation applications. Drops are also formed during condensation in distillation devices that work with diverse fluids ranging from water to liquid metals. Design of such equipment requires careful understanding of the condensation cycle, starting from the birth of nuclei, followed by molecular clusters, direct growth of droplets, their coalescence, all the way to instability and fall-off of condensed drops. The model described here considers these individual steps of the condensation cycle. Additional discussions include drop shape determination under static conditions, a fundamental study of drop spreading in sessile and pendant configurations, and the details of the drop coalescence phenomena. These are subsequently incorporated in the condensation model and their consequences are examined. As the mathematical model is spread over multiple scales of length and time, a parallelization approach to simulation is presented. Special topics include three-phase contact line modeling, surface preparation techniques, fundamentals of evaporation and evaporation rates of a single liquid drop, and measurement of heat transfer coefficient during large-scale condensation of water vapor. We hope that this significantly expanded text meets the expectations of design engineers, analysts, and researchers working in areas related to phase-change phenomena and heat transfer.

Author: Sameer Khandekar
Publisher: Springer
ISBN: 9781461484486
Category : Science
Languages : en
Pages : 141

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Book Description
Dropwise Condensation on Textured Surfaces presents a holistic framework for understanding dropwise condensation through mathematical modeling and meaningful experiments. The book presents a review of the subject required to build up models as well as to design experiments. Emphasis is placed on the effect of physical and chemical texturing and their effect on the bulk transport phenomena. Application of the model to metal vapor condensation is of special interest. The unique behavior of liquid metals, with their low Prandtl number and high surface tension, is also discussed. The model predicts instantaneous drop size distribution for a given level of substrate subcooling and derives local as well as spatio-temporally averaged heat transfer rates and wall shear stress.

Author: Petros Antonis
Publisher:
ISBN: 9781681173085
Category :
Languages : en
Pages : 294

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Book Description
Heat is the kinetic energy of particles as they vibrate. If we heat the particles at one end of a material the particles at that end vibrate more (have more kinetic energy) and bump into the neighboring particles which causes them to vibrate more. They collide with their neighbors and so the energy passes from one particle to another through the material. Evaporation and condensation are two processes through which matter changes from one state to another. Matter can exist in three different states: solid, liquid, or gas. In evaporation, matter changes from a liquid to a gas. In condensation, matter changes from a gas to a liquid. All matter is made of tiny moving particles called molecules. Evaporation and condensation happen when these molecules gain or lose energy in the form of heat. Evaporation happens when a liquid is heated. The heat gives the liquid's molecules more energy. This energy causes the molecules to move faster. If they gain enough energy, the molecules near the surface break away. These molecules escape the liquid and enter the air as gas. Condensation happens when molecules in a gas cool down. As the molecules lose heat, they lose energy. As a result they slow down. They move closer to other gas molecules. Finally these molecules collect together to form a liquid. The theoretical analysis and modeling of heat and mass transfer rates produced in evaporation and condensation processes are noteworthy concerns in a design of extensive range of industrial processes and devices. The book Evaporation, Condensation and Heat transfer emphasizes on the current issues of modeling on evaporation, water vapor condensation, heat transfer and exchanger, and on fluid flow in different aspects. The approaches would be applicable in various industrial purposes as well. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society..

Author: Yuri B. Zudin
Publisher: Springer
ISBN: 9783030138141
Category : Science
Languages : en
Pages : 404

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Book Description
This monograph is focused mostly on the exposition of analytical methods for the solution of problems of strong phase change. A new theoretical model is proved useful in describing, with acceptable accuracy, problems of strong evaporation and condensation. The book is the first to treat the problem of asymmetry for evaporation/condensation. A semi-empirical model for the process is proposed for purposes of practical calculation of the process of strong evaporation. The “limiting schemes” of the vapor bubble growth are analyzed. The thermo-hydrodynamic problem of evaporating meniscus of a thin liquid film on a heated surface is considered. A theoretical analysis of the problem of evaporation of a drop levitating over a vapor cushion is performed. The problem of vapor condensation upon a transversal flow around a horizontal cylinder is considered. The second edition is extended by (i) the conjugate “strong evaporation - heat conduction” problem, (ii) the influence of accommodation coefficients on intensive processes of evaporation and condensation, (iii) the problem of supersonic condensation. This book is the first to present a comprehensive theoretical approach of boiling problems: nucleate boiling, superfluid helium phase transition, similarity between pseudo-boiling and subcritical pressure nucleate boiling. The target audience primarily comprises research experts in the field of thermodynamics and fluid dynamics, but the book may also be beneficial for graduate students.

Author: Ch Marvillet
Publisher: Elsevier Science Limited
ISBN: 9782906077782
Category : Technology & Engineering
Languages : en
Pages : 219

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Book Description
Hardbound. This book deals with condensation, one of the most complex heat and mass transfer processes, involving mass, momentum, energy and chemical species transport in the vapour and liquid phases. Condensers are of many types including large power plant condensers, shell-and-tube process condensers, in-tube condensers, and plate heat exchangers. The size of condensers varies by a factor of around a million from the condenser of a motor vehicle air conditioning unit to that used in steam power plant.

Author: Daniel Beysens
Publisher:
ISBN: 9783030904432
Category : Heat engineering
Languages : en
Pages :

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Book Description
Humid Air -- Boundary Layers -- Nucleation -- Single Droplet Growth -- Drop Coalescence -- Drop Pattern Evolution -- Humidity Sink and Inhibited Condensation -- Border Effects -- Spatio-Temporal Dynamics.