Добірка наукової літератури з теми "Dispersion de liquide"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся зі списками актуальних статей, книг, дисертацій, тез та інших наукових джерел на тему "Dispersion de liquide".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Статті в журналах з теми "Dispersion de liquide":
1
Sauret, Alban, Guillaume Saingier, and Pierre Jop. "Érosion et accrétion de matériaux granulaires humides." Reflets de la physique, no. 64 (January 2020): 17–22. http://dx.doi.org/10.1051/refdp/202064017.
Анотація:
Le comportement des matériaux granulaires humides hétérogènes, éléments incontournables de nombreux processus industriels et géophysiques, résiste encore à une modélisation complète. L’interaction des grains avec une phase liquide doit être éclaircie afin d’optimiser les procédés de mélange, notamment la dispersion des grains d’un agrégat cohésif. Modéliser ces interactions permettrait aussi de mieux décrire des éboulements granulaires dont les propriétés mécaniques évoluent avec des variations de teneur en liquide et de répartition spatiale. Des recherches actuelles se tournent vers la compréhension des échanges dans ces matériaux, pour isoler les mécanismes par lesquels des grains se mélangent à un liquide ou à une phase granulaire humide.
2
Bascoul, A., J. P. Riba, C. Alran, and J. P. Couderc. "Influence de la distribution du liquide sur le coefficient de dispersion axiale en fluidisation liquide—solide." Chemical Engineering Journal 38, no. 2 (June 1988): 69–79. http://dx.doi.org/10.1016/0300-9467(88)80064-9.
3
Gonzalez Ortiz, Danae, Celine Pochat-Bohatier, Julien Cambedouzou, Mikhael Bechelany, and Philippe Miele. "Exfoliation of Hexagonal Boron Nitride (h-BN) in Liquide Phase by Ion Intercalation." Nanomaterials 8, no. 9 (September 12, 2018): 716. http://dx.doi.org/10.3390/nano8090716.
Анотація:
A green approach to prepare exfoliated hexagonal boron nitride nanosheets (h-BNNS) from commercially pristine h-BN involving a two-step procedure was investigated. The first step involves the dispersion of pristine h-BN within an aqueous solution containing gelatin and potassium or zinc chloride using a sonication method. The second involves the removal of larger exfoliated h-BNNS through a centrifugation procedure. The exfoliation was caused not only by the sonication effect but also by intercalation of K+ and Zn2+ ions. Transmission electronic microscopy, X-ray diffraction and Raman spectroscopy techniques show that the obtained h-BNNS generally display a thickness of about a few (2–3) layers with an exfoliation efficiency as high as 16.3 ± 0.4%.
4
Safronova, Ekaterina Yu, Daria Yu Voropaeva, Dmitry V. Safronov, Nastasia Stretton, Anna V. Parshina, and Andrey B. Yaroslavtsev. "Correlation between Nafion Morphology in Various Dispersion Liquids and Properties of the Cast Membranes." Membranes 13, no. 1 (December 22, 2022): 13. http://dx.doi.org/10.3390/membranes13010013.
Анотація:
Nafion is a perfluorosulfonic acid polymer that is most commonly used in proton-exchange membrane fuel cells. The processes of pretreatment and formation of such membranes strongly affect their properties. In this work, dispersions of Nafion in various ionic forms and dispersing liquids (ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone and isopropyl alcohol–water mixtures in different ratios) were obtained and studied. Membranes fabricated by casting of the various dispersions were also studied. The effect of the nature of the dispersing liquid and the counterion on the properties of Nafion dispersions, the morphology of the polymer in the dispersions and the characteristics of the membranes obtained from them has been shown. Based on the overall results, it can be concluded that the use of perfluorosulfonic acid dispersions in aprotic polar solvents is advisable for obtaining membranes by the casting procedure. This is because it provides optimal polymer morphology in the dispersion, which leads to the formation of films with good selectivity, mechanical and transport properties. The performed investigations show the relationship between the composition of dispersions, the morphology of the polymer and the properties of the membranes formed from them by the casting procedure.
5
Htet, Kyaw Myo, M. P. Glotova, and A. L. Galinovsky. "Innovative Research of Ultra-Jet Dispersion and Suspension Technologies for Processing and Modifying Liquids." Advanced Materials & Technologies, no. 3(19) (2020): 068–75. http://dx.doi.org/10.17277/amt.2020.03.pp.068-075.
Анотація:
Currently used dispersion methods are not able to provide sufficient dispersion of nanomodifiers in liquids. This circumstance significantly reduces the effectiveness of the subsequent use of liquid-phase nanomodifiers which are widely used in the production of a variety of composite polymer and ceramic structures. The article discusses a new method of dispersing and suspending liquids using ultra-jet technology. The results of experimental testing confirming the effectiveness of ultra-jet technologies for producing liquid suspensions with nanomodifiers are presented. Two different types of powder were chosen as liquid modifiers: boehmite and carbon nanotubes. Moreover, special technological equipment was developed to conduct the experiment. The results of the analysis of the obtained liquid suspensions containing nanomodifiers allow us to recommend this dispersion technology for use on an industrial scale.
6
Tabassum, Shagufta, and V. P. Pawar. "Complex permittivity spectra of binary polar liquids using time domain reflectometry." Journal of Advanced Dielectrics 08, no. 03 (June 2018): 1850019. http://dx.doi.org/10.1142/s2010135x18500194.
Анотація:
The study of complex properties in a binary mixture of polar liquids has been carried out in the frequency range of 10[Formula: see text]MHz to 30 GHz at 293[Formula: see text]K and 298[Formula: see text]K temperatures using time domain reflectometry. The complex properties of polar liquids in binary mixture give information about the frequency dispersion in the dielectric permittivity ([Formula: see text]) and dielectric loss ([Formula: see text]). The information regarding the orientation of electric dipoles in a polar liquid mixture is given by Kirkwood parameters. The Bruggeman parameters are used as the indicator of liquid1 and liquid2 interaction. Molar entropy ([Formula: see text]) and molar enthalpy ([Formula: see text]) are also discussed at the end of the paper.
7
Texter, John. "Liquid Polymerized Ionic Liquids." ECS Meeting Abstracts MA2022-02, no. 55 (October 9, 2022): 2089. http://dx.doi.org/10.1149/ma2022-02552089mtgabs.
Анотація:
Polymerized ionic liquids (PIL) are being used in many advanced materials applications. An interesting subclass of PILs is composed of liquid PIL, LPIL. Such materials exhibit classical liquid properties and offer insight into the physics and physical chemistry of liquids and particles. We present an overview of LPIL and a classification scheme to usefully compartmentalize such materials for further design, optimization, and application. Several members of this class of LPIL are described in detail along with multiple applications. One member consists of organosiloxanes condensed on themselves to produce a novel type of solvent-free nanofluid. These materials are the first to experimentally illustrate polydispersity frustration of crystallization and to show that both freezing and glass transitions are lambda transitions. Another member comprises a functional core decorated with ionic liquid salts. Such materials can be used to mitigate embrittlement accompanying using nanofillers and to incorporate such nanofluids in diverse new materials and functional coatings. Linear LPIL offer similar advantages to those provided by molecular IL and promise to overcome leaching limitations in liquid supported membranes and polyeletrolyte membranes in batteries and fuel cells. Lastly, extension of PILs to polyurethanes and polyureas (PUs) and to polyesters (PEs) has resulted in the first known self-dispersing polyurethane and polyester dispersions (PUDs and PEDs, respectively). Several of their applications in stimuli responsive coatings and graphene dispersions are illustrated.
8
Gruszczyński, Maciej, and Małgorzata Lenart. "Liquid Penetration Depth and Strength of Concretes Modified with Polymer Admixtures Under the Action of Crude-Oil Products." Materials 12, no. 23 (November 26, 2019): 3900. http://dx.doi.org/10.3390/ma12233900.
Анотація:
In the present article, the research results of concretes modified with a polymer dispersion of vinyl-benzene and acrylic (PC1) and with a styrene–butadiene dispersion (PC2) are discussed. Concretes were exposed to diesel, non-ethylated fuel, and the standard mixture of light liquids for 1000 h. Concretes modified with polymer dispersions, especially with the styrene–butadiene dispersion (PC2), indicated a smaller degree of liquid penetration into the depth of samples compared to the control concrete. The compressive strength for tested concretes, determined after 1000 h of storage in crude-oil products, in comparison to the strength of samples stored in de-mineralized water was significantly decreased, with the maximum differences equal to 12% for PC2 concrete.
9
Kolikov, Kiril Hristov, Dimo Donchev Hristozov, Radka Paskova Koleva, and Georgi Aleksandrov Krustev. "Model of Close Packing for Determination of the Major Characteristics of the Liquid Dispersions Components." Scientific World Journal 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/615236.
Анотація:
We introduce a close packing model of the particles from the disperse phase of a liquid dispersion. With this model, we find the sediment volumes, the emergent, and the bound dispersion medium. We formulate a new approach for determining the equivalent radii of the particles from the sediment and the emergent (different from the Stokes method). We also describe an easy manner to apply algebraic method for determining the average volumetric mass densities of the ultimate sediment and emergent, as well as the free dispersion medium (without using any pycnometers or densitometers). The masses of the different components and the density of the dispersion phase in the investigated liquid dispersion are also determined by means of the established densities. We introduce for the first time a dimensionless scale for numeric characterization and therefore an index for predicting the sedimentation stability of liquid dispersions in case of straight and/or reverse sedimentation. We also find the quantity of the pure substance (without pouring out or drying) in the dispersion phase of the liquid dispersions.
10
Levchenko, Yevhenii, Olga Sverdlikovska, Denys Chervakov, and Oleh Chervakov. "Development of coalescents for paints and varnishes based on ionic liquids – the products of diethanolamine and inorganic acids interaction." Eastern-European Journal of Enterprise Technologies 2, no. 6 (110) (April 12, 2021): 21–29. http://dx.doi.org/10.15587/1729-4061.2021.228546.
Анотація:
This paper reports the synthesis of ionic liquids through the interaction between diethanolamine and orthophosphate and boric acids in order to establish the possibility of replacing volatile coalescents in a formulation for paints and varnishes with ionogenic compounds. The results from studying the influence of polymeric coalescents based on ionic liquids on the rheological properties of water-dispersion paints and varnishes of different nature are presented. It has been established that the synthesized coalescents could be used to modify the properties of paints and varnishes based on polyurethane and styrene-acrylic aqueous dispersions. It has been shown that the product of the interaction between diethanolamine and boric acid in aqueous solutions forms an ionogenic complex compound with a unipolar conductivity in terms of ОН─ ions. It was also established that when introduced to the formulation of water-dispersion paints and varnishes, the solutions of modifiers produce a diluting action. The influence of ionic liquids on the process of film formation of aqueous dispersions of polymers and pigmented paints and varnishes based on them was investigated. It was established that the synthesized ionogenic compounds are not inferior, in terms of their effectiveness, to the widespread conventional industrial coalescents of the Texanol→ type. Therefore, there is reason to assert the possibility of replacing the industrial coalescent Texanol→ in the formulation of pigmented water-dispersion paints and varnishes based on styrene-acrylic and polyurethane dispersions with fundamentally new synthesized ionogenic modifiers. Thus, the coatings with a coalescent based on ion liquid of diethanolamine borate have a higher level of conditional hardness, which exceeds by 17 % the hardness index of the paint made on the basis of the conventional Texanol→ type coalescent, without changing its decorative properties, such as color and shine
Дисертації з теми "Dispersion de liquide":
1
Felis-Carrasco, Francisco. "Atomisation et dispersion d'un jet liquide : approches numérique et expérimentale." Thesis, Ecole centrale de Marseille, 2017. http://www.theses.fr/2017ECDM0001/document.
Анотація:
L'atomisation d'un jet circulaire d'eau typique des applications agricoles est présentée dans cette étude. Maîtriser la dispersion de l'eau à des fins d'irrigation ou de traitements phytosanitaires implique de réduire la consommation d’eau et la pollution de l'environnement. Un cas d'étude simplifié est construit : une buse ronde dn=1.2 mm et d'une longueur Ln=50dn y est considérée. La vitesse d'injection est fixée à UJ=35 m/s et alignée avec la gravité, plaçant le jet liquide dans un régime d'atomisation turbulent. L'écoulement est statistiquement axisymétrique. L'approche est à la fois expérimentale et numérique.Un modèle multiphasique Eulérien de mélange décrit l'écoulement constitué de deux phases. Plusieurs modèles de turbulence U-RANS sont utilisés: k-ε et RSM. Une attention particulière est alors portée à la modélisation des effets de masse volumique variable issus de la formulation du fluide de mélange. Un solveur numérique spécifique est développé à l'aide du code CFD OpenFOAM. Une série de cas d'étude est construite pour tester l'influence de la modélisation de la turbulence et des fermetures de premier/second-ordre des flux massiques turbulents.Les techniques optiques (LDV et DTV) sont déployées pour recueillir des informations statistiques des phases liquide et gazeuse du spray. La campagne expérimentale est réalisée de x/dn=0 jusqu'à x/dn=800. En ce qui concerne la LDV, des gouttelettes d'huile d'olive (~1 µm) permettent d'analyser la phase gazeuse. Une distinction entre les gouttes de liquide et ces traceurs est obtenue par une configuration spécifique de la source laser et le paramétrage de la détection des bouffées Doppler (Filtre-BP et le SNR). Dans la zone dispersée, les mesures par DTV permettent d'estimer les vitesses et les tailles des gouttes. Une attention particulière est portée à l'estimation de la profondeur de champ (DOF) afin d'obtenir une corrélation taille-vitesse des gouttes moins biaisée.Les résultats numériques et expérimentaux concordent pour le champ de vitesse moyenne. Une forte dépendance au modèle de turbulence est trouvée. Cependant, le modèle RSM ne simule pas le comportement du tenseur de Reynolds. En effet, ni l'anisotropie trouvée expérimentalement (R22/R11≈0.05), ni la vitesse de glissement liquide-gaz ne peuvent être reproduites; même avec une fermeture au 2nd-ordre des flux massiques turbulents. Le fort rapport de masse volumique (eau/air), la directionnalité de l'écoulement et la production d'énergie cinétique turbulente peuvent être à l'origine d'une faible dispersion et d'un faible mélange entre les deux fluides. Ce mécanisme n'est pas encore clarifié du point de vue de la modélisation RSMA typical water round-nozzle jet for agricultural applications is presented in this study. The dispersion of a liquid for irrigation or pesticides spraying is a key subject to both reduce water consumption and air pollution. A simplified study case is constructed to tackle both scenarios, where a round dn=1.2 mm nozzle of a length Ln=50dn is considered. The injection velocity is chosen to be UJ=35 m/s, aligned with gravity, placing the liquid jet in a turbulent atomization regime. The flow is considered statistically axisymmetric. Experimental and numerical approaches are considered.An Eulerian mixture multiphase model describes the original two-phase flow. Several U-RANS turbulence models are used: k-ε and RSM; where special attention is taken to the modelling of variable density effects from the mixture formulation. A custom numerical solver is implemented using the OpenFOAM CFD code. A series of study cases are constructed to test the influence of the turbulence modeling and first/second-order closures of the turbulent mass fluxes. LDV and DTV optical techniques are used to gather statistical information from both the liquid and the gas phases of the spray. The experimental campaign is carried out from x/dn=0 to x/dn=800. Concerning the LDV, small (~1 µm) olive-oil tracers are used to capture the gas phase, where a distinction between the liquid droplets and tracers is achieved by a specific set-up of the laser power source and the burst Doppler setting (BP-Filter and SNR). On the dispersed zone, DTV measurements are carried out to measure velocities and sizes of droplets. Special attention to the depth-of-field (DOF) estimation is taken in order to obtain a less biased droplet’s size-velocity correlation.Numerical and experimental results show good agreement on the mean velocity field. A strong dependence on the turbulence model is found. However, the RSM does not capture the same behaviour on the calculated Reynolds stresses. Indeed, neither the experimental anisotropy (R22/R11≈0.05), nor the liquid-gas slip-velocity can be reproduced, even with a second-order closure for the turbulent mass fluxes. The strong density ratio (water/air), flow’s directionality and production of turbulent kinetic energy may be the cause of a weak dispersion and mixing between the two fluids. This mechanism is not yet clarified from a RSM modeling point-of-view
2
Lobry, Emeline. "Batch to continuous vinyl chloride suspension polymerization process : a feasibility study." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/11498/1/lobry.pdf.
Анотація:
Continuous processes present the benefit to be safer and more cost saving than batch processes. Many researches have been carried out in fine chemistry but few contributions refer to polymerization. We focus on the vinyl chloride suspension polymerization. This process has been extensively studied in batch with lots of improvement regarding the formulation and the technologies. This polymerization process is highly complex due to the toxic nature of the monomer, the good manage of heat transfer and stirring. Moreover the reaction step remains the only batch step of the PVC production. According to the PVC grain formation, the process can be divided into three steps (i) a liquid-liquid dispersion step in which the monomer droplet (30-50 µm) are generated and stabilized, (ii) a controlled agglomeration step of the reacting droplets exhibiting a sticky behaviour, (iii) a reaction step until the conversion rate is around 80-90% and the particles size is stable. In this study, the different technologies suitable for the different steps are pointed out. Based on the state of the art of the grain behaviour depending on the reaction conversion and on the literature concerning polymerization continuous process, static mixers and different co-current pulsed columns are proposed. Three technologies with different model system were chosen to study the liquid-liquid dispersion step. Static mixers allow the control of the droplet size under turbulent flow. In the range of the operating conditions, the dispersed phase concentration does not have a significant effect on the droplet size. The interfacial tension appears to be the most significant physico-chemical parameters. Correlation to predict the mean droplet size is proposed depending on different dimensionless numbers based on the hydrodynamics and on the systems: the Reynolds and Weber numbers. Given the promising results, static mixers are implemented at pilot scale to load the batch prior to polymerization. Their use demonstrates a noticeable reduction of the loading time and a better homogenisation of the different suspending agents and initiator inside the PVC grain. The two co-current pulsed columns design studied are the discs and doughnuts pulsed column and the COBR (continuous oscillatory baffled reactor, Nitech). For the first one, the effect of the packing materials (type and height), of the physico-chemical parameters (dispersed phase concentration, surfactant) and of hydrodynamic parameters (flowrate and oscillation conditions) on the droplet size are investigated where as for the second one the study is limited to the hydrodynamic parameters. A mean droplet size correlation is proposed based on the characteristic dimensionless numbers. The three continuous contactors used for liquid-liquid dispersion are compared in term of energy dissipation rate. The reaction is carried out in a continuous tubular reactor (the pulsed column). The column is suitable to transport solid-liquid suspension. Vinyl acetate suspension polymerization is performed to demonstrate the feasibility and particularly to study the encrusting and fouling problem. The first results are very promising.
3
Wahl, Jacques. "Caractérisation d'une dispersion gaz/liquide par échos d'impulsions ultrasonores /." [S.l.] : [s.n.], 1987. http://library.epfl.ch/theses/?nr=590.
4
Dames, Maysoun Xuereb Catherine Azzaro-Pantel Catherine. "Gestion de procédés discontinus méthodologie de modélisation et d'optimisation d'opérations de dispersion liquide-liquide en cuve agitée /." Toulouse : INP Toulouse, 2005. http://ethesis.inp-toulouse.fr/archive/00000173.
5
Dames, Maysoun. "Gestion de procédés discontinus : méthodologie de modélisation et d'optimisation d'opérations de dispersion liquide-liquide en cuve agitée." Phd thesis, Toulouse, INPT, 2005. https://hal.science/tel-04582971.
Анотація:
Les dispersions liquide-liquide et les émulsions sont présentes dans un grand nombre de domaines industriels ainsi que dans une grande variété de produits. Leur élaboration est parmi les opérations les plus complexes. L'influence très importante et combinée, des propriétés physico-chimiques des produits et de l'hydrodynamique dans l'appareil utilisé rend extrêmement difficile la prédiction des caractéristiques de la dispersion et, a fortiori, l'optimisation du procédé. Notre étude porte sur le cas de deux types de dispersions liquide-liquide, ayant en commun d'être réalisées en cuve agitée, mais à vocations très différentes. Le premier cas concerne une opération d'extraction, tandis que le deuxième vise la fabrication d'un produit dont une propriété doit être contrôlée (la taille des gouttes). Selon la nature et la complexité des phénomènes envisagés, nous avons développé deux démarches différentes. Dans le premier cas, nous avons adopté une démarche expérimentale pour optimiser le rendement d'une étape de procédé de purification des acrylates multi-fonctionnels. Le résultat a mis en évidence l'influence prépondérante de certains paramètres opératoires et a ouvert la voie vers le développement d'un nouveau procédé répondant à des exigences environnementales et économiques. Dans la deuxième application, concernant l'élaboration d'émulsions présentant des propriétés particulières, nous avons appliqué une démarche synthétique, basée sur le couplage entre un réseau de neurones, en tant qu'outil de modélisation non linéaire de la relation fonctionnelle entre le diamètre moyen de gouttes et les différentes variables opératoires, et un algorithme génétique, comme un moyen de prédiction de conditions opératoires satisfaisant à un critère donné (d32). L'application de ces outils dans le domaine physique s'est révélée d'un grand intérêt. Elle ouvre une immense voie vers la maîtrise de la complexité des procédés en imposant plusieurs scénarii d'opération possiblesLiquid-liquid dispersions and emulsions are formed in a large number of industrial domains, as well as in a wide range of products. However, their development presents one of the most complex operations. Dispersions are highly dependant on the physicochemical properties of products used and the hydrodynamics in the apparatus, which makes the prediction of the dispersion characteristics, and in particular, the optimization of the process, extremely difficult. This thesis investigates two types of liquid-liquid dispersions. Each type is discussed via separate case studies both created in an agitated vessel. The first case investigates an extraction operation, while the second concerns emulsions manufacturing, where by the drop size must be controlled. According to the nature and the complexity of the phenomena considered, two different approaches have been developed. In the first case, an experimental approach has been employed in order to optimize the yield in the purification step of a multi-functional acrylates process. The results show that there are predominant influences of certain operating parameters. It argued therefore that there is a need to develop a new process which considers environmental and economic requirements. In the second case, the development of emulsions with particular properties was investigated. The case adopts a synthetic approach that is based upon coupling a neural network and a genetic algorithm. Neural network is used as a non-linear modelling tool to determine the functional relationships between the means drop diameter and different operating variables. The genetic algorithm is used as a means for prediction the operating conditions that enable a given criteria (d32) to be reached. The application of these tools in the physical domain studied was shown to be of great interest. It is anticipated that such tools will lead to the development of new ways to control complex processes
6
Vu, Tuyet-Oanh. "Dispersion d'une poudre dans un liquide : caractérisation des interactions interfaciales et effets de différents facteurs sur la vitesse de dispersion." Saint-Etienne, EMSE, 2002. http://www.theses.fr/2002EMSE0029.
Анотація:
L'objectif de ce travail est d'étudier un système poudre/liquide permettant de disperser instantanément une poudre dans un liquide. Les interactions entre le solide granulaire choisi, le cacao, et l'eau ont été caractérisées afin de déterminer le comportement en dispersion. Les angles de contact et le travail d'adhésion ont été mesurés par la méthode de la goutte posée et par la mesure de l'ascension capillaire (méthode de Washburm modifiée). L'eau est un très mauvais liquide mouillant pour la poudre de cacao. La vitesse de dispersion est mesurée à l'aide d'un capteur à fibres optiques. L'augmentation de la puissance fournie par le mobile d'agitation ou l'élévation de la température du liquide dispersant permet d'accélérer la vitesse de dispersion. La poudre a été granulée par deux procédés : l'atomisation et le mélange à haut cisaillement. L'atomisation permet d'obtenir une meilleure qualité de dispersion tandis que le mélangeur donne des granules se dispersant plus rapidementThe aim of this work is to study a powder/liquid system for instantizing a powder in a liquid. The model powder chosen, cocoa, and its interaction with water were characterised to determine the dispersion behaviour. Contact angles and adhesion forces were measured by the sessile drop method and by a modified Washburm method. Water is a non-wetting liquid with respect to cocoa powder. Dispersion kinetics were measured by using an optical fibre detector. The most significant parameters on dispersion speed were the power of the agitation and the rise in temperature. Granulated powder was prepared by two processes : atomisation and high shear granulation. Atomisation lead to better dispersion while high shear granulation gave granules having an increased speed of dispersion
7
Kibboua, Rachid. "Etude d'une dispersion liquide-liquide soumise à un écoulement cisaillé simple : caractérisation vis à vis de la coalescence." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10167.
Анотація:
L'ecoulement d'une dispersion eau-huile a ete analyse experimentalement et theoriquement pour differentes huiles dans le cas d'un ecoulement de couette circulaire. Les mesures locales effectuees ont porte sur le profil radial de concentration des gouttes par imagerie dans le cas ou l'un ou l'autre des deux cylindres est tournant. D'autres mesures globales ont ete faites et portent sur la mesure du diametre de sauter de la population de gouttes par attenuation lumineuse a l'aide d'une sonde optique. Un modele de melange a ete etabli pour la prediction du profil radial de concentration. Ce modele nous a permis de degager une relation empirique de la diffusivite hydrodynamique. D'autre part les mesures du diametre de sauter ont permis d'estimer le taux de coalescence dans une dispersion eau-huile par confrontation des mesures avec une equation de bilan de population
8
Segovia, Mera Alejandro. "Effets de la dispersion de nanoparticules dans un cristal liquide ferroélectrique sur les propriétés ferroélectriques et de relaxations diélectriques." Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0461/document.
Анотація:
Ces travaux de thèse ont porté sur des matériaux constitués de dispersions de particules colloïdales nanométriques, issues d'un matériau ferroélectrique, dans un cristal liquide chiral à phase smectique ferroélectrique. Ils ont pour but d'étudier les effets occasionnés par ces dispersions sur les propriétés du nanocolloïde, notamment celles liées à leur ferroélectricité. Cette étude a montré que les comportements mésomorphes et ferroélectriques de ces matériaux sont conservés. Une baisse de polarisation spontanée ainsi qu'un recul des températures des transitions ont été mis en évidence pour des faibles concentrations en NPs. Une "transition" de ces comportements a été observée pour une concentration critique au-delà de laquelle les particules s'agrègent pour former des amas au sein du milieu cristal liquide. Nous nous sommes intéressés ensuite à deux modes de relaxation diélectriques. Le premier lié aux mouvements de distorsions de l'hélice dans la phase ferroélectrique, le second aux mouvements de compression des couches smectiques de part et d'autre de la transition ferroélectrique-paraélectrique. Les comportements observés semblent être gouvernés par les modifications des propriétés visco-élastiques des nanocolloïdes, occasionnés par l'intercalation des nanoparticules entre les couches smectiquesThe present thesis work concerns materials made of dispersions of nanometric colloidal particles, from a bulk ferroelectric material, dispersed within a chiral smectic phase of a ferroelectric liquid crystal. The goal of this work is to study the effect of the dispersed nanoparticles over the nanocolloïd properties, specially the ones related to ferroelectricity. This study showed no change over mesomorphic and ferroelectric behavior of the materials. A decrease in spontaneous polarization and phase transition temperatures was found for low nanoparticle concentrations. A "transition" of these behaviors was observed for a critical concentration, beyond which, nanoparticles aggregate and form clusters inside the liquid crystal matrix. Afterwards, we have studied two dielectric relaxation modes. The first one related to distorsions of the helix in the ferroelectric phase and the second one to the compression movements of the smectic layers around the ferroelectric-paralectric transition. The observed behaviors seem to be due to modifications of the visco-elastic properties of nanocolloids, produced by intercalation of nanoparticles between the smectic layers
9
Rivière, Annise. "Granulométrie d'un liquide dispersé par explosif." Electronic Thesis or Diss., Ecole nationale des Mines d'Albi-Carmaux, 2024. http://www.theses.fr/2024EMAC0003.
Анотація:
Dans le cadre de ses études sur la détonique, le CEA de Gramat s'intéresse à la dispersion de liquides dans l'air, avec des contraintes de haute vitesse/énergie, et des aspects multi-échelles. La mesure de la granulométrie du liquide dispersé suscite un vif intérêt et s'avère complexe car aucune solution commerciale n'est utilisable dans ces conditions particulières. Toutefois, dans ces conditions et avec l'impossibilité d'utiliser des sources laser en environnement pyrotechnique, aucune solution commerciale n'est disponible. Pour ce travail de thèse, une nouvelle méthode d'identification de la granulométrie a donc été développée, et se base sur une mesure dite "par extinction", particulièrement simple de déploiement et robuste en environnement sévère. Il s'agit d'une approche multispectrale (mesure avec des caméras ou un spectromètre) faisant appel à une méthode d'inversion régularisée au sens de Tikhonov, s'appuyant sur la mesure de transmissions spectrales, et qui permet de reconstruire la granulométrie de ce dernier a posteriori à l'aide de la loi de Beer-Lambert combinée au modèle de Mie. De par la complexité des phénomènes liée à l'usage d'explosif pour la dispersion, la méthode développée a été testée sur des dispersions de liquide reproduites à petite échelle sur des sprays. La méthode générale a été développée en exploitant les informations spectrales provenant de sprays d'eau contrôlés et confinés dans une enceinte placée dans un spectromètre infrarouge à transformée de Fourier (haute résolution). Cependant, cet appareillage étant peu adapté aux conditions terrain, la méthode de mesure a été dégradée en utilisant des caméras permettant des mesures à "faible résolution" mais plus rapides. Ainsi, l'utilisation d'une caméra infrarouge opérant en bande spectrale 2-5 µm avec des filtres spectraux et d'un corps noir plan a été testée pour suivre l'évolution de granulométrie du spray en fonction du temps. Par la suite, cette méthode a pu être appliquée à des dispersions d'eau par explosif et a fourni des résultats prometteurs. La démarche complète de mesure et d'analyse a donc pu être validée à chaque étape de l'étudeAs part of its studies on detonation, the CEA at Gramat is interested in the dispersion of liquids in air, with high speed/energy constraints and multi-scale aspects. Measuring the particle size of the dispersed liquid is attracting a great deal of interest, but is proving complex because no commercial solution can be used under these particular conditions. However, under these conditions and given the impossibility of using laser sources in a pyrotechnic environment, no commercial solution is available. For this thesis, a new granulometry identification method was developed, based on a measurement known as "extinction", which is particularly easy to deploy and robust in harsh environments. This is a multispectral approach (measurement with cameras or a spectrometer) using a regularised inversion method in the sense of Tikhonov, based on the measure of spectral transmissions and which makes it possible to reconstruct the granulometry of the latter a posteriori using the Beer-Lambert law combined with the Mie model. Given the complexity of the phenomena involved in using explosives for dispersion, the method developed was tested on liquid dispersions reproduced on a small scale on sprays. The general method was developed by exploiting spectral information from controlled water sprays confined in an enclosure placed in a Fourier transform infrared spectrometer (high resolution). However, as this equipment is poorly suited to field conditions, the measurement method was downgraded by using cameras that allow "low resolution" but faster measurements. The use of an infrared camera operating in the 2-5 µm spectral band with spectral filters and a flat black body was therefore tested to monitor changes in spray particle size as a function of time. This method was subsequently applied to water dispersions using explosives, with promising results. The complete measurement and analysis process was therefore validated at each stage of the study
10
Abdoune, Fatima-Zohra. "Dispersion de nano- et micro-domaines de cristal liquide dans des matrices polymères." Lille 1, 2006. http://www.theses.fr/2006LIL10163.
Анотація:
Une étude détaillée des propriétés optiques, électro-optiques, thermophysiques et morphologiques des matériaux composites de polymères et cristaux liquides de type PDLC (polymer dispersed liquide crystals) a été effectuée. Ces matériaux ont été formés par des processus de séparation de phases induite par polymérisation : un mélange homogène comportant le cristal liquide E7, un monomère et un photoamorceur a été exposé au rayonnement de la lumière visible ou ultraviolette. Les matériaux PDLC dont la taille des domaines de cristal liquide se trouve dans la gamme des longueurs d'ondes du visible ont été élaborés et étudiés en utilisant le tripropylèneglycoldiacrylate comme monomère. Ces systèmes ont une fonctionnalité électro-optique très spéciale puisqu'ils peuvent commuter d'un état initial opaque à un état transparent sous l'effet d'un champ électrique. Des systèmes nano-PDLC dont les dimensions des domaines de cristal liquide sont inférueures à la longueur d'onde du visible ont été également préparés et étudiés pour un monomère à base d'un composé thiol-ène. L'analyse de la cinétique de la polymérisation/réticulation des mélanges monomère/cristal liquide/photoamorceur à l'aide de la spectroscopie infrarouge a montré en général un taux de conversion élevé du monomère. L'influence de la composition, la source et la dose du rayonnement ont été étudiées à l'aide de plusieurs techniques expérimentales et en particulier par spectroscopie UV-visible, calorimétrie différentielle, miccroscopie optique à lumière polarisée et microscopie électronique à balayage.
Книги з теми "Dispersion de liquide":
1
F, Tadros Th, and Royal Society of Chemistry (Great Britain), eds. Solid/liquid dispersions. London: Academic Press, 1987.
2
Drzaic, Paul S. Liquid crystal dispersions. Singapore: World Scientific, 1995.
3
Dobiáš, B. Solid-liquid dispersions. New York: Marcel Dekker, 1999.
4
Dobiáš, Bohuslav. Solid-liquid dispersions. New York: Marcel Dekker, 1999.
5
S, Gerardo A. Sanchez. Coalescence phenomena in liquid-liquid dispersions. Birmingham: University of Birmingham, 1996.
6
Nelson, RalphD. Dispersing powders in liquids. Amsterdam: Elsevier, 1988.
7
Nelson, Ralph D. Dispersing powders in liquids. Amsterdam: Elsevier, 1988.
8
Tatterson, Gary B. Fluid mixing and gas dispersion in agitated tanks. New York: McGraw-Hill, 1991.
9
Stein, H. N. The preparation of dispersions in liquids. New York: M. Dekker, 1996.
10
Evdokimov, I︠U︡ M. DNA liquid-crystalline dispersions and nanoconstructions. Boca Raton: Taylor & Francis, 2012.
Частини книг з теми "Dispersion de liquide":
1
Gooch, Jan W. "Dispersion, Particles and Liquids." In Encyclopedic Dictionary of Polymers, 235–36. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_3845.
2
Haerle, Andrew G., and Kevin J. Nilsen. "Solids Dispersion in Liquids." In Carbide, Nitride and Boride Materials Synthesis and Processing, 505–23. Dordrecht: Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-009-0071-4_20.
3
Bedair, Alaa, and Fotouh R. Mansour. "Dispersive Liquid–Liquid Microextraction." In Microextraction Techniques, 275–313. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-50527-0_9.
4
Stark, H., A. Borštnik, and S. Žumer. "Liquid Crystal Colloidal Dispersions." In Defects in Liquid Crystals: Computer Simulations, Theory and Experiments, 37–85. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0512-8_3.
5
Bernhardt, Claus. "Dispersion of solids in liquids." In Particle Size Analysis, 76–108. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1238-3_4.
6
Pietro, Argurio. "Strip Dispersion Supported Liquid Membrane." In Encyclopedia of Membranes, 1–3. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-40872-4_556-5.
7
Argurio, Pietro. "Strip Dispersion Supported Liquid Membrane." In Encyclopedia of Membranes, 1827–29. Berlin, Heidelberg: Springer Berlin Heidelberg, 2016. http://dx.doi.org/10.1007/978-3-662-44324-8_556.
8
Hartland, Stanley. "Coalescence in Dense-Packed Dispersions." In Thin Liquid Films, 663–766. New York: Routledge, 2023. http://dx.doi.org/10.1201/9780203735732-10.
9
Gerbeth, G., and D. Hamann. "Dispersion of Small Particles in MHD Flows." In Liquid Metal Magnetohydrodynamics, 97–102. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0999-1_12.
10
Podgórska, Wioletta. "Fluid–Fluid Dispersions: Liquid–Liquid and Gas–Liquid Systems." In Multiphase Particulate Systems in Turbulent Flows, 221–355. First edition. | New York, NY : CRC Press, Taylor & Francis Group, 2020.: CRC Press, 2019. http://dx.doi.org/10.1201/9781315118383-6.
Тези доповідей конференцій з теми "Dispersion de liquide":
1
Hartland, S. "SEPARATION OF LIQUID-LIQUID DISPERSIONS." In International Symposium on Liquid-Liquid Two Phase Flow and Transport Phenomena. Connecticut: Begellhouse, 1997. http://dx.doi.org/10.1615/ichmt.1997.intsymliqtwophaseflowtranspphen.330.
2
Kinugasa, Takumi, Kunio Watanabe, Tsuneo Sonobe, and Hiroshi Takeuchi. "PHASE INVERSION OF STIRRED LIQUID-LIQUID DISPERSIONS." In International Symposium on Liquid-Liquid Two Phase Flow and Transport Phenomena. Connecticut: Begellhouse, 1997. http://dx.doi.org/10.1615/ichmt.1997.intsymliqtwophaseflowtranspphen.520.
3
Kawase, Yoshinori, and Kazuhiro Shimizu. "EFFECT OF NON-NEWTONIAN FLOW BEHAVIORS ON SHEAR STRESS IN LIQUID-LIQUID DISPERSION." In International Symposium on Liquid-Liquid Two Phase Flow and Transport Phenomena. Connecticut: Begellhouse, 1997. http://dx.doi.org/10.1615/ichmt.1997.intsymliqtwophaseflowtranspphen.500.
4
Said Mohamed, A., Jose Lopez-Herrera, M. A. Herrada, and A. Gañan-Calvo. "Video: New modes in liquid-liquid dispersion." In 68th Annual Meeting of the APS Division of Fluid Dynamics. American Physical Society, 2015. http://dx.doi.org/10.1103/aps.dfd.2015.gfm.v0074.
5
Panoussopoulos, K., S. Hartland, P. E. Gramme, and T. Sontvedt. "DROP SIZE AND HOLD-UP PROFILES IN THE SEPARATION OF CRUDE OIL - WATER DISPERSIONS." In International Symposium on Liquid-Liquid Two Phase Flow and Transport Phenomena. Connecticut: Begellhouse, 1997. http://dx.doi.org/10.1615/ichmt.1997.intsymliqtwophaseflowtranspphen.370.
6
Nowinowski-Kruszelnicki, Edward, Andrzej Walczak, and Piotr Marciniak. "Refractive dispersion by means of Fabry-Perot filter." In XIV Conference on Liquid Crystals, Chemistry, Physics, and Applications, edited by Jolanta Rutkowska, Stanislaw J. Klosowicz, and Jerzy Zielinski. SPIE, 2002. http://dx.doi.org/10.1117/12.472202.
7
Escalante, H., A. I. Alonso, I. Ortiz, and A. Irabien. "MODELLING OF LIQUID-LIQUID NON-DISPERSIVE EXTRACTION PROCESSES IN HOLLOW FIBER MODULES." In International Symposium on Liquid-Liquid Two Phase Flow and Transport Phenomena. Connecticut: Begellhouse, 1997. http://dx.doi.org/10.1615/ichmt.1997.intsymliqtwophaseflowtranspphen.160.
8
Khan, Zurwa, Reza Tafreshi, MD Ferdous Wahid, and Albertus Retnanto. "Prediction of Pressure Drops in Liquid-Liquid Two-Phase Flow Across Circular Channels." In ASME 2021 40th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/omae2021-62861.
Анотація:
Abstract Mechanistic models are necessary for understanding and predicting the behavior of liquid-liquid flow for multiple pipe dimensions, mixture properties, and flow patterns. In this paper, a mechanistic model is proposed to calculate pressure drop across circular channels for liquid-liquid two-phase flow. The developed model considers several key aspects of liquid-liquid flow, such as mixed and wavy liquid-liquid interfaces and dispersion within each liquid’s layers. Unique identifiers, such as height, turbulence, and dispersion, are calculated for each phase, using an augmented separated flow model and nonlinear optimization. Comparison of the proposed model with experimental data, comprising of multiple inclination angles and flow patterns, shows accurate predictions for a variety of liquid-liquid flow patterns, including double- and triple-layered flow.
9
Habchi, Charbel, Sofiane Ouarets, Thierry Lemenand, Dominique Della-Valle, Jerome Bellettre, and Hassan Peerhossaini. "VISCOSITY EFFECTS ON LIQUID-LIQUID DISPERSION IN LAMINAR FLOWS." In CONV-09. Proceedings of International Symposium on Convective Heat and Mass Transfer in Sustainable Energy. Connecticut: Begellhouse, 2009. http://dx.doi.org/10.1615/ichmt.2009.conv.1280.
10
Pillapakkam, Shriram B., and Pushpendra Singh. "Dispersion of Particles on Liquid Surfaces." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-64514.
Анотація:
In a recent study we have shown that when small particles, e.g., flour, pollen, glass, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. The vertical motion of a particle during its adsorption causes a radially-outward lateral (secondary) flow on the interface that causes nearby particles to move away. We present direct numerical simulation results for the adsorption of particles and show that the inertia of a particle plays an important role in its motion in the direction normal to a fluid-liquid interface. Although the importance of inertia diminishes with decreasing particle size, on an air-water interface the inertia continues to be important even when the size is as small as a few nanometers.
Звіти організацій з теми "Dispersion de liquide":
1
Gorbov, Alexander. Converted fuels for smart home infrastructure. Part 1 - Converted types of innovative fuels and fuel mixtures. Intellectual Archive, June 2023. http://dx.doi.org/10.32370/iaj.2854.
Анотація:
A device for dynamic mixing and homogenization of liquid fuels and fuel mixtures, as well as for the formation of gasified (compressible) fuel mixtures. Industrial plant for the homogenization of liquid fuels in the range from Diesel fuel No. 6 (fuel oil) to diesel fuel No. 2, as well as for micro minimization and optimization of dispersion during injection of biofuels, methanol, ethanol and kerosene obtained from the processing of plastic waste masses and automobile and other tires; Productivity of installation, despite the small sizes, - 1000 liters an hour.
2
Brydie, Dr James, Dr Alireza Jafari, and Stephanie Trottier. PR-487-143727-R01 Modelling and Simulation of Subsurface Fluid Migration from Small Pipeline Leaks. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), May 2017. http://dx.doi.org/10.55274/r0011025.
Анотація:
The dispersion and migration behavior of hydrocarbon products leaking at low rates (i.e. 1bbl/day and 10 bbl/day) from a pipeline have been studied using a combination of experimental leakage tests and numerical simulations. The focus of this study was to determine the influence of subsurface engineered boundaries associated with the trench walls, and the presence of a water table, upon the leakage behavior of a range of hydrocarbon products. The project numerically modelled three products including diesel, diluted bitumen (dilbit) and gasoline; which were chosen to span a range of fluid types and viscosities. Laboratory simulations of leakage were carried out for the most viscous product (i.e. dilbit) in order to capture plume dispersion in semi-real time, and to allow numerical predictions to be assessed against experimental data. Direct comparisons between observed plume dimensions over time and numerically predicted behavior suggested a good match under low moisture conditions, providing confidence that the numerical simulation was sufficiently reliable to model field-scale applications. Following a simulated two year initialization period, the leakage of products, their associated gas phase migration, thermal and geomechanical effects were simulated for a period of 365 days. Comparisons between product leakage rate, product type and soil moisture content were made and the spatial impacts of leakage were summarized. Variably compacted backfill within the trench, surrounded by undisturbed and more compacted natural soils, results porosity and permeability differences which control the migration of liquids, gases, thermal effects and surface heave. Dilbit migration is influenced heavily by the trench, and also its increasing viscosity as it cools and degases after leakage. Diesel and gasoline liquid plumes are also affected by the trench structure, but to a lesser extent, resulting in wider and longer plumes in the subsurface. In all cases, the migration of liquids and gases is facilitated by higher permeability zones at the base of the pipe. Volatile Organic Compounds (VOCs) migrate along the trench and break through at the surface within days of the leak. Temperature changes within the trench may increase due liquid migration, however the change in predicted temperature at the surface above the leak is less than 0.5�C above background. For gasoline, the large amount of degassing and diffusion through the soil results in cooling of the soil by up to 1�C. Induced surface displacement was predicted for dilbit and for one case of diesel, but only in the order of 0.2cm above baseline. Based upon the information gathered, recommendations are provided for the use and placement of generic leak detection sensor types (e.g liquid, gas, thermal, displacement) within the trench and / or above the ground surface. The monitoring locations suggested take into account requirements to detect pipeline leakage as early as possible in order to facilitate notification of the operator and to predict the potential extent of site characterization required during spill response and longer term remediation activities.
3
Lavrentovich, Oleg. Electric field effects in liquid crystals with dielectric dispersion. Office of Scientific and Technical Information (OSTI), November 2014. http://dx.doi.org/10.2172/1164712.
4
RENSSELAER POLYTECHNIC INST TROY NY. An Experimental Study of Plunging Liquid Jet Induced Air Carryunder and Dispersion. Fort Belvoir, VA: Defense Technical Information Center, March 1992. http://dx.doi.org/10.21236/ada248315.
5
Vanderkooy and McAlary. PR-445-133727-R01 Vapor Plume Detection - Report Compilation and Summary. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), April 2015. http://dx.doi.org/10.55274/r0010835.
Анотація:
Detecting small leaks of liquid hydrocarbons from underground pipelines is difficult using currently available techniques. Hundreds of thousands of miles of aging pipelines run through North America alone and the incidence of small leaks is expected to increase as time goes on. This research was aimed at evaluating two alternative methods for leak detection: 1) monitoring petroleum hydrocarbon (PHC) vapors at or above ground surface over the leaked product, or 2) using plants as visual sensors to indicate the presence of a leak below. Four reports were generated, including: 1) mathematical modeling of subsurface vapor transport and atmospheric dispersion, 2) comparison of the model simulations to empirical data, 3) a review of available portable sensing technologies to detect PHC vapors, and 4) a review of mechanisms and species of plants that could be used as pipeline leak sensors.
6
Bray, Jonathan, Ross Boulanger, Misko Cubrinovski, Kohji Tokimatsu, Steven Kramer, Thomas O'Rourke, Ellen Rathje, Russell Green, Peter Robertson, and Christine Beyzaei. U.S.—New Zealand— Japan International Workshop, Liquefaction-Induced Ground Movement Effects, University of California, Berkeley, California, 2-4 November 2016. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, March 2017. http://dx.doi.org/10.55461/gzzx9906.
Анотація:
There is much to learn from the recent New Zealand and Japan earthquakes. These earthquakes produced differing levels of liquefaction-induced ground movements that damaged buildings, bridges, and buried utilities. Along with the often spectacular observations of infrastructure damage, there were many cases where well-built facilities located in areas of liquefaction-induced ground failure were not damaged. Researchers are working on characterizing and learning from these observations of both poor and good performance. The “Liquefaction-Induced Ground Movements Effects” workshop provided an opportunity to take advantage of recent research investments following these earthquake events to develop a path forward for an integrated understanding of how infrastructure performs with various levels of liquefaction. Fifty-five researchers in the field, two-thirds from the U.S. and one-third from New Zealand and Japan, convened in Berkeley, California, in November 2016. The objective of the workshop was to identify research thrusts offering the greatest potential for advancing our capabilities for understanding, evaluating, and mitigating the effects of liquefaction-induced ground movements on structures and lifelines. The workshop also advanced the development of younger researchers by identifying promising research opportunities and approaches, and promoting future collaborations among participants. During the workshop, participants identified five cross-cutting research priorities that need to be addressed to advance our scientific understanding of and engineering procedures for soil liquefaction effects during earthquakes. Accordingly, this report was organized to address five research themes: (1) case history data; (2) integrated site characterization; (3) numerical analysis; (4) challenging soils; and (5) effects and mitigation of liquefaction in the built environment and communities. These research themes provide an integrated approach toward transformative advances in addressing liquefaction hazards worldwide. The archival documentation of liquefaction case history datasets in electronic data repositories for use by the broader research community is critical to accelerating advances in liquefaction research. Many of the available liquefaction case history datasets are not fully documented, published, or shared. Developing and sharing well-documented liquefaction datasets reflect significant research efforts. Therefore, datasets should be published with a permanent DOI, with appropriate citation language for proper acknowledgment in publications that use the data. Integrated site characterization procedures that incorporate qualitative geologic information about the soil deposits at a site and the quantitative information from in situ and laboratory engineering tests of these soils are essential for quantifying and minimizing the uncertainties associated site characterization. Such information is vitally important to help identify potential failure modes and guide in situ testing. At the site scale, one potential way to do this is to use proxies for depositional environments. At the fabric and microstructure scale, the use of multiple in situ tests that induce different levels of strain should be used to characterize soil properties. The development of new in situ testing tools and methods that are more sensitive to soil fabric and microstructure should be continued. The development of robust, validated analytical procedures for evaluating the effects of liquefaction on civil infrastructure persists as a critical research topic. Robust validated analytical procedures would translate into more reliable evaluations of critical civil infrastructure iv performance, support the development of mechanics-based, practice-oriented engineering models, help eliminate suspected biases in our current engineering practices, and facilitate greater integration with structural, hydraulic, and wind engineering analysis capabilities for addressing multi-hazard problems. Effective collaboration across countries and disciplines is essential for developing analytical procedures that are robust across the full spectrum of geologic, infrastructure, and natural hazard loading conditions encountered in practice There are soils that are challenging to characterize, to model, and to evaluate, because their responses differ significantly from those of clean sands: they cannot be sampled and tested effectively using existing procedures, their properties cannot be estimated confidently using existing in situ testing methods, or constitutive models to describe their responses have not yet been developed or validated. Challenging soils include but are not limited to: interbedded soil deposits, intermediate (silty) soils, mine tailings, gravelly soils, crushable soils, aged soils, and cemented soils. New field and laboratory test procedures are required to characterize the responses of these materials to earthquake loadings, physical experiments are required to explore mechanisms, and new soil constitutive models tailored to describe the behavior of such soils are required. Well-documented case histories involving challenging soils where both the poor and good performance of engineered systems are documented are also of high priority. Characterizing and mitigating the effects of liquefaction on the built environment requires understanding its components and interactions as a system, including residential housing, commercial and industrial buildings, public buildings and facilities, and spatially distributed infrastructure, such as electric power, gas and liquid fuel, telecommunication, transportation, water supply, wastewater conveyance/treatment, and flood protection systems. Research to improve the characterization and mitigation of liquefaction effects on the built environment is essential for achieving resiliency. For example, the complex mechanisms of ground deformation caused by liquefaction and building response need to be clarified and the potential bias and dispersion in practice-oriented procedures for quantifying building response to liquefaction need to be quantified. Component-focused and system-performance research on lifeline response to liquefaction is required. Research on component behavior can be advanced by numerical simulations in combination with centrifuge and large-scale soil–structure interaction testing. System response requires advanced network analysis that accounts for the propagation of uncertainty in assessing the effects of liquefaction on large, geographically distributed systems. Lastly, research on liquefaction mitigation strategies, including aspects of ground improvement, structural modification, system health monitoring, and rapid recovery planning, is needed to identify the most effective, cost-efficient, and sustainable measures to improve the response and resiliency of the built environment.
7
Reporte de Estabilidad Financiera - Primer semestre 2024. Banco de la República, June 2024. http://dx.doi.org/10.32468/rept-estab-fin.sem1-2024.
Анотація:
El análisis presentado en esta edición del Reporte de Estabilidad Financiera corresponde a un contexto global en el que ha aumentado la confianza en un aterrizaje suave de la economía mundial. En los últimos meses de 2023 y los primeros de 2024 se observó una menor inflación (aunque persistente), una mayor resiliencia de la actividad económica y un relajamiento de las condiciones financieras con respecto a las que se observaban un año atrás. No obstante, la posibilidad de un escalamiento de los conflictos geopolíticos en Medio Oriente y Ucrania plantea riesgos al alza, que impactarían potencialmente la inflación (en particular en Estados Unidos y Europa), el ritmo de disminución de las tasas de interés en los mercados globales y las expectativas de crecimiento económico mundial. Durante 2023 e inicios de 2024 la actividad económica en Colombia se desaceleró, siguiendo un proceso de ajuste, caracterizado por la disminución de la inflación, del déficit en la cuenta corriente y del déficit fiscal. El crecimiento del producto interno bruto (PIB) se redujo, después de un período de fuerte crecimiento en 2021 y 2022 impulsado por la demanda interna. La corrección de los excesos de gasto y la dilución de varios choques de oferta contribuyeron a la caída de la inflación en un contexto de disminución de sus expectativas. Estos procesos fueron apoyados por una postura contractiva de la política monetaria encaminada a alcanzar la meta de inflación del 3 % en 2025 y encauzar el crecimiento del PIB en una senda sostenible de largo plazo. La menor demanda interna fue el principal determinante de la reducción del déficit en la cuenta corriente, el cual se redujo del 7,1 % del PIB en el tercer trimestre de 2022 al 2,3 % en el cuarto trimestre de 2023. Por su parte, durante 2023 el déficit fiscal y el endeudamiento público como porcentaje del producto interno bruto se redujeron en forma consistente con lo establecido por la regla fiscal. El activo de los establecimientos de crédito continuó registrando crecimientos reales negativos, aunque en lo corrido de 2024 se observan menores contracciones. La cartera y las inversiones de los establecimientos de crédito (EC) presentan contracciones reales desde mayo de 2023, en un contexto de menor asunción de riesgos por parte de estas entidades. En particular, tras un ritmo acelerado de expansión en 2022, la cartera de consumo continúa presentando decrecimientos, incluso en términos nominales; no obstante, desde comienzos de 2024 se observa una menor contracción real de todas las carteras y una leve recuperación en los desembolsos, lo que, junto con los resultados más recientes de algunas encuestas realizadas por el Banco de la República, podría estar dando señales de un mayor dinamismo del crédito en el segundo semestre del presente año. Los indicadores de deterioro de la cartera se ubican en niveles altos respecto al promedio de los últimos cinco años. Este comportamiento ha respondido a la fuerte toma de riesgo por parte de algunos EC durante 2022, al proceso de ajuste de la economía y a algunas iniciativas regulatorias que impactaron la información disponible sobre los deudores para la evaluación de riesgo por parte de los EC y sus métodos de cobranza. La coincidencia de un crecimiento bajo o negativo de la cartera total, con elevados aumentos de la cartera vencida, se ha reflejado en altos niveles del indicador de calidad por mora (ICM). Es importante resaltar el deterioro de la cartera de microcrédito, la cual se ubica en niveles máximos históricos. En este contexto de materialización del riesgo de crédito, algunos EC han utilizado el componente contracíclico de las provisiones, el cual está diseñado para hacer frente a escenarios de deterioro de la calidad del crédito. Cabe anotar, además, que los indicadores de deudamiento y carga financiera de los hogares se han ajustado a la baja, y el nivel de ahorro se ha venido recuperando después de la caída en el periodo pospandemia, mientras el endeudamiento de las firmas ha disminuido. La cartera vencida, que corresponde al saldo de créditos que registran un incumplimiento con un plazo mayor a treinta días, sigue expandiéndose, pero ha reducido su ritmo de crecimiento desde finales de 2023.Durante el último trimestre de 2023 y lo corrido de 2024 la rentabilidad agregada de los EC, medida por el indicador de rentabilidad del activo (ROA), se ha mantenido relativamente estable alrededor del 0,7 %, el cual es un nivel inferior al promedio de los últimos cinco años, pero que sugiere una corrección de la tendencia decreciente que traía a lo largo del año anterior. Se observa una gran dispersión de este indicador entre los EC, y un número elevado de establecimientos registran rentabilidades negativas. Este comportamiento está explicado, principalmente, por el mayor gasto en provisiones, en especial en la cartera de consumo, junto con un menor ingreso por intereses. Los EC en Colombia cuentan con niveles de solvencia y liquidez adecuados para enfrentar la materialización de diversos riesgos. En términos agregados, los indicadores de solvencia de los EC han aumentado y se ubican en niveles superiores a los mínimos regulatorios. Por su parte, los indicadores de liquidez, tanto estructural como de corto plazo, han aumentado desde mediados de 2023 y se sitúan también por encima de los límites regulatorios. Por otra parte, el activo de las instituciones financieras no bancarias (administradoras de fondos de pensiones, sociedades fiduciarias, comisionistas de bolsa, aseguradoras, entre otras) continuó creciendo. Este comportamiento se explica, principalmente, por la dinámica del portafolio de terceros que este tipo de entidades administra. Asimismo, la rentabilidad se mantuvo en niveles positivos y estables. Este Reporte también presenta un análisis de la resiliencia de las entidades financieras mediante ejercicios de sensibilidad que evalúan su respuesta ante hipotéticos escenarios adversos extremos y de baja probabilidad. Los resultados sugieren que el sistema financiero cuenta con la capacidad suficiente para enfrentar choques adversos de gran magnitud, lo cual corrobora su resiliencia durante el proceso de ajuste macroeconómico de Colombia en estos últimos años. En cumplimiento de sus objetivos constitucionales y en coordinación con la red de seguridad del sistema financiero, el Banco de la República continuará monitoreando de cerca el panorama de estabilidad financiera en esta coyuntura, y tomará las decisiones necesarias para garantizar el adecuado funcionamiento de la economía, facilitar los flujos sostenibles de recursos suficientes de crédito y liquidez y promover el buen funcionamiento del sistema de pagos. Leonardo Villar Gómez. Gerente General