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A dryout mechanism model for rectangular narrow channels at high pressure conditions is developed by assuming that the Kelvin–Helmholtz instability triggered the occurrence of dryout. This model combines the advantages of theoretical analysis and empirical correlation. The unknown coefficients in the theoretical derivation are supported by the experimental data. Meanwhile, the decisive restriction of the experimental conditions on the applicability of the empirical correlation is avoided. The expression of vapor phase velocity at the time of dryout is derived, and the empirical correlation of liquid film thickness is introduced. Since the CHF value obtained from the liquid film thickness should be the same as the value obtained from the Kelvin–Helmholtz critical stability under the same condition, the convergent CHF value is obtained by iteratively calculating. Comparing with the experimental data under the pressure of 6.89–13.79 MPa, the average error of the model is −15.4% with the 95% confidence interval [-20.5%, −10.4%]. And the pressure has a decisive influence on the prediction accuracy of this model. Compared with the existing dryout code, the calculation speed of this model is faster, and the calculation accuracy is improved. This model, with great portability, could be applied to different objects and working conditions by changing the expression of the vapor phase velocity when the dryout phenomenon is triggered and the calculation formula of the liquid film.

Graphical abstract, Liquid loading causes undesirable occurrences such as premature death of wells, as well as significant reduction in production. However, most available models consider vertical wells and only a few focus on deviated gas wells. In order to reduce the impact of liquid loading on gas production, gas well load-up should be diagnosed at its early stage so as to proffer adequate solution. Unfortunately, most gas wells will experience liquid loading at some stage or point in their production life. Therefore, it is of utmost importance to predict liquid loading at the early life of such wells in order to develop apt liquid management strategies as corrective measures. Liquid film flow reversal concept has been identified as one of the major concepts responsible for the occurrence of liquid loading in deviated gas wells. This study develops an improvement on Chen’s liquid loading model. The model specifically introduces the concept of non-uniform film thickness around the pipe wall, as against previous works which considered uniform film thickness. A modified friction factor is also introduced to account for large film thicknesses around the pipe wall. Results from the model were compared with those of previous models, and data from published literature was used to validate the new model. The new model gave accurate predictions for 11 of 12 unloaded wells while for the loaded wells, the estimated data gave accuracies for 29 out of 30 loaded wells. This then implies that the new model is accurate for predicting liquid loading in deviated gas wells. • Predictions from the new model show a good improvement over existing models. • The uniform film assumption made in Chen liquid loading model was modified, and a different interfacial friction factor was applied. • The method proposed in this study introduces the concept of non-uniform film thickness around the pipe wall as against previous works which considered uniform film thickness.

The paper presents novel control-oriented transport models for evaporating liquid films in the tubes of a falling film evaporator. In this context, our goal consists in qualitatively mapping the experimentally observed input-output behavior. Two transport models are proposed, where the difference between them is that one allows overtaking of liquid particles and the other does not. The transport models are equipped with two new models of evaporation which are different from the commonly assumed uniform evaporation. The models are initially developed from the conservation laws in the form of partial differential equations. Using the method of characteristics we then obtain the input-output relations for the proposed models in the form of time-delay equations. The time-delay representation is advantageous for simulation and for the future control design. In a simulation study, we observe the principal properties of the models and find that they correspond well with the experimentally observed input-output behavior.

Annular flow with liquid entrainment occurs in a wide variety of two-phase flow system. A novel control volume finite element method with adaptive unstructured meshes is employed here to study three-dimensional droplet deposition process in annular two-phase flow. The numerical framework consists of a ‘volume of fluid’ type method for the interface capturing and a force-balanced continuum surface force model for the surface tension on adaptive unstructured meshes. The numerical framework is validated against experimental measurements of a droplet impact problem and is then used to study the droplet deposition onto a flowing liquid film at atmospheric and high pressure conditions. Detailed complex interfacial structures during droplet impact are captured during the simulation, which agree with the experimental observations, demonstrating the capability of the present method. It is found that the effect of the ambient pressure on the fluid properties and interfacial tension plays an important role in the droplet deposition process and the associated interfacial phenomena.

The results of an experimental study on droplet impactions in the flow of a gas-sheared liquid film are presented. In contrast to most similar studies, the impacting droplets were entrained from film surface by the gas stream. The measurements provide film thickness data, resolved in both longitudinal and transverse coordinates and in time together with the images of droplets above the interface and images of gas bubbles entrapped by liquid film. The parameters of impacting droplets were measured together with the local liquid film thickness. Two main scenarios of droplet-film interaction, based on type of film perturbation, are identified; the parameter identifying which scenario occurs is identified as the angle of impingement. At large angles an asymmetric crater appears on film surface; at shallow angles a long, narrow furrow appears. The most significant difference between the two scenarios is related to possible impact outcome: craters may lead to creation secondary droplets, whereas furrows are accompanied by entrapment of gas bubbles into the liquid film. In addition, occurrence of partial survival of impacting droplet is reported.

[EN] Annular flow is characterized by a thin liquid film flowing on the pipe wall and a high velocity gas core flowing in its center, which normally carries liquid droplets. This review presents and analyzes most of the extensive literature existing on the annular two-phase flow, focusing specifically on the analysis of the main phenomena that are involved. In particular, the paper focuses on the study of the liquid droplets that are entrained by the gas stream from the gas-liquid interface, due to the strong influence that these droplets exert in many important parameters of both, flow and heat transfer processes. Consequently, it is important to be able to know the maximum amount of information about them, in order to characterize droplets' size and velocity, and to determine the amount of them that are entrained into the gas stream and, finally, apply this knowledge in all processes in which annular flow is involved. This review analyzes most of the extensive literature on droplets, specifically analyzes its main characteristics once they have been formed, such as its sizes, speeds and total amount. A vast amount of data has been found in the open literature and collected here. Their analysis leads to two major observations: their huge scattering and the existence of remaining knowledge gaps. Some of the experimental data have been also used to derive new correlations on variables as important as amount and size of entrained droplets., The authors are indebted to the plan of I + D support of the project REMODERN ENE2010-21368-C02-01/CON.

© 2014 The Authors. The flow of a liquid film sheared by high velocity gas stream in a horizontal rectangular duct was investigated using a high-speed laser-induced fluorescence technique. Measurements of local film thickness were resolved in both longitudinal and transverse coordinates with high spatial and temporal resolution. It was found that the generation of fast and slow ripples by the disturbance waves was qualitatively the same as it was observed earlier in completely different conditions. The transverse size and curvature of the disturbance waves and ripples were measured. A relationship between the three-dimensional structure of ripples on top of disturbance waves and the two mechanisms of liquid entrainment, known as 'bag break-up' and 'ligament break-up', is proposed.

[EN] Annular two-phase flow has been vastly investigated because of its large and deep involvement in industrial processes, particularly in nuclear engineering. This paper reviews most of the recent literature on the matter, with emphasis in all those variables and processes occurring in the liquid-gas interface that cause droplet entrainment. Further than presenting correlations, the paper shows the existing scattering found when expressions are compared to each other and it highlights the gaps of knowledge still existing. Additionally, based on some of the open data, alternate equations are derived for key variables in the annular flow descriptions, like liquid film thickness and wave celerity and frequency., The authors are indebted to the plan of I + D support of project REMODERN ENE2010-21368-C02-01/CON.

Experimental results of liquid film thickness distribution of an air–water mixture flowing through a vertical 180° return bend are reported. Measurements of liquid film thickness were achieved using flush mounted pin and parallel wire probes. The bend has a diameter of 127 mm and a curvature ratio (R/D) of 3. The superficial velocities of air ranged from 3.5 to 16.1 m/s and those for water from 0.02 to 0.2 m/s. At these superficial velocity ranges, the flow pattern investigated in this work focused on churn and annular flows. It was found that at liquid and gas superficial velocities of 0.02 m/s and 6.2 m/s, respectively, the averaged liquid film thickness peak at 90°. At gas superficial velocity of 16.1 m/s, the relationship between them is linear due to the shear forces overcoming gravity. Additionally, it was found that deposition of entrained droplets keeps the liquid film on the outside of the bend. The results of polar plots of average liquid film thickness in the bend showed that the distribution of the liquid film is not symmetrical with thicker films on the inside of the bend due to the action of gravity. Experimental results on average liquid film thickness showed good agreement with the simulation data reported in the literature.

Submitted by Jairo Amaro (jairo.amaro@sibi.ufrj.br) on 2019-06-26T17:47:10Z No. of bitstreams: 1 2013_MAGALHAES_v50_p30-40-min.pdf: 246011 bytes, checksum: c76d443121ef75544e21a3ac7c2cd049 (MD5) Made available in DSpace on 2019-06-26T17:47:10Z (GMT). No. of bitstreams: 1 2013_MAGALHAES_v50_p30-40-min.pdf: 246011 bytes, checksum: c76d443121ef75544e21a3ac7c2cd049 (MD5) Previous issue date: 2012-10-30 Indisponível. The present work investigates the effects of gas solubility on the fluid dynamic properties of a horizontal two-phase slug flow. Measurements of the size distributions of the liquid slug and of the long bubbles are provided, as well as local measurements of the liquid velocity in the slug, the velocity in the liquid film, the velocity of propagation of the nose of the long bubbles and the pressure drop. These parameters were obtained through two optical techniques: Shadow Sizer (SS) and Particle Image Velocimetry (PIV). The experiments indicate that the solubility has a substantial influence on the flow properties resulting, in particular, in a significant reduction of the local pressure gradient over a relatively short distance (8 m). The data are compared with modified versions of the mechanistic models of Dukler and Hubbard (Dukler, A.E., Hubbard, M., 1975, A model for gas–liquid slug flow in horizontal and near horizontal tubes, Ind. Eng. Chem. Fund. 14(4), 337–347) and of Orell (Orell, A., 2005, Experimental validation of a simple model for gas–liquid slug flow in horizontal pipes, Chem. Eng. Sci. 60, 1371–1381) so that the solubility effects can be taken into account.

In this work, a new flow regime transition model is proposed for two-phase flows in a vertical annulus. Following previous works, the flow regimes considered are bubbly (B), slug (S) or cap-slug (CS), churn (C) and annular (A). The B to CS transition is modeled using the maximum bubble package criteria of small bubbles. The S to C transition takes place for small annulus perimeter flow channels and it is assumed to occur when the mean void fraction over the entire region exceeds that over the slug–bubble section. If the annulus perimeter is larger that the distorted bubble limit the cap-slug flow regime will be considered since in these conditions it is not possible to distinguish between cap and partial-slug bubbles. The CS to C transition is modeled using the maximum bubble package criteria. However, this transition considers the coalescence of cap and spherical bubbles in order to take into account the flow channel geometry. Finally, the C to A transition is modeled assuming two different mechanisms, (a) flow reversal in the liquid film section along large bubbles; (b) destruction on liquid slugs or large waves by entrainment or deformation. In the S to C and C to A flow regime transitions the annulus flow channel is considered as a rectangular flow channel with no side walls. In all the modeled transitions the drift-flux model is used to obtain the final correlations. The final equations for every flow regime transition are easy to be implemented in computational codes and not experimental input is needed. The prediction accuracy of the newly developed model has been checked against air–water as well as boiling flow regime maps. In all the cases, the new developed model shows better predicting capabilities than the existing correlations most used in literature.

International audience; In this paper we report experimental results on evaporation of a volatile wetting liquid in a capillary tube of square internal cross section, when conditions are such that liquid films develop along the tube internal corners under the effect of capillary forces, as the bulk meniscus recedes inside the tube. Combining an infrared thermography technique with visualizations by ombroscopy makes it possible to determine the time-space evolution of the temperature minimum on the capillary outer surface together with the bulk meniscus position within the tube. When the tube is held horizontal, the temperature minimum stays at the tube entrance and the evaporation rate reaches a stationary value. In contrast with the horizontal case, the position of the temperature minimum changes when the bulk meniscus has sufficiently receded inside the tube when the tube is vertical and opened at the top. The rate of evaporation then decreases significantly. This is explained by the thinning of the corner films in the vertical tube entrance region, under the conjugated effects of gravity and viscous forces up to the depinning of the films from the tube entrance. When the tube is held horizontal, the capillary effects are dominant and the film thickness remains essentially constant in the tube entrance region. This analysis is supported by a simple model of liquid flow within the corner films.

Publisher Summary The method of calculating a critical velocity will be shown to be applicable at any point in the well. It should be used in conjunction with methods of nodal analysis if possible. In this chapter, the relatively simple “critical velocity” method is presented to predict the onset of liquid loading. This technique was developed from a substantial accumulation of well data and has been shown to be reasonably accurate for vertical wells. In critical flow concepts, the study explains the transport of liquids in near vertical wells is governed primarily by two complementing physical processes before liquid loading becomes more predominate and other flow regimes such as slug flow and then bubble flow begin. The critical velocity is generally defined as the minimum gas velocity in the production tubing required to move liquid droplets upward. A “velocity string” is often used to reduce the tubing size until the critical velocity is obtained. Lowering the surface pressure (e.g., by compression) also increases velocity. The study explains the Turner droplet model; it is generally believed that the liquids are both lifted in the gas flow as individual particles and transported as a liquid film along the tubing wall by the shear stress at the interface between the gas and the liquid before the onset of severe liquid loading.

Thin liquid films form automatically in all colloidal systems in liquid dispersion media, where they arise when two particles of the disperse phase (solid particles, liquid drops, or gas bubbles) come close to each other. The liquid film is symmetrical when two particles are identical—that is, in the case of homo-interaction. Samples of such thin liquid films are foam films, emulsion films, and films between identical particles in a sol. The most important asymmetric films are the wetting films: thin liquid films separating a solid from a gas phase. The properties of thin liquid films are decisive for the properties of the corresponding disperse systems of which the films are a part. This chapter describes foam and emulsion films. The chapter focuses on the experimental methods involved in thin liquid film research. Most specific properties of thin liquid films cannot be studied using the well-known physicochemical methods for investigating the properties of bulk phases and single interfaces.

When a copper and a silicon test specimen were rubbed against each other under a very low contact pressure, with a load applied in the direction to pull apart the test specimens (negative normal load) to offset the attraction active between them., the friction coefficient decreased. The decrease of friction coefficient was considered to be due to the lubricating effect of a liquid film formed between the solid surfaces, and friction tests were carried out with variable sliding speeds to test this hypothesis. The result showed two cases: one of friction coefficient increasing and the other decreasing with sliding speed. This can be explained by the decreased surface area of direct contact between the two solids, and the viscous resistance of fluids, respectively.

The atomization process and spray quality was studied for a prefilming airblast atomizer, using visualization techniques and phase-Doppler anemometry. All the tests were carried out at atmospheric pressure and using water. Results are presented and discussed for a liquid film thickness of 0.2mm, a liquid mass flow rate of 10.8 g/s, primary air velocity of 155 m/s and high swirl levels of the secondary air. The SMD is shown to be independent of liquid film velocity for coaxial swirling flows, providing the primary air velocity is kept above 120 m/s. The related drop size velocity distribution is shown to contribute to the optimization of combustion efficiency.

This study provides the effects of heating at the tube surface on the flow instability and the onset of a dry patch in a subcooled liquid film. A simplified approach to analyze the wave structure was used by adding the shear stress due to the Marangoni effects to the isothermal film-flow equation. Theoretical analysis shows the liquid film for low flow rate conditions becomes unstable at a constant Marangoni number. Thermography technique was employed for determining the temperature distribution along the liquid surface. The dynamic process to the liquid film breakdown was discussed in relation to the wave structure.

Mass transfer into liquid film flowing concurrently with gas flow is investigated experimentally and theoretically. In the present paper, fluid dynamics of thin liquid film flow and a theoretical prediction of concentration variation in the liquid film in the flow direction are examined based on the theoretical model of mass transfer. And a theoretical prediction method of the average mass transfer coefficient α DL is proposed. A simple new correlation of α DL is also proposed, in which the effective use of liquid is taken into consideration.

Publisher Summary The process of drying of a porous material can be divided into several stages. At first, the body shrinks by an amount equal to the volume of liquid that evaporates and the liquid-vapor interface remains at the exterior surface of the body. The second stage begins when the body becomes too stiff to shrink and the liquid recedes into the interior, leaving air-filled pores near the surface. Even as air invades the pores, a continuous liquid film supports flow to the exterior, so evaporation continues to occur from the surface of the body. Eventually, the liquid becomes isolated into pockets and drying can proceed only by evaporation of the liquid within the body and diffusion of the vapor to the outside. This chapter discusses the transport processes acting during these stages. It also discusses the factors affecting stress development and various strategies for avoiding warping and cracking.

Publisher Summary Foam, a dispersion of gas in liquid with bulk density approaching that of the gas, is an agglomeration of gas bubbles separated from each other by a thin liquid film. Foam formation is a common phenomenon in many industrial processes including chemical and fermentation processes. Its formation is a desirable property in some processes such as in the production of beer. However, foam in submerged fermentations poses a serious problem and results in the loss of material through the exhaust lines as well as the danger of contamination of the fermentation batch and the environment. The preferred method of foam control in fermentation is by the use of antifoam agents, although in a few instances, a mechanical foam breaker is used along with the chemical antifoam. In fermentations, the control of foam is a costly and nonproductive operation and therefore an effective foam control with reduced costs greatly influences the economics of the process.

This paper presents a literature review and an analysis of the significance of mass transport into biological floc particles. Utilizing measured values and activated sludge floc sizes, the effect of the liquid film around the floc particles and the biophase resistance of the floc particle itself is evaluated. The required dissolved oxygen concentration at the surface of a floc to insure no oxygen limitation on reaction rate is calculated based on measured values of pure culture floc mass transfer diffusivities.

Synopsis Few design procedures for plain, liquid lubricated, cylindrical journal bearings attempt to account for the effects due to a consideration of the reformation of the lubricant film. Whilst it is clearly recognised that a consideration of film reformation will not significantly influence the magnitude of the predicted load carrying capacity, the same cannot be said of the lubricant flow rate. The importance of an accurate estimation of flow rate is apparent because it is a parameter upon which the prediction of all other operating characteristics depend. A number of workers have undertaken numerical analysis studies of techniques designed to enable the location of the reformation boundary to be determined effectively. No completely satisfactory approach has yet been identified; coding complexities have arisen normally due to attempts to achieve satisfactory pressure gradient conditions on the reformation boundary. The present paper investigates in depth the usefulness of an algorithm first identified in the mid 1970's as a means of positioning both rupture and reformation boundaries.

Values of the physico-chemical quantities discussed in Part I are often not available, and are difficult or impossible to measure. The second and third models considered do not require explicit knowledge of these quantities, but only measurements of transient rates of absorption for short times of contact between gas and liquid. Such transient rates have been measured in an apparatus incorporating a rotating drum. Carbon dioxide was absorbed into water, solutions of salts, buffer solutions and sodium hydroxide solution. Times of exposure were less than 0 25 sec. Comparison with rates of absorption in a packed column suggests that none of the three models gives an adequate description of the absorption process.

I. SUMMARY The normal electrostatic pressure between two solid surfaces, with an aqueous solution between them, has been determined in an apparatus which enabled the thickness of the liquid film and the applied pressure to be measured simultaneously. One solid surface was an optically polished glass prism and the other an optically smooth spherical cap of transparent rubber. The electrostatic charge on the surfaces was effected by the adsorption of sodium dodecyl sulphate. The experimental curves obtained were in reasonable agreement with those expected from theory.

In the first part the authors summarize the theory leading to practical formulae for computing the damping constants and the equivalent mass of liquid film dampers. The importance of the equivalent mass of the liquid film on the natural frequency of the systems is emphasized. Corrections are introduced for the border effect. The limits of the linear behaviour are discussed taking into account the cavitation due to vapour pressure, absorbed and free air in the oil. The order of magnitude of the different effects is shown with practical examples.

The effect of insoluble surface-active agents on the stability of a falling liquid layer subjected to finite amplitude filtered waves is investigated. The mechanism of non-linear stability is elucidated by investigating the effects of surfactants on the energy transfer between the mean flow and the finite amplitude disturbances.

A theoretical and experimental study was made of the mechanism of absorption of gases of low solubility by a turbulent mass of water. It is concluded that the most satisfactory physical model for this mechanism is an interfacial laminar liquid film which is being continuously replaced in a random manner by liquid from beneath the surface. This model leads to a mathematical formulation which provides a good fit to the experimental results.

Variations in the distillation rates effected by the non-condensable gas pressure were studied in a short path, wiped wall, distillation unit. The materials used for the distillation test at highly turbulent liquid film conditions were di-ethyl hexyl sebacate, di-ethyl sebacate, Apiezon A, Apiezon C and Silicone Oil 705. Experimental results showing the extent of the variation in the distillation rate by such factors as the interposition of an entrainment separator, the molecular weight of the evaporating material and the molecular weight of the non-condensable gas are given and discussed. Selection of suitable pressure conditions in relation to the vacuum equipment used in these tests is discussed. In einem Kurzwegdestillationsgerat mit mechanischer Wandreinigung wurden die anderungen der Aufdampfrate als Funktion des Gaspartialdruckes untersucht. Hierzu wurden folgende Stoffe genommen: Di-athyl-hexyl-sebacat, Di-athyl-sebacat, Glyzerol, Apiezon A, Apiezon C und Siliconol 705. Diese Stoffe wurden unter Bedingungen hoher Turbulenz der dunnen Flussigkeitsschichten untersucht. Es werden experimentelle Ergebnisse mitgeteilt, die zeigen, in welchem Masse verschiedene Gaspartialdrucke bei einigen genau eingestellten Verdampfertemperaturen die Verdampfungsrate beeinflussen. Es wurde auch der Einfluss des Molekulargewichtes des Gases, das den Partialdruck ausubt, untersucht. Im Zusammenhang mit unseren Untersuchungen wird die Wahl geeigneter Druckbedingungen fur die Hochvakuumdestillation besprochen. Des etudes ont ete faites sur les variations de la vitesse d'evaporation sous l'effet de la pression partielle de gaz dans un appareil de distillation moleculaire a balayage. Parmi les quelques materiaux choisis pour ces recherches, faites dans des conditions de turbulence extreme de la couche de liquide, citons le di-ethyl-hexyl-sebacate, le di-ethyl-sebacate, le glycerol, l'Apiezon A, l'Apiezon C et l'huile de silicone 705. Les resultats experimentaux indiquant l'importance des effets produits sur differents gaz a differentes temperatures d'evaporation sont communiques et discutes. La variation du poids moleculaire du gaz exercant la pression de gaz partielle est egalement etudiee. On examine egalement dans le cadre de cette etude, le choix de conditions de pressions convenables pour une distillation sous vide pousse.

Data for unobstructed coating of wires by continuous withdrawal from Newtonian fluids are reported for a wide range of fluid properties and operating conditions. The data cover a 500fold range of liquid film to wire radius ratios (h/R), that stretches from 0.1 to 50. The range of Capillary numbers (μu0/σ) covered is from 0.04 to 1000 (25,000fold). The wide range of data presently reported allows the authors to assess the validity and applicability of the various withdrawal theories appearing in the literature.

Reference EPFL-ARTICLE-147397doi:10.1016/j.ces.2008.08.030View record in Web of Science Record created on 2010-03-19, modified on 2017-05-10