Hydrodynamics Of Slug Flow Research Articles

Spatial distribution of void fraction in the liquid slug in the whole range of pipe inclinations

A wire mesh sensor was used to detect the local instantaneous cross-sectional distribution of the phases in gas-liquid slug flow. Data were obtained for a wide range of flow rates and for pipe inclinations ranging from shallow to vertical. Processing of the wire mesh sensor data yielded detailed information of the 3D void fraction distribution in the liquid slug. These results shed additional light on the hydrodynamics of slug flow, in particular, regarding the formation and distribution of dispersed bubbles in the liquid slug. Comparison with available data was carried out. The present results compared favorably with model predictions.

Dynamic Models in Multiphase Flow

Transport of oil and gas mixtures in pipelines involves flow dynamics on a wide range of time and length scales. Liquid slugs and waves occur at scales extending from diameters (“hydrodynamic slug flow”) and up to riser lengths (“severe slugging”). The approach in one-dimensional dynamic multiphase flow models for analysis of flow dynamics depends upon the scale to be resolved. Types of models are discussed, and a hybrid two-fluid model and a slug tracking model are in particular described. A two-fluid model is applied on a stationary grid in the gas–liquid stratified flow region until a slug is formed (or initiated), when a slug tracking method with a moving grid takes over. The performance of the model is demonstrated in relation to three types of cases with different time and length scales: Two- and three-phase severe slugging, hydrodynamic slugging after a bend, and a pigging case to simulate the rapid release of a hydrate plug. The computations are compared to experimental laboratory data.

Hydrodynamics of gas-liquid slug flow in capillaries: Comparing theory and experiment

The hydrodynamics of slug flow in a horizontal capillary with a diameter of 0.92 mm is experimentally studied using water-air and aqueous glycerol solution-air systems. The experimental data (the velocity of bubbles, the volume fraction of the gas, the relative length of bubbles, and the pressure drop) are compared with the results of calculation by the previously constructed mathematical model of the slug flow of a gas-liquid mixture in capillaries. The developed model is in satisfactory agreement with experimental data in the range of capillary numbers from 0.05 to 0.12.

CFD modelling of slug flow inside square capillaries

An attempt is made to model slug flow inside square capillaries containing Newtonian liquids. In square micro-channels, slug flows proved to promote high rates of heat and mass transfer between the solid boundaries and the bulk flow. This is due to the combination of bubble induced secondary flows and the creation of very thin liquid films. There are many industrial applications for which it is necessary to predict this rate of transfer. The volume of fluid (VOF) method implemented in the commercial CFD package, FLUENT is used for this numerical study. A comprehensive description of such flow is obtained and a comparative study is conducted on the hydrodynamics of slug flow inside circular capillaries and their square counterparts. Computed values of the bubble velocity and diameter were in excellent agreement with published experimental measurements. The detailed velocity field around the bubble was also computed and compared favourably with those experimental results reported in literature. Based on the hydrodynamic study explanation of mass and heat augmentation due to slug flow is drawn.

Slug Flow Hydrodynamics in the Presence of Catalyst Rods

A design for a slug flow reactor, referred to as the confined slug flow (CSF) reactor, is presented and some hydrodynamic issues for this reactor are considered. Particular attention is given to the prediction of gas bubble and liquid slug velocities and lengths. These parameters are found to be described adequately by modified forms of relationships for conventional slug flow operation. In combination with the continuity equations for slug flow, the modified velocity relationships enable the evaluation of liquid film properties (and subsequently mass transfer coefficients), as well as liquid and gas residence times. The studies demonstrate the possibilities of using catalyst inserts within monolith blocks under slug flow operation, and thus improved flexibility in the design of mass-transfer-enhanced, three-phase, structured reactor systems. © 2004 Institution of Chemical Engineers.

Enhancing hollow fibre ultrafiltration using slug-flow — a hydrodynamic study

Gas—liquid slug flow is commonly employed as an enhancement technique for cross-flow ultrafiltration. This technique worked well on flat sheet and larger diameter membrane modules, but hydrodynamics and mass transfer, hence optimal operation, differs for the smaller diameter hollow fibre membranes where the technique proved less effective. This study investigates slug-flow hydrodynamics in capillary tubes in order to characterise the flow and predict optimal operation in hollow fibre membranes. Experiments investigated the effect of bubble size, bubble-supply frequency, operating pressure and capillary diameter on bubble shape and rise-velocity in non-porous tubes of 0.89 mm bore. Computational fluid dynamics (CFD) was employed to predict the flow behaviour inside capillaries. The CFD model and experimental results compared well. The CFD model yielded detailed information of the flow parameters and the flow patterns inside the capillaries and this allowed for better understanding of the hydrodynamics of the capillary tube slug-flow process.

Hydrodynamics of slug flow applied to cross‐flow filtration in narrow tubes

AbstractThis article focuses on the characterization of slug‐flow hydrodynamics in two sizes of tubular membrane diameters (6 and 15 mm) to quantify the main mechanical phenomena involved in the limitation of particle fouling during cross‐flow filtration of suspensions. By using a conductance probe technique, the flow structure was accurately identified for two geometries, and noticeable differences were observed in terms of void fractions, velocities and lengths of Taylor bubbles, and liquid slugs. This characterization allowed some data to be theoretically estimated (wall shear stress, “falling” film velocity, film thickness) thanks to the application of a phenomenological model initially developed for oil pipes. The results obtained in a 15‐mm tube showed that the ultrafiltration flux improvement, experimentally achieved with bentonite and yeast suspensions, was partly due to the increase in the wall shear stress, induced by continuous gas sparging inside the tubular filtration module. Other hydrodynamic phenomena linked to the quasi‐periodic succession of Taylor bubbles and liquid slugs were also involved in the control of the particle entrainment: intermittency frequency, reversal of the wall shear stress, instantaneous pressure variations in the long bubble wake with a higher level of turbulence, and an enhanced local mixing.

A transient two-fluid model for the simulation of slug flow in pipelines—I. Theory

A one-dimensional transient two-fluid model is developed to predict transient slug flow in pipelines. To account for the interphase interactions, new constitutive relations for the drag coefficient and the virtual mass force for the slug flow regime are derived by applying the conservation equations to a geometrically simplified slug unit. New coefficients in the pressure gradient term in the two-fluid momentum conservation equations are also obtained to account for the non-uniform distribution of the phases and of the pressure drop along a slug unit. The new relations yield a more accurate treatment of the hydrodynamics of slug flow than traditional two-fluid models. Constitutive relations for other flow regimes can also be incorporated into the model, allowing the analysis of general transient two-phase flows in pipelines.