A so-called “slug-flow” capillary microreactor has been proposed for the investigation of mass-transfer-limited liquid−liquid reactions. Internal circulation within the slug leads to an intensified and tunable mass transfer. Understanding the development of the circulatory flows and the influence of operating parameters upon them is thus crucial. In this study, experiments were carried out to visualize the internal circulations using particle image velocimetry (PIV) technique. State-of-the-art computational fluid dynamics (CFD) simulations were used to predict the internal circulation within the liquid slugs and a CFD particle tracing algorithm employed to visualize them. Each slug was modeled as a distinct single-phase flow domain. The effect of the flow velocity and slug length on the velocity profile and stagnant zones of the internal circulations for a slug with and without a wall film is discussed. The internal circulations could be qualitatively and quantitatively characterized with the help of the ...

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Internal Circulation within the Liquid Slugs of a Liquid-Liquid Slug-Flow Capillary Microreactor

An alkaline hydrolysis reaction was used as the model reaction to investigate the performance of liquid–liquid slug flow microchannel. The specific interfacial area was determined through the photographic snapshot method physically by means of measuring the lengths of relevant slugs. The overall volumetric mass transfer coefficients were calculated through the Danckwerts’ model chemically. The influences of various operating conditions on the slug length, the overall volumetric extraction rate and the mass transfer coefficient were investigated quantitatively. A decreasing trend of volumetric mass transfer coefficients along the channel length was found. The linear dependence of the volumetric extraction rate on the volumetric mass transfer coefficient indicates that the overall rate of the process is determined by the mass transfer process. In addition, the volumetric mass transfer coefficients were correlated for different channel lengths.

Mass transfer behavior of liquid–liquid slug flow in circular cross-section microchannel

Computational modelling of slug flow in a capillary microreactor

In this paper we report results of two-dimensional simulations of the motion of elliptic capsules carried by a Poiseuille flow in a channel. The numerical method allows computation of the capsule motion and the fluid flow around the capsule, and accurate evaluation of the lift force and torque. Results show that the motion of a capsule which is heavier than the carrying fluid may be decomposed into three stages: initial lift-off, transient oscillations and steady flying. The behaviour of the capsule during initial lift-off and steady flying is analysed by studying the pressure and shear stress distributions on the capsule. The dominant mechanism for the lift force and torque is lubrication or inertia or a combination of the two under different conditions. The lift-off velocity for the ellipse in two dimensions is compared with experimental values for cylindrical capsules in pipes. Finally, the mechanisms of lift for capsules are applied to flying core flows, and it is argued that inertial forces are responsible for levitating heavy crude oil cores lubricated by water in a horizontal pipeline.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002211209500070X

Dynamic simulation of the motion of capsules in pipelines

As the first part of an experimental investigation of the transport of shaped solids through pipelines, laboratory studies have been made on the transport of single cylindrical and spherical capsules by a stream of water, the capsules having the same density as the water. The studies were concerned with the effects of water velocity and capsule/pipe diameter ratio on the velocity of both cylindrical and spherical capsules, and also with the effects of capsule length/diameter ratio and end-shape on the velocity of cylindrical capsules.



The investigation was carried out in a 35-ft. horizontal length of 1 1/4 in. diameter transparent acrylic plastic pipe. The velocity of the capsules was found to vary from 1.05 to about 1.5 times the average water velocity, which ranged from 0.20 to 12.15 ft./sec. A decrease of diameter increased the velocity of both cylindrical and spherical capsules relative to the average water velocity. Increasing the length of cylindrical capsules had a similar effect, while an ellipsoidal nose increased the velocity of smaller diameter cylindrical capsules, but the effect on the largest diameters was negligible. The presence of a capsule appeared to delay the onset of turbulence in the annulus between the capsule and the pipe wall to a much higher value of Reynolds number than would hold in unobstructed fluid flow.



Des etudes en laboratoire ont ete entreprises sur le transport de capsules cylindriques et spheriques de měme densite que l'eau, dans un courant d'eau. Les variables etudiees sont: vitesse de l'eau, rapport des diametres capsule/tuyau, rapport longueur/diametre et geometrie des extremites des capsules cyclindriques.



Un tuyau transparent de plastique acrylique d'une longueur de 35 ft. et diametre 1 1/4 in. a ete utilise dans cette recherche. La vitesse des capsules a varie de 1.05 a 1.5 fois la vitesse moyenne de l'eau dont la vitesse a varie de 0.20 a 12.15 pi/sec. II a ete determine que la vitesse des capsules augmente relativement a la vitesse moyenne de l'eau, avec une diminution de diametre des capsules cylindriques et spheriques et avec une augmentation de la longueur d'une capsule cylindrique. D'autre part une geometrie amont ellipsoidale augmente la vitesse des capsules cylindriques de faible diametre. Cette augmentation de vitesse est negligeable pour des capsules de gros diametre. La presence de capsules retarde l'apparition de turbulence, jusqu'a des Re beaucoup plus eleves, dans l'espace annulaire cree entre le capsule et le tuyau.

The pipeline flow of capsules: Part 3 ‐ An experimental investigation of the transport by water of single cylindrical and spherical capsules with density equal to that of the water

Pipelining science and technology may be regarded as developing through several generations, the first two being fluid and slurry pipelining, respectively. Third generation pipelining in which it may be possible to extend the practice and economies of such transportation methods to an even wider spectrum of commodities may be defined as the flow of materials in capsule forms, as massive rigid or semi-rigid segments of the supporting fluid. The flow of such capsule forms is recognized as a flow configuration which is stable, being normally encountered in the flow of equal-density immiscible fluids over a wide range of conditions. Because the capsule forms occupy appreciably less than the total cross-sectional area of the pipe, they move at a velocity greater than the average over-all velocity. In addition, the pressure gradient of a stream in turbulent flow tends to be reduced, rather than increased, by the presence of capsule forms.



La science et technique des transports par pipeline peut ětre consideree comme s'acheminant vers une troisieme generation (les deux premieres s'appliquant aux fluides et aux suspensions) dans laquelle il sera possible d'accroǐtre les avantages pratiques et economiques de ce mode de transport en confinant des materiaux dans des capsules ou sous forme de segments rigides ou semi-rigides du fluide continu. L'ecoulement sous forme capsulaire, normallement obtenu avec des fluides immiscibles de densite egale, donne une configuration stable de l'ecoulement. La vitesse d'ecoulement des capsules est plus grande que celle de la masse du fluide puisqu'elles occupent une section moindre que celle du tuyau. De plus, la perte de charge en regime turbulent tend a diminuer en presence des capsules.

M. E. Charles

Papers

The pipeline flow of capsules: Part 1: The concept of capsule pipelining