Pressure changes associated with the ascent and bursting of gas slugs in liquid-filled vertical and inclined conduits.

A novel continuous crystallizer design is described with the potential to provide improved control of crystal properties, improved process reproducibility, and reduced scale-up risk. Liquid and gas are introduced into one end of the tube at flow rates selected to spontaneously generate alternating slugs of liquid and gas that remain stable while cooling crystallization occurs in each liquid slug. Mixing within each stable self-circulating slug is maximized by controlling the slug aspect ratio through specification of liquid and gas flow rates. The crystallizer is designed so that nucleation and growth processes are decoupled to enhance the individual control of each phenomenon. Coaxial or radial mixers combine liquid streams to generate seed crystals immediately upstream of the growth zone where nucleation is minimized, and crystal growth is controlled by the varying temperature profile along the length of the tube. The slug-flow crystallizer design is experimentally demonstrated to generate large uniform...

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Continuous-Flow Tubular Crystallization in Slugs Spontaneously Induced by Hydrodynamics

It has become a well-known fact that finding sustainable solutions to the unavoidable high pressure losses accompanying pipeline flows to increase the pumping capacity without necessarily adding more pump stations is inevitable. Polymers, as one of the drag reducing agents which have been found to offer such an economic relieve, is the most widely investigated and most often employed in industries because they can produce drag reduction up to 80% when they are added in minute concentrations. In addition, polymer additives modify the flow configurations of multiphase flows to such an extent that stratification of individual phases is enhanced thereby making the separation of the phases at the fluid destination much easier. The achievements so far made and the challenges facing the use of polymers as drag reducers in turbulent single and multiphase flows are comprehensively reviewed. This review discusses the experimental studies of the effects of polymer additives in turbulent flows, the analytical studies, and the proposed models as well as the suggested mechanisms that explain the drag reduction. Likewise, specific areas of interest in the review include phenomena of drag reduction by polymers, factors influencing the effectiveness of the drag reducing polymers, methods of injecting the polymers into the base fluids, degradation of the polymers and industrial applications of polymers as drag reducing agents. The current and future research interests are also addressed. Although finding reveals that there are quite a lot of research in this area, most of the experimental and theoretical works are devoted to single phase flows while the remaining ones are mostly directed towards gas–liquid flows except in very recent time when investigation into the use of polymers in liquid–liquid flows is being focused. Despite this voluminous works on drag reducing polymers, there are no universally accepted models and hence the mechanisms of drag reductions by polymers.

Roles of drag reducing polymers in single- and multi-phase flows

Effect of drag-reducing polymers on annular gas–liquid flow in a horizontal pipe

Drag reduction with polymers in gas-liquid/liquid-liquid flows in pipes: A literature review

The effect of drag reducing agents (DRA) on pressure gradient and flow regime has been studied in horizontal and 2-deg upward inclined pipes. Experiments were conducted for different flow regimes in a JO-cm i.d., 18-m long plexiglass system. The effectiveness of DRA was examined for concentrations ranging from 0 to 75 ppm. Studies were done for superficial liquid velocities between 0.03 and 1.5 mls and superficial gas velocities between I and 14 mls. The results indicate that DRA was effective in reducing the pressure gradients in single and multiphase flow. The DRA was more effective for lower superficial liquid and gas velocities for both single and multiphase flow. Pressure gradient reductions of upto 42 percent for full pipe flow, 81 percent for stratified flow, and 35 percent for annular flow were achieved ill horizontal pipes. In 2 deg upward inclination, the pressure gradient reduction for slug flow, with a concentration of 50 ppm DRA, was found to be 28 and 38 percent at superficial gas velocities of 2 and 6 mis, respectively. Flow regimes maps with DRA were constructed in horizontal pipes. Transition to slug flow with addition of DRA was observed to occur at higher superficial liquid velocities.

Effect of Drag-Reducing Agents in Multiphase Flow Pipelines

This paper reports the application of novel, digital image analysis techniques in the study of slug flow characteristics, under dynamic conditions in two-phase gas-liquid mixtures. Water and an oil of viscosity 18 cP were used for the liquid phase and carbon dioxide was used for the gas phase. Flow in a 75-mm i.d., 10-m long acrylic pipeline system was studied. Images of slugs were recorded on video by S-VHS cameras, using an audio-visual mixer. Each image was then digitized frame -by-frame and analyzed on a SGI workstation. Detailed slug characteristics, including liquid film heights, slug translational velocity, mixing length, and, slug length, were obtained.

The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part I: Flow Visualization

Mass transfer studies in oil-containing multiphase flow provide fundamental knowledge towards the understanding of hydrodynamics and the subsequent effect on corrosion in pipelines Mass transfer coefficient measurements in two-phase (oil/ferri-ferrocyanide) and three phase (oil/ferri-ferrocyanide/nitrogen) flow using limiting current density technique were made in 10-cm-dia pipe at 25 and 75 percent oil percentage Mass transfer coefficients in full pipe oil/water flow and slug flow were studied A relationship is developed between the average mass transfer coefficient in full pipe flow and slug flow The mass transfer coefficient decreased with a decrease of in-situ water cut This was due to the existence of oil phase, which decreased the ionic mass transfer diffusion coefficient

Mass Transfer Coefficient Measurement in Water/Oil/Gas Multiphase Flow

This paper studies the liquid holdup within the mixing zone of the slug. The results of the study show that the liquid holdup begins at the liquid holdup of the liquid film before the slug and then increases until the end of the mixing zone is reached. Once past the mixing zone of the slug, the average liquid holdup becomes constant. As the height of the liquid film and/or viscosity increases, so does the liquid holdup at any given film Froude number. Since the liquid holdup becomes constant once past the mixing zone of the slug, the mixing zone length was determined for the film Froude numbers studied. The results show that the mixing zone length increases linearly with film Froude number and is independent of the viscosity of the liquid in the slug for a viscosity range of 1 to 16.6 cP.

Liquid Holdup in Large-Diameter Horizontal Multiphase Pipelines

A definition is given for a Froude number in the liquid film ahead of the slug and it is seen that slug characteristics are strongly influenced by the Froude number. The mechanisms in the mixing zone of the slug are described in detail and are shown to be a function of the film Froude number. It is shown that the Hubbard and Dukler model for mixing length is inadequate. A new expression is proposed for the slug mixing length as a function of the film Froude number.

W. P. Jepson

Papers

Effect of Drag-Reducing Agents in Multiphase Flow Pipelines

The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part I: Flow Visualization

Mass Transfer Coefficient Measurement in Water/Oil/Gas Multiphase Flow

Liquid Holdup in Large-Diameter Horizontal Multiphase Pipelines

The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part II: Modeling Results