Showing papers on "Slug flow published in 2012"

Hydrodynamics and Mass Transfer in Gas-Liquid Flows in Microreactors

Abstract: Over the last ten to fifteen years, microreaction echnology has become of increased interest to both academics and industrialists for intensification of multiphase processes. Amongst the vast application possibilities, fast, highly exothermic and/or mass transfer-limited gas-liquid reactions benefit from process miniaturization. Recent studies of hydrodynamics and mass transfer in gas-liquid microreactors with closed and open microchannels, e.g., falling-film microreactors, are reviewed and compared. Special attention is paid to Taylor or slug flow in closed channels, as this regime seems to be most adapted for practical engineering applications.

The thickness of the falling film of liquid around a Taylor bubble

Abstract: We present the results of laboratory experiments that quantify the physical controls on the thickness of the falling film of liquid around a Taylor bubble, when liquidgas interfacial tension can be...

Liquid–Liquid Two-Phase Flow Patterns in a Serpentine Microchannel

Abstract: Liquid–liquid two-phase flow patterns in a serpentine glass microchannel have been studied using a camera with very high shutter speed. The phase system is equilibrated water−succinic acid−n-butanol system. Observed flow patterns have been classified into seven different types: slug flow, slug and droplet flow, droplet flow, unstable annular flow, annular flow, annular dispersed flow, and fully dispersed flow. Two different ways of introducing the aqueous and organic phases into the microchannel have been studied. Flow regime maps are presented and discussed. Voronoi diagrams of the flow regime maps are also presented.

Drift-Velocity Closure Relationships for Slug Two-Phase High-Viscosity Oil Flow in Pipes

Abstract: The drift velocity of a gas bubble penetrating into a stagnant liquid is investigated experimentally in this paper. It is part of the translational slug velocity. The existing equations for the drift velocity are either developed by using the results of Benjamin (1968) analysis assuming inviscid fluid flow or correlated using air-water data. Effects of surface tension and viscosity usually are neglected. However, the drift velocity is expected to be affected with high oil viscosity. In this study, the work of Gokcal et al. (2009) has been extended for different pipe diameters and viscosity range. The effects of high oil viscosity and pipe diameter on drift velocity for horizontal and upward inclined pipes are investigated. The experiments are performed on a flow loop with a test section 50.8, 76.2 and 152.4 mm ID for inclination angles of 0o to 90o. Water and viscous oil are used as test fluids. New correlation for drift velocity in horizontal pipes of different diameters and liquid viscosities is developed based on experimental data. A new drift velocity model/ approach are proposed for high oil viscosity valid for inclined pipes inclined from horizontal to vertical. The proposed comprehensive closure relationships are expected to improve the performance of two-phase flow models for high viscosity oils in the slug flow regime.

Experimental constraints on the outgassing dynamics of basaltic magmas

Abstract: [1] The dynamics of separated two-phase flow of basaltic magmas in cylindrical conduits has been explored combining large-scale experiments and theoretical studies. Experiments consisted of the continuous injection of air into water or glucose syrup in a 0.24 m diameter, 6.5 m long bubble column. The model calculates vesicularity and pressure gradient for a range of gas superficial velocities (volume flow rates/pipe area, 10−2–102 m/s), conduit diameters (100–2 m), and magma viscosities (3–300 Pa s). The model is calibrated with the experimental results to extrapolate key flow parameters such as Co (distribution parameter) and Froude number, which control the maximum vesicularity of the magma in the column, and the gas rise speed of gas slugs. It predicts that magma vesicularity increases with increasing gas volume flow rate and decreases with increasing conduit diameter, until a threshold value (45 vol.%), which characterizes churn and annular flow regimes. Transition to annular flow regimes is expected to occur at minimum gas volume flow rates of 103–104 m3/s. The vertical pressure gradient decreases with increasing gas flow rates and is controlled by magma vesicularity (in bubbly flows) or the length and spacing of gas slugs. This study also shows that until conditions for separated flow are met, increases in magma viscosity favor stability of slug flow over bubbly flow but suggests coexistence between gas slugs and small bubbles, which contribute to a small fraction of the total gas outflux. Gas flow promotes effective convection of the liquid, favoring magma homogeneity and stable conditions.

Asymmetrical breakup of bubbles at a microfluidic T-junction divergence: feedback effect of bubble collision

Abstract: This paper aims at studying the asymmetrical breakup of bubbles at a microfluidic T-junction divergence stemming from the feedback effect of bubble behaviors at the T-junction convergence in a loop with the symmetrical branches by a high-speed digital camera. The experiments were performed under gas/liquid flow rates ratio ranging from 0.084 to 4.333. The microfluidic channels have uniform square cross-section with 400 μm wide and 400 μm deep. Four bubble behaviors (bubble pair asymmetrical collision, bubble pair staggered flow, single bubble flow and dynamic transformation flow) were observed at the T-junction convergence in different gas and liquid flow rates. The feedback effects of asymmetrical collision and staggered flow of bubble pairs at the T-junction convergence on bubble behavior at the T-junction divergence were mainly investigated. The result showed that the feedback effect is negligible at relatively low flow rates when no collision of bubble pairs occurs. And the bubble pair asymmetrical collision at T-junction convergence or an amplified effect of structured blemish of microchannel at relatively high flow rates is primarily responsible for the asymmetric breakup of bubbles at the T-junction divergence.

Vertically Downward Two-Phase Flow, (II)

Abstract: Following Part (I) of the present paper, which presented the experimental results obtained on the void distribution and average void fraction shown by nearly fully-developed, vertically downward two-phase flow of air-water mixture, this Part (?) covers the flow regime transition criteria among the three basic flow regimes : bubbly, slug and annular flows. The annular flow further was divided into two subregions of falling film flow and annular drop flow. The general situation of the transition criteria is as follows : (1) bubbly-to-slug flow transition occurs when the local void fraction in the central region of the tube is 0.3; (2) slug-to-annular drop flow transition criterion is given as a case which equations giving average void fraction for the slug flow and the annular flow are simultaneously satisfied; (3) slug-to-falling film flow transition occurs when the pressure difference between the crest of large wave and the bottom overcomes the surface tension; (4) the occurrence of liquid droplets from w...

Churn and Wispy Annular Flow Regimes in Vertical Gas–Liquid Flows

Abstract: Two-phase flows are extremely complex and, traditionally, attempts have been made to classify the myriad of possible flow configurations into “flow regimes” or “flow patterns”. Classically, vertical two-phase flows have been classified into the regimes of bubbly flow, slug flow, and annular flow. This paper makes an appeal for two other regimes, namely, “churn flow” and “wispy annular flow”, to be given more attention. As shown, these regimes are of considerable technological importance and possess unusual features that justify their separate designation and make them ripe for further study.

On the Dynamic Response of Flexible Risers Caused by Internal Slug Flow

Abstract: Slug flow through flexible risers is a frequent phenomenon which occurs during production of a mixture of oil and gas. The dynamic nature of the slug pattern induces time varying forces, which leads to structural vibrations of the riser. These vibrations can produce large deflections and stresses, which can leave it to fail by fatigue, excessive bending or local buckling.In this work the influence from slug flow on the structural dynamic response of a lazy wave flexible riser is analyzed using a computational tool consisting of one program for calculation of slug flow dynamics, and another program for structural dynamic response. Both programs apply a time integration method, and since slug flow will lead to dynamic motion response of the riser, and riser motion dynamics will influence slug flow dynamics, the two codes need to exchange information during the integration process. Information exchange is established by making a federation based on High Level Architecture (HLA).The federation is composed of SLUGIT and RISANANL. SLUGGIT is a two-phase flow code written in C++ which simulates dynamic slug flow through pipes and riser using a Lagrangian tracking model. RISANANL is a FORTRAN program for static and dynamic structural analysis of slender marine structures based on a finite element formulation. Using the HLA standard these two programs can carry out synchronized time integration and exchange information for each time step.In this work the structural analysis code accomplishes the dynamic response using a linear finite element (FE) formulation. Hence, forces from centripetal acceleration of the internal flow, relative velocity between the riser and surrounding water, and varying gravity of the pipe and content will be accounted for in the dynamic analysis. Displacements, stresses, internal pressure, and outlet flow rates of liquid and gas will be accounted for. The results encourage us to carry out a fully non-linear finite element analysis, in order to have a better understanding of the dynamic behaviour of flexible risers undergoing an unsteady internal two-phase flow.Copyright © 2012 by ASME