Showing papers on "Slug flow published in 2018"

Formation of liquid–liquid slug flow in a microfluidic T-junction: Effects of fluid properties and leakage flow

Abstract: Characteristics of liquid–liquid slug flow are investigated in a microchannel with focus on the leakage flow that bypasses droplets through channel gutters. The results show that the leakage flow rate varies in a range of 10.7–53.5% and 8.3–30.9% of the feed flow rate, during the droplet formation (i.e., at T-junction) and downstream flow (i.e., in the main channel), respectively, which highly depends on Ca number and wetting condition. Empirical correlations are proposed to predict them for perfectly and partially wetting conditions. Leakage flow contribution is further used to improve the Garstecki model for size scaling in order to extend its suitability for both squeezing and shearing regimes. The instantaneous flow rates of the immiscible phases are found to fluctuate periodically with the formation cycles, but in opposite behavior. The effect of the presence of leakage flow on such fluctuation are investigated and compared with gas–liquid systems. © 2017 American Institute of Chemical Engineers AIChE J, 2017

Mass transfer enhancement as a function of oscillatory baffled reactor design

Abstract: Air-water two-phase flow regimes were identified quantitatively and qualitatively for four designs of oscillatory baffled reactor (OBR) over a range of oscillation conditions in semi-batch mode operation (continuous gas phase; batch liquid phase). The baffle designs assessed were helical baffles, smooth periodic constrictions, single orifice plate baffles and multi-orifice plate baffles. Oscillation in a smooth-walled tube was also characterised for comparison purposes. The designs were characterised over a range of oscillatory Reynolds number (Reo = 0–8000) and aeration rates, vvm = 0–1. All the reactors had the same geometrical parameters such as diameter, ratio of length to diameter etc. Three distinct flow regimes (bubbly flow, slug flow, and churn flow) were identified, which were similar to those found in conventional bubble columns (BCs), but the bubbly flow regime, which exhibits the highest rates of mass transfer, was observed over a wider range of oscillatory liquid velocities in OBRs. This was due to the flow patterns (usually vortices) and shear engendered by the interactions of the oscillatory flows and the baffle designs, which resulted in coalescence and breakage of the bubbles. The volumetric mass transfer coefficients, kLa, were significantly increased in the multi-orifice design, up to 7-fold, compared with that for a steady flow (no oscillatory flow) in a smooth tube (unbaffled column).

CFD modeling of air and highly viscous liquid two-phase slug flow in horizontal pipes

Abstract: Computational Fluid Dynamics (CFD) approach, encoded on STAR-CCM+ was used to simulate air and highly viscous liquid two-phase slug flow in a 50.8-mm (2-in.) ID and 18.9-m (62 ft.) long horizontal pipe. The Volume of Fluid (VOF) method, the Continuum Surface Force (CSF) model and the High Resolution Interface Capturing (HRIC) scheme were utilized. The liquid viscosity varied from 161 to 567 mPa s based on the experimental data. A sensitivity analysis of the sharpening factor, the angle factor, and the Interface Momentum Dissipation (IMD) model was carried out to obtain the best combination of parameters. Besides, comparison with experimental measurements concerning slug frequency, average liquid holdup and velocity profiles in the liquid region was carried out. The comparison shows a fair correspondence in terms of behavior and magnitude with the experimental results obtained by Particle Image Velocimetry (PIV). It was observed that the velocity profile is not fully developed near the bottom of slug body. Finally, extrapolation to the extended velocity conditions was performed. The reduction of translational velocity at higher mixture velocity conditions was investigated. A certain amount of gas passing from the tail to the front of the liquid slug body was visualized by three-dimensional velocity profiles. This phenomenon supports the reduction of translational velocity above the certain level of mixture velocity.

Experimental study of viscous effects on flow pattern and bubble behavior in small diameter bubble column

Abstract: An experimental study was carried out to explore viscous effects on the flow pattern and bubble behavior in a small diameter bubble column using silicone oil fluids of viscosities 5, 100, 1000, and 5000 mPa s The flow pattern was obtained from the probability density function using the time-averaged void fraction traces of the real-time qualitative and quantitative measurements from Electrical Capacitance Tomography (ECT) This was confirmed from the high-speed camera and ECT images which also gave a vivid description of the bubble behavior Further confirmation of the observed flow pattern was obtained using the diameter ratio, λ, where for slug flow λ > 06 The flow pattern was observed to vary from spherical cap bubbles to developing slug and slug flow within the gas superficial velocities considered (002 ≤ Ugs ≤ 0361 m/s) As viscosity increases, the appearance of spherical cap bubbles decreases, while slug flow tendency increases The observed flow patterns were compared with previous work The developing slugs in liquid viscosities of 5 and 100 mPa s were observed to be deformed The Taylor bubble obtained from 1000 mPa s is called prolate spheroid, while that obtained from 5000 mPa s is called oblate spheroid In addition, as the superficial gas velocity increases, the length of Taylor bubbles increases, while that of slug flow decreases The bubble behavior was further characterised using the inverse dimensionless viscosity and Eotovos number The process of leading and trailing bubble merging to form Taylor bubbles via coalescence was also captured and explained using the high-speed camera video

Study of high viscous multiphase phase flow in a horizontal pipe

Abstract: Heavy oil accounts for a major portion of the world’s total oil reserves Its production and transportation through pipelines is beset with great challenges due to its highly viscous nature This paper studies the effects of high viscosity on heavy oil two-phase flow characteristics such as pressure gradient, liquid holdup, slug liquid holdup, slug frequency and slug liquid holdup using an advanced instrumentation (ie Electrical Capacitance Tomography) Experiments were conducted in a horizontal flow loop with a pipe internal diameter (ID) of 00762 m; larger than most reported in the open literature for heavy oil flow Mineral oil of 10–50 Pas viscosity range and compressed air were used as the liquid and gas phases respectively Pressure gradient (measured by means differential pressure transducers) and mean liquid holdup was observed to increase as viscosity of oil is increased Obtained results also revealed that increase in liquid viscosity has significant effects on flow pattern and slug flow features