Gas-Liquid Bubbly Flow in Vertical Pipes

1996 ◽  
Vol 118 (2) ◽  
pp. 377-382 ◽  
Author(s):  
V. E. Nakoryakov ◽  
O. N. Kashinsky ◽  
V. V. Randin ◽  
L. S. Timkin
Keyword(s):  
Shear Stress ◽  
Single Phase ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Upward Flow ◽  
Flow Conditions ◽  
Downward Flow ◽  
Velocity Fluctuations ◽  
Turbulent Fluctuations ◽  
Diameter Pipe

Gas-liquid bubbly flow was investigated in vertical pipes for different flow conditions: fully developed turbulent downward flow in a 42.3 mm diameter pipe and upward flow in a 14.8 mm diameter pipe with liquid of elevated viscosity. Wall shear stress, local void fraction, and liquid velocity profiles, shear stress, and velocity fluctuations were measured using an electrodiffusional method. Results obtained demonstrate the existence of “universal” near-wall velocity distribution in a downward bubbly flow. The reduction of turbulent fluctuations is observed in downward flow as compared to a single-phase turbulent flow. The development of bubble-induced liquid velocity fluctuations in a “laminar” bubbly flow was studied.

Numerical Investigation on Turbulence Models in Bubbly Flow Using Euler-Lagrange Approach

2020 ◽  
Author(s):  
Yujia Zhou ◽  
Jingyu Du ◽  
Chenru Zhao ◽  
Hanliang Bo
Keyword(s):  
Fluid Flow ◽  
Stokes Equations ◽  
Liquid Velocity ◽  
Saturated Vapor ◽  
Bubbly Flow ◽  
Continuous Phase ◽  
Mass Force ◽  
Bubble Plume ◽  
Flow Conditions ◽  
Interaction Forces

Abstract To accurately simulate the bubble motions in the turbulent flow liquids, two way coupled Euler–Lagrange method is adopted in this work. The continuous phase is solved with the Navier–Stokes equations based on the Euler grid, while the individual bubble is tracked by using the Lagrange frame of reference. Two–way coupling is realized by transferring the interaction forces to the momentum equation of the continuous phase at each fluid flow timestep and in turn influencing the bubble motion. The interaction forces including the drag force, lift force, wall lubrication force and virtual mass force are carefully selected. Turbulent models are of significance to capture the fluid flow conditions. Comparing the different cases treated by the k-ε, PANS and LES models with the experimental data, the results of the PANS with RWM and BIT, and LES can dynamically display the oscillation of the bubble plume and the calculated time averaged axial liquid velocity reasonably agrees with the measured data. In the case of bubble injective flow conditions in large containers, the bubble induced turbulent effect can be almost neglected. However, the RWM describes the fluctuating velocity should be considered applied with the PANS model. In addition, the saturated vapor–liquid system under high pressure of 6.9 MPa is numerically simulated by implementing the PANS with R WM and BIT.

scholarly journals Energy spectra in turbulent bubbly flows

2016 ◽  
Vol 791 ◽  
pp. 174-190 ◽  
Author(s):  
Vivek N. Prakash ◽  
J. Martínez Mercado ◽  
Leen van Wijngaarden ◽  
E. Mancilla ◽  
Y. Tagawa ◽  
...  
Keyword(s):  
Energy Spectrum ◽  
Kinetic Energy ◽  
Viscous Dissipation ◽  
Energy Production ◽  
Single Phase ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Bubbly Flows ◽  
Energy Spectra ◽  
Physical Reason

We conduct experiments in a turbulent bubbly flow to study the nature of the transition between the classical $-5/3$ energy spectrum scaling for a single-phase turbulent flow and the $-3$ scaling for a swarm of bubbles rising in a quiescent liquid and of bubble-dominated turbulence. The bubblance parameter (Lance & Bataille J. Fluid Mech., vol. 222, 1991, pp. 95–118; Rensen et al., J. Fluid Mech., vol. 538, 2005, pp. 153–187), which measures the ratio of the bubble-induced kinetic energy to the kinetic energy induced by the turbulent liquid fluctuations before bubble injection, is often used to characterise bubbly flow. We vary the bubblance parameter from $b=\infty$ (pseudoturbulence) to $b=0$ (single-phase flow) over 2–3 orders of magnitude (0.01–5) to study its effect on the turbulent energy spectrum and fluctuations in liquid velocity. The probability density functions (PDFs) of the fluctuations in liquid velocity show deviations from the Gaussian profile for $b>0$, i.e. when bubbles are present in the system. The PDFs are asymmetric with higher probability in the positive tails. The energy spectra are found to follow the $-3$ scaling at length scales smaller than the size of the bubbles for bubbly flows. This $-3$ spectrum scaling holds not only in the well-established case of pseudoturbulence, but surprisingly in all cases where bubbles are present in the system ($b>0$). Therefore, it is a generic feature of turbulent bubbly flows, and the bubblance parameter is probably not a suitable parameter to characterise the energy spectrum in bubbly turbulent flows. The physical reason is that the energy input by the bubbles passes over only to higher wavenumbers, and the energy production due to the bubbles can be directly balanced by the viscous dissipation in the bubble wakes as suggested by Lance & Bataille (1991). In addition, we provide an alternative explanation by balancing the energy production of the bubbles with viscous dissipation in the Fourier space.

Hydrodynamical similarities between bubble column and bubbly pipe flow

2001 ◽  
Vol 437 ◽  
pp. 203-228 ◽  
Author(s):  
ROBERT F. MUDDE ◽  
TAKAYUKI SAITO
Keyword(s):  
Pipe Flow ◽  
Single Phase ◽  
Liquid Velocity ◽  
Bubble Column ◽  
Laser Doppler Anemometry ◽  
Bubbly Flow ◽  
Bubble Velocity ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Superficial Liquid Velocity

The hydrodynamical similarities between the bubbly flow in a bubble column and in a pipe with vertical upward liquid flow are investigated. The system concerns air/water bubbly flow in a vertical cylinder of 14.9 cm inner diameter. Measurements of the radial distribution of the liquid velocity, gas fraction and the bubble velocity and size are performed using laser Doppler anemometry for the liquid velocity and a four-point optical fibre probe for the gas fraction, bubble velocity and size. The averaged gas fraction was 5.2% for the bubble column (with a superficial liquid velocity of zero) and 5.5% for the bubbly pipe flow at a superficial liquid velocity of 0.175 m s−1. From a hydrodynamical point of view, the two modes of operation are very similar. It is found that in many respects the bubbly pipe flow is the superposition of the flow in the bubble column mode and single-phase flow at the same superficial liquid velocity.The radial gas fraction profiles are the same and the velocity profiles differ only by a constant offset: the superficial liquid velocity. This means that the well-known large-scale liquid circulation (in a time-averaged sense) of the bubble column is also present in the bubbly pipe flow. For the turbulence intensities it is found that the bubbly pipe flow is like the superposition of the bubble column and the single-phase flow at the superficial liquid velocity of the pipe flow, the former being at least an order of magnitude higher than the latter. The large vortical structures that have been found in the bubble columns are also present in the bubbly pipe flow case, partly explaining the much higher ‘turbulence’ levels observed.

Investigation on the Characteristic of Bubbles in Horizontal Channel Flow by Fiber Optic Sensor

2019 ◽  
Author(s):  
Takamichi Hiroi ◽  
Tatsuya Hamada ◽  
Chiharu Kawakita
Keyword(s):  
Void Fraction ◽  
Single Phase ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Fiber Optic Sensor ◽  
Bulk Liquid ◽  
Friction Drag ◽  
Single Phase Flow ◽  
Optic Sensor ◽  
The Mean

Abstract Friction drag and characteristic of bubbles in horizontal water channel are investigated at bulk liquid velocity Um = 1 ∼ 5 m/s (Reynolds number Rem = 16,000 ∼ 120,000 (based on the channel height)) and mean void fraction α = 0.5, 1, 2 %. Firstly, shear stress sensor is applied to investigate the relation between friction drag with bubbles and bulk liquid velocity. Friction drag in the bubbly flow is larger than it in the single-phase flow at Um = 1 ∼ 2 m/s. It in the bubbly flow, however, decreases with the mean liquid velocity. Furthermore, it in bubbly flow is smaller than it in the single-phase flow at Um ≥ 3 m/s. Secondly, fiber optic sensor is applied to investigate the void fraction distribution, bubble diameter distribution and streamwise velocity of bubbles. The peak value of the void fraction decreases with increasing of the bulk liquid velocity at Um = 2 ∼ 5 m/s. Bubbles exist in only y/δ = 0 ∼ 0.5 at Um = 1, 2 m/s. The mean bubble velocity increases with the bulk liquid velocity. The mean Sauter diameter decreases with increasing of the bulk liquid velocity. It appears that the high void ratio near the wall causes the increasing of drag and friction drag decreases when bubbles exist in whole of upper half of channel.

Prediction of Pump Performance Under Air-Water Two-Phase Flow Based on a Bubbly Flow Model

1993 ◽  
Vol 115 (4) ◽  
pp. 781-783 ◽  
Author(s):  
Kiyoshi Minemura ◽  
Tomomi Uchiyama
Keyword(s):  
Two Phase Flow ◽  
Bubbly Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Flow Conditions ◽  
Two Phase ◽  
Performance Change ◽  
Void Fractions ◽  
Two Phases

This paper is concerned with the determination of the performance change in centrifugal pumps operating under two-phase flow conditions using the velocities and void fractions calculated under the assumption of an inviscid bubbly flow with slippage between the two phases. The estimated changes in the theoretical head are confirmed with experiments within the range of bubbly flow regime.

scholarly journals Endothelial cell monolayer formation on a small-diameter vascular graft surface under pulsatile flow conditions

2021 ◽  
Vol 23 (3) ◽  
pp. 101-114
Author(s):  
M. Yu. Khanova ◽  
E. A. Velikanova ◽  
V. G. Matveeva ◽  
E. O. Krivkina ◽  
T. V. Glushkova ◽  
...  
Keyword(s):  
Shear Stress ◽  
Endothelial Cell ◽  
Pulsatile Flow ◽  
Vascular Graft ◽  
Cell Monolayer ◽  
Small Diameter ◽  
Flow Conditions ◽  
Endothelial Cell Culture ◽  
Monolayer Formation ◽  
Whole Transcriptome

Objective: to create a cell-populated small-diameter vascular graft (SDVG) using autologous endothelial cells and extracellular matrix proteins, and to evaluate the efficiency of endothelial cell monolayer formation during shear stress preconditioning in a SDVG.Materials and methods. PHBV/PCL tubular scaffolds of vascular grafts were made by electrospinning from a mixture of polyhydroxybutyrate-valerate (PHBV) copolymer and polycaprolactone (PCL) and modified with fibrin. To populate the graft, an endothelial cell culture was isolated from the blood of patients with coronary heart disease. Phenotyping of endothelial colony-forming cell (ECFC) culture was performed by flow cytometry and immunofluorescence microscopy. Cell proliferative and angiogenic activity were also studied. Cell-populated vascular scaffolds were cultured in a pulsatile flow setup with a final shear stress of 2.85 dyne/cm2. The effect of pulsatile flow on monolayer formation was assessed by immunofluorescence, scanning electron microscopy, atomic force microscopy, and whole-transcriptome RNA sequencing.Results. Under the influence of pulsatile flow, endothelial cells that were seeded into the tubular scaffold showed an increase in the expression level of endothelial profile proteins, focal adhesion and cytoskeleton. In contrast to endothelial cell culture on a vascular graft surface under static conditions, when cultured under pulsatile flow with 2.85 dyne/ cm2 shear stress, endothelial lining cells have an increased ability to adhere and are oriented along the pulsatile flow path. Whole-transcriptome RNA sequencing showed that induced shear stress increased expression levels of differentially expressed genes encoding proteins that ensure vascular development, endothelial integrity, and endothelial metabolism. A protocol for fabrication of a personalized cell-populated biodegradable SDVG under pulsatile flow conditions was developed.Conclusion. The use of autologous fibrin and ECFC culture, as well as shear stress preconditioning, allow to obtain a personalized cell-populated SDVG with continuous functional endothelial monolayer adapted to the flow.

Analysis of Laminar Mixed Convective Plumes Along Vertical Adiabatic Surfaces

1984 ◽  
Vol 106 (3) ◽  
pp. 552-557 ◽  
Author(s):  
K. V. Rao ◽  
B. F. Armaly ◽  
T. S. Chen
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Leading Edge ◽  
Vertical Surface ◽  
Stream Velocity ◽  
Thermal Source ◽  
Flow Conditions ◽  
Velocity Overshoot ◽  
Wall Shear ◽  
Prandtl Numbers

Laminar mixed forced and free convection from a line thermal source imbedded at the leading edge of an adiabatic vertical surface is analytically investigated for the cases of buoyancy assisting and buoyancy opposing flow conditions. Temperature and velocity distributions in the boundary layer adjacent to the adiabatic surface are presented for the entire range of the buoyancy parameter ξ (x) = Grx/Rex5/2 from the pure forced (ξ(x) = 0) to the pure free (ξ(x) = ∞) convection regime for fluids having Prandtl numbers of 0.7 and 7.0. For buoyancy-assisting flow, the velocity overshoot, the temperature, and the wall shear stress increase as the plume’s strength increases. On the other hand, the velocity overshoot, the wall shear stress, and the temperature decrease as the free-stream velocity increases. For buoyancy opposing flow, the velocity and wall shear stress decrease but the temperature increases as the plume’s strength increases.

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