scholarly journals CFD Modeling of Gas-Liquid Bubbly Flow in Horizontal Pipes: Influence of Bubble Coalescence and Breakup

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
K. Ekambara ◽  
R. Sean Sanders ◽  
K. Nandakumar ◽  
J. H. Masliyah
Keyword(s):  
Volume Fraction ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Gas Bubbles ◽  
Bubbly Flows ◽  
Cfd Modeling ◽  
Horizontal Pipe ◽  
The Impact

Modelling of gas-liquid bubbly flows is achieved by coupling a population balance equation with the three-dimensional, two-fluid, hydrodynamic model. For gas-liquid bubbly flows, an average bubble number density transport equation has been incorporated in the CFD code CFX 5.7 to describe the temporal and spatial evolution of the gas bubbles population. The coalescence and breakage effects of the gas bubbles are modeled. The coalescence by the random collision driven by turbulence and wake entrainment is considered, while for bubble breakage, the impact of turbulent eddies is considered. Local spatial variations of the gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, and liquid velocity are compared against experimental data in a horizontal pipe, covering a range of gas (0.25 to 1.34 m/s) and liquid (3.74 to 5.1 m/s) superficial velocities and average volume fractions (4% to 21%). The predicted local variations are in good agreement with the experimental measurements reported in the literature. Furthermore, the development of the flow pattern was examined at three different axial locations ofL/D= 25, 148, and 253. The first location is close to the entrance region where the flow is still developing, while the second and the third represent nearly fully developed bubbly flow patterns.

scholarly journals A Combined Numerical and Experimental Study of Hydrodynamics for an Air-Water External Loop Airlift Reactor

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Deify Law ◽  
Samuel T. Jones ◽  
Theodore J. Heindel ◽  
Francine Battaglia
Keyword(s):  
Liquid Velocity ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Airlift Reactor ◽  
Cfd Modeling ◽  
Bubble Column Reactor ◽  
Ensemble Averaging ◽  
3D Simulations ◽  
External Loop

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because they can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR was simulated using an Eulerian–Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems. The computational fluid dynamics (CFD) simulations were compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 cm/s to 20 cm/s. The effect of specifying a mean bubble diameter to represent the gas phase in the CFD modeling was investigated, and 2D and 3D simulations were found to be in good agreement with the experimental data. The ELALR flow regimes were compared for the reactor operating in bubble column, closed vent, and open vent modes, and the 2D simulations qualitatively predicted the behavior of bubble growth in the downcomer. However, it was found that 3D simulations were necessary to capture the physics of the ELALR for gas holdup, bulk density differences, and riser superficial liquid velocity.

Effects of Increased Tooth Clearance on the Performance of a Labyrinth Seal With Oil-Rich Bubbly Laminar Flow

2021 ◽  
Author(s):  
Min Zhang ◽  
Dara W. Childs
Keyword(s):  
Smooth Surface ◽  
Volume Fraction ◽  
Silicone Oil ◽  
Bubbly Flow ◽  
Labyrinth Seal ◽  
Test Fluid ◽  
Axial Thrust ◽  
Rotordynamic Coefficients ◽  
Piston Seal ◽  
The Impact

Abstract In recent years, multiphase pumps have become more and more popular because of the capability to simplify the process, reduce the footprint, and lower the cost. To compensate for the axial thrust force, an annular seal is normally used as a balance piston seal, and the labyrinth seal is one of the choices. A typical labyrinth seal consists of a surface with teeth and a smooth surface. The teeth are either on the rotor or the stator. To protect the machine, one side (either the teeth or the smooth surface) is made of a material that can be safely sacrificed during a rub. After the rub, the teeth clearance is increased. This paper studies the impact of the increased teeth clearance on the performance of the labyrinth seal under oil-rich bubbly flow conditions. The test fluid is a mixture of silicone oil (PSF 5cSt) and air with inlet Gas Volume Fraction GVF up to 9%. Tests are conducted with pressure drop PD = 34.5 bars, rotor speed ω = 5 krpm, and radial tooth clearance Cr = 0.102 mm and 0.178 mm. Test results show that, for all test conditions (before and after injecting air bubbles into the oil flow), increasing Cr from 0.102 mm to 0.178 mm increases the mass flow rate by about 40% but barely changes the test seal’s rotordynamic coefficients; i.e., the increased tooth clearance would not change the pump vibration performance.

Impact of Bubble Size on Flow Response to Transient Pressure Drop Through Converging Nozzle

2020 ◽  
Author(s):  
Aleksey Garbaly ◽  
Thomas Shepard
Keyword(s):  
Transient Response ◽  
Liquid Flow ◽  
Speed Of Sound ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Bubbly Flows ◽  
Chamber Pressure ◽  
Convergent Nozzle ◽  
Flow Rates ◽  
The Impact

Abstract For homogenous two-phase bubbly flows, the theoretical speed of sound is dramatically reduced at moderate void fractions to speeds much lower than the speed of sound for either single phase. This theoretical speed of sound would suggest a propensity for bubbly flows to reach choked conditions when traveling through a convergent nozzle. However, for a bubbly flow to be considered homogenous requires assumptions that may not be realized in practical applications. In this experimental study, a bubbly flow was sent through a convergent nozzle before entering a large chamber. By setting steady flow conditions upstream and then reducing the chamber pressure via a vacuum pump, the transient response in terms of gas and liquid flow rates and upstream channel pressure was determined. The bubble size was carefully varied from ∼0.3–1 mm while holding gas and liquid flow rates constant in order to study how bubble size affects the transient flow characteristics. High-speed imaging was used for measuring the bubbles. Experiments were also conducted at two gas-liquid mass flow ratios. Results are presented to demonstrate the impact of bubble size and gas-liquid ratio on the transient response of upstream gas and liquid flow rates, upstream pressure and exit Mach number to the lowering of pressure downstream of the convergent nozzle. Results are presented both for flows that remained in the bubbly regime and for flows that transitioned to an annular flow regime during a trial.

scholarly journals Modeling of Multisize Bubbly Flow and Application to the Simulation of Boiling Flows with the Neptune_CFD Code

2009 ◽  
Vol 2009 ◽  
pp. 1-8 ◽  
Author(s):  
Christophe Morel ◽  
Jérôme M. Laviéville
Keyword(s):  
Heat Transfer ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Mathematical Expression ◽  
Original Model ◽  
Bubbly Flows ◽  
Condensation Rate ◽  
Interface Heat Transfer ◽  
Interface Heat ◽  
Transfer Term

This paper describes the modeling of boiling multisize bubbly flows and its application to the simulation of the DEBORA experiment. We follow the method proposed originally by Kamp, assuming a given mathematical expression for the bubble diameter pdf. The original model is completed by the addition of some new terms for vapor compressibility and phase change. The liquid-to-interface heat transfer term, which essentially determines the bubbles condensation rate in the DEBORA experiment, is also modeled with care. First numerical results realized with the Neptune_CFD code are presented and discussed.

scholarly journals Thermal Analysis of 3D Electromagnetic Radiative Nanofluid Flow with Suction/Blowing: Darcy–Forchheimer Scheme

Micromachines ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1395
Author(s):  
Hammad Alotaibi ◽  
Mohamed R. Eid
Keyword(s):  
Activation Energy ◽  
Differential Equations ◽  
Melt Spinning ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Brownian Diffusion ◽  
Force Coefficient ◽  
Catalytic Reactors ◽  
Nanofluid Flow ◽  
The Impact

This paper discusses the Darcy–Forchheimer three dimensional (3D) flow of a permeable nanofluid through a convectively heated porous extending surface under the influences of the magnetic field and nonlinear radiation. The higher-order chemical reactions with activation energy and heat source (sink) impacts are considered. We integrate the nanofluid model by using Brownian diffusion and thermophoresis. To convert PDEs (partial differential equations) into non-linear ODEs (ordinary differential equations), an effective, self-similar transformation is used. With the fourth–fifth order Runge–Kutta–Fehlberg (RKF45) approach using the shooting technique, the consequent differential system set is numerically solved. The influence of dimensionless parameters on velocity, temperature, and nanoparticle volume fraction profiles is revealed via graphs. Results of nanofluid flow and heat as well as the convective heat transport coefficient, drag force coefficient, and Nusselt and Sherwood numbers under the impact of the studied parameters are discussed and presented through graphs and tables. Numerical simulations show that the increment in activation energy and the order of the chemical reaction boosts the concentration, and the reverse happens with thermal radiation. Applications of such attractive nanofluids include plastic and rubber sheet production, oil production, metalworking processes such as hot rolling, water in reservoirs, melt spinning as a metal forming technique, elastic polymer substances, heat exchangers, emollient production, paints, catalytic reactors, and glass fiber production.

Manufacturing Modeling of Three-Dimensional Resin Injection Pultrusion Process Control Parameters for Polyester/Glass Rovings Composites

2006 ◽  
Vol 129 (1) ◽  
pp. 143-156 ◽  
Author(s):  
A. L. Jeswani ◽  
J. A. Roux
Keyword(s):  
Process Parameters ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Fiber Reinforcement ◽  
Resin Flow ◽  
Molding Process ◽  
Fiber Volume ◽  
Liquid Resin ◽  
Pultrusion Process ◽  
The Impact

Pultrusion, sometimes referred to as continuous resin transfer molding process, is a continuous, cost-effective method for manufacturing composite materials with constant cross sections (such as rod stock, beams, channels, and tubing). The objective of this study is to improve the fiber reinforcement wetout and thus the quality of the pultruded part in the injection pultrusion process. The complete wetout of the dry reinforcement by the liquid resin depends on various design and process parameters. The process parameters modeled in this study are fiber pull speed, fiber volume fraction, and viscosity of the resin. In the present work, a three-dimensional finite volume technique is employed to simulate the liquid resin flow through the fiber reinforcement in the injection pultrusion process. The numerical model simulates the flow of polyester resin through the glass rovings and predicts the impact of the process parameters on wetout, resin pressure field, and resin velocity field. The location of the liquid resin flow front has been predicted for an injection slot as well as for five discrete injection ports.

scholarly journals On bubble clustering and energy spectra in pseudo-turbulence

2010 ◽  
Vol 650 ◽  
pp. 287-306 ◽  
Author(s):  
JULIÁN MARTÍNEZ MERCADO ◽  
DANIEL CHEHATA GÓMEZ ◽  
DENNIS VAN GILS ◽  
CHAO SUN ◽  
DETLEF LOHSE
Keyword(s):  
Isotropic Turbulence ◽  
Liquid Velocity ◽  
Pair Correlation ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Radial Distance ◽  
Energy Spectra ◽  
Bubble Velocity ◽  
Vertical Orientation ◽  
Gaussian Form

Three-dimensional particle tracking velocimetry (PTV) and phase-sensitive constant temperature anemometry in pseudo-turbulence – i.e. flow solely driven by rising bubbles – were performed to investigate bubble clustering and to obtain the mean bubble rise velocity, distributions of bubble velocities and energy spectra at dilute gas concentrations (α ≤ 2.2 %). To characterize the clustering the pair correlation function G(r, θ) was calculated. The deformable bubbles with equivalent bubble diameter db = 4–5 mm were found to cluster within a radial distance of a few bubble radii with a preferred vertical orientation. This vertical alignment was present at both small and large scales. For small distances also some horizontal clustering was found. The large number of data points and the non-intrusiveness of PTV allowed well-converged probability density functions (PDFs) of the bubble velocity to be obtained. The PDFs had a non-Gaussian form for all velocity components and intermittency effects could be observed. The energy spectrum of the liquid velocity fluctuations decayed with a power law of −3.2, different from the ≈ −5/3 found for homogeneous isotropic turbulence, but close to the prediction −3 by Lance & Bataille (J. Fluid Mech., vol. 222, 1991, p. 95) for pseudo-turbulence.

Influence of Bubbles on the Turbulence Anisotropy

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Igor A. Bolotnov
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Stress ◽  
Bubbly Flow ◽  
Bubbly Flows ◽  
Cfd Modeling ◽  
Two Phase ◽  
Cfd Models ◽  
Turbulence Anisotropy ◽  
Multiphase Fluid ◽  
Turbulent Models

Direct numerical simulation (DNS) with interface tracking of turbulent bubbly flows is becoming a major tool in advancing our knowledge in the area of multiphase modeling research. A comprehensive analysis of the turbulent flow structure allows us to evaluate the state-of-the-art computational multiphase fluid dynamics (CMFD) models and to propose new closure laws. The presented research will demonstrate how the multiphase DNS data can inform the development of computational fluid dynamics (CFD) models. In particular, the Reynolds stress distribution will be evaluated for single- and two-phase bubbly flows and the level of turbulence anisotropy will be measured in several scenarios. The results will help determine if the isotropic turbulent models are suitable for bubbly flow applications or if there is a strong need to apply and develop Reynolds-stress turbulent models for two-phase flow CFD modeling.

Experiments and Modeling in Bubbly Flows at Elevated Pressures

2003 ◽  
Author(s):  
R. Kumar ◽  
T. A. Trabold ◽  
C. C. Maneri
Keyword(s):  
Void Fraction ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Bubbly Flows ◽  
Rise Velocity ◽  
Two Phase ◽  
Flow Models ◽  
Gamma Densitometer ◽  
Visualization Techniques

Measurements of local void fraction, rise velocity and bubble diameter have been obtained for cocurrent, wall-heated, upward bubbly flows in a pressurized refrigerant. The instrumentation used was the gamma densitometer and the hot-film anemometer. Departure bubble size and bulk size measurements were also made and correlated with appropriate parameters. Flow visualization techniques have also been used to understand the two-phase flow structure and the behavior of the bubbly flow for different bubble shapes and sizes, and to obtain the rise velocity. Such insight, coupled with quantitative local and averaged data on void fraction and bubble size at different pressures, has aided in developing bubbly flow models applicable to heated two-phase flows at high pressure.

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.

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