scholarly journals Development of Bubble Size Correlation for Adiabatic Forced Convective Bubbly Flow in Low Pressure Condition Using CFD Code

2020 ◽  
Vol 10 (16) ◽  
pp. 5443
Author(s):  
Jinyeong Bak ◽  
Huiyung Kim ◽  
Jae Jun Jeong ◽  
Dongjin Euh ◽  
Byongjo Yun
Keyword(s):  
Bubble Size ◽  
Bubbly Flow ◽  
Flow Analysis ◽  
Low Pressure ◽  
Good Prediction ◽  
Two Phase ◽  
Local Bubble ◽  
Computational Fluid Dynamics Cfd ◽  
Bubble Number ◽  
Bubble Number Density

In a multidimensional two-phase flow analysis, bubble size significantly affects interfacial transfer terms such as mass, momentum, and energy. With regard to bubbly flow, the application of a simple correlation-type bubble size model presents certain advantages, including short calculation times and ease of usage. In this study, we propose a semi-theoretical correlation developed from a steady state bubble number density transport equation for predicting the distribution of local bubble size using a computational fluid dynamics (CFD) code. The coefficients of the new correlation were determined using the local bubble parameters obtained on the basis of three existing vertical air-water experiments. Finally, these were implemented in commercial CFD code and evaluated against experimental data, which showed that the proposed correlation exhibits good prediction capability for forced convective air-water bubbly flows under low pressure conditions.

Study of Bubbly Flow Through a Packed Bed

2011 ◽  
Author(s):  
Daeseong Jo ◽  
Shripad T. Revankar
Keyword(s):  
Experimental Data ◽  
Comparative Study ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Packed Bed ◽  
Bubble Coalescence ◽  
Size Distributions ◽  
Two Phase ◽  
Bubble Breakup ◽  
Flow Through

A two phase bubbly flow through a packed bed was studied for dominant bubble breakup and coalescence mechanisms through experiments and CFD modeling. Data on various two-phase parameters, such as local void fraction, bubble velocity, size, number, and shape were obtained from the high speed video images. Results indicated that when a flow regime changed from bubbly to either trickling or pulsing flow, the number of average size bubbles significantly decreased and the shape of majority of bubbles was no longer spherical. The bubble coalescence and breakup mechanisms depend on local conditions such as local velocity of the bubble and pore geometry. The CFD analysis using CFX software package was carried out to study bubble size distributions. In the analysis the models for interactions were examined for each case of bubble breakup flow and bubble coalescence. A comparative study was performed on the resulting bubble size distributions, breakup and coalescence rates estimated by individual models. For change of bubble size distributions along the axial direction medians was used as an comparative parameter and the CFD results on bubble medians were compared against the experimental data. This comparative study showed that the predictions estimated by CFD analyses with the bubble breakup and coalescence models currently available in the literature do not agree with the experimental data.

Velocity Profile Measurements of Two-Phase Flow in Rectangular Channel Using Ultrasonic Time-Domain Correlation Method

2007 ◽  
Author(s):  
Takuya Hayashida ◽  
Hideki Murakawa ◽  
Hiroshige Kikura ◽  
Masanori Aritomi ◽  
Michitsugu Mori
Keyword(s):  
Flow Measurement ◽  
Two Phase Flow ◽  
Rectangular Channel ◽  
Correlation Method ◽  
Phase Flow ◽  
Number Density ◽  
Two Phase ◽  
Bubble Number ◽  
Bubble Number Density ◽  
Time Domain Correlation

Velocity measurement using ultrasound has attracted much attention in engineering fields and medical science field. Especially, Ultrasonic velocity profile monitor (UVP) has been in the spotlight in engineering fields, because of its many diagnostic advantages. The major advantage is that UVP can obtain instantaneous velocity distributions on beam line by measuring Doppler shift frequencies of echo signals. And UVP is applicable to existing pipes, because it is non-contact measurement technique. In recent years, various studies about UVP have been done, and UVP has already been put to practical use in engineering plants. The authors especially focused on two-phase flow measurement using ultrasound. Previously, we developed a way to measure bubbly flow using UVP. By this method, we are able to separate liquid information from bubbles information to some degrees. However, when the bubble number density is low, a problem occurs. Because the effect of liquid information is strong under that condition. From this fact, we applied the ultrasound time domain correlation method (UTDC) to two-phase flow measurement. This method is our original technique to measure the velocity distribution. It is based on the cross-correlation between two consecutive echoes of ultrasonic pulses. With this method, we can separate liquid information from bubble information even when the bubble number density is low, because reflected signals depend on the size of reflectors and frequency of ultrasound. In this study, the authors applied the UTDC to two-phase flow measurements in rectangular channel using a multi-wave ultrasonic transducer (TDX). The multi-wave TDX has two kinds of basic frequencies. One is 2MHz for the velocity of rising bubbles and the other is 8MHz for the liquid velocity. So it enables us to measure the velocity of the liquid and that of bubbles at the same point and time. The 2MHz ultrasonic element of TDX has 10mm diameter and the 8MHz ultrasonic element has 3mm diameter.

Optimum Configuration of an Expanding-Contracting-Nozzle for Thrust Enhancement by Bubble Injection

2010 ◽  
Author(s):  
Sowmitra Singh ◽  
Jin-Keun Choi ◽  
Georges Chahine
Keyword(s):  
Bubble Dynamics ◽  
Bubbly Flow ◽  
Outlet Section ◽  
Inlet Section ◽  
Concept Design ◽  
Two Phase ◽  
Approximate Analytical Expression ◽  
Analytical Expression ◽  
Bubble Number ◽  
Analytical Approaches

This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle. Two-phase models for bubbly flow in an expanding-contracting nozzle are developed, in parallel with laboratory experiments, and used to ascertain the geometry configuration for the nozzle that would lead to maximum thrust enhancement upon bubble injection. For preliminary optimization of experimental setup’s design, a quasi 1-D approach is used. Averaged flow quantities (such as velocities, pressures, and void fractions) in a cross-section are used for the analysis. The mixture continuity and momentum equations are numerically solved simultaneously, along with equations for bubble dynamics, bubble motion, and an equation for conservation of bubble number. Various geometric parameters such as the exit and inlet areas, the area of the bubble injection section, the presence of a throat and its location, the length of the diffuser section and the length of the contraction section are varied, and their effects on thrust enhancement are studied. Investigation on the effect of the injected void fraction is also carried out. The key objective function of the optimization is the normalized thrust parameter, which is the difference between the thrust with the bubble injection and the thrust before the bubble injection, normalized by the inlet momentum. An approximate analytical expression for the normalized thrust parameter was also derived starting from the mixture continuity and momentum equations. This analytical expression involved flow variables only at three locations; inlet section, injection section, and outlet section, and the expression is simple enough to produce a quick concept design of the diffuser-nozzle thruster. The numerical and analytical approaches are verified against each other and the limitations of the analytical approach are discussed.

Optimum Configuration of an Expanding-Contracting-Nozzle for Thrust Enhancement by Bubble Injection

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Sowmitra Singh ◽  
Jin-Keun Choi ◽  
Georges Chahine
Keyword(s):  
Bubble Dynamics ◽  
Bubbly Flow ◽  
Outlet Section ◽  
Inlet Section ◽  
Concept Design ◽  
Two Phase ◽  
Approximate Analytical Expression ◽  
Analytical Expression ◽  
Bubble Number ◽  
Analytical Approaches

This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle. Two-phase models for bubbly flow in an expanding-contracting nozzle are developed, in parallel with laboratory experiments and used to ascertain the geometry configuration for the nozzle that would lead to maximum thrust enhancement upon bubble injection. For preliminary optimization of experimental setup’s design, a quasi 1-D approach is used. Averaged flow quantities (such as velocities, pressures, and void fractions) in a cross section are used for the analysis. The mixture continuity and momentum equations are numerically solved simultaneously along with equations for bubble dynamics, bubble motion, and an equation for conservation of the total bubble number. Various geometric parameters such as the exit and inlet areas, the area of the bubble injection section, the presence of a throat and its location, the length of the diffuser section and the length of the contraction section are varied, and their effects on thrust enhancement are studied. Investigation on the effect of the injected void fraction is also carried out. The key objective function of the optimization is the normalized thrust parameter, which is the thrust with bubble injection minus the thrust with liquid only divided by the inlet liquid momentum. An approximate analytical expression for the normalized thrust parameter was also derived starting from the mixture continuity and momentum equations. This analytical expression involved flow variables only at three locations; inlet section, injection section, and outlet section, and the expression is simple enough to produce a quick concept design of the diffuser-nozzle thruster. The numerical and analytical approaches are verified against each other and the limitations of the analytical approach are discussed.

Bubble Size Reduction Using Mesh Bubble Breakers in Two-Phase Vertical Co-Flow

2015 ◽  
Author(s):  
Alan Kalbfleisch ◽  
Kamran Siddiqui
Keyword(s):  
Pore Size ◽  
Bubble Size ◽  
Slug Flow ◽  
High Speed ◽  
Imaging System ◽  
Bubbly Flow ◽  
High Speed Imaging ◽  
Two Phase ◽  
Vertical Column ◽  
Experimental Apparatus

Bubble breakers have been shown to reduce the bubble size and hence increasing the bubble surface-to-volume ratio facilitating higher mass transfer. We report on an experimental study investigating the effect of mesh-type bubble breaker on two-phase co-flow in a vertical column. A range of gas-liquid flow rates ratios (GLR) has been considered that covers the two-phase regimes from bubbly flow to slug flow. A vertical glass tube was used as the experimental apparatus which provides full optical access. A high speed imaging system was used to capture the flow dynamics for bubble characterization. The results show that the bubble size generated by the mesh bubble breaker is greatly affected by the pore size. For a bubbly flow regime, the initial bubble size was reduced by approximately 60%–70% for a pore size of 1mm and by about 45%–50% for a pore size of 4mm. It is found that the transition from bubbly flow to slug flow can be affected by the mesh bubble breaker. The results show that in general, the mesh bubble breaker increases the GLR limit for the transition from bubbly to slug flow.

An Optical Method for Determining Bubble Size Distributions—Part I:Theory

1988 ◽  
Vol 110 (3) ◽  
pp. 325-331 ◽  
Author(s):  
P. R. Meernik ◽  
M. C. Yuen
Keyword(s):  
Statistical Analysis ◽  
Size Distribution ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Bubble Size Distribution ◽  
Phase Flow ◽  
Size Distributions ◽  
Optical Technique ◽  
Narrow Beam ◽  
Two Phase

A new optical technique is developed to determine the size distribution of bubbles in a two-phase flow. Implementation involves passing a narrow beam of light through the bubbly flow and monitoring the transmitted light intensity. The basic units of data are the rate at which each bubble blocks off the beam and the duration of blockage. Adding the hypothesis that the distance of closest approach between a bubble’s center and the beam axis is randomly distributed, a statistical analysis yields the bubble size distribution.

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.

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