**Commenced**in January 2007

**Frequency:**Monthly

**Edition:**International

**Paper Count:**1469

# Search results for: bubble growth

##### 1469 Bubble Growth in a Two Phase Upward Flow in a Miniature Tube

**Authors:**
R. S. Hassani,
S. Chikh,
L. Tadrist,
S. Radev

**Abstract:**

A bubbly flow in a vertical miniature tube is analyzed theoretically. The liquid and gas phase are co-current flowing upward. The gas phase is injected via a nozzle whose inner diameter is 0.11mm and it is placed on the axis of the tube. A force balance is applied on the bubble at its detachment. The set of governing equations are solved by use of Mathematica software. The bubble diameter and the bubble generation frequency are determined for various inlet phase velocities represented by the inlet mass quality. The results show different behavior of bubble growth and detachment depending on the tube size.

**Keywords:**
Two phase flow,
bubble growth,
minichannel,
generation frequency.

##### 1468 Perfect Plastic Deformation of a Circular Thin Bronze Plate due to the Growth and Collapse of a Vapour Bubble

**Authors:**
M.T. Shervani-Tabar,
M. Rezaee,
E. Madadi Kandjani

**Abstract:**

Dynamics of a vapour bubble generated due to a high local energy input near a circular thin bronze plate in the absence of the buoyancy forces is numerically investigated in this paper. The bubble is generated near a thin bronze plate and during the growth and collapse of the bubble, it deforms the nearby plate. The Boundary Integral Equation Method is employed for numerical simulation of the problem. The fluid is assumed to be incompressible, irrotational and inviscid and the surface tension on the bubble boundary is neglected. Therefore the fluid flow around the vapour bubble can be assumed as a potential flow. Furthermore, the thin bronze plate is assumed to have perfectly plastic behaviour. Results show that the displacement of the circular thin bronze plate has considerable effect on the dynamics of its nearby vapour bubble. It is found that by decreasing the thickness of the thin bronze plate, the growth and collapse rate of the bubble becomes higher and consequently the lifetime of the bubble becomes shorter.

**Keywords:**
Vapour Bubble,
Thin Bronze Plate,
Boundary Integral
Equation Method.

##### 1467 Dynamics of a Vapour Bubble inside a Vertical Rigid Cylinder in the Absence of Buoyancy Forces

**Authors:**
S. Mehran,
S. Rouhi,
F.Rouzbahani,
E. Haghgoo

**Abstract:**

**Keywords:**
Vapour bubble,
Vertical rigid cylinder,
Boundaryelement method,
Finite difference method,
Buoyancy forces.

##### 1466 Investigation of Bubble Growth during Nucleate Boiling Using CFD

**Authors:**
K. Jagannath,
Akhilesh Kotian,
S. S. Sharma,
Achutha Kini U.,
P. R. Prabhu

**Abstract:**

**Keywords:**
Bubble growth,
computational fluid dynamics,
detachment diameter,
terminal velocity.

##### 1465 Dynamics of a Vapour Bubble inside a Vertical Rigid Cylinder with a Deposit Rib

**Authors:**
S. Mehran,
S. Rouhi,
F.Rouzbahani,
E. Haghgoo

**Abstract:**

**Keywords:**
Vapour bubble,
Vertical rigid cylinder,
Boundaryelement method.

##### 1464 Investigation Bubble Growth and Nucleation Rates during the Pool Boiling Heat Transfer of Distilled Water Using Population Balance Model

**Authors:**
V. Nikkhah Rashidabad,
M. Manteghian,
M. Masoumi,
S. Mousavian

**Abstract:**

In this research, the changes in bubbles diameter and number that may occur due to the change in heat flux of pure water during pool boiling process. For this purpose, test equipment was designed and developed to collect test data. The bubbles were graded using Caliper Screen software. To calculate the growth and nucleation rates of bubbles under different fluxes, population balance model was employed. The results show that the increase in heat flux from q=20 kw/m2 to q= 102 kw/m2 raised the growth and nucleation rates of bubbles.

**Keywords:**
Heat flux,
bubble growth,
bubble nucleation,
population balance model.

##### 1463 CFD Simulation of Condensing Vapor Bubble using VOF Model

**Authors:**
Seong-Su Jeon,
Seong-Jin Kim,
Goon-Cherl Park

**Abstract:**

In this study, direct numerical simulation for the bubble condensation in the subcooled boiling flow was performed. The main goal was to develop the CFD modeling for the bubble condensation and to evaluate the accuracy of the VOF model with the developed CFD modeling. CFD modeling for the bubble condensation was developed by modeling the source terms in the governing equations of VOF model using UDF. In the modeling, the amount of condensation was determined using the interfacial heat transfer coefficient obtained from the bubble velocity, liquid temperature and bubble diameter every time step. To evaluate the VOF model using the CFD modeling for the bubble condensation, CFD simulation results were compared with SNU experimental results such as bubble volume and shape, interfacial area, bubble diameter and bubble velocity. Simulation results predicted well the behavior of the actual condensing bubble. Therefore, it can be concluded that the VOF model using the CFD modeling for the bubble condensation will be a useful computational fluid dynamics tool for analyzing the behavior of the condensing bubble in a wide range of the subcooled boiling flow.

**Keywords:**
Bubble condensation,
CFD modeling,
Subcooled boiling flow,
VOF model.

##### 1462 Electric Field Effect on the Rise of Single Bubbles during Boiling

**Authors:**
N. Masoudnia,
M. Fatahi

**Abstract:**

An experimental study of saturated pool boiling on a single artificial nucleation site without and with the application of an electric field on the boiling surface has been conducted. N-pentane is boiling on a copper surface and is recorded with a high speed camera providing high quality pictures and movies. The accuracy of the visualization allowed establishing an experimental bubble growth law from a large number of experiments. This law shows that the evaporation rate is decreasing during the bubble growth, and underlines the importance of liquid motion induced by the preceding bubble. Bubble rise is therefore studied: once detached, bubbles accelerate vertically until reaching a maximum velocity in good agreement with a correlation from literature. The bubbles then turn to another direction. The effect of applying an electric field on the boiling surface in finally studied. In addition to changes of the bubble shape, changes are also shown in the liquid plume and the convective structures above the surface. Lower maximum rising velocities were measured in the presence of electric fields, especially with a negative polarity.

**Keywords:**
Single bubbles,
electric field,
boiling,
effect.

##### 1461 Study of the Particle Size Effect on Bubble Rise Velocities in a Three-Phase Bubble Column

**Authors:**
Weiling Li,
Wenqi Zhong,
Baosheng Jin,
Rui Xiao,
Yong Lu,
Tingting He

**Abstract:**

Experiments were performed in a three-phase bubble column to study variations of bubble rise velocities. The dynamic gas disengagement (DGD) technique and the fast response pressure transducers were utilized to investigate the bubble rise in the column. The superficial gas velocity of large bubbles and small bubbles, the rise velocities of larger and small bubble fractions were studied considering the effect of particle sizes. The results show that the superficial gas velocity associated with large bubbles linearly increase as superficial gas velocity increasing. Particle size has little effect on the both large and small bubble superficial gas velocities. The rise velocities of larger bubble fractions are larger than that of small bubble fractions, and it had different tendency at low and high superficial gas velocities when changing the particle sizes. The rise velocities of small bubble fractions increased and then had a decrease tendency when the particle size became greater.

**Keywords:**
Bubble rise velocity,
gas–liquid–solid,
particle size effect,
three–phase bubble column.

##### 1460 Hydrodynamic Force on Acoustically Driven Bubble in Sulfuric Acid

**Authors:**
Zeinab Galavani,
Reza Rezaei-Nasirabad,
Rasoul Sadighi-Bonabi

**Abstract:**

**Keywords:**
Bjerknes force,
History force,
Reynolds
number,
Sonoluminescence.

##### 1459 Role of Acoustic Pressure on the Dynamics of Moving Single-Bubble Sonoluminescence

**Authors:**
Reza Rezaei-Nasirabad,
Zeinab Galavani,
Rasoul Sadighi-Bonabi,
Mohammad Asgarian

**Abstract:**

**Keywords:**
Bubble dynamics,
Equation of the gas state,
Hydrodynamic force,
Moving sonoluminescence.

##### 1458 Vapor Bubble Dynamics in Upward Subcooled Flow Boiling During Void Evolution

**Authors:**
Rouhollah Ahmadi,
Tatsuya Ueno,
Tomio Okawa

**Abstract:**

**Keywords:**
Subcooled flow boiling,
Bubble dynamics,
Void
fraction,
Sliding bubble.

##### 1457 Simulations of Cryogenic Cavitation of Low Temperature Fluids with Thermodynamics Effects

**Authors:**
A. Alhelfi,
B. Sunden

**Abstract:**

Cavitation in cryogenic liquids is widely present in contemporary science. In the current study, we re-examine a previously validated acoustic cavitation model which was developed for a gas bubble in liquid water. Furthermore, simulations of cryogenic fluids including the thermal effect, the effect of acoustic pressure amplitude and the frequency of sound field on the bubble dynamics are presented. A gas bubble (Helium) in liquids Nitrogen, Oxygen and Hydrogen in an acoustic field at ambient pressure and low temperature is investigated numerically. The results reveal that the oscillation of the bubble in liquid Hydrogen fluctuates more than in liquids Oxygen and Nitrogen. The oscillation of the bubble in liquids Oxygen and Nitrogen is approximately similar.

**Keywords:**
Cryogenic liquids,
cavitation,
rocket engineering,
ultrasound.

##### 1456 Design and Fabrication of Micro-Bubble Oxygenator

**Authors:**
Chiang-Ho Cheng,
An-Shik Yang,
Hong-Yih Cheng

**Abstract:**

This paper applies the MEMS technology to design and fabricate a micro-bubble generator by a piezoelectric actuator. Coupled with a nickel nozzle plate, an annular piezoelectric ceramic was utilized as the primary structure of the generator. In operations, the piezoelectric element deforms transversely under an electric field applied across the thickness of the generator. The surface of the nozzle plate can expand or contract because of the induction of radial strain, resulting in the whole structure to bend, and successively transport oxygen micro-bubbles into the blood flow for enhancing the oxygen content in blood. In the tests, a high magnification microscope and a high speed CCD camera were employed to photograph the time evolution of meniscus shape of gaseous bubbles dispensed from the micro-bubble generator for flow visualization. This investigation thus explored the bubble formation process including the influences of inlet gas pressure along with driving voltage and resonance frequency on the formed bubble extent.

**Keywords:**
Micro-bubble,
nozzle,
oxygenator,
piezoelectric.

##### 1455 Direct Numerical Simulation of Subcooled Nucleate Pool Boiling

**Authors:**
Sreeyuth Lal,
Yohei Sato,
Bojan Niceno

**Abstract:**

With the long-term objective of Critical Heat Flux (CHF) prediction, a Direct Numerical Simulation (DNS) framework for simulation of subcooled and saturated nucleate pool boiling is developed. One case of saturated, and three cases of subcooled boiling at different subcooling levels are simulated. Grid refinement study is also reported. Both boiling and condensation phenomena can be computed simultaneously in the proposed numerical framework. Computed bubble detachment diameters of the saturated nucleate pool boiling cases agree well with the experiment. The flow structures around the growing bubble are presented and the accompanying physics is described. The relation between heat flux evolution from the heated wall and the bubble growth is studied, along with investigations of temperature distribution and flow field evolutions.

**Keywords:**
CFD,
interface tracking method,
phase change model,
subcooled nucleate pool boiling.

##### 1454 Terminal Velocity of a Bubble Rise in a Liquid Column

**Authors:**
Mário A. R. Talaia

**Abstract:**

**Keywords:**
Bubbles,
terminal velocity,
two phase-flow,
vertical
column.

##### 1453 CFD Modeling of Boiling in a Microchannel Based On Phase-Field Method

**Authors:**
Rahim Jafari,
Tuba Okutucu-Özyurt

**Abstract:**

The hydrodynamics and heat transfer characteristics of a vaporized elongated bubble in a rectangular microchannel have been simulated based on Cahn-Hilliard phase-field method. In the simulations, the initially nucleated bubble starts growing as it comes in contact with superheated water. The growing shape of the bubble compared well with the available experimental data in the literature.

**Keywords:**
Microchannel,
boiling,
Cahn-Hilliard method,
Two-phase
flow,
Simulation.

##### 1452 Identification of the Main Transition Velocities in a Bubble Column Based on a Modified Shannon Entropy

**Authors:**
Stoyan Nedeltchev,
Markus Schubert

**Abstract:**

*U*

_{G}=0.034 m/s) of the transition flow regime and the beginning (at

*U*

_{G}=0.089 m/s) of the churn-turbulent flow regime. The results were compared with the Kolmogorov entropy (KE) results. A slight discrepancy was found, namely the transition velocities identified by means of the KE were shifted to somewhat higher (0.045 and 0.101 m/s) superficial gas velocities

*U*

_{G}.

**Keywords:**
Bubble column,
gas holdup fluctuations,
Modified Shannon entropy,
Kolmogorov entropy.

##### 1451 A Comparison between Heterogeneous and Homogeneous Gas Flow Model in Slurry Bubble Column Reactor for Direct Synthesis of DME

**Authors:**
Sadegh Papari,
Mohammad Kazemeini,
Moslem Fattahi

**Abstract:**

**Keywords:**
Modelling,
Slurry bubble column,
Dimethyl ether
synthesis,
Homogeneous gas flow,
Heterogeneous gas flow

##### 1450 Entropy Analysis in a Bubble Column Based on Ultrafast X-Ray Tomography Data

**Authors:**
Stoyan Nedeltchev,
Markus Schubert

**Abstract:**

By means of the ultrafast X-ray tomography facility, data were obtained at different superficial gas velocities *U*_{G} in a bubble column (0.1 m in ID) operated with an air-deionized water system at ambient conditions. Raw reconstructed images were treated by both the information entropy (IE) and the reconstruction entropy (RE) algorithms in order to identify the main transition velocities in a bubble column. The IE values exhibited two well-pronounced minima at *U*_{G}=0.025 m/s and *U*_{G}=0.085 m/s identifying the boundaries of the homogeneous, transition and heterogeneous regimes. The RE extracted from the central region of the column’s cross-section exhibited only one characteristic peak at *U*_{G}=0.03 m/s, which was attributed to the transition from the homogeneous to the heterogeneous flow regime. This result implies that the transition regime is non-existent in the core of the column.

**Keywords:**
Bubble column,
ultrafast X-ray tomography,
information entropy,
reconstruction entropy.

##### 1449 A Preliminary Study of Drug Perfusion Enhancement by Microstreaming Induced by an Oscillating Microbubble

**Authors:**
Jin Sun Oh,
Kyung Ho Lee,
S ang Gug Chung,
Kyehan Rhee

**Abstract:**

Microbubbbles incorporating ultrasound have been used to increase the efficacy of targeted drug delivery, because microstreaming induced by cavitating bubbles affects the drug perfusion into the target cells and tissues. In order to clarify the physical effects of microstreaming on drug perfusion into tissues, a preliminary experimental study of perfusion enhancement by a stably oscillating microbubble was performed. Microstreaming was induced by an oscillating bubble at 15 kHz, and perfusion of dye into an agar phantom was optically measured by histology on agar phantom. Surface color intensity and the penetration length of dye in the agar phantom were increased more than 70% and 30%, respectively, due to the microstreaming induced by an oscillating bubble. The mass of dye perfused into a tissue phantom for 30 s was increased about 80% in the phantom with an oscillating bubble. This preliminary experiment shows the physical effects of steady streaming by an oscillating bubble can enhance the drug perfusion into the tissues while minimizing the biological effects.

**Keywords:**
Bubble,
Mass Transfer,
Microstreaming,
Drug Delivery,
Acoustic Wave.

##### 1448 Measurement of Steady Streaming from an Oscillating Bubble Using Particle Image Velocimetry

**Authors:**
Yongseok Kwon,
Woowon Jeong,
Eunjin Cho,
Sangkug Chung,
Kyehan Rhee

**Abstract:**

Steady streaming flow fields induced by a 500 mm bubble oscillating at 12 kHz were measured using microscopic particle image velocimetry (PIV). The accuracy of velocity measurement using a micro PIV system was checked by comparing the measured velocity fields with the theoretical velocity profiles in fully developed laminar flow. The steady streaming flow velocities were measured in the sagittal plane of the bubble attached on the wall. Measured velocity fields showed upward jet flow with two symmetric counter-rotating vortices, and the maximum streaming velocity was about 12 mm/s, which was within the velocity ranges measured by other researchers. The measured streamlines were compared with the analytical solution, and they also showed a reasonable agreement.

**Keywords:**
Oscillating bubble,
Particle-Image-Velocimetry microstreaming.

##### 1447 DNS of a Laminar Separation Bubble

**Authors:**
N. K. Singh,
S. Sarkar

**Abstract:**

Direct numerical simulation (DNS) is used to study the evolution of a boundary layer that was laminar initially followed by separation and then reattachment owing to generation of turbulence. This creates a closed region of recirculation, known as the laminar-separation bubble. The present simulation emulates the flow environment encountered in a modern LP turbine blade, where a laminar separation bubble may occur on the suction surface. The unsteady, incompressible three-dimensional (3-D) Navier-Stokes (NS) equations have been solved over a flat plate in the Cartesian coordinates. The adverse pressure gradient, which causes the flow to separate, is created by a boundary condition. The separated shear layer undergoes transition through appearance of ╬ø vortices, stretching of these create longitudinal streaks. Breakdown of the streaks into small and irregular structures makes the flow turbulent downstream.

**Keywords:**
Adverse pressure gradient,
direct numerical simulation,
laminar separation bubble.

##### 1446 Evaluation of Exerting Force on the Heating Surface Due to Bubble Ebullition in Subcooled Flow Boiling

**Authors:**
M. R. Nematollahi

**Abstract:**

**Keywords:**
Subcooled boiling,
vibration mechanism,
bubble
behavior.

##### 1445 Liquid Temperature Effect on Sound Propagation in Polymeric Solution with Gas Bubbles

**Authors:**
S. Levitsky

**Abstract:**

**Keywords:**
Sound propagation,
gas bubbles,
temperature effect,
polymeric liquid.

##### 1444 Simulation of Ammonia-Water Two Phase Flow in Bubble Pump

**Authors:**
Jemai Rabeb,
Benhmidene Ali,
Hidouri Khaoula,
Chaouachi Bechir

**Abstract:**

The diffusion-absorption refrigeration cycle consists of a generator bubble pump, an absorber, an evaporator and a condenser, and usually operates with ammonia/water/ hydrogen or helium as the working fluid. The aim of this paper is to study the stability problem a bubble pump. In fact instability can caused a reduction of bubble pump efficiency. To achieve this goal, we have simulated the behaviour of two-phase flow in a bubble pump by using a drift flow model. Equations of a drift flow model are formulated in the transitional regime, non-adiabatic condition and thermodynamic equilibrium between the liquid and vapour phases. Equations resolution allowed to define void fraction, and liquid and vapour velocities, as well as pressure and mixing enthalpy. Ammonia-water mixing is used as working fluid, where ammonia mass fraction in the inlet is 0.6. Present simulation is conducted out for a heating flux of 2 kW/m² to 5 kW/m² and bubble pump tube length of 1 m and 2.5 mm of inner diameter. Simulation results reveal oscillations of vapour and liquid velocities along time. Oscillations decrease with time and with heat flux. For sufficient time the steady state is established, it is characterised by constant liquid velocity and void fraction values. However, vapour velocity does not have the same behaviour, it increases for steady state too. On the other hand, pressure drop oscillations are studied.

**Keywords:**
Bubble pump,
drift flow model,
instability,
simulation.

##### 1443 CFD Simulations to Validate Two and Three Phase Up-flow in Bubble Columns

**Authors:**
Shyam Kumar,
Nannuri Srinivasulu,
Ashok Khanna

**Abstract:**

**Keywords:**
Bubble column,
Computational fluid dynamics,
Gas
holdup profile,
k-ε model.

##### 1442 Mathematical Simulation of Bubble Column Slurry Reactor for Direct Dimethyl Ether Synthesis Process from Syngas

**Authors:**
Zhen Chen,
Haitao Zhang,
Weiyong Ying,
Dingye Fang

**Abstract:**

Based on a global kinetics of direct dimethyl ether (DME) synthesis process from syngas, a steady-state one-dimensional mathematical model for the bubble column slurry reactor (BCSR) has been established. It was built on the assumption of plug flow of gas phase, sedimentation-dispersion model of catalyst grains and isothermal chamber regardless of reaction heats and rates for the design of an industrial scale bubble column slurry reactor. The simulation results indicate that higher pressure and lower temperature were favorable to the increase of CO conversion, DME selectivity, products yield and the height of slurry bed, which has a coincidence with the characteristic of DME synthesis reaction system, and that the height of slurry bed is lessen with the increasing of operation temperature in the range of 220-260℃. CO conversion, the optimal operation conditions in BCSR were proposed.

**Keywords:**
Alcohol/ether fuel,
bubble column slurry reactor,
global kinetics,
mathematical model.

##### 1441 Detecting Financial Bubbles Using Gap between Common Stocks and Preferred Stocks

**Authors:**
Changju Lee,
Seungmo Ku,
Sondo Kim,
Woojin Chang

**Abstract:**

How to detecting financial bubble? Addressing this simple question has been the focus of a vast amount of empirical research spanning almost half a century. However, financial bubble is hard to observe and varying over the time; there needs to be more research on this area. In this paper, we used abnormal difference between common stocks price and those preferred stocks price to explain financial bubble. First, we proposed the ‘W-index’ which indicates spread between common stocks and those preferred stocks in stock market. Second, to prove that this ‘W-index’ is valid for measuring financial bubble, we showed that there is an inverse relationship between this ‘W-index’ and S&P500 rate of return. Specifically, our hypothesis is that when ‘W-index’ is comparably higher than other periods, financial bubbles are added up in stock market and vice versa; according to our hypothesis, if investors made long term investments when ‘W-index’ is high, they would have negative rate of return; however, if investors made long term investments when ‘W-index’ is low, they would have positive rate of return. By comparing correlation values and adjusted R-squared values of between W-index and S&P500 return, VIX index and S&P500 return, and TED index and S&P500 return, we showed only W-index has significant relationship between S&P500 rate of return. In addition, we figured out how long investors should hold their investment position regard the effect of financial bubble. Using this W-index, investors could measure financial bubble in the market and invest with low risk.

**Keywords:**
Financial bubbles,
detection,
preferred stocks,
pairs trading,
future return,
forecast.

##### 1440 Bubble Point Pressures of CO2+Ethyl Palmitate by a Cubic Equation of State and the Wong-Sandler Mixing Rule

**Authors:**
M. A. Sedghamiz,
S. Raeissi

**Abstract:**

This study presents three different approaches to estimate bubble point pressures for the binary system of CO2 and ethyl palmitate fatty acid ethyl ester. The first method involves the Peng-Robinson (PR) Equation of State (EoS) with the conventional mixing rule of Van der Waals. The second approach involves the PR EOS together with the Wong Sandler (WS) mixing rule, coupled with the UNIQUAC GE model. In order to model the bubble point pressures with this approach, the volume and area parameter for ethyl palmitate were estimated by the Hansen group contribution method. The last method involved the Peng-Robinson, combined with the Wong-Sandler method, but using NRTL as the GE model. Results using the Van der Waals mixing rule clearly indicated that this method has the largest errors among all three methods, with errors in the range of 3.96-6.22%. The PR-WS-UNIQUAC method exhibited small errors, with average absolute deviations between 0.95 to 1.97 percent. The PR-WS-NRTL method led to the least errors, where average absolute deviations ranged between 0.65-1.7%.

**Keywords:**
Bubble pressure,
Gibbs excess energy model,
mixing
rule,
CO2 solubility,
ethyl palmitate.