Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
17
1-2
2005
NUMERICAL SIMULATIONS OF LIQUID JET DEFORMATION BASED ON HYBRID COMBINATION OF INTERFACE TRACKING AND BUBBLE TRACKING METHODS
23-41
10.1615/MultScienTechn.v17.i1-2.20
Akira
Sou
Graduate School of Maritime Sciences, Kobe University, Japan
Akio
Tomiyama
Department of Mechanical Engineering, Graduate School Engineering, Kobe
University, 1-1 Rokkodai, Nada, Kobe, Hyogo, 657-8501 Japan
A hybrid numerical method, which is based on a combination of a two-way bubble tracking method and an interface tracking method, is proposed in the present study for the prediction of atomization of liquid jet. Numerical simulation of liquid jet injected through a single hole nozzle in which cloud cavitation takes place is performed to examine the potential of the proposed method. It is confirmed through comparisons between measured and predicted cavitating flows that (1) the combination of bubble and interface tracking methods enables us to examine the effect of cavitation bubbles on liquid jet deformation, and (2) the bubble tracking function of the hybrid method gives reasonable predictions for the distributions of pressure and bubbles within the nozzle, the relation between injection pressure and liquid flow rate, and the behavior of cavitation, though several constitutive models such as cavitation, drag, lift and turbulence models should be based on more sophisticated ones in the future.
ANALYSIS OF WAVE PROPAGATION IN A BUBBLY LIQUID BASED ON A TWO-FLUID AND THREE-PRESSURE MODEL
1-21
10.1615/MultScienTechn.v17.i1-2.10
Ryu
Egashira
Division of Mechanical Science, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan; Department of Intelligent Mechanical Engineering, Fukuoka Institute of Technology, 3-30-1 Wajiro-higashi, Higashi-ku, Fukuoka 811-0295, Japan
Takeru
Yano
Division of Mechanical Science, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
Shigeo
Fujikawa
Professor Emeritus, Hokkaido University, Kita 8, Nishi 5, Kita-ku, Sapporo, Hokkaido 060-0808, Japan
A new set of space-averaged equations for a mixture of liquid and gas bubbles is derived on the basis of two-fluid and three-pressure model, where a surface-averaged liquid pressure at the gas-liquid interface is introduced as well as volume-averaged pressures and the liquid compressibility is taken into account. To verify the appropriateness of the equations, the propagation of linear wave in a quiescent mixture is studied theoretically and numerically. A fast mode of the wave is generated owing to the liquid compressibility, whilst there only exists a classical slow mode for the special case of incompressible liquid. Since the assumption of incompressibility has been made in general in previous studies, the fast mode has not been investigated in detail. Several important characteristics of the slow and fast modes are clarified. In particular, it is shown that the amplitude of the fast mode is not always small and it becomes prominent for a typical wave number larger than the critical one.
SIMULTANEOUS VISUALIZATION OF PARTICLE/BUBBLE BEHAVIOR AND SURROUNDING FLOW
43-55
10.1615/MultScienTechn.v17.i1-2.30
G.
Matsui
Dept. of Mechanical Engineering and Biomimetics, Kinki University, Wakayama 649-6493, Japan
H.
Monji
Institute of Engineering Mechanics and Systems, University of Tsukuba, Tsukuba 305-8573, Japan
This study deals with a simultaneous visualization technique and image analysis of particle/bubble behavior on its position of the center of gravity, shape, and attitude of motion, in addition to flow field around it. In the multiphase flow field, the interaction between a particle/bubble and surrounding fluid or two-way effect is very important to understand complex phenomena of dispersed flow. Therefore, simultaneous visualization of both particle/bubble motion and surrounding flow has been requested. In addition, determination of the 3D-position of the center of gravity of the particle/bubble and the distance between its center of gravity and the plane of velocity field obtained has been required. In the study, such a visualization technique and image analysis namely Moving Object-Flow Image Analyzer (MOFIA) was developed to determine the distance. Furthermore, image analysis for obtaining particle/bubble behavior on its shape and attitude was settled in order to obtain basic data for discussing the essential interaction. The results of measurement made using MOFIA for both a single particle and two particles in stagnant water show that adequate data are obtainable for discussing the interaction based on the composite of two images of particle/bubble and flow field.
MEASUREMENT TECHNIQUE FOR ANALYSIS IN TWO-PHASE FLOWS INVOLVING DISTRIBUTED SIZE OF DROPLETS AND BUBBLES USING INTERFEROMETRIC METHOD — PLANAR SIMULTANEOUS MEASUREMENT OF SIZE AND VELOCITY VECTOR FIELD
57-77
10.1615/MultScienTechn.v17.i1-2.40
Tatsuya
Kawaguchi
Dept. of Mechanical and Control Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama Meguro-ku, Tokyo, 152-8552 Japan
Masanobu
Maeda
Dept. of System Design Engineering, Keio University, 3-14-1 Hiyoshi Kohoku-ku, Yokohama, 223-8522, Japan
Not only the size and velocity distrib ution but also the spatial information of those instantaneous properties of individual droplets and bubbles are required to understand the complex behavior of dispersed multi-phase flow. In the present paper, an interferometric laser imaging technique investigating two-phase flow characeristics was demonstrated examining the simultaneous measurement of planar distributions on particle size, velocity vector and number density concentration from a frozen image, and the time series information was obtained by processing sequential imagtes of the interferogram. The measurement results with velocity vectors were precisely discriminated by size, the transient spray showed the significant difference of their flow behavior. Interferometric technique was further applied to investigate the characteristics of the size distribution of microscale gas bubble in liquid and to measure such bubbly flows on the different basis as air injection bubbly flow, electrolytic hydrogen and oxygen bubble injection and alcoholic beverages with gas bubbles.
PSEUDO-LAMINARIZATION OF MICRO-BUBBLE CONTAINING MILKY BUBBLY FLOW IN A PIPE
79-101
10.1615/MultScienTechn.v17.i1-2.50
Akimi
Serizawa
Department of Nuclear Engineering, Kyoto University, Yoshida-Honmachi, Kyoto 606-8501, Japan
Tomohiko
Inui
Department of Nuclear Engineering, Kyoto University, Yoshida-Honmachi, Kyoto 606-8501, Japan
Toshihiko
Yahiro
Aura Tec Co., Ltd, 1725-2, Tsubuku-Honmachi, Kurume, Fukuoka 830-0047, Japan
Zensaku
Kawara
Department of Nuclear Engineering, Kyoto University, Kyoto-Daigaku katsura, Nishikyo-ku, Kyoto, 615-8540, Japan
Micro bubble technology has become to attract people's concerns due to its wide potential in practical applications to a variety of advanced and conventional science and technologies. However, our knowledge of micro bubbles containing bubbly two-phase flow is almost nothing. We developed a specially designed nozzle which generates micro air bubbles with high bubble number density (mean diameter ≈ 40microns, number density higher than 2×105/cc). Using this micro-bubble generator, we carried out a measurement of two-phase frictional pressure drop, cross-sectional average void fraction, local void fraction profiles and liquid velocity profiles. The range of cross-sectional average void fraction covered was up to 0.6 % which is high enough to realize milky bubbly flow. The most exciting result we found is that the two-phase flow becomes pseudo-laminarized by injecting such ultra small bubbles into the water flow. For 0.3 ≈ 0.5% void fractions, pseudo-laminar-to-turbulent transition occurred at Re= 10,000 ≈ 20,000, showing a significant reduction in wall friction. The radial liquid velocity profiles show typical turbulent 1/7 th power law profile. However, the liquid velocity profiles in milky bubbly flow obviously shifted from von Karman's universal velocity profile towards lower values of the non-dimensional distance from the wall. The cross sectional averaged void fraction correlates well with a homogeneous flow model, which is verified by uniform profiles of the local void fraction distribution over the whole channel cross section. The mechanisms of pseudo-laminarization and flow structures have been discussed.
EXPERIMENTS ON THE TURBULENT STRUCTURE AND THE VOID FRACTION DISTRIBUTION IN THE TAYLOR BUBBLE WAKE
103-122
10.1615/MultScienTechn.v17.i1-2.60
Lev
Shemer
School of Mechanical Engineering, Tel-Aviv University, Tel-Aviv, Israel
A.
Gulitski
School of Mechanical Engineering, Tel-Aviv University, Tel-Aviv, Israel
Dvora
Barnea
School of Mechanical Engineering, Faculty of Engineering, Tel-Aviv University, Ramat-Aviv 69978, Israel
An experimental approach is developed to carry out PIV measurements and to perform digital processing of the recorded PIV images to measure simultaneously the instantaneous turbulent velocity field and the void fraction distribution in the wake region of a Taylor bubble. Advanced methods of data processing, such as ensemble averaging and Proper Orthogonal Decomposition (POD), are applied. Results of measurements performed in our newly constructed experimental facility are presented. Two liquid flow rates were employed, corresponding to Reynolds numbers of 820 for laminar background flow and 7500 for turbulent flow. The mean characteristics of the velocity field in the wake region are calculated by ensemble-averaging the instantaneous velocity fields measured around 200 different bubbles. An algorithm to estimate the void fraction distribution in the axial pipe cross-section from the recorded PIV images is developed.
NUMERICAL ANALYSIS AND EXPERIMENTAL VALIDATION OF BUBBLE SIZE DISTRIBUTIONS IN TWO-PHASE BUBBLE COLUMN REACTORS
123-145
10.1615/MultScienTechn.v17.i1-2.70
F.
Bertola
Dept. of Materials Science and Chemical Engineering, Politecnico di Torino, C.soDuca degli, Abruzzi, 24,10129 Torino
J.
Grundseth
Dept. of Chemical Engineering, Norwegian University of Science and Technology, Sem Sælands vei 4, NO-7491 Trondheim, Norway
L.
Hagesaether
C. A.
Dorao
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim
H.
Luo
K. W.
Hjarbo
H. F.
Svendsen
Dept. of Chemical Engineering, Norwegian University of Science and Technology, Sem Sælands vei 4, NO-7491 Trondheim, Norway
Marco
Vanni
Dept. of Materials Science and Chemical Engineering, Politecnico di Torino, C.soDuca degli, Abruzzi, 24,10129 Torino
Giancarlo
Baldi
Dept. of Materials Science and Chemical Engineering, Politecnico di Torino, C.soDuca degli, Abruzzi, 24,10129 Torino
H. A.
Jakobsen
Dept. of Chemical Engineering, Norwegian University of Science and Technology, Sem Sælands vei 4, NO-7491 Trondheim, Norway
This paper focuses on the inclusion of a population balance module into a 2D two-phase flow model. An in- house CFD code has been developed adopting a dynamic mixture model for the characterization of the flow pattern in the column. The turbulence closure adopted is in accordance with the work of Lopez de Bertodano [30]. Two concepts are used, one for the liquid shear induced turbulence and a second one for the bubble induced turbulence. The turbulence production due to the gas jets at the inlet zone, determined by the bubbles leaving the holes in the distributor plate and retarding until they reach their terminal velocity, is also accounted for in accordance with the work of Grevskott [33].
The main objective of this study is to validate the combined CFD-population balance model including appropriate closures both for the momentum transfer-, turbulence-, and the coalescence and break-up phenomena. The population model including six bubble size classes is validated with experimental data obtained in our own laboratory for the radial bubble size and volume fraction distributions at two axial levels in the column. The flow model has been validated against experimental data on the radial velocity profiles for both phases at several axial levels.
EXPERIMENTAL AND ANALYTICAL STUDIES OF GAS ENTRAINMENT PHENOMENA IN SLUG FLOW IN HORIZONTAL AND NEAR HORIZONTAL PIPES
147-168
10.1615/MultScienTechn.v17.i1-2.80
Colin P.
Hale
Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
Geoffrey F.
Hewitt
Department of Chemical Engineering & Chemical Technology, Imperial College of Science, Technology & Medicine, Prince Consort Road, London SW7 2B Y, England, UK
I. G.
Manolis
Dept. of Chemical Engineering, Imperial College, London, UK
M. A.
Mendes
Department of Chemical Engineering and Chemical Technology, Imperial College London, South Kensington Campus, London SW72AZ, UK
S. M.
Richardson
Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
W. L.
Wong
EPTG Pipelines Team, BP Exploration, Sunbury-on-Thames, TW16 7LN, UK
For analysing cases of slug flow in which the slug body contains gas bubbles, a common assumption is that the liquid and gas enter the slug to form a homogeneous mixture which passes through the slug and discharges at the tail. The liquid holdup in the slug calculated by this assumption is simply the ratio of the liquid volume flowrate entering the slug divided by the sum of the gas and liquid flowrates entering the slug.
In this paper the validity of the homogeneous assumption in the prediction of the liquid holdup within the slug body has been examined by conducting several campaigns of experiments in horizontal and 1° upwardly inclined test-sections. A special ("push-in") experiment is also described which allows an objective measurement of the gas entrainment rate.
Comparisons between the predictions of the homogeneous "unit cell" model and the experimental data showed good agreement at superficial mixture velocities above 6 ms1. However, the model under-predicts the experimental holdup values at lower superficial mixture velocities. Gamma tomographic measurements of gas content distributions in the liquid slugs show that the gas tends to separate towards the top of the tube at lower flowrate. A two-fluid type model for the slug body is described for a stratified flow consisting of a bubbly layer at the top of the tube flowing over a pure liquid layer at the bottom. This appears to match the experimental observations.
THE PRINCIPLES OF COMPLEXITY IN BUBBLY FLOW
169-190
10.1615/MultScienTechn.v17.i1-2.90
Iztok
Zun
Laboratory for Fluid Dynamics and Thermodynamics, Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, Slovenia
There are evidences of complexity that may play a crucial role in flow regime transition of bubbly flow in vertical pipes of centimeter scale. Such a complex nature most likely contributes to several unresolved questions about transient conditions Even much less is known about bubbly flow in complex geometry that is designed for special applications. The reason is two fold, first because there are a vast number of possible apparatuses that utilize bubbly flow. Second, the initial and boundary conditions may alter the appearance of dispersed structure so that there seems to be no common first principles applicable to several cases. Different examples were undertaken in these studies to prove that this may not be so. They are: bubbly to slug flow transition in a vertical pipe under adiabatic conditions, cavitating bubbly structures and suspended bubbles in forced mixing. Although different cases by nature, they enable a common approach that can be described roughly as a two-part process: first, the scale information is broken into parts, and once the information is analyzed by the discrimination system lower level, it can be reassembled by the system higher level to tell us what is where in the environment. The following features of complexity are pointed out: significant interaction, high number of parts or degrees of freedom, nonlinearity, broken symmetry, and nonholonomic constraints. It is shown in this paper how these principles of complexity can eventually explain a controversial behavior on macroscale by identifying key phenomena that are rooted in microscale.