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INTRODUCTION TO THE SPECIAL ISSUE ON THE 5TH EUROPEAN-JAPANESE TWO-PHASE FLOW GROUP MEETING GUEST EDITORS: G.P. CELATA & A. TOMIYAMA
i-ii
10.1615/MultScienTechn.v22.i3.10
DIMENSIONAL ANALYSIS OF TERMINAL VELOCITY OF A TAYLOR BUBBLE IN A VERTICAL PIPE
197-210
10.1615/MultScienTechn.v22.i3.20
Kosuke
Hayashi
Graduate School of Engineering, Kobe University, 1-1, Rokkodai, Nada, Kobe
657-8501, Japan
Ryo
Kurimoto
The Univevrsity of Shiga Prefecture
Akio
Tomiyama
Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, 657-8501, Japan
taylor bubble
slug flow
terminal velocity
dimensional analysis
An empirical correlation of the terminal velocity of a Taylor bubble in a vertical pipe is proposed.
A fundamental functional form, Fr = f (ReD, EoD), of the correlation is deduced by carrying out
a dimensional analysis based on the local instantaneous field equations and the jump conditions.
Here Fr is the Froude number, ReD the bubble Reynolds number, and EoD the Eötvös number.
In the two limiting cases, (EoD→∞ and ReD→∞) and (EoD→∞ and ReD → 0), the
deduced functional form approaches those of the well-known Fr models. Coefficients appearing in
the correlation are determined by making use of the limiting cases and available experimental data.
Comparisons between the proposed Fr correlation and the experimental data show that the correlation
gives a good estimation of terminal velocities of Taylor bubbles for a wide range of fluid properties
and pipe diameters, i.e., 10 -7< Re
D < 10 4, 4 < Eo
D < 3 ×10 3, 10 -2 < N < 10 5, and -11 < log
M < 10, where N is the inverse viscosity number and M the Morton number.
EFFECTS OF BUBBLES ON TURBULENCE PROPERTIES IN A DUCT FLOW
211-232
10.1615/MultScienTechn.v22.i3.30
Shigeo
Hosokawa
Kansai University
Takashi
Suzuki
Toyohashi University of Technology, Hibarigaoka 1-1, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan
Akio
Tomiyama
Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, 657-8501, Japan
turbulence
bubbly flow
photobleaching
molecular tagging velocimetry
duct flow
Influence of bubbles on turbulence properties depends on the ratio of bubble size dB to turbulence
length scale lt and the ratio of relative velocity V R between bubbles and liquid to turbulence velocity
v'. Since most studies on turbulent bubbly flow have been carried out for flows with large dB/ lt, little
is known regarding the turbulence modulation in bubbly flows with small dB/ lt and large V R/ v'.
Hence, turbulence properties are measured for bubbly flows with small dB/ lt and large V R/v' using a
molecular tagging method based on a photobleaching reaction (PB-MTV). This method can measure
not only velocity components but also the gradients by making use of the translation and deformation
of a tag and enables us to evaluate the turbulence kinetic energy (TKE) budget. The experimental
result indicates that the boundary between the linear sublayer and the log region shifts toward the
wall by addition of bubbles in the buffer layer. The bubbles migrating toward the vicinity of the wall
increase the liquid velocity gradient at the wall, that is, the shear-induced turbulence is enhanced in
the near wall region. When the bubble size is comparable to the Kolmogorov scale, the influence of the
bubble-induced pseudo turbulence on the TKE budget is not prominent, in spite of the large relative
velocity. The expression of eddy viscosity used in the low-Reynolds-number k-ϵ model is applicable
to the bubbly flows in which the bubble-induced pseudo turbulence is not prominent. The expression
of eddy viscosity used in the standard k-ϵ model is also applicable, provided that accurate boundary
conditions for frictional velocity, TKE, and dissipation rate of TKE are given.
LARGE-SCALE ANALYSIS OF INTERACTIVE BEHAVIORS OF BUBBLES AND PARTICLES IN A LIQUID BY A COUPLED IMMERSED BOUNDARY AND VOF TECHNIQUE
233-246
10.1615/MultScienTechn.v22.i3.40
Ryuichi
Iwata
Dept. Mechanical Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 565-0871
Shintaro
Takeuchi
Department of Mechanical Engineering,
Osaka University, 2-1 Yamada-oka, Suita-city, Osaka 565-0871 Japan
Takeo
Kajishima
Department of Mechanical Engineering,
Osaka University, 2-1 Yamada-oka, Suita-city, Osaka 565-0871 Japan
three-phase flow
gas-liquid-solid system
VOF method
immersed boundary method
DNS
A new approach for direct numerical simulation of three-phase (gas-liquid-solid) flows is proposed. Implementation of a moving rigid surface in a fluid is based on an immersed boundary/solid-object method developed by the present authors, and the gas-liquid interface is captured by the volume-of-fluid (VOF) method with an interface reconstruction scheme. The proposed coupling technique enables simulation of flow structures induced by both bubbles and particles of comparable size, including the flow pattern around the gas-liquid and solid-liquid interfaces. In a suspension of 1024 solid particles and a bubble, some typical behaviors of bubble-particle interaction and liquid flow pattern are captured. Detailed analysis on the motion of the falling particles suggests that the particle rotation is strongly influenced by the behaviors of the rising bubble, giving rise to a snap reversal of the rotating directions of the particles due to the flow induced by the bubble.
SPLITTING CHARACTERISTICS AND FLOW DISTRIBUTION OF GAS-LIQUID FLOW IN TWO PARALLEL PIPES
247-266
10.1615/MultScienTechn.v22.i3.50
Yehuda
Taitel
School of Mechanical Engineering, Tel-Aviv University, Israel
Bella
Gurevich
School of Mechanical Engineering, Tel-Aviv University
Dvora
Barnea
School of Mechanical Engineering, Tel-Aviv University, Tel-Aviv
two-phase flow
parallel pipes
splitting
The behavior of adiabatic two-phase flow in parallel pipes is quite complex and difficult to predict. The manner in which the phases are distributed among the pipes depends on the inlet flow rates, physical properties of the phases, the geometry of the common manifold, and pipes inclination. Pustylnik (2007) studied experimentally the distribution of an adiabatic air{water mixture in four horizontal and slightly inclined parallel pipes with common inlet and outlet manifolds. A mechanistic model was suggested to predict the distribution of the phases. The model is based on the assumption of ideal splitting, namely, the ratio of gas to liquid flow rates in each of the parallel pipes is equal to that in the inlet manifold. This study tests the validity of this assumption and experimentally determines the actual splitting characteristics at the inlet manifold for a system of two pipes. The experimental results show that the splitting rule differs slightly from the ideal splitting assumption and that it is not sensitive to the inlet flow rates within the measured range. The splitting rule obtained is used in the predictive model for the two-phase flow distribution in the pipes. The calculated transition boundaries are compared to the experimental transition boundaries and to those obtained by the ideal splitting assumption.
STUDY ON A MECHANICAL EQUILIBRIUM CONDITION AT A THREE-PHASE CONTACT LINE: WETTABILITY ON SOLID SURFACES
267-278
10.1615/MultScienTechn.v22.i3.60
Yukihiro
Yonemoto
Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1 Kurokami, Chuo, Kumamoto 860-8555, Japan
Tomoaki
Kunugi
Department of Nuclear Engineering, Kyoto University, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto, Japan
Youngs equation
Zismans plot
wettability
contact angle
Young's equation describes an interfacial equilibrium condition at a contact line of a liquid droplet on a smooth solid surface. This relation was derived by Thomas Young in 1805 and has been examined continuously up to the present. This equation is generally discussed from a thermodynamic viewpoint and is derived by minimizing the total free energy of a system while keeping constant the intensive parameters in the total free energy. In our previous study [Yonemoto, Y. and Kunugi, T., (2009) J. Chem. Phys., 130, pp. 144106-1-144106-12], a modified Young's equation was derived based on a new thermodynamic approach. In this derivation, the virtual work variation in a droplet on a smooth solid surface was considered at the contact line by taking the incline of the droplet surface into account. An analytical solution derived from the modified Young's equation can predict some experimental data for the relationship between the droplet radius and the contact angle. In the present work, we consider the Zisman's plot based on a macroscopic concept. In concrete terms, a modified Zisman's function is derived from the modified Young's equation. Finally, we compared the modified Zisman's function to experimental data for the relationship between liquid surface tension and the contact angle.