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INTRODUCTION TO THE SPECIAL ISSUE ON THE 5TH EUROPEAN-JAPANESE TWO-PHASE FLOW GROUP MEETINGGUEST EDITORS: G.P. CELATA & A. TOMIYAMA
i-ii
10.1615/MultScienTechn.v22.i2.10
FLOW BOILING IN HORIZONTAL MINICHANNELS: FLOW PATTERN OF CO2 AT HIGH PRESSURE
115-132
10.1615/MultScienTechn.v22.i2.20
Mamoru
Ozawa
Department of Safety Science, Kansai University, 7-1 Hakubai-cho, Takatsuki-shi, Osaka 569-1098, Japan
Hisashi
Umekawa
Department of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680, Japan
T.
Ami
Kansai University, Suita, Osaka
Ryosuke
Matsumoto
Department of Mechanical Systems Engineering Kansai University, 3-3-35 Yamate-cyo, Suita, Osaka 564-8680
T.
Hara
Department of Mechanical Engineering, Kansai University, Suita, Osaka 564-8680
carbon dioxide
boiling heat transfer
flow pattern
mini-channel
discrete bubble model
This paper describes the flow patterns of carbon dioxide two-phase flow at high pressure observed in horizontal minichannels ranging from 0.51 to 3.0 mm in diameter, together with the flow pattern maps and related boiling heat-transfer characteristics. The observed flow patterns are mainly classified into bubbly, slug, slug-annular, and annular flows, similar to conventional pipes, while phase stratification tendency is still significant even in a 1.0 mm tube, so that heat transfer at high pressure shows significant differences in the upper and lower walls, especially in 2.0 and 3.0 mm tubes. Such phase stratification with reference to heat transfer is roughly scaled by means of boiling number and Bond number. The newly developed simulation model by the authors for conventional-sized tubes is successfully applied to 2.0 and 3.0 mm pipes, but not to 0.51 and 1.0 mm tubes. This model suggests that thermal flow behavior at higher Bond number Bo than 8.2 is similar to that of conventional-sized tube, and cases less than Bo = 8.2 show minichannel behavior. The heat transfer in these minichannels is well-predicted with Schrock{Grossman type correlation with nucleate and forced-convective effects, while in larger tubes, e.g., 2.0 and 3.0 mm, the heat transfer is mainly dominated by nucleate boiling in the present experimental ranges.
EXPERIMENTAL INVESTIGATION OF GEOMETRIC SCALING ON ATOMIZATION IN A TWO-PHASE GAS/LIQUID SPRAY
133-155
10.1615/MultScienTechn.v22.i2.30
C. E.
Ejim
Schlumberger REDA Production Systems, Singapore 629971
Mohammad Azizur
Rahman
Department of Biochemistry and Molecular Biology, Jahangirnagar University, Savar, Dhaka, Bangladesh; Mushroom Research Centre, Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia
Alidad
Amirfazli
Department of Mechanical Engineering, York University, Toronto, Ontario, Canada M3J 1P3
Brian A.
Fleck
Mechanical Engineering Department, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, AB, T6G 2G8, Canada
scaling
two-phase gas/liquid spray
Sauter mean diameter
phase-Doppler particle anemometer
gas-to-liquid ratio
fluid coker nozzle
In this study the atomization performance of a full-scale industrial air-liquid nozzle is compared to a one-quarter model. The objective is to establish a global Sauter mean diameter D32(gb) correlation as a function of nozzle size (D) in a two-phase gas/liquid (TPGL) spray atomization. This information is to be used in the design and development of nozzles for heavy oil upgrading industry. Compressed air was used as the gas phase; the liquids were water, canola oil, and glycerine solutions all at room temperature. The liquid flow rates were varied from 0.095 to 0.195 L/s, and the gas-to-liquid-ratio (β), by mass, was fixed at 1%, similar to commercial fluid coker nozzles. Fluid mixing pressures in the test were between 516 and 1000 kPa. The D32 within the spray was measured using a Dantec 2-D phase-Doppler particle anemometer (PDPA) with measurements performed at axial distances of 100, 202, and 405 mm from the nozzle exit and within spray widths of +50 to -50 mm in the horizontal plane. Experimental results show that if the D is increased from 3.1 to 4.1 mm (1.3 times), D does not show a change on D32 and equates to the power of 0.1 (glycerine solution sprays at μ;L = 67 mPa s) to 0.9 (water sprays at μ;L = 1 mPa s). Finally, the D32(gb) correlation as a function of geometric scaling estimated drop size within a 17% maximum deviation between the experimental and curve fit data.
SHAPE OSCILLATIONS OF A BOILING BUBBLE
157-175
10.1615/MultScienTechn.v22.i2.40
Cees W. M.
van der Geld
Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
bubble oscillations
contact angle
Euler-Lagrange
generalized forces
interfacial forces
stability analysis
PIV
added mass
The shape of a free bubble or of a boiling bubble at an artificial cavity or needle may exhibit strong, axisymmetric shape oscillations. The Euler-Lagrangian approach facilitates computation of such oscillations. A derivation of the generalized forces needed in such an approach is presented. This derivation eliminates ambiguity in the description of the driving forces involved. Both increasing amplitude of oscillation and decreasing distance to the wall lower the radian frequency of oscillation of a free bubble. These two effects are quantified. A two-equation model to predict growth and detachment of a bubble with the shape of a truncated sphere on a plane wall is derived with the Euler-Lagrange approach. The period of oscillation of a fundamental mode of a free bubble, Tosc, is known to be proportional to the initial radius, R, cubed. That of a boiling bubble attached to a cavity has a similar dependency but with a difference in the proportionality constant of nearly a factor 2. This factor can be explained with the aid of a stability analysis of the two-equation model for a truncated sphere. The high factor results from the combination of two added mass force contributions: one related to isotropic deformation (expansion and contraction), the other related to motion of the center of mass above the plane wall. The amplitude of the oscillatory motion of a boiling bubble at a wall can be large during a long time of observation, e.g., a quarter of a second. Some dedicated experiments reveal the source of kinetic energy of this motion.
A TRANSIENT ONE-DIMENSIONAL MODEL OF MIXING AND SEGREGATION OF LIQUIDS IN PIPES
177-196
10.1615/MultScienTechn.v22.i2.50
Raad I.
Issa
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
A.
Tomasello
Mechanical Engineering Department, Imperial College London
liquid-liquid flow
mixing and segregation model
dispersions
phase inversion
A one-dimensional model is proposed for the prediction of transient two-phase flow of two immiscible liquids in pipes. The approach treats the liquid{liquid flow as being composed of two layers, each made up of either pure liquid or an emulsion of the two liquids. Each layer is treated as a single mixture where the relative slip between dispersed and continuous phases is determined from a drift-flux model. Closure relations are proposed for the calculation of the entrainment rate of drops from one layer into the other, and for the reverse process of deposition of the dispersed phase drops. Closure relations are also used to evaluate the dispersed phase drop diameter, the mixture viscosity, and the phase inversion point. Phase inversion is catered to in an automatic way. Predictions obtained from the model are compared against experimental data for oil-water flow; in particular, dispersed phase fractions, pressure losses, and schematic flow regime maps are used to assess performance. The model reproduces with reasonable accuracy the experimental dispersed phase fraction trends and the changes in flow regime as functions of the flow parameters. Computed pressure losses at low mixture velocity are in good agreement with the experiments. Two factors influencing the results at high mixture velocities, secondary dispersion and drag reductions effects, are briefly discussed.