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Multiphase Science and Technology
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19
2
2007
MOVEMENT OF TWO CONSECUTIVE TAYLOR BUBBLES IN VERTICAL PIPES
99-120
10.1615/MultScienTechn.v19.i2.10
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
The development of slug flow along vertical pipes is governed by the interaction between consecutive elongated bubbles. It is generally assumed that the trailing bubble's shape and velocity are affected by the flow field in the liquid phase ahead of it. To examine this assumption, a facility is used that allows controlled injection of pairs of Taylor bubbles into vertical pipes filled with stagnant or flowing liquid. An experimental approach is developed to perform particle image velocimetry measurements of the velocity field in front of the trailing Taylor bubble, simultaneously with video imaging of Taylor bubble pairs, to be able to relate the instantaneous parameters (shape and velocity) of the trailing bubble to the instantaneous velocity distribution in the liquid ahead of it. Experiments are performed in pipes of two diameters and for a number of Reynolds numbers based on mean water velocity, corresponding to both laminar and turbulent background flows. A model relating the propagation velocity of the trailing Taylor bubble to the local mean centerline velocity of the leading bubble is suggested and verified experimentally. The effect of the velocity fluctuations in the leading Taylor bubble's wake on the instantaneous propagation velocity of the trailing bubble is studied.
INTERFACE TRACKING SIMULATION OF BUBBLES AND DROPS IN COMPLEX GEOMETRIES
121-140
10.1615/MultScienTechn.v19.i2.20
Kosuke
Hayashi
Department of Mechanical Engineering, Graduate School Engineering, Kobe
University, 1-1 Rokkodai, Nada, Kobe, Hyogo, 657-8501 Japan
The interface tracking method based on a nonuniform subcell scheme (NSS) and a level set function (LS) is applied to three-dimensional (3-D) general curvilinear and cylindrical coordinate systems. The method for 3-D general curvilinear coordinates is based on the combination of NSS, LS, a finite volume method, and a multiblock method. The method for cylindrical coordinates is based on the combination of NSS, LS, the variable transformation proposed by Verzicco and Orlandi (1996), and a simple method for evaluating surface tension force at the singular point r = 0. Simulations of single air and vapor bubbles in rod bundle geometry are carried out using the former method. Predicted bubble shapes and terminal velocities agree well with measured data and an available terminal velocity model. Bubbles and drops in pipes are simulated using the latter method. Terminal velocities of single drops confined in a pipe are well predicted. The bouncing motion of an air bubble in a laminar water flow in a vertical pipe is successfully simulated. Volumes of bubbles and drops are well conserved in all simulations.
POOL BOILING IN MICROGRAVITY AND IN ELECTRIC FIELDS: OLD AND RECENT RESULTS
141-165
10.1615/MultScienTechn.v19.i2.30
Paolo
Di Marco
Department of Energy, Systems, Constructions and Territory Engineering, University of Pisa, largo Lucio Lazzarino 1, Pisa 56122, Italy
Walter
Grassi
Lo.Th.A.R. (Low gravity and Thermal Advanced Research Laboratory), DESTEC (Department of Energy, Systems, Territory and Constructions Engineering), University of Pisa−Largo Lucio Lazzarino, 56122 Pisa, Italy
The main outcomes of a 10-year research activity on pool boiling in microgravity, carried out at Low Gravity and Thermal Advanced Research Laboratory of Pisa University, are summarized. A large part of the article also deals with the effect of electrostatic fields on microgravity boiling. The reported results were obtained in several microgravity experimental campaigns and mainly during one sounding rocket (MASER-8) and one orbital flight on the Russian satellite FotonM2. They refer to wire and plate heaters in FC-72, subjected to the action of strongly nonuniform and nearly uniform electrostatic fields, respectively. Long-term steady state nucleate boiling seems to be possible in microgravity, especially in subcooled conditions, though impaired bubble removal and coalescence lead to an increase of void fraction and could degrade nucleate boiling heat transfer and anticipate CHF. It has been shown that the addition of an appropriate electric field widens the nucleate boiling region (increase of CHF), and the heat transfer coefficient becomes almost insensitive to gravity. These effects are more marked on wires than on plates, where, due to the different field geometry, a higher voltage is needed to attain the same effect and demonstrate the progressive dominance of electric forces over buoyancy.
JET IMPINGEMENT BOILING IN HOT SURFACES WELL ABOVE THE LIMITING TEMPERATURE FOR SOLID-LIQUID CONTACT
167-181
10.1615/MultScienTechn.v19.i2.40
M. A.
Islam
Dept. of Mechanical Engineering, Saga University, 1 Honjo Saga City, Saga 840-8502, Japan
Masanori
Monde
Department of Mechanical Engineering, Saga University, 1 Honjo Saga City, Saga 840-8502, Japan
P. L.
Woodfield
Dept. of Mechanical Engineering, Saga University, 1 Honjo Saga City, Saga 840-8502, Japan
Yuichi
Mitsutake
Department of Mechanical Engineering, Saga University, 1 Honjo Saga City, Saga 840-8502, Japan
A. K.
Mozumder
Dept. of Mechanical Engineering, Saga University, 1 Honjo Saga City, Saga 840-8502, Japan
Jet impingement boiling phenomena in hot surfaces were investigated by means of temperature measurements and video records. A 2-mm water jet of 5−80 K subcooling and of 3−15 m/s velocity was impinged on the flat surface of a cylindrical steel or brass block that was preheated to 400−600°C. During the quench, the transient temperature responses of 16 thermocouples embedded in two depths beneath the surface were recorded to estimate surface temperature by an inverse heat conduction technique. A high-speed video camera was also employed to capture images of boiling and flow phenomena. Sometimes the flow became explosive/noisy and sometimes very calm and quiet. Different flow patterns, as identified from video images, resulted from the interactions between the jet and vapor bubbles formed at/near the impinging surface. The flow patterns are found to be dependent on the block material and its surface temperature. It is also found that for a certain period of time, the surface temperature (Tω) remains well above the thermodynamic limiting temperature (Tmax) for solid-liquid contact. The cooling curves at the center of the impinging surface for different experimental conditions are explained in relation to the limiting temperature. A theoretical approach to elucidate the early-stage phenomena is also outlined in this study.
FLOW PATTERN ANALYSIS OF FLOW BOILING IN MICROGRAVITY
183-210
10.1615/MultScienTechn.v19.i2.50
Gian Piero
Celata
ENEA, Institute of Thermal Fluid Dynamics, ENEA TERM/ISP Heat Transfer Laboratory C.R.E.
Maurizio
Cumo
ENEA, Rome; DINCE, University of Rome “La Sapienza”, Corso Vittorio Emanuele II, 244, Rome, Italy
M.
Gervasi
ENEA, Institute for Thermal Fluid Dynamics, Via Anguillarese 301, 00123 S.M. Galeria, Rome, Italy
Giuseppe
Zummo
ENEA, Institute for Thermal Fluid Dynamics, via Anguillarese, 301, Rome, Italy
This paper describes the results of an experimental investigation on the flow pattern in pipe flow boiling under microgravity conditions, aiming at obtaining quantitative data and observations on the flow pattern for low gravity conditions. The test tubes are made of Pyrex® with two different inner diameters, 4.0 and 6.0 mm, respectively. Fluid flow is vertical upward, while the test fluid is FC-72, a Fluorinert™ liquid. Measurements included wall temperatures along the flow channel, inlet and outlet temperatures, pressures, and mass flow rate. A video camera allows one to take movies of the flow pattern in the last part of the flow channel. The observed flow pattern in the present experimental range is typically bubbly flow and intermittent flow (plug and disordered intermittent flow). Different flow pattern maps are verified with the experimental data and a modification of one of them is proposed.