Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
19
4
2007
ON THE DEPOSITION RATE OF DROPLETS IN ANNULAR FLOW AROUND A FLOW OBSTACLE
305-321
10.1615/MultScienTechn.v19.i4.10
Tomio
Okawa
Department of Mechanical & Intelligent Systems Engineering The University of Electro-Communications 1-5-1, Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan
Takayuki
Fujita
Dept. of Mechanical Engineering, Osaka University, Osaka, Japan
Jun
Minamitani
Dept. of Mechanical Engineering, Osaka University, Osaka, Japan
Isao
Kataoka
Dept. of Mechanical Engineering, Osaka University, Osaka, Japan
Measurement of the deposition rate of droplets in vertical upward annular flow was carried out using air and water as test fluids. The test section was a 5-mm-diameter circular tube, in which a small tube was placed concentrically to test the influence of the presence of a flow obstacle on the deposition rate of droplets. The local deposition rate of droplets was measured at the inlet and downstream of the obstacle section to investigate the mechanism of deposition augmentation caused by the flow obstacle. In contrast to the hypothesis used in available models for the obstacle effect, significant deposition augmentation was detected not only downstream, but also at the inlet of the obstacle section. Simple models for the local deposition rates of droplets around the flow obstacle were developed based on the present experimental results.
AN ADVANCED MICROBUBBLE GENERATOR AND ITS APPLICATION TO A NEWLY DEVELOPED BUBBLE-JET-TYPE AIR-LIFT PUMP
323-342
10.1615/MultScienTechn.v19.i4.20
Michio
Sadatomi
Department or Advanced Mechanical System, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Chuo-Ku, Kumamoto City, 860-8555, Japan
Akimaro
Kawahara
Advanced Thermal and Fluid Energy System
Division of Industrial Fundamentals
Faculty of Advanced Science and Technology, Graduate School of Science and Technology, Kumamoto University, Chuo-ku,
Kurokami 2-39-1, Kumamoto, Japan
Fuminori
Matsuyama
Dept. of Mechanical System Engineering, Kumamoto University, Kumamoto, 860-8555; Dept. of Mechanical Engineering, Sasebo National College of Technology, Sasebo, 857-1193
Takanao
Kimura
Air-Conditioning & Refrigeration Systems Works, Mitsubishi Electric Corporation, Wakayama, 640-8686, Japan
An advanced microbubble generator with a spherical body in a flowing water tube was patented by Sadatomi in 2003. The generator can suck air by a vacuum pressure behind the spherical body and has three advantages over existing generators: (i) its fabrication is easy because of a simple structure; (ii) it can produce any sizes of bubbles by controlling the flow rates of air and water introduced; and (iii) it requires less electric power. In the present paper, a simple model has been presented to predict its performance, i.e., the bubble generation rate (= air suction rate) and the water pressure at the generator inlet, when water is supplied at different rates to the generator at different water depths. From the validation test of the model against the present experimental data, it has been clarified that the model can predict reasonably well. As an industrial application of the generator, a bubble-jet-type air-lift pump with the generator at the riser bottom is presented together with the results of its feasibility test. In the field test, the air-lift pump could lift up water with fine sediments from the seabed in Amakusa Islands, leading to the purification of seawater there.
PATTERN DYNAMICS SIMULATION OF VOID WAVE PROPAGATION
343-361
10.1615/MultScienTechn.v19.i4.30
Mamoru
Ozawa
Department of Safety Science, Kansai University, 7-1 Hakubai-cho, Takatsuki-shi, Osaka 569-1098, Japan
T.
Ami
Kansai University, Suita, Osaka
Hisashi
Umekawa
Department of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680, Japan
Masahiro
Shoji
Department of Mechanical Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686; and Energy Technology Research Institute, AIST, 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan
Gas-liquid two-phase flow is a typical complex system with intrinsic spatiotemporal fluctuation in phase distribution, pressure drop, heat transfer, and so on, being an important subject left behind after extensive research on two-phase flow dynamics. Previously developed modeling is not appropriate in application to CHF problems at low quality and/or in downward flow. This is mainly because conventional modeling, including two-fluid modeling, is based on the continuous flow hypothesis. The proposed model, represented by the discrete bubble model, consists of a void propagation equation as a global rule and only a limited number of mechanical and geometrical relationships as local rules, i.e., a wake effect, gas compressibility, and a phase redistribution mechanism. Neglecting detailed mechanisms of two-phase flow, the spatiotemporal fluctuations in void fraction and pressure drop are numerically realized within the framework of the pattern dynamics approach.
VISUALIZATION OF DRYOUT PHENOMENON AND LIQUID FILM BEHAVIOR USING A SINGLE SUBCHANNEL OF A TIGHT LATTICE BUNDLE
363-372
10.1615/MultScienTechn.v19.i4.40
Miyuki
Akiba
Toshiba Corporation, Yokohama, Kanagawa, Japan
Shinichi
Morooka
Toshiba Corporation, Nuclear Engineering Laboratory, Yokohama, Kanagawa, Japan
Junji
Mimatsu
Dept. of Mechanical Engineering, Gifu University, Gifu, Japan
Sinji
Sakai
Gifu University, Gifu, Japan
Akira
Inoue
Research Laboratory of Nuclear Reactor, Tokyo Institute of Technology, Tokyo, Japan
The development of fast neutron spectrum boiling water reactors requires understanding of flow behavior in a tight lattice bundle. We conducted experiments to visualize single-channel flow under atmospheric conditions and to measure the critical heat flux (CHF) location and liquid film behavior. The observed flow pattern in the tight lattice was in agreement with the Hewitt-Roberts flow pattern map. CHF occurred at the wider rod gap location. Furthermore, the liquid film flow rate at this location was less than that at the narrow rod gap location. The CHF mechanism in a tight lattice would be the film dryout occurring by decreasing the liquid film flow rate.
DIRECT NUMERICAL SIMULATION OF TURBULENT HEAT TRANSFER IN WATER FLOW WITH IMMISCIBLE DROPLETS
373-391
10.1615/MultScienTechn.v19.i4.50
Yoshimichi
Hagiwara
Department of Mechanical and System Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
T.
Kawai
Daikin Industries Ltd., Osaka, Japan
Mitsuru
Tanaka
Dept. of Mechanical and System Eng., Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Kyoto 606, Japan
Direct numerical simulation has been carried out for turbulent upward water flow with two immiscible droplets in a vertical channel. The density of the droplets is higher than that of water. The flow is heated from the channel walls. The governing equations are solved with finite difference schemes. The grid is allocated nonuniformly, except for a region including the droplets. The grid is uniformly and densely allocated in the region. The grid is used as the overset grid so that it reduces the computational errors due to high interfacial tension and complicated flow near the interface. The interface is tracked with the modified version of the volume-of-fluid method. It is found that the computational errors are reduced by using the overset grid. A large number of small-scale vortices are generated around the falling droplets. The secondary flow in the wallward direction is induced below the droplets, and the secondary flow in the outward direction is induced above the droplets. These flows are effective for the enhancement of the near-wall heat transfer. These flows are attenuated by the adjacent droplet in the axial direction. The droplets deform large-scale streamwise vortices and attenuate small-scale streamwise vortices.