JAPANESE JOURNAL OF MULTIPHASE FLOW
Online ISSN : 1881-5790
Print ISSN : 0914-2843
ISSN-L : 0914-2843
Volume 23 , Issue 5
Showing 1-16 articles out of 16 articles from the selected issue
Papers
  • Eiji ISHII, Yoshihiro SUKEGAWA, Hiroshi YAMADA, Toru ISHIKAWA
    2010 Volume 23 Issue 5 Pages 497-505
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    The fuel spray contains multi-scale free surfaces; liquid films formed at the fuel-injector outlet, ligaments generated by the liquid-film breakup, and droplets generated from the ligaments within air/fuel mixture region. In order to simulate the multi-scale free surfaces, we previously developed a fuel spray simulation combining the liquid-film breakup near the injector outlet with the air/fuel mixture. In the air/fuel mixture simulation, droplet-motions were calculated by using Discrete Droplet Model (DDM). Distributions of droplet diameters and velocities, calculated in liquid-film breakup simulation, were used as an injection condition of DDM. We apply our method to simulate fuel sprays from two kinds of fuel injectors: a multi-hole fuel injector and a collision fuel injector. The simulation results are compared with the measurements. The spray distributions qualitatively agree well with measurements. We also study the effects of injection condition of DDM on the fuel spray from collision fuel injector; some sets of velocity and diameter distributions of droplets are simulated. It is found that the diameter distribution of droplets near the injector outlet mainly affects the leading edge of spray.
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  • Tomomi UCHIYAMA
    2010 Volume 23 Issue 5 Pages 507-514
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    The vortex method for gas-particle two-phase flow is applied to simulate a spray jet. Water jets issue from two nozzles into an unbounded quiescent air; their impingement results in the spray, or the two-phase flow of air and water droplets. The water jet velocity is 17 m/s, and the droplet mean diameter is 72μm. Droplet breakup, collision, coalescence and evaporation are ignored. It is confirmed that the simulated distribution of droplet diameter agrees well with the measured distribution. The simulation also highlights that the air flow induced by the injected droplets takes its maximum velocity at the spray centerline and that the large-scale circulating air flows cause the smaller droplets to disperse more in the lateral direction; these demonstrate the applicability of the present numerical method for spray analyses.
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  • Yosuke MATSUKUMA, Yuichi KOGA, Masaki MINEMOTO, Gen INOUE
    2010 Volume 23 Issue 5 Pages 515-521
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    This paper demonstrates numerical simulations of droplet on gas diffusion layer of the polymer electrolyte fuel cell. The lattice Boltzmann method for incompressible two-phase flows at high density ratios were applied for the simulations in order to precisely predict the shape and moving velocity of water droplet surrounding by the air in the gas channel. Simulations were conducted in 2D and 3D and height and moving velocity of droplet were compared with experiment as a function of mean gas velocity in the gas channel. The droplet heights by the simulations were qualitatively agreed with the experimental data, while the simulation results of moving speed of droplet somewhat overestimated the experimental results.
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  • Koji HASEGAWA, Akiko KANEKO, Kazuyoshi AOKI, Yutaka ABE
    2010 Volume 23 Issue 5 Pages 523-530
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    One of the major recent advances for experiments in containerless processing is acoustic levitation. Although there are a lot of previous studies for acoustic levitation, the characteristics of internal and external flow of an acoustically levitated droplet is not experimentally examined enough. In this study, flow fields of an acoustically levitated droplet were experimentally investigated by observing those of a droplet simultaneously. The flow field has been obtained using Particle Image Velocimetry (PIV). In an empty chamber, vertical upward flow is generated along its central axis of test section by an acoustic wave. Velocity distributions of external and internal flow of a levitated droplet were obtained from PIV results. Also, comparing our experimental result with Yarin' s theory[12], our experimental data is in good agreement with the theoretical approach.
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  • Ryuichi IWATA, Takeo KAJISHIMA, Shintaro TAKEUCHI
    2010 Volume 23 Issue 5 Pages 531-538
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    We analyze rising motions of a bubble passing through array of particles by numerical simulations. Fluid-solid interaction is treated by an immersed boundary method (IBM) which is proposed by the present authors. The interaction force is incorporated into a 3rd order Runge-Kutta method in order to improve the numerical stability. Gas-liquid interfaces are captured by a volume of fluid (VOF) method with surface tension. A level set function is reconstructed from the volumetric fraction of fluid to evaluate the curvature of gas-liquid interfaces. Applications of these numerical improvements are validated through comparison with theoretical and experimental results. Also, it is found that the finite size effect of dispersed-phases on the rise velocity of the bubble is not negligible when diameter ratio of bubble to particle is relatively small.
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  • Hisato MINAGAWA, Takahiro YASUDA
    2010 Volume 23 Issue 5 Pages 539-545
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    LDV, PIV and some methods using ultrasonic sound have been often employed to measure multiphase flows. Fine particles are usually added into flows as tracer or scattering particles. The effect of particles added in on the flow characteristics is, however, not examined in detail. In this study, the authors measured the movement of linearly and helically rising bubbles to investigate the effect of fine particles mixed into liquid phase. Polyethylene particles of 160μm medium diameter were used. The bubble size, terminal rising velocity, migration velocity of bubbles, diameter and wave length of helix, and helical period were measured. The reductions of bubble diameter, velocities of bubbles, and helical sizes were recognized by adding particles for some cases.
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  • Motoki OHTA, Shigeo HOSOAKWA, Kosuke HAYASHI, Akio TOMIYAMA
    2010 Volume 23 Issue 5 Pages 547-554
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    Pressure drops in air-water two-phase flows in a four by four rod bundle with partial length rods (PLR) are measured by using differential pressure transducers. The sampling frequency is 0.2 kHz and sampling number is 50000. The experimental apparatus consists of an acrylic channel box and 16 stainless rods. Air and water at atmospheric pressure and room temperature are used for the gas and liquid phases, respectively. The ranges of the gas and liquid volume fluxes, JG and JL, are 0.4 < JL < 2.0 m/s and 0.06 < JG < 8.85 m/s, which cover typical two-phase flow patterns appearing in the fuel bundle. As a result, the following conclusions are obtained: (1) Although the pressure drop decreases with increasing the number of PLRs, the magnitude of the pressure reduction scarcely depends on their locations. (2) The pressure drop is well evaluated by using the void correlation proposed by Ishizuka et al. and the homogeneous model for the frictional pressure drop.
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  • Toshihiko SHAKOUCHI, Takuya SHIMIZU, Koichi TSUJIMOTO, Toshitake ANDO
    2010 Volume 23 Issue 5 Pages 555-561
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    The tube bundle of heat exchanger is arranged with an equal space pitch arrangement generally, but using a tube bundle with unequal space pitch one the flow pattern changes and the flow resistance and heat transfer performance may be reduced and improved, respectively. In this study, as a first step the flow resistance of a single raw tube bundle with an unequal spacing is examined experimentally. The equal spacing is the tube pitch of p/d=1.5 (d: tube diameter, =15.0mm), and a unequal spacing is formed by moving only the odd' s number tube.
    The experiment showed that using an unequal space pitch the flow resistance was reduced and the heat transfer performance was improved under some conditions. For example, for Reynolds number Re=Ud/ν=5×103 (U: mean superficial water velocity of coming to tube bundle), p/d=1.33, volumetric flow rate ratio of air to mixture α=0% (single-phase water flow), 10% (air-water two-phase bubbly flow), the flow resistance of the single raw tube bundle with p/d=1.33 decreases about 35, 9%, respectively, and for α=5% the heat transfer performance Num is improved about 10.5%.
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  • Takaaki NISHIMOTO, Takeyuki AMI, Hisashi UMEKAWA, Mamoru OZAWA
    2010 Volume 23 Issue 5 Pages 563-570
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    Flooding is one of very important designing factors of actual boiling system with counter-current two-phase flow, such as a reflux condenser and a high-performance heat exchanger. Consequently, many investigations have been conducted so far, but most of those investigations have been done with large diameter tubes. Thus, flooding characteristics under a small diameter channel (I.D. < 10 mm) have not been fully understood so far. In this study, flooding experiment was conducted by using air-water system in 5 mm glass tube. As results, typical flow patterns under counter-current two-phase flow were observed, and these flow patterns could be determined by the pressure drop fluctuation and the probability density function of pressure drop. Those flow pattern transitions could be correlated with Wallis's flooding correlation, and the flooding velocity also corresponded to Wallis's flooding correlation. Moreover, on the basis on the present experimental results with adiabatic system, the dryout under counter-current two-phase flow condition has been examined. As the calculation results, two kinds of dryout , i.e. the liquid film dryout at the bottom of the tube under low mass flux condition and the critical heat flux due to the flooding at the top of the tube under high mass flux condition, have been proposed.
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  • Fuminori MATSUYAMA, Thoru FURUKAWA
    2010 Volume 23 Issue 5 Pages 571-577
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    The purpose of this study is to investigate experimentally the effects of reducing surface tension on the liquid film structure and interfacial shear stress in vertical-upward air-liquids annular flows in a 19.2 mm i.d. and 5.4 m long circular tube. The test liquids were water and polyoxyethylene-lauryl-ether-water solution, and the surface tension of these liquids ranged from 72 to 45 dyne/cm. The liquid film structure was observed using the still photography and the maps of time and spatial characteristics of peripheral-mean liquid holdup detected with a series of 63 liquid holdup sensors each axially 15 mm apart in a constant current method. In the present paper, it was first described that the liquid film structure strongly depends on the reduced surface tension. Next, the effects of the reducing surface tension on the mean liquid film thickness, the gas-liquid interfacial shear stress and the interfacial friction factor were discussed with relation to the result of the observation of liquid film structure.
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  • Hideki MATSUO, Akimaro KAWAHARA, Michio SADATOMI, Keitaro NEI, Takatos ...
    2010 Volume 23 Issue 5 Pages 579-587
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    Rectangular and circular microchannels and four kinds of test liquid were used to study the effects of channel geometry and liquid properties on two-phase flow characteristics, i.e., flow regime, bubble length, bubble velocity, void fraction, frictional pressure drop, interfacial friction force. Three types of flow regime were observed, i.e., quasi-homogeneous flow, quasi-separated flow and layered flow. The bubble length data for the quasi-homogeneous flow were well correlated by the scaling law proposed by Garstecki et al (2006). The bubble velocity data and/or the void fraction data were well correlated with the well-known drift flux model (Zuber and Findlay, 1965). The distribution parameter, C0, in the model was found to depend on both the liquid properties and the channel geometries. Thus, C0 correlation was developed with three dimensionless numbers, i.e., Bond number, liquid Reynolds number and gas Weber number. The frictional pressure drop data were also found to depend on both the liquid properties and the channel geometries. And, the pressure drop data were well correlated with Lockhart-Martinelli method with a new two-phase friction multiplier correlation developed also. By substituting these correlations as well as those in literatures into a one-dimensional two-phase two-fluid model, the void fraction was calculated. The calculation with new correlations was found agree with the present data.
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  • Hideo IDE, Ryuji KIMURA, Masahiro KAWAJI
    2010 Volume 23 Issue 5 Pages 589-596
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μm diameter. By using multiple optical fibers and infrared photodiodes, void fraction and gas slug and liquid slug lengths, and their velocities were measured successfully. Experiments were conducted with 146 mm and 1571 mm long microchannels. The effects of inlet configurations and gas-liquid mixing, i.e., (a) reducer and (b) T-junction, on the two-phase flow phenomena were also investigated. The mean void fraction data obtained in a 146 mm microchannel with the reducer inlet agreed well with the equation by Kawahara and Kawaji which was previously proposed. On the other hand, the mean void fraction obtained in a 1571 mm microchannel corresponded well with the homogeneous flow model and Armand's equation for both reducer and T-junction inlet configurations. Thus, both the microchannel length and inlet geometry were found to affect the two-phase flow characteristics such as mean void fraction and gas slug and liquid slug lengths in a microchannel.
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  • Hiroaki TSUBONE, Michio SADATOMI, Akimaro KAWAHARA
    2010 Volume 23 Issue 5 Pages 597-604
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    In recently years, both the downsizing and the optimization of a heat exchanger with phase change have been requested, and a variety of working fluids have been utilized as refrigerants. Therefore, the clarification of gas-liquid two-phase flow in small diameter pipes is necessary for various liquids other than water. The purpose of this study is to clarify experimentally the effects of surface tension and liquid viscosity on the flow characteristics of two-phase slug flows in vertical small diameter pipes. In the experiment, flow structures such as void fractions in liquid slug and large gas bubble sections, ratio of large gas bubble length to slug unit length, and liquid film thickness around large gas bubbles were measured using 9 and 5 mm i.d. vertical circular pipes. As the test fluids, air and three kinds of test liquids in the property ranges of 0.042-0.071 N/m in surface tension and 0.797-19.6 mPa·s in liquid viscosity. New correlations of the above parameters were obtained from the present data, and compared with correlations in literatures and the present data.
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  • Xiuzhong SHEN, Kaichiro MISHIMA, Hideo NAKAMURA
    2010 Volume 23 Issue 5 Pages 605-613
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    In this study, local measurements of flow parameters, such as void fraction, liquid velocity and turbulence intensity were performed in a vertical upward air-water two-phase flow in a 200 mm inner diameter and 24 m in height pipe by using a hot-film anemometer. The measured mean void fraction and mean liquid velocity agreed well with those by the differential pressure method and the liquid Venturi flow meter respectively. The experimental results are summarized as follows: (1) The radial profile of void fraction changes from a wall peak shape to a core peak shape and the radial profile of liquid velocity changes from a flat shape to a core peak shape as the flow develops. (2) When the average void fraction increases, the shape of void fraction radial profile changes from a wall peak to a core peak and the radial profile of liquid velocity shows a gradually increasing core peak shape. (3) The turbulence intensity increases with the increase in void fraction, flow direction and radial direction. The predicted liquid velocities by using existing algebraic turbulence models of Sato et al.[1, 2] and Kataoka and Serizawa [3] were compared with the present experimental data. The comparison indicates that those models do not reasonably predict the liquid velocity distribution in a two-phase flow in a large diameter pipe mainly due to the defect in the predictive model of the liquid shear stress. It is necessary for us to establish a new model for the radial pressure distribution when we predict the liquid velocity distribution by using the measured void fraction distribution and algebraic turbulence models in a large diameter pipe.
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  • Zu-peng GU, Ryosuke AKAHORI, Syunsuke IKEDA
    2010 Volume 23 Issue 5 Pages 615-626
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    Sediment transport, which causes the deformation of river bed, is an important issue in the field of river engineering. In this paper, a laboratory experiment and a three-dimensional calculation with a group of permeable dikes in an open channel were conducted in order to investigate the relationship between instantaneous flow structures and suspended sediment transport mechanisms. For the calculation of suspended sediment transport, the particle-based method was used. The comparison of the experimental results and the calculation results shows that the concentration distributions of suspended sediment in cross-sections are influenced by a secondary flow and horizontal eddies in the shear layer.
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  • Michio SADATOMI, Akimaro KAWAHARA, Tatsunori GOTO
    2010 Volume 23 Issue 5 Pages 627-634
    Published: March 15, 2010
    Released: June 23, 2010
    JOURNALS FREE ACCESS
    The bubble-jet-type air-lift-pump developed by Sadatomi can dredge sediments hardly deposited on lake and sea beds by striking water jet with small bubbles against them and causing air-lift force on gas-liquid-solid mixture in the riser of the pump. In order to make the pump efficient even in deep-water zones, the pump was revised in our previous study. In the present study, results of additional experiments and performance predictions on the revised one of laboratory size are reported. In the experiment, 26 mm I.D. riser and a new 50 mm I.D. riser, each 5.0 m in length, and four kinds of solid particles of different size and density were used. Air supply rate was varied systematically at three submergence ratios from 0.76 to 0.84. The experimental results on the revised system has better particle discharge rate than the original system under the same power consumption condition. In the performance prediction, Yoshinaga et al.'s model was modified for the present purpose because their model is applicable only to a usual air-lift-pump. In addition, a new correlation of flow rate ratio of particles was derived based on the present data, and the new correlation was included in the model. As a result, the particle discharge rate at any air supply rate could be well predicted.
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