JSME International Journal Series B Fluids and Thermal Engineering
Online ISSN : 1347-5371
Print ISSN : 1340-8054
ISSN-L : 1340-8054
Volume 48 , Issue 3
Special Issue on Advanced Fusion of Functional Fluids Engineering
Showing 1-33 articles out of 33 articles from the selected issue
REVIEW
  • Oleg Pavlovich SOLONENKO, Vladimir Vladimirovich KUDINOV, Andrey Vladi ...
    2005 Volume 48 Issue 3 Pages 366-380
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Over the last one and half decades the constantly growing interest to a problem of rapid solidifying the melted micro-droplets of various materials at their impact with a surface has been marked. This phenomenon is at the basis of many technologies, such as plasma, detonation and flame spraying, arc-spray, spray-casting, micro-atomization of powders, solder-drop-printing in microelectronic, making the microcrystal and amorphous materials, and producing the high-temperature superconductors. The system micro-droplet - substrate is very suitable for a physical materials science in studies of the non-equilibrium phase diagrams of different alloys and composite materials under extreme conditions. Practically speaking we have dealings with independent scientific and technological line of investigation - micro-metallurgy of a small volume of melt at its collision with an obstacle surface or, in other words, splats’ micro-metallurgy. The paper presented is devoted to a brief review of theoretical, computational and experimental investigations carried out by composite authors during the last decade.
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PAPERS
  • Hideya NISHIYAMA, Katsuhisa HAMADA, Toshiyuki UCHII, Hiromichi KAWANO, ...
    2005 Volume 48 Issue 3 Pages 381-388
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    A transient response of SF6 thermofluid field inside the exhaust tube in a Gas Circuit Breaker under high temperature, high pressure and high velocity conditions is analyzed by taking compressible effect and some realistic processes into account related to the available experimental data of GCB test facility. Furthermore, computational simulation is conducted to clarify the effective cooling process of SF6 hot gas flow inside the exhaust tube for transient time to avoid the SF6 hot gas breakdown near exhaust tube exit after the arc current interruption. It is found that the SF6 hot gas flow can be effectively cooled down for the rough inside wall of exhaust tube due to the separation of SF6 hot gas flow from the inside wall and also active mixing with upstream cold gas. The effect of roughness pattern on the real time thermofluid field of SF6 hot gas flow and possible breakdown region are also clarified. Finally, the computed temperature in GCB shows the good agreement with the available experimental data for smooth surface of exhaust tube.
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  • Hidemasa TAKANA, Yoshihiro OKUNO
    2005 Volume 48 Issue 3 Pages 389-396
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    The characteristics of the annular Hall MHD device under the wide range of operating conditions are investigated in detail by carrying out time-dependent three-dimensional numerical simulations with the purpose of providing fundamental data for the future industrial application of the device. Because of the configuration of the device, it can be operated both as generator and accelerator. Under power extraction, the highest enthalpy extraction of 5% for the load resistance of 3.0Ω and the highest isentropic efficiency of 15% for 2.0Ω are obtained. The nonuniform plasma induced by weak ionization of seed forms a clockwise spiral structure in θ-z plane. Due to this unsteady behavior of the discharge, output electrical power fluctuates periodically at the frequency of approximately 20-40kHz. Finally, the Lorentz efficiency is evaluated under power input. The highest Lorentz efficiency of 58% can be obtained for -0.5kV.
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  • Manabu TANAKA, Masao USHIO, John James LOWKE
    2005 Volume 48 Issue 3 Pages 397-404
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    In order to clarify the formative mechanism of weld penetration in an arc welding process, a numerical model is useful to understand quantitative values of the balances of mass, energy and force in the welding phenomena. In the present paper, the whole region of welding process using a free-burning arc, namely, tungsten cathode, arc plasma and weld pool is treated in a unified numerical model to take into account the close interaction between the arc plasma and the liquid metal. Calculations are made for the time dependent development of the weld pool for the free-burning arc in helium at atmospheric pressure. It is shown that the calculated convective flow in the weld pool is dominated by the surface tension gradient force and the electromagnetic force. It is also shown that different surface tension properties can change the direction of re-circulatory flow in the weld pool and dramatically vary the weld penetration geometry.
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  • Masaya SUGIMOTO, Koichi TAKEDA
    2005 Volume 48 Issue 3 Pages 405-410
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    An arc in a vacuum was applied to clean a metal surface contaminated with organic matter and its cleaning characteristics were investigated. The cleaning began in the central region of a round area covered with a small vacuum chamber and gradually moved to the peripheral region. The cleaning velocities, defined as the cleaned surface area and the weight of the removed contaminant per second, were measured for various surface densities of the contaminant. The surface layer of the metal was stripped simultaneously during cleaning, and it was revealed that the total erosion rate of the contaminant and the metal is constant and that the thickness of the stripped surface layer is not dependent on the surface density of the contaminant but on the discharge current.
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  • Norifumi ONO, Kazuhiro MUSHA, Kazuo KOIKE
    2005 Volume 48 Issue 3 Pages 411-416
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    A fundamental study of functional enhancement of plasma jet with external magnetic field was carried out to utilize the attractive properties effectively. The magnetic field was applied to the jet in a vacuum chamber by using a pair of superconducting coils. The behavior of the jet between two coils was taken by a digital camera through the window for observation. The image analysis shows that the jet is constricted radially by the strong magnetic field. However, high brightness region around the center of the jet increases with the field strength. Measurement on the emission was also performed at lateral positions from the center to the outer edge of the jet. The results of emission measurement also supported the constriction of the jet illustrated by the image analysis. It is clarified from these results that the plasma jet can be controlled significantly by using the strong magnetic field.
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  • Yasunori TANAKA, Toru NUMADA, Shuhei KANEKO, Shigemitsu OKABE
    2005 Volume 48 Issue 3 Pages 417-424
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Thermodynamic and transport properties of Ar thermal plasmas with polymer ablated vapors at atmospheric pressure were calculated in temperature range up to 30000K on the assumption of thermal equilibrium condition. The polymers such as POM (polyoxymethylene), PE (polyethylene) and PMMA (polymethlmethacrylate) are being used in low-voltage circuit breakers or load-break switches as an insulation material and a wall material of arc quenching chamber. These polymers are ablated into the arc plasma during the arc interruption processes in the circuit breakers. The thermodynamic and transport properties are indispensable for the prediction of arc or thermal plasma simulation. The first order approximation of Chapman-Enskog method was adopted to derive the transport properties. The calculated thermodynamic and the transport properties were used to compute the temperature distributions of Ar induction thermal plasmas to investigate influence of the polymer ablated vapors on the thermal plasma temperature. It can be found out that PMMA vapor inclusion into Ar thermal plasmas decreases the thermal plasma temperature markedly compared with those of POM and PE, which indicates that the PMMA vapor has a higher plasma-quenching efficiency.
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  • Masaya SHIGETA, Takayuki WATANABE
    2005 Volume 48 Issue 3 Pages 425-431
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Numerical analysis is conducted for silicon-based intermetallic nano-particle preparation in induction thermal plasma flow systems. In the nucleation region, the temperature decreases drastically (104-105K/s), which results in a great promotion of nano-particle nucleation. In Mo-Si system, nuclei of molybdenum are produced and grow in the upstream region and then silicon vapor condenses on the molybdenum particles. The composition shows wide range since condensations of molybdenum and silicon occur at the different positions. On the other hand in Ti-Si system, it shows narrow range since condensations of titanium and silicon occur simultaneously. The difference of the formation mechanisms leads to the preparation of disilicides as well as the sub-products which are estimated from the phase diagrams. The particle size distributions and the compositions obtained from the present model show good agreements with the experimental results.
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  • Takehiko SATO, Makoto KAMBE, Hideya NISHIYAMA
    2005 Volume 48 Issue 3 Pages 432-439
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    In the present study, experimental and numerical analyses were adopted to clarify key reactive species for methanol decomposition processes using a nonthermal plasma flow. The nonthermal plasma flow was generated by a dielectric barrier discharge (DBD) as a radical production source. The experimental methods were as follows. Working gas was air of 1-10Sl/min. The peak-to-peak applied voltage was 16-20kV with sine wave of 1Hz-7kHz. The characteristics of gas velocity, gas temperature, ozone concentration and methanol decomposition efficiency were measured. Those characteristics were also numerically analyzed using conservation equations of mass, chemical component, momentum and energy, and state of equation. The simulation model takes into account reactive species, which have chemical reaction with the methanol. The detailed reaction mechanism used in this model consists of 108 elementary reactions and 41 chemical species. Inlet conditions are partially given by experimental results. Finally, effects of reactive species such as O, OH, H, NO, etc. on methanol decomposition characteristics are numerically analyzed. The results obtained in this study are summarized as follows. (1) Existence of excited atoms of O, N and excited molecular of OH, N2(B3Πg), N2(A3Σu+), NO are implied in the discharge region. (2) The methanol below 50ppm is decomposed completely by using DBD at discharge conditions as V=16kVpp and f=100Hz. (3) The reactive species are most important factor to decompose methanol, as the full decomposition is obtained under all injection positions. (4) In numerical analysis, it is clarified that OH is the important radical to decompose the methanol.
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  • Tomoyuki KUROKI, Shingo TANAKA, Masaaki OKUBO, Toshiaki YAMAMOTO
    2005 Volume 48 Issue 3 Pages 440-447
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    CF4 is one of the most stable gases among perfluorocompounds (PFCs) whose decomposition is extremely difficult. In this study, CF4 decomposition was investigated using a pulse-modulated radio frequency (RF) plasma of 2MHz, which is applicable to plasma etching and novel functional material manufacturing processes. When the absolute pressure and 100% CF4 and 99.5% O2 flow rates were set at 80Pa and 0.1 and 0.2NL/min, respectively, almost complete CF4 decomposition was achieved at the pulse modulation frequency range of 25kHz to 99kHz. The analysis of the by-product of CF4 decomposition was carried out using a CO2 gas analyzer and a Fourier transform infrared spectrophotometer (FTIR) with a pulse modulation frequency of 75kHz. It was known that 10%, 50% and 24% of CF4 are converted to CO, CO2 and COF2, respectively. It was considered that the remaining 16% of carbon is converted to carbon particles or other organic substances.
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  • Satoyuki KAWANO, Takashi MISAKA
    2005 Volume 48 Issue 3 Pages 448-455
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    In this research, numerical simulation of oxygen plasma produced by dielectric barrier discharge (DBD) is made as a basic research for the application of bioprocesses such as sterilization. Numerical simulation is based on an appropriate modeling of microdischarges including 9 kinds of species and 54 chemical reactions. Behavior of the oxygen plasma is analyzed by finite difference method in two-dimensional computational region. The detailed characteristics of filamentous discharge formed between parallel dielectric surfaces which cover the electrodes are investigated. The qualitative tendency of the discharge formation process agrees with the previous experimental observation. Ozone production efficiency (OPE) is obtained and compared with experimental results. Dependency of reduced electric field E/n on OPE is investigated by comparing the numerical results with previous experimental results by other researcher, where E/n is the ratio of electric field EE to number density n of neutral molecule in the gas. It is confirmed that the present numerical simulation has practically enough accuracy for the evaluation of the OPE to optimize the oxygen plasma sterilization devices.
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  • Satoyuki KAWANO, Youhei MARUYAMA
    2005 Volume 48 Issue 3 Pages 456-463
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    In this work, the charge transport in deoxyribonucleic acid (DNA) is theoretically analyzed. We develop an novel mathematical model based on the polaron model by Komineas et al. We improve the model for considering the effect of bulk temperature. In order to conserve the norm of the wavefunction, the numerical code based on implicit Successive Over Relaxation (SOR) scheme is developed for solving time-dependent Schrödinger equation. The equations of motions of DNA base pairs and the bulk molecules are also efficiently solved simultaneously. It is found that the mean velocity of the polaron in DNA becomes faster as bulk temperature. Futhermore, detailed systematical study for various parameters in the model is made by the use of the code developed here. Consequently, we can accumulate the basic understanding of charge transport phenomena in DNA.
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  • Seiichi SUDO, Yuji TAKAKI, Yasunari HASHIGUCHI, Hideya NISHIYAMA
    2005 Volume 48 Issue 3 Pages 464-470
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    This paper is concerned with the development of micro magnetic fluid devices for driving micro machines. Two kinds of new magnetic fluid devices are proposed. One is the magnetic fluid motor, and another one is reciprocating actuator. These micro devices are composed of a permanent NdFeB magnet and kerosene-based magnetic fluid HC-50. They are characterized by wireless operation with alternating magnetic field. The driving characteristics of micro magnetic fluid devices are examined by using a digital high speed video camera system. The rotary motion of the micro magnetic fluid motor shows the existence of rotational regions and irrotational regions in frequencies of external magnetic field. The amplitude of reciprocating actuator depends on the frequency of magnetic field. The effect of the volume of magnetic fluid adsorbed to the permanent magnet is also revealed experimentally.
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  • Masaaki MOTOZAWA, Yoshiyuki MATSUMOTO, Tatsuo SAWADA
    2005 Volume 48 Issue 3 Pages 471-477
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Experimental results for the properties of ultrasonic propagation velocity in kerosene-based and water-based magnetic fluids are reported. Ultrasonic wave frequencies of 1MHz, 2MHz and 4MHz are used and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0mT to 550mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. The ultrasonic propagation velocity in magnetic fluids is dependent on temperature, elapsed time of applying the magnetic field, and magnetic field intensity. Hysteresis and anisotropy of ultrasonic propagation velocity are observed. These interesting results seem to be related to chain-like cluster formation in the magnetic fluids and the characteristic period of Brownian motion of the magnetic particles.
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  • Jun ISHIMOTO, Shinichi KAMIYAMA
    2005 Volume 48 Issue 3 Pages 478-487
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    The fundamental multiphase flow characteristics of the two-dimensional cavitating flow of magnetic fluid in a vertical venturi channel under a strong nonuniform magnetic field are numerically predicted to realize the further development and high performance of the new type of a two-phase fluid driving system using magnetic fluids. First, the governing equations of the cavitating flow of a hexane-based magnetic fluids based on the unsteady thermal nonequilibrium two-fluid model are presented and several two-phase flow characteristics are numerically calculated taking into account the effect of the strong nonuniform magnetic field. Based on the numerical results, the two-dimensional structure of the cavitating flow and cloud cavity formation of the magnetic fluid through a vertical venturi channel are shown in detail. The numerical results demonstrate that effective two-phase magnetic driving force and fluid acceleration at the venturi channel are obtained by the practical use of the magnetization of the working fluid. Also clarified is the precise control of the cavitating flow of magnetic fluid that is possible by effective use of the magnetic body force which acts on cavitation bubbles.
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  • Yasushi IDO
    2005 Volume 48 Issue 3 Pages 488-493
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    A complete set of basic equations for magnetic fluids with internal rotation is proposed in this paper. The basic equations are derived from the conservation laws of mass, linear momentum, angular momentum and energy, while the constitutive equations are obtained by the thermodynamical method that is based on the free energy and the dissipation function. The concrete expression of constitutive equations are determined by the principle of material frame indifference and the principle of maximal dissipation rate. The Abraham expression of the electromagnetic momentum and E-Banalogy are adopted in this theory. It is shown that the difference in the basic equations in case of adopting the Abraham expression and the Minkowski expression, respectively. The constitutive equation of magnetization which includes the Shliomis relaxation equation (1972) is proposed.
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  • Masami NAKANO, Akira SATOU, Yoshitake SUGAMATA, Hideya NISHIYAMA
    2005 Volume 48 Issue 3 Pages 494-500
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    The transient shear stress variation and the flow patterns of an MR fluid have been investigated simultaneously under constant shear rate and relatively weak magnetic field using a parallel disk rotary rheometer. The effects of magnetic field, shear rate and gap height on the induced shear stress and the flow behavior of the MR fluid were evaluated. The behavior of shear stress changes remarkably and various flow patterns (cracks in packed MR fluid structure, grain-like particle’s agglomeration, line of grains, etc.) with MR fluid leakage out of the gap can be observed, depending on these parameters. The amount of the MR fluid leakage due to the centrifugal force also depends on these parameters. Both the evolution of pattern and the leakage of MR fluid might be responsible for the transient variation of shear stress.
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  • Hokuto HAKOGI, Motoyoshi OHABA, Naimu KURAMOCHI, Hidenori YANO
    2005 Volume 48 Issue 3 Pages 501-507
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    A new robot that makes use of MR-fluid clutches for simulating torque is proposed to provide an appropriate device for training physical therapy students in knee-joint rehabilitation. The feeling of torque provided by the robot is expected to correspond to the torque performance obtained by physical therapy experts in a clinical setting. The torque required for knee-joint rehabilitation, which is a function of the rotational angle and the rotational angular velocity of a knee movement, is modeled using a mechanical system composed of typical spring-mass-damper elements. The robot consists of two MR-fluid clutches, two induction motors, and a feedback control system. In the torque experiments, output torque is controlled using the spring and damper coefficients separately. The values of these coefficients are determined experimentally. The experimental results show that the robot would be suitable for training physical therapy students to experience similar torque feelings as needed in a clinical situation.
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  • Tsutomu ANDO, Kazuyuki UENO, Keisuke SAWADA
    2005 Volume 48 Issue 3 Pages 508-516
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Numerical simulation at the same condition as an experiment is carried out under the magnetic Stokes approximation for small shielding parameter. Results of the simulation compensate for the information of molten metal flow that we could not directly obtain in the experiment. In this paper, we study the molten metal flow at a starting condition and quasi-steady state. Besides, the energy conversion in the MHD pump is discussed. The simulation result shows that the proposed MHD pump causes the spiral induced current in a molten gallium and produces an axial flow with swirl. At quasi-steady state, it is confirmed that the centrifugal force by the excessive swirl flow produces high pressure at a duct wall and low pressure around the central axis. Since the excessive swirl flow results in large viscous dissipation, the mechanical power output of the pump uses only about 1% of the mechanical energy production in the molten gallium.
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  • Tetsuhiro TSUKIJI, Eitaro KOYABU, Tomohiro TSUJI, Shigeomi CHONO
    2005 Volume 48 Issue 3 Pages 517-523
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Two types of circular-pipe electrode are designed to control the pressure and flow rate of electrorheological(ER) fluids under the application of an electric field. The shape of the electrode is a circular pipe and some parts of the inner surface of the pipe are made of electrode strips. A liquid crystal mixture is selected as a homogeneous ER fluid and the pressure drop in the circular-pipe electrode is measured at constant flow rates. On the other hand, numerical analysis of the electric field and the fluid flow in the circular-pipe electrode is conducted. It is assumed that the viscosity, which depends on the electric field intensity, is distributed in the flow fields. The relationships between the flow rate and the pressure are simulated numerically for various electric field intensities, which agree with experimental results. The difference in the ER effect between the two types of electrodes is discussed on the basis of the distributions of the electric field intensity and the pressure drop. Furthermore, the influence of both the number of electrode strips and the gaps between electrode strips in the pipe on the flow rate vs. pressure characteristics is investigated numerically, and a comparison of the flow characteristics between the present electrodes and two types of parallel-plate electrodes is conducted.
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  • Takatsune NARUMI, Howard SEE, Yasuhiro YAMAGUCHI, Tomiichi HASEGAWA
    2005 Volume 48 Issue 3 Pages 524-531
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    We have investigated the electro-rheological (ER) properties of liquid crystals in an oscillatory squeezing flow. A Micro Fourier Rheometer was utilized to estimate the complex viscosity and phase shift. A clear dip in the phase angle was observed, centred around a frequency which increased with electric field strength. It was found that this critical frequency was proportional to the inverse of the response time required for the liquid crystal molecules to align under the electric field. Similar ER effects to those observed under steady shearing were obtained in the oscillatory flow, but the ER effect at high frequency is smaller than that under no electric field. In other words, a negative ER effect was obtained under low electric fields. A rheological model for the dynamic response was obtained through the control theory and the transfer function thus derived will be useful for estimating the output response in a flow or motion control system.
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  • Satoru YAMAMOTO, Masayuki TORATANI, Yasuhiro SASAO
    2005 Volume 48 Issue 3 Pages 532-539
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    A numerical method for simulating near-critical carbon-dioxide flows in a micro-channel is presented. This method is based on the preconditioning method applied to the compressible Navier-Stokes equations. The Peng-Robinson equation of state is introduced to evaluate the properties of near-critical fluids. As numerical examples, Near-critical carbon-dioxide flows in a square cavity and in a micro-channel are calculated and the calculated results are compared with the experimental data and the theoretical results. Finally, we demonstrate that the compressibility dominates the near-critical carbon-dioxide flows in a micro-channel even if the flow is very slow and the Reynolds number is very low.
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  • Xin-Rong ZHANG, Hiroshi YAMAGUCHI, Katsumi FUJIMA, Masatoshi ENOMOTO, ...
    2005 Volume 48 Issue 3 Pages 540-547
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    An experiment study was carried out in order to investigate feasibility of CO2-based Rankine cycle powered by solar energy. The proposed cycle is to achieve a cogeneration of heat and power, which consists of evacuated solar tube collectors, power generating turbine, heat recovery system, and feed pump. The Rankine cycle of the system utilizes solar collectors to convert CO2 into high-temperature supercritical state, used to drive a turbine and produce electrical power. The cycle also recovers thermal energy, which can be used for absorption refrigerator, air conditioning, hot water supply so on for a building. A set of experimental set-up was constructed to investigate the performance of the CO2-based Rankine cycle. The results show the cycle can achieve production of heat and power with reasonable thermodynamics efficiency and has a great potential of the application of the CO2-based Rankine cycle powered by solar energy. In addition, some research interests related to the present study will also be discussed in this paper.
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  • Satoyuki KAWANO, Futoshi NISHIMURA
    2005 Volume 48 Issue 3 Pages 548-554
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    By improving our previous mathematical model for discharge, we developed a simple model of charge characteristics for lithium ion batteries. Through numerical analysis, stable solutions can be obtained for various parameters and operated conditions. From these results, we accumulate understanding of transport phenomena during the charge. Furthermore, a detailed comparison of numerical and experimental results in a commercial battery for PC can be made. Those results concur reasonably well from the viewpoint of engineering applications. Consequently, we confirmed the validity of the simple model proposed here and the numerical method for coupling the equation of transport phenomena with the Poisson equation.
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  • Mehrzad SHAMS, Mojtaba Mosavi NAEEINIAN, Goodarz AHMADI
    2005 Volume 48 Issue 3 Pages 555-561
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Dispersion of inextensible flexible fibers in a simulated isotropic pseudo- turbulent flow field is studied. Turbulence fluctuation velocities are simulated by the Kraichnan Gaussian random field model. Fibers are assumed to be inextensible but completely flexible. That is, fibers have no stiffness and offer no resistance to bending. In the simulation, a flexible fiber is divided into many segments. Interactions of each element with the adjacent elements are through axial forces that are evaluated as part of the solution. For different fiber diameters, aspect ratios, and initial configurations, deposition velocities are evaluated, and the fiber dispersion is analyzed. An empirical equation for the deposition velocity of flexible fibers is also developed. The results for flexible fiber deposition rate are compared with those for rigid straight fibers and the empirical equation predictions.
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PAPERS
  • Shin Hyung RHEE, Shitalkumar JOSHI
    2005 Volume 48 Issue 3 Pages 562-570
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Results of computational fluid dynamics validation for flow around a marine propeller are presented. Computations were performed for various advance ratios following experimental conditions. The objectives of the study are to propose and verify a hybrid mesh generation strategy and to validate computational results against experimental data with advanced computational fluid dynamics tools. Computational results for both global and local flow quantities are discussed and compared with experimental data. The predicted thrust and torque are in good agreement with the measured values. The limiting streamlines on and the pathlines off the propeller blade as well as the pressure distribution on the blade surface reproduce the physics of highly skewed marine propeller flow with tip vortex very well. The circumferentially averaged velocity components compare well with the measured values, while the velocity magnitude and turbulence kinetic energy in the highly concentrated tip vortex region are under-predicted. The overall results suggest that the present approach is practicable for actual propeller design procedures.
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  • Kenji YAMAMOTO, Masayuki TANIGUCHI, Hironobu KOBAYASHI, Taro SAKATA, K ...
    2005 Volume 48 Issue 3 Pages 571-578
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Applicability of a coal combustion model was validated by comparing its predictions with experimental data of utility boilers. The coal combustion model had gasification and NOx reaction submodels and it was developed by using a small drop-tube-furnace (coal feed rate 0.6kg/h). A turbulence combustion simulation program was developed by introducing the coal combustion model. The program was validated by comparing its predictions with 23 sets of experimental results which contained different plant, load and coal data. The temperature difference between simulated and experimental results was within 30°C at the furnace exit. The decreasing characteristic of coal burnout with increasing load was well predicted. The NOx emission difference between simulated and experimental results was less than 15%. The coal combustion model was judged applicable to utility boilers.
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  • Eitaro KOYABU, Ken-ichi FUNAZAKI, Manabu KIMURA
    2005 Volume 48 Issue 3 Pages 579-588
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    This study investigates wake-induced bypass transition of boundary layers on a flat plate which is subjected to favorable and adverse pressure gradients. Inlet free-stream turbulence level is controlled with a turbulence grid. Detailed boundary layer measurements are executed by use of a single hot-wire probe. The main focus of this paper is on how and to what extent the wake-induced bypass transition of a flatplate boundary layer can be affected by favorable - adverse pressure gradient as well as enhanced turbulence intensity. A spoked-wheel-type wake generator creates periodic wakes in front of the flat plate. Two types of the wakes are generated by altering the direction of the movement of the wake-generating bars. Instantaneous velocity signals successfully reveal the flow events associated with the wake passage happening inside the boundary layer, such as the emergence of turbulent spots and calmed regions behind them. Noticeable differences in the transitional behavior due to the wake passage also appear between these two types of the wakes.
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  • Masaya OHTSUKA, Shohei YOSHIDA, Shin’ichi INAGE, Nariyoshi KOBAY ...
    2005 Volume 48 Issue 3 Pages 589-596
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    A new analytical time lag flame model based on Bloxidge’s flame model was introduced, which calculates the combustion oscillation of premixed flame to take into account the distribution of heat release rate and flame speed that was calculated by analytical formulas dependent on pressure, temperature, fuel-to-air ratio and velocity. The transfer matrix technique using the new flame model was applied to the calculation of acoustic resonance characteristics. To verify the model, combustion oscillation experiments were performed for methane-air premixed flames stabilized by a swirl burner at elevated pressures in a range of 0.6-0.9MPa. The fluctuating pressure had a maximum peak at a specific value of f, where f is the resonance frequency and τf is the passing time of premixed gas through the flame zone. The analytical model could simulate the dependency of the fluctuating pressure local peak on the fuel-to-air ratio and the static pressure.
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  • Seok-woo KIM, Yasuo MORIYOSHI
    2005 Volume 48 Issue 3 Pages 597-602
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    The authors have performed experiments on compression-ignition (CI) for a single-cylinder Schnurle-type two-stroke gasoline direct injection (DI) engine which employs a variable exhaust port, area, and deduced two presumptions from the experimental results. Firstly, the spatial distributions of fuel concentration and in-cylinder gas temperature are indispensable to enable CI operation under stratified charge conditions, because CI operation is not possible in a DI system although the necessary conditions of the scavenging efficiency and the in-cylinder gas temperature for the initiation of CI in homogeneous charge conditions are satisfied. Secondly, it is possible that flame propagation occurs in stratified charge CI conditions, because the combustion period in the later stage after 80% mass burned becomes longer than that with homogeneous charge CI combustion. In this report, in order to verify the above two presumptions deduced from experiments, the gas exchange process and mixture formation process were numerically analyzed, and the initiation conditions of CI were estimated using a CHEMKIN application. As a result, in case of CI with a late injection timing in DI system, it was found that CI was possible because high temperature but no fuel region and low temperature but rich fuel region exist in the cylinder due to inhomogeneous spatial distributions of fuel and temperature. Also, in case of CI with a late injection timing, the flame propagation was possible in the low-temperature and diluted rich region. Thereby, the two presumptions deduced from the experimental results were validated from the numerical analysis results.
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  • Yasuhiro OGAMI, Hideaki KOBAYASHI
    2005 Volume 48 Issue 3 Pages 603-609
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    Experimental and numerical studies on laminar burning velocities of stoichiometric CH4/air flames were performed at high pressure and high temperature. A stoichiometric CH4/air mixture was diluted by helium in order to restrain the intrinsic flame instabilities occurring at high pressure. Measurements of laminar burning velocity for burner-stabilized flames were conducted by a technique employing particle tracking velocimetry (PTV) and planar laser induced fluorescence for OH radical (OH-PLIF) simultaneously, which measures the instantaneous local burning velocity. Laminar burning velocities were determined by the average values of local burning velocities in the region where the Karlovitz number are sufficiently small, meaning that the effect of flame stretch and curvature can be neglected. Numerical simulations were also conducted using a one-dimensional premixed flame code. Detailed reaction mechanisms and the 4-step reduced mechanism were examined, and their results were compared with experimental results to investigate the feasibility of predicting the flame characteristics at high pressure and high temperature, based on the reaction mechanisms.
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  • Takahisa YAMAMOTO, Koshi MITACHI, Takashi SUZUKI
    2005 Volume 48 Issue 3 Pages 610-617
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    The Molten Salt Reactor (MSR) is a thermal neutron reactor with graphite moderation and operates on the thorium-uranium fuel cycle. The feature of the MSR is that fuel salt flows inside the reactor during the nuclear fission reaction. In the previous study, the authors developed numerical model with which to simulate the effects of fuel salt flow on the reactor characteristics. In this study, we apply the model to the steady-state analysis of a small MSR system and estimate the effects of fuel flow. The model consists of two-group neutron diffusion equations for fast and thermal neutron fluxes, transport equations for six-group delayed neutron precursors and energy conservation equations for fuel salt and the graphite moderator. The following results are obtained: (1) in the rated operation condition, the peaks of the neutron fluxes slightly move toward the bottom from the center of the reactor and the delayed neutron precursors are significantly carried by the fuel salt flow, and (2) the extension of residence time in the external-loop system and the rise of the fuel inflow temperature show weak negative reactivity effects, which decrease the neutron multiplication factor of the small MSR system.
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  • Chi-Kyung KIM
    2005 Volume 48 Issue 3 Pages 618-623
    Published: 2005
    Released: February 15, 2006
    JOURNALS FREE ACCESS
    The primary objective of this study is to develop a space-time finite element formulation of heat transfer involving a moving heat source so that small time steps can be used in area of large time rates of change of temperature. The weighted residual process will be used to formulate a finite element method in a space and time domain based upon the continuous Galerkin method. A mesh refinement algorithm which will be on adaptively controlling the time step is developed and implemented for one-dimensional moving heat source simulation. A moving heat source will produce steep gradients of the temperature within and near the region of moving source. The space-time domain is divided into time-slabs and the mesh generator produces a triangular mesh that has small elements close to the front of moving source and relatively large elements away from the front. A series solution to the moving heat source problem derived will be used to compare to the numeric results obtained from the adaptive refinement technique developed in this study.
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