Transactions of the Japan Society of Mechanical Engineers Series B
Online ISSN : 1884-8346
Print ISSN : 0387-5016
Volume 76, Issue 771
Displaying 1-40 of 40 articles from this issue
  • Atsushi SAKURAI, Koji MATSUBARA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1681-1684
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Radiative Properties of high temperature water vapor play an important role for radiative heat transfer analysis in combustion engineering, fire safety science, etc. Absorption spectrum of visible to infrared light inherently depends on the wavelength of electromagnetic waves. Ignoring the spectral dependence makes radiative heat transfer analyses wrong results. To overcome the problem, various nongray gas models have been proposed. However, there are a few studies for summarizing these characteristics in prediction. The goal of this study is to give valuable information for engineering applications. In the present study, radiative properties and simulation characteristics of high-temperature water vapor using the Planck-mean approximation, the statistical narrow band model, and the full-spectrum k-distribution model are assessed rigorously by comparing with the Line-by-Line method. The recent HITRAN/HITEMP databases are employed to calculate Line-by-Line spectrum.
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  • Toru TAKAHASHI, Eiichi KODA, Yoshinobu NAKAO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1685-1692
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    It is necessary to maintain or improve the thermal efficiency in actual thermal power generation plants to reduce CO_2 emission and energy consumption. And also it is important to decrease the maintenance cost in commercial plants. Thus, when the thermal efficiency decreases, it is crucials to identify the performance deterioration factors and solve the problems promptly by sufficient energy management. However, it is difficult to understand the internal state of the plants sufficiently and to determine performance deterioration factors only from operation data because actual thermal power generation plants are composed of many components and they are very complex systems. Therefore, we develop a method based on heat and mass balance analysis to calculate the immeasurable quantity of state and the component performance in the plants, and to correct the component performance to standard state using the performence function obtained from long-term operation data. Through the method, the analysis of the influence of deterioration factors on thermal efficiency becomes possible. As the results, we can determine the main factor that affects thermal efficiency deterioration using this method.
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  • Takashi KUROISHI, Takuji FUJIKAWA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1693-1702
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    New steam temperature control logic for supercritical once thru boilers was developed from the view point of simplicity similar to the conventional sub-critical drum type boilers. Water wall outlet steam temperature can be controlled more easily due to larger specific heat capacity of steam than superheater outlet steam temperature. Dividing temperature control into two parts, one at water wall outlet by fuel flow and another at superheater outlet by spray water flow, boiler steam temperature control was much improved. This paper introduces results of analysis on the characteristics of the new steam temperature control system for supercritical once thru boilers.
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  • Hideaki NANRI, Naoki TANI, Hiroki KANNAN, Yoshiki YOSHIDA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1703-1711
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    We investigated the effect of a phase lag/lead of unsteady cavitation characteristics on cavitation surge using a one-dimensional analytical model and applying the acoustic effect of the inlet pipe. The phase lag/lead of cavitation compliance was found to strongly affect the instability of cavitation surge, even though that of the mass flow gain factor does not so. An actual liquid rocket propulsion system is usually equipping a POGO suppression device (PSD). We thus modified the analytical model to consider the effect of the PSD. The frequency of cavitation surge was found to basically become the Helmholtz frequency, defined by the cavitation compliance and the length of pipeline between the PSD and the turbopump. And when the frequency of cavitation surge matches one of the acoustic resonance frequency of inlet pipeline, the cavitation surge is strongly excited.
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  • Takahiro NISHIOKA, Toshio KANNO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1712-1719
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    The rotor-tip flow fields in a low-speed axial-flow fan were experimentally and numerically investigated to clarify the mechanism behind the modal stall inception. The interface between the incoming flow and the reversed tip-leakage flow does not become parallel to the leading edge plane, although backflow from the trailing edge initiates near the stall condition. The reversed tip-leakage flow does not spill from the leading edge at the stall condition. Moreover, the tip-leakage vortex breakdown does not occur near or at the stall condition. A threee-dimensional separation vortex is induced by secondary flow on the suction surface near the stall condition and develops at the stall condition. It is concluded from these results that the rotor-tip flow fields in the modal stall inception differ from those in the spike stall inception and that the three-dimensional separation vortex induced by the secondary flow influences the initiation of the modal disturbance.
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  • Toru SHIGEMITSU, Junichiro FUKUTOMI, Yuki OKABE, Kazuhiro IUCHI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1720-1726
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Small-sized axial fans are used as air cooler for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted although, it causes the deterioration of efficiency and the increase of noise. Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance. In the present paper, the performance curves of the contra-rotating small-sized axial fan with 100mm diameter are shown and the velocity distributions with the designed flow rate at the inlet and the outlet of each front and rear rotors are clarified with experimental results. Furthermore, the flow conditions between front and rear rotors of the contra-rotating small-sized axial fan are investigated by numerical analysis results and higher performance design of the contra-rotating small-sized axial fan are discussed.
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  • Nobuyuki YAMAGUCHI, Masayuki OGATA, Shinki TANAKA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1727-1735
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Radial-vaned air separators show a strong stall improvement effect in axial flow fans. Changes in the fan internal flow patterns achieved by the device have been made clear by Pitot-traversing mesurements. With a decrease in the fan flow rate the meridional streamline inclinations through the rotor blades have become more and more abrupt together with the circumferential velocities enlarged in the region, in contrast to relatively insensitive behavior tendency of the streamlines and flow patterns in the solid-wall condition. The stall suppression are suggested to have been achieved by the followings air separator effects; (1) suction of inflow casing boundary layers and elimination of embryos of stall, (2) separation of reversed flow from the main flow, (3) induction of the flow toward the casing wall and strengthening of stream-surface inclination, and (4) reinforcement of axi-symmetric flow structure. Combination of them appears to have caused the great stall suppression effect that would have been impossible by other types of stall prevention devices.
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  • Yoshihito YASUKAWA, Motoyuki ABE, Tohru ISHIKAWA, Yasuo NAMAIZAWA, Mas ...
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1736-1741
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Reducing exhaust emissions and improving fuel economy of gasoline engines have been very important for global environment. For exhaust emissions reduction, we developed boundless injector by separating moving part into two parts to minimize coarse droplets due to valve bounce at closing. For better fuel economy, reduction in minimum injection quantity decreases fuel consumption. Pulse width controls injection quantity, so quick response fuel injector enables reducing minimum injection quantity. Valve closing delay time is dominant for injection period compared to valve opening time, so minimum injection quantity depends on the closing delay time. Injector needs to reduce the closing delay time for decreasing the minimum injection quantity. We listed two factors (electromagnetism and kinematics delay). For quick response of the magnetic circuit, injector needs big magnetic force at low current. The diameter of magnetic suction area is extended and is shorten the magnetic circuit. For quick response of moving parts, injector needs to decrease the hydraulic resistance of moving parts. So we improved the anchor shape. Consequently we developed the quick response fuel injector.
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  • Nobuhiko KAMAGATA, Akitoshi MATSUI, Koichi HISHIDA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1742-1749
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Active flow control, which can adapt to variable cross flow direction, is an effective technique to achieve drag reduction. The present study has investigated the effect of flap actuators to the blunt body and established a drag reduction control system for variation of cross flow direction. Numerical simulations were performed in order to obtain the optimal flap positions for drag reduction. A three force components transducer was introduced to measure drag force in order to investigate optimal flap angle to the flow direction. And flow structure around the body was examined using PIV (Particle Image Velocimetry). In this drag reduction system, flap actuators were controlled to the optical angle by detection of flow direction by investigation of non-separating flow, using pressure transducers as sensors. The flap actuators at the leading edge of the body promoted separated shear layer to approach to the body and lead to drag reduction at the optimal flap angle. Drag reduction rate is up to about 30%. This drag reduction control system adapted to variable cross flow direction raging from 0 to 40deg. and reacted for drag reduction in 0.1s.
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  • Tomotake SAITOU, Taku NAGASAWA, Fumihiko MIKAMI, Nobuhide NISHIKAWA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1750-1760
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    In the present study, flow structure behind a sphere falling through aqueous solutions of CTAB/NaSal are examined using a dye visualization and a PIV. Visualized dye patterns indicate that aqueous solutions of CTAB/NaSal forms multi layered structure behind a falling sphere. At relatively low salt concentrations, it is observed that the dye detaches from a sphere with its end moving upward where the velocity of fluid in the wake is in the opposite direction to the sphere sedimentation. On the other hand, at relatively high salt concentrations, these phenomena are not observed. At the moment of sudden acceleration of the sphere during sedimentation, the dye string behind the sphere contracts rapidly, accompanied by the rapid increase of upward velocity of flow behind the sphere inducing strong flow of the ambient fluid.
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  • Haruki OBARA, Masaki TATEOKA, Mariko HONDA, Akinori KOYAMA, Tohru SASA ...
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1761-1766
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    In this report, we propose equations, named relaxation equations, to treat multiphase viscous flow for the smoothed particle hydrodynamics (SPH) method, suited to suppress the numerical disorder around the interface of two different fluids. They are possible to be applied for particles across the interface between different fluids to evaluate stress and acceleration of the particles, and make it possible to analyze the flow explicitly without separating the flow in each fluid. Errors of these equations are discussed and numerical simulations are carried out for the water-kerosene two-phase Poieuille flow between two plates to confirm the effects of these equations.
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  • Masaki TATEOKA, Haruki OBARA, Tohru SASAKI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1767-1772
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    The relaxation equations for smoothed particle hydrodynamics (SPH) are able to suppress the numerical disorder around the interface of different fluids. It makes it possible to treat inviscid multi phase flow without separating it in each fluid, but the error of them is not small enough. In this paper, the error of relaxation equations is discussed for the case of same size particles and the case of different size particles composed of different fluids. Formulas to suppress the numerical error around the interface of multi phase flow are proposed, and methods to determine the smoothing length are discussed. Numerical simulations are carried out for air-water 2-phase flow to know the effects of these equations and methods. Results show that the method to determine the smoothing length is the most important to suppress the numerical disorder around the interface of multi phase flow.
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  • Koji FUKUDOME, Oaki IIDA, Yasutaka NAGANO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1773-1778
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    The direct numerical simulation (DNS) with a spectral method is performed to study the large-scale structure in relaminarizing channel flow at low Reynolds number. The flow structure coined as turbulent-laminar pattern simultaneously contains the quasi-laminar and turbulent regions, outlines of which are maintained over time. In the quasi-laminar region, streamwise vortical structure almost disappears though weak streamwise vorticity is arrayed regularly around the channel center. Moreover, very long streak structure appears in the quasi-laminar region. In the turbulent region, however, many quasi-streamwise vortices are clustered around the curved streak structure. The criterion is defined to quantitatively distinguish these regions by using streamwise vorticity, and the turbulent energy budget is calculated over each region. As a result, it is found that quasi-laminar and turbulent regions simultaneously interact with each other; in the region away from the wall, there is the inrush of high-speed fluid toward the turbulent region, while in the near-wall region, low- and high-speed streaks are swept to quasi-laminar region. It is also found that the turbulent-laminar pattern is sustained by the energy transfer between two regions and the generation of the flow along the turbulent region.
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  • Tsubasa OHSHIMA, Hirotoshi YANAGI, Hiroyuki OHTSUKA, Koji MORINISHI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1779-1784
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Condensation heat transfer in condenser is strongly affected by non-condensable gas. To establish the computational model of non-condensable gas bahavior in condenser, numerical simulation of gas/gas two-phase flow (vapor/non-condensable gas) was carried out. In this model, the changes of mass and momentum by condensation were considered and condensation heat transfer coefficient was affected by local density of non-condensable gas. The results obtained from the proposed model showed quantitative agreement in stagnation region and behavior of non-condensable gas. Decreasing rate of mean heat transfer coefficient by non-condensable gas was enlarged with increasing of condensate rate of vapor. Coincidentally, the comparative effect of natural convection in vent tube was enlarged in an exponential manner. It means dischaege of non-condensable gas from condenser is affected by natural convection and forced convection.
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  • Yoshiyuki TAGAWA, Ami FUNAKUBO, Shu TAKAGI, Yoichiro MATSUMOTO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1785-1792
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    To investigate surfactant effects on path instability of a single bubble, measurements of 3D trajectories, velocities, and aspect rations are carried out with a tank of 1.0m height filled with super purified water and a small amount of surfactant using two high-speed digital cameras. The experimental parameter is the concentration of 1-Pentanol (surfactant) which controls surface slip conditions of the bubble from free-slip to no-slip. The bubble size of 2.0±0.1mm is chosen to avoid shape oscillations. Our results of 3D motions in free-slip, no-slip and intermediate slip conditions agree with previous results. When bubble rise velocity is decided by slip condition, the trajectory is also decided. It indicates that the slip condition decides not only the drag force but also the wake structure. The maximum amplitude of the horizontal projection of the spiral motion is 4.7 times as large as the minimum one and- corresponds not to the maximum rise velocity but to the maximum horizontal velocity. As a result of the comparison with simple models, the mechanism of the trajectory change by surfactant is explained by effects of drag force and the direction of motion affected by non-axisymmetric wake structure.
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  • Katsuji AKAMATSU, Michihisa TSUTAHARA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1793-1801
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Direct numerical simulation of compression wave produced when a high-speed train enters a tunnel, distortion of the compression wave front as it travels in the tunnel, radiation of micropressure wave from the tunnel exit are performed using the finite difference lattice Boltzmann method. The discrete Boltzmann equation for the 3D39Q thermal BGK model is solved in three-dimensional space using a second-order Runge-Kutta scheme in time and a third-order-upwind finite difference scheme in space. The arbitrary Lagrangian-Eulerian formulation (ALE) is applied to model the interaction of the moving train nose and the tunnel portal. Detailed numerical calculations were carried out for axisymmetric trains with the blockage of 0.2 and various nose profiles entering a long circular cylindrical tunnel with straight and stepwise flared portals. The predicted compression wave profiles are found to be in good agreement with linear theory predictions obtained from the analytic expression derived by Howe. It is shown that the distortion of the compression wave front is consistent with the time-domain computation of one-dimensional Burgers equation. Longer nose profiles and tunnel entrance with flared portals are confirmed not only to decrease the initial steepness of the compression wave front but also to counteract the effect of nonlinear steepening.
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  • Tetsuya KANAGAWA, Masao WATANABE, Takeru YANO, Shigeo FUJIKAWA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1802-1810
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Based on the unified theory by the present authors (T. Kanagawa, et al., J. Fluid Sci. Tech., 5, 2010), the Korteweg-de Vries-Burgers (KdVB) equation and the nonlinear Schrodinger (NLS) equation with an attenuation term for weakly nonlinear waves in bubbly liquids are re-derived from a system of bubble-liquid mixture model equations composed of the conservation equations of mass and momentum, the Keller equation for bubble dynamics, and supplementary equations. We show that the re-derived KdVB equation and NLS equation are essentially the same as those derived from a system of two-fluid model equations except for the coefficients of nonlinear, dissipation, and dispersion terms. The differences in these coefficients are studied in detail, and we find that for the case of KdVB equation, the mixture model is valid only for sufficiently small initial void fractions. On the other hand, for the case of NLS equation, the range of validity of the mixture model depends on not only the initial void fraction but also the wavenumber concerned.
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  • Tomonori WATANABE
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1811-1818
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    We have investigated the properties of the numerical method for a one-dimensional lattice model (Sakanishi model), which is associated with the material nonlinearity of the arterial vessel wall, in order to analyze the pulse wave propagation by the numerical method which keeps the physical properties intrinsically possessed by the system. As the numerical method for the analysis, we have focused on Cellular Automaton (CA) scheme which is derived from the integrable difference scheme by means of the ultra discrete limit. We have compared the CA scheme with the integrable difference scheme and the general-purpose methods such as Euler method and Leapfrog method on the efficiency of the calculation. The properties of the CA scheme for the Sakanishi model are shown. Especially, it is presented that the CA scheme can maintain a certain accuracy for the long time behavior of the pulse wave. Moreover, we find that the peaking and steepening can be observed by the CA scheme.
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  • Junya ONISHI, Masahide INAGAKI, Nariaki HORINOUCHI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1819-1830
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    A numerical method based on the sharp interface assumption is presented for simulating two-phase flows with phase change. In this method, the ghost fluid method is used to handle boundary conditions imposed at liquid-gas interfaces, including pressure jump conditions due to surface tension and velocity jump conditions due to phase change. Also, the ghost fluid method is applied to boundary conditions imposed at solid walls. A novel treatment for contact lines on solid surface with arbitrary shape is proposed. With these methods combined together, two-phase flows in arbitrary geometry can be simulated successfully. As a demonstration of the capability of the present method, numerical results of a Stefan problem of evapolation and two analyses related to single bubble behavior during nucleate boiling are described.
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  • Osamu TERASHIMA, Yasuhiko SAKAI, Yuichi SHOJI, Yuki KOJIMA, Kouji NAGA ...
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1831-1840
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    The new combined probe for the simultaneous measurement of instantaneous static pressure and two velocity components is developed. The probe consists of X-type hot-wire, and newly-devised static pressure probe. The pressure probe is miniaturized by using 0.1 inch microphone and MEMS fabrication technique for the improvement of spatial resolution and it is placed between two hot-wire sensors. The tip shape of the static pressure probe is hemispherical like the pitot tube also for the miniaturization of the combined probe. The spatial arrangement of pressure probe and X-wires in the new combined probe is determined carefully so that there is no interference in the velocity and pressure statistics measured by each sensor. The simultaneous measurement of instantaneous two velocity components and static pressure is carried out in the two-dimensional turbulent jet by this new combined probe. The results show that the distributions of mean streamwise velocity U and fluctuating velocity u, v and pressure p are consistent with the previous work. Furthermore, the turbulent energy budget is estimated. It is shown that the integral value of diffusion term (that should be equal to zero in theory) is closer to zero than the previously reported result by the measuring of diffusion rate <vw^2>^^^- in the diffusion term.
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  • Dan ZHANG, Osami KITOH, Tatsuo USHIJIMA, Yoshihiro IWAMOTO, Daisuke HI ...
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1841-1848
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Based on diffuse double layer model, the definition of the interface current that flows in an electric double layer (EDL) is given and formulated. To meet the requirement that the experimentally measured interface current assuming that the EDL thickness being extremely thin coincides with the definition, a correction factor is introduced to compensate its simple assumption. The relationship between the interface current and the electroosmotic velocity is also given. Using the experimentally measured interface current and electroosmotic velocity, the effective temperature rise in EDL due to the joule heating by the interface current was estimated and the effect of the interface current on EDL was discussed.
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  • Shigeomi CHONO, Tomohiro TSUJI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1849-1854
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    For the purpose of developing liquid crystalline microactuators, we have performed experiments to drive a plate which is movable in its planar direction, by applying an electric field to a liquid crystal confined with two parallel plates. We have succeeded in moving the upper plate of an experimental cell continuously by applying a square-wave electric field. With the increase in the frequency of the electric field, the speed of the upper plate increases abruptly, reaches the maximum value, and decreases gradually. The maximum value is 120μm/s at the frequency of 175Hz when the applied voltage is 10V, the duty ratio is 5%, and the cell gap is 10μm. This frequency is considerably high compared to the response characteristics of the liquid crystal used in this experiment. It is supposed from the fact that the molecules do not return to the initial posture when the electric field is released. The effects of the applied voltage, the duty ratio and the cell gap on the speed of the upper plate have been studied and an interesting result is that the speed of the upper plate does not monotonically increase with the applied voltage but reaches a constant value.
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  • Kiyoshi OTANI, Ryouhei YAMAMOTO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1855-1861
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    This paper describes a detailed study on effects of both cavity and orifice height on flow field governing a single synthetic jet in a quiescent air. The synthetic jet, known as a zero net mass-flux jet, is generated by a vibrating diaphragm to oscillate flow through a small orifice. The tested synthetic jet actuator consists of the orifice with the rectangular slot and cavity installed the PZT disk of 31.2mm diameter. The orifice height is chosen from 0.5, 1.0, 2.0 and 4.0mm, and the cavity height from 0.5 to 8.9mm, respectively. The test is conducted in variable input voltages and frequencies to PZT disk. With both the displacement of PZT disk on sinusoidal voltages and jet velocities above the orifice, the synthetic jet depends on not only oscillation of the PZT disk but sound pressure in the actuator. The simple lumped elements modeling is tested for the various cavity and orifice height, which does not require the iterative calculation on 1 degree forced oscillating. The analytical and experimental results are in good agreement on the maximum synthetic jet velocities for the orifice height of 0.5, 1.0 and 2.0mm in the cavity height higher than 0.75mm. The actuator with the cavity height of 2.5mm gives the maximum synthetic jet velocities to a high level, optimizing actuator size have to be considered the effect of both the cavity and orifice height for a micro synthetic jet actuator.
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  • Naoki ONO, Hirotaka FUKUSHIMA, Yusuke INUI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1862-1869
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Microbes can move smoothly in water environment with high efficiency, which could offer innovative ideas for micro hydro machines in future. In this study, we investigated the spiral movement of flagellum by using numerical and exerimental models. We simulated a microbe's fluid environment of Re number of 10^<-4>. The model study revealed that the maximum values of driving force and fluid velocity appeared depending on the model's roll number and spiral diameter. The occurrence of the maximum was explained by the two competing factors, which were the increase in longitudinal velocity and the decrease of spiral wave velocity as the roll number increased.
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  • Hajime NAKAMURA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1870-1878
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    Spatio-temporal distribution of convective heat transfer behind a backward-facing step was measured in order to explore the mechanisms of the heat transfer caused by flow separation and reattachment. This measurement was achieved using a high-speed infrared thermograph that recorded temperature fluctuations on a thin foil heated electrically. The attenuation resulting from both the thermal inertia and lateral conduction of the test surface was restored by solving heat conduction equations inside the surface. As a result, it was clarified that the heat transfer enhancement in the flow reattaching region had a spot-like characteristics. Each spot spread with time and overlapped with others to form a complex feature in terms of spatio-temporal characteristics of the heat transfer. The typical spanwise wavelength of this structure was approximately 1.2 times the step height for Reynolds number of 2000&le;Re_H&le;5500, regardless of the step height. The typical frequency of the fluctuation in the reattaching region was St=0.04-0.08, although there was no clear periodicity. This fluctuation is likely to be related to the low-frequency unsteadiness reported in previously published literature.
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  • Daisuke NAGAI, Koji MIYAZAKI, Hiroshi TSUKAMOTO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1879-1883
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    We investigate heat conduction of silicon nano-porous structures by molecular-dynamics simulations (MDs). We calculated the phonon dispersion curves of the nano-structured Si to understand the effects of nano-structures on phonon properties, such as phonon group velocity and phonon density of states. The dispersion curves were calculated from MDs results by using the 2D time-space Fourier transformation. Frequency gaps in phonon dispersion curves reduce the phonon group velocity in the periodic nano-porous structures. Moreover the group velocity of phonon is reduced due to new phonon modes even though the nano-porous was random. The results show that nano-porous structures reduce the thermal conductivity as well as superlattices.
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  • Takashi FUKUE, Masaru ISHIZUKA, Shinji NAKAGAWA, Tomoyuki HATAKEYAMA, ...
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1884-1892
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    This paper describes air cooling performance for electronic circuit boards set in the thin enclosure, where cooling air flow pass is very narrowed by many mounted devices. Especially, we focused on the effects of various heat dissipation values from chips and the space on the board. To discuss the cooling performance in the thin enclosure, we designed a test enclosure model which is composed of a model cardboard including 5 heat sources and a narrow heatsink duct and inspected a temperature rise of the model board and heat sources. From the result, it is found that we obtained a similar cooling performance regardless of different heat dissipation values and heat dissipation locations. This is caused by the high thermal conductivity electronic boards and a heatsink on the board to dissipate the heat, even with narrow cooling flow pass on the board. On the other hand, natural convection and radiation from the enclosure also have an important effect to heat release in the high-density packaging device. However, by the effect of forced convection cooling, temperature rise of components is decreased of 20℃ as compared to the result without air flow. Therefore, local forced convection by the narrow duct is effective for the heat release from the high-packaging density device.
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  • Yoshihisa SATO, Hiroki MORIMOTO, Kazuya YOSHIMINE, Tatsuya MATSUKAWA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1893-1900
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    The purpose of this research is to improve the rotation mechanism theory of the SMA engine. The main results obtained by this research are as follows. After having taken the bending moment (occurs when the SMA belt is pulled back) into consideration and having incorporated that into the rotation mechanism theory, we have stepped up to the next level of accuracy. According to our modified theory, we will be able to calculate the predicted values of rotation speed ω and output power P with higher accuracy. We designed and assembled a large-sized equipment which allowed us to measure the rotation speed and the torque simultaneously. We compared the experimental values of the output power with the theoretical values, and partially verified the validity of the theory. We obtained the maximum output power 3.74W.
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  • Atsushi TOKUNAGA, Gyoko NAGAYAMA, Takaharu TSURUTA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1901-1907
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Problem of the inverted temperature profile in condensation has been discussed at length in kinetic theory. The possible occurrence of the inverted temperature profile raised serious doubts about the validity of the previous theory, because the result seemed physically unreasonable. In this study, non-equilibrium molecular dynamics (NEMD) simulation with two facing surfaces of evaporation and condensation is carried out in order to obtain further evidence for the occurrence of the inverted temperature profile. Heat and mass transfer rates across the liquid-vapor interface during the condensation of argon are calculated for different non-equilibrium conditions given by changing the temperature of evaporating surface. From a view point of irreversible thermodynamics, the criteria for the inverted temperature profile are examined with the NEMD data and we have a conclusion that the inverted temperature profile may occur without contradiction to the second law of thermodynamics. In addition, we found that the molecular reflection at the condensing surface has an important role in the inverted temperature phenomenon. The reflected molecules do not accommodate with the condensing surface so that those molecules raise the temperature in the vicinity of the condensing surface under the non-equilibrium conditions.
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  • Shoji MORI, Lujie SHEN, Kunito OKUYAMA
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1908-1916
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    The critical heat flux (CHF) in saturated pool boiling of water was investigated experimentally on the heated surface with the attachment of honeycomb porous plates. In a previous study, the CHF was shown experimentally to be enhanced to more than twice that of a plain surface in the case of a honeycomb porous plate with a vapor escape channel of 1.4mm in width and 1.0mm in plate thickness. It was considered that the enhancement resulted from the capillary supply of liquid onto the heated surface and the release of generated vapor through the channels. In the present paper, the vapor escape channel width was varied in the range of 1.4mm to 7.9mm, which was smaller than the Taylor instability wavelength (approximately 15.6mm), and the effect of the channel width on the saturated pool boiling CHF of water has been investigated. The CHF values predicted by capillary limit models were compared with measured values. As a result, it became clear that the main mechanisms for CHF enhancement using a honeycomb porous plate were due to liquid supply to the heated surface as a result of not only capillary suction but also the inflow of liquid through vapor escape channels from the top surface.
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  • Yasuhiro RAI, Kazuya TATSUMI, Masashi KAWABE, Kazuyoshi NAKABE
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1917-1923
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    A compact tubular-typed fuel reformer was fabricated in this study, and was applied to produce hydrogen from methanol, focusing on the partial oxidation reaction (POR). The reformer was composed of a stainless steel pipe as the reactor exterior and ceramic honeycomb blocks inserted in two locations of the pipe. The upstream-side honeycomb blocks are expected to enhance the reforming stability and reaction efficiency by performing as an effective heat exchanger to the reactant gas. In addition, the downstream-side block acts as a heat regenerater which absorb the heat energy of the exhaust gas. The maximum hydrogen production was achieved in the condition of equivalence ratio, around 3.5, which is fuel rich condition of POR. The downstream-side honeycomb block enhanced the reforming efficiency by 8% at the maximum. This improvement was caused by the temperature rise at the reaction region due to the insertion of the downstream-side honeycomb block, while gas temperatures in the far-most downstream region became lower. These results indicate that the thermal energy possessed by the reforming gas was regenerated to the reaction region by the downstream-side honeycomb block.
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  • Takao KOSHIMIZU, Hiromi KUBOTA, Yasuyuki TAKATA, Takehiro ITO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1924-1931
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    A numerical analysis has been performed to clarify how heat pumping in a regenerator is generated in oscillatory flows and to investigate the effect of heat pumping on the phase difference between pressure and velocity. Pulse tube refrigerators of the 1st and 2nd generations are used as physical models in this study. In the 1st generation, the phase difference between pressure and velocity is nearly 90° and in the 2nd generation, nearly 0°. Transient one-dimensional equations of continuity, momentum and energy are solved utilizing a TVD scheme. It was found that heat pumping in a regenerator is shown by analyzing the fields of velocity and temperature of gas elements without thermoacoustic theory. It was also found that heat pumping in a regenerator is enhanced when the phase difference between pressure and velocity is nearly 0°.
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  • Tomohide YABUKI, Osamu NAKABEPPU
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1932-1941
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
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    This paper describes a novel approach method to the heat transfer mechanism beneath isolated bubble during nucleate boiling with MEMS (Micro-Electro-Mechanical Systems) sensors. Fast and local temperature variation beneath an isolated bubble measured with the MEMS sensor obviously showed the microlayer formation, evaporation, dry-out and rewetting phenomena. The heat transfer due to the bubble growth process was numerically evaluated by two-dimensional transient heat conduction simulation with the measured data as a boundary condition. Heat transfer from surrounding superheated liquid layer was also estimated. The approach method was verified through a comparison between a bubble growth process and the heat transfer analysis results both from the heating wall and from the liquid phase. Moreover, the measurement and analysis showed some heat transfer characteristics related to the mechanism of microlayer evaporation, heat transport by an isolated boiling bubble, initial thickness of the microlayer and liquid-vapor interface superheat for high heat flux evaporation.
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  • So MANABE, Yuki UEMURA, Takuto ARAKI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1942-1949
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Polymer Electrolyte Fuel cell (PEFC) gained wider interest as a clean and efficient energy conversion device. Proper water management is needed, because vapor and liquid transport effects strongly on PEFC power generation characteristics and efficiency. However, water transport factors have not been well understood especially during unsteady operation, which is often observed in uses of vehicles or distributed stationary power generators. In this paper, to grasp and generalized effects of the local water transport on the PEFC performance, we have developed unsteady numerical model considering water transports and compared its calculated results with experimental responses to verify the model adequacy and discuss water transport factors. In the numerical model, mass conservation equations and charge conservation equations in gas channel, GDL and MEA were solved. As necessary parameters for developing them, we measured membrane resistivity, activation over-voltage etc by ourselves. The membrane resistivity increases extremely as relative humidity decrease, and activation over-voltage is also affected by relative humidity, not only by current density and oxygen activity. The measured and calculated transient responses were agreed well in most operating conditions, then adequacy of our measurement methods of water transport properties and numerical model have been confirmed. Then, we have discussed the effects of transport resistance at MEA surfaces on PEFC transient power generation.
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  • Mitsuru ONODA, Kazuma NISHIMURA, Beini ZHOU, Tetsuo TAKE, Yasuo TAKAGI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1950-1955
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    This study investigates the characteristics of performance degradation caused by repeated cold starts of an MEA below freezing point in PEFC. It was made clear by this study that significant decay of performance was caused by repeated sequence of 50 cycles of freeze, cold start, operation and thaw under constant environmental temperature of -30deg. C. By applying Tafel analysis, it was made clear that performance degradation is expressed mainly by the increase in activation overpotential and concentration overpotential and the increases are in proportion to repeated cycle number. It was also found that performance decay appeared mainly in the cathode as measured by cyclic voltammetery (CV) and AC impedance spectroscopy (ACIS). New Diagnostic measurement that is application of Transmission Line Model as equivalent circuit revealed that increase of impedance in proton conductivity of ionomer in cathode catalyst layer was dominant.
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  • Tatsumi KITAHARA, Toshiaki KONOMI, Hironori NAKAJIMA, Yuji SEGUCHI
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1956-1963
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Polymer electrolyte fuel cells (PEFCs) generally have external humidifiers to supply humidified hydrogen and oxidant gases. If a PEFC could be operated under no-humidification, humidifiers may be removed, resulting in a simplified PEFC system with increased total efficiency and reduced cost. The present study was carried out to clarify the influence of gas diffusion layers (GDLs) on PEFC performance under no-humidification using anode gas recirculation. For the anode GDL, it is important to increase water transport between the anode gas and the membrane electrode assembly (MEA). The anode GDL without a microporous layer (MPL) is effective for enhancing PEFC performance. For the cathode GDL, it is important to maintain humidity and prevent drying-up of the MEA. A double hydrophobic MPL coated on both sides of the GDL is effective for reducing gas permeability, thereby preventing removing the water in the MEA through the GDL via dry air at the cathode. The hydrophilic layer coated on the double MPL enhances the ability of the GDL to prevent drying-up. Appropriate hydrophilic layer thickness of 40μm is effective for enhancing PEFC performance. Reducing the pore diameter of the hydrophobic intermediate layer between the hydrophilic layer and the substrate is also effective for enhancing PEFC performance.
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  • Yosio UTAKA, Yutaka TASAKI, Shixue WANG, Daigo IWASAKI, Norihisa WAKI, ...
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1964-1972
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Mass transfer characteristics of gas diffusion layer (GDL) are closely related to cell performance in polymer electrolyte fuel cell (PEFC). The four types of GDLs (Paper, Cloth, New structure with hydrophilic and hydrophobic layers and paper with MPL) were evaluated as specimens. The images of liquid water distribution in the GDLs were taken by neutron radiography. The images led to a further understanding of relation between the specifications and liquid water distribution. Simulaneous measurement of oxygen diffusivity characteristics was conducted in parallel. The experimental results led to a further understanding of relation between the liquid water distribution and oxygen diffusivity characteristics. It is clarified that the methods of visualization by neutron radiography and simultaneous measurement of oxygen diffusivity characteristics by an experimental appatatus consisting of oxygen sensor based on Galvanic battery can be used to evaluate the effect of GDL specification to liquid water distribution and the resultant oxygen diffusivity characteristics as effective tools. These elucidate the relations and its mechanisms. The following findings are revealed; The specification of GDL greatly influences its water distribution under the experimental condition of evaporation from one edge face, The findings on liquid water distribution increases the understanding of oxygen diffusivity characteristics.
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  • Nobushige TAMAKI, Kousuke KATO, Atsushi KATO, Keita IMANO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1973-1981
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    The purpose of this study is to improve of spray characteristics of direct injection Diesel nozzle, which the spray with large spray angle, short liquid core length and small droplet diameter is obtained. In the previous study, the single hole atomization enhancement nozzle, which excellent spray characteristics are obtained at relatively low injection pressure, was developed. In this study, it was investigated about atomization of the spray of the multi-hole atomization enhancement nozzle, and aimed to improve atomization characteristics and to obtain excellent spray characteristics. The effects of dimensions of the atomization enhancement nozzle such as hole number, hole diameter, position of nozzle hole on atomization of the spray and atomization characteristics were investigated. As a result, it was cleared that in case of the multi-hole nozzle with hole number of N=4, breakup length becomes short about 70% and spray angle becomes large about three times, droplet diameter of the spray becomes considerably small compared with the single hole nozzle. Atomization characteristics were improved considerably by using the multi-hole nozzle with hole number of N=4.
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  • Hideyuki OGAWA, Atsushi MATSUMOTO
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1982-1988
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Lower alcohols have very strong inhibiting effects on low temperature oxidation in HCCI combustion of normal heptane and the inhibiting effect of ethanol is slightly stronger than that of methanol while there is only weak inhibiting effect with other low ignitability fuels. This inhibiting effect of ethanol is due to significant reductions in OH radical and peroxides including HO_2, and H_2O_2 before the onsets of low temperature oxidation. The inhibiting effect of ethanol on the low temperature oxidation also suppresses the temperature rise after the low temperature oxidation, resulting in retarded high temperature oxidation. The heat release with low temperature oxidation decreases with increasing ethanol energy fraction and disappears at 30% ethanol. The onset of high temperature oxidation can be controlled by the ethanol fraction as the delay period increases linearly with the increase in ethanol. As the mol fraction of OH radicals at the onset and end of the low temperature oxidation are around 10^<-7> almost irrespective of temperature, the condition where the OH radical exceeds 10^<-7> is necessary for low temperature oxidation to progress. With ethanol addition, OH radicals are consumed in significant amount with reactions including C_2H_5OH+OH=sC_2H_4OH+H_2O and C_2H_5OH+OH=C_2H_5O+H_2O.
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  • Masahiro SUZUKI, Takeshi SUEKI, Takehisa TAKAISHI, Koji NAKADE
    Article type: Article
    2010 Volume 76 Issue 771 Pages 1989-1991
    Published: November 25, 2010
    Released on J-STAGE: June 09, 2017
    JOURNAL FREE ACCESS
    Vortex shedding behind bluff bodies slackens off when they are covered with porous materials. To clarify this mechanism we simulate a flow around a circular cylinder covered with a porous material. To solve the fluid flow with a porous interface, we impose a permeable boundary condition in which the transpiration is assumed to be proportional to the local pressure fluctuation. The simulated flow fields are compared with experimental ones and good agreements are obtained. The computation reveals blowing flows at the porous interface play a vital role in the vortex shedding suppression.
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