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Saburo TODA
1991 Volume 57 Issue 535 Pages
779-780
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Teruhide HAMAMATSU
1991 Volume 57 Issue 535 Pages
781-789
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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The 21st century is the new era of fossil fuel utilization for the global environmental problems. This paper takes a view of those advanced thermal power generation systems and the technologies, such as IGCC (Integrated Gasification Combined Cycle), PFBC (Pressurized Fluidized Bed Combustion) combined cycle and fuel cells working at higher temperatures, which are to be developed and prepared for the century of the emerging coal age.
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Jun INUMARU, Saburo HARA, Masami ASHIZAWA, Yuichi KOBAYASHI, Teruhide ...
1991 Volume 57 Issue 535 Pages
790-795
Published: March 25, 1991
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Experimental study using a 2T/D air-blown pressurized two-stage entrained flow coal gasifier was initiated in 1983. Various tests and research efforts with the gasifier have been conducted to investigate the characteristics of coal gasification, slag discharge, etc. Sixteen bituminous coals have been tested and the total gasification time (as of August 1989) has reached 1500 hours. This report presents the experimental test results on the coal gasification characteristics for 5 typical coals. As a result of the gasification tests, it should be noted that steady discharge of molten slag was accomplished under air-blown conditions also for high-ash-melting coals. The HHV of the product gas, cold gas efficiency, and carbon conversion efficiency were highly dependent on the air ratio and the carbon recycle rate. The per pass carbon conversion efficiency and the amount of product char were affected by the gasifier air ratio and the coal types.
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Akio UEDA, Kazunori SHOJI, Naoki FUJIWARA, Shuntaro KOYAMA, Eiji KIDA
1991 Volume 57 Issue 535 Pages
796-802
Published: March 25, 1991
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Gasification characteristics were studied in a single-burner gasifier and a four-burner gasifier to determine the upper and lower burner structures for two-stage circling gasifiers. In order to achieve high efficiencies under stable gasification conditions, it is necessary to obtain long residence times of reactive chars injected from the upper burners and to obtain short flames for the lower burners. It was found that an internal mixing-type burner could achieve a better coal/oxygen mixture than an external type, and favorable mixing was easily attained by adding swirling action to both burner types. The flame length of the internal mixing burner with swirl was shorter than that of the other burner without swirl. Carbon conversion of the internal mixing burners with strong angular momentum was higher than that of the other type of burner.
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Mikio SATO, Toru NINOMIYA, Toshihiko NAKATA, Hiroshi ISHIKAWA, Toshiyu ...
1991 Volume 57 Issue 535 Pages
803-810
Published: March 25, 1991
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This paper describes the development of a 1300°C class gas turbine combustor burning coal-derived low-Btu gaseous fuels. Coal-derived gaseous fuels contain NH
3 if a gas cleaning system is hot type and NH
3 will be converted to NO
x in the gas turbine combustion process. Combustion tests were conducted by using the newly designed, advanced rich-lean combustor. Combustion stability was excellent for the testing combustor because of a subcombustor, so combustion stability could be obtained even when the calorific value of fuel decreased to about 2 600 KJ/m
3N. As for NO
x emission, NH
3 conversion to NO
x was 40% under the full load condition at 1300°C of the combustor exit gas temperature for 1000ppmv of NH
3 concentration and 0.7vol% of CH
4 in the fuel.
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Kouji YAMAUCHI, Mikio SATO, Toshihiko NAKATA
1991 Volume 57 Issue 535 Pages
811-818
Published: March 25, 1991
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The main combustible gas components of the coal-derived gas fuel are CO and H
2. Moreover, a small amount of NH
3 and CH
4 will be contained. NH
3 contained in coal gas fuel will be converted to NO
x in the gas turbine combustion process. This paper describes the study of the influence of the coal gas fuel properties such as CH
4 on NO
x formation from NH
3, using experimental study by a laboratory-scale combustor and study of the reaction kinetics. As a result, a small amount of CH
4 in coal gas fuel was found to strongly influence NO
x formation from NH
3 in coal gas fuel.
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Toru HISAMATSU, Toshio ABE, Toshio MIMAKI, Hiroshi MIYATA, Takashi MAC ...
1991 Volume 57 Issue 535 Pages
819-824
Published: March 25, 1991
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In order to apply ceramics to the structual materials of a gas turbine, it is necessary to improve the reliability of ceramics, because ceramics are superior as heat-resisting materials, but are brittle. This report describes the application of ceramics to improve the reliability as structural materials of a gas turbine. From the combustion tests using 20MW-class ceramic combustors and stator vanes, and numerical analysis, the following were discussed: (1) The establishment of the structural design concept which is appropriate for the application of ceramics as brittle materials: (2) The adoption of ceramic materials which have characteristics which reduce the thermal stress: (3) The proposal of the gas turbine trip operation which is able to shut off the fuel gradually.
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Hidekazu FUJIMURA, Nariyoshi KOBAYASHI, Keizou OHTSUKA
1991 Volume 57 Issue 535 Pages
825-830
Published: March 25, 1991
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A large-scale stack model of a molten carbonate fuel cell was developed for evaluating the variation of cell performance and temperature in the cell stacking direction. A numerical method for the solution of the performance and the three-dimensional temperature distribution in a stack was proposed and examined. For the temperature distribution, calculated results, taking the heat transfer at the end plate surface into account, have been compared with the measured temperature distribution of the cell stack, and the comparison showed good accordance. For several stacks which were composed of 12 cells with different gas flow configurations, the total stack performance and the temperature distribution were investigated analytically. As a result, it was shown that the temperature distribution of a cell becomes more uniform by the effect of heat exchange in the stacking direction.
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Takao WATANABE, Yoshiyuki IZAKI, Yoshihiro MUGIKURA, Toshio ABE, Teruh ...
1991 Volume 57 Issue 535 Pages
831-836
Published: March 25, 1991
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Molten carbonate fuel cell (MCFC) power generation systems will provide a number of merits such as high efficiency, various fuel choices (coal, LNG, methanol), fast load response, and clean exhaust gas to the electric utilities. In order to realize such attractive power sources, it is important to develop not only high-performance large cells and stacks but also suitable system control technologies. The Central Research Institute of Electric Power Industry has recently constructed a 10-kW-class MCFC power generation system test facility and started a series of stack and system tests. Using 10-kW-class MCFC stacks, CRIEPI has clarified those thermal characteristics and gas recycling performance. One of those test results show a 53% energy conversion efficiency with anode gas recycling only.
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Guang-yi CAO, Masami MASUBUCHI
1991 Volume 57 Issue 535 Pages
837-842
Published: March 25, 1991
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This paper first presents a mathematical model which describes the temperature variations at each place in the molten carbonate fuel cell based upon the thermal and material balances and electrochemical reaction in the electrodes. Then, the coefficients of these derived dynamic equations are all nondimensionalized. Since these are partial differential equations with respect to the non-dimensional place and time, they are approximated by using the Method of Weighted Residuals and dynamic responses of the temperatures in the cell for load change are shown. The theoretical and experimental results are in good agreement. The difference between the counterflow and parallelflow types of fuel and oxidizing gases is discussed.
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Yasuaki MATSUDAIRA, Yoshihisa GOMI, Risaburo OBA
1991 Volume 57 Issue 535 Pages
843-848
Published: March 25, 1991
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The flow patterns and the bubbles-collapse pressures on the Karman-vortex cavity behind a circular cylinder are investigated for Reynolds numbers ranging from 4.5×10
5 to 6.0×10
5 and cavitation numbers, 0.9 to 1.6. The time history and the intensity distribution of the pressures are messured with a pressure transducer and pressure-sensitive films, respectively, fixed on the side walls of a cavitation tunnel test section. The cavitation aspect is observed by high-speed cinematography. The bubble collapses are frequently induced at the instant of the separation of the Karman-vortex cavity from the cylinder or the cavity itself. The high impulsive pressures with spike pulses over 60MPa occur in the separation or first formation region of it, and as the cavitation number decreases, their regions are combined into one. For an increase in Reynolds number, the distributions of the impulsive pressures show qualitatively the same tendency because they have the same Strouhal number, but the pulse frequency and maximum local impulsive pressure quantitatively increase.
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Toyohiko SUZUKI, Yoshitaka OCHIAI, Toshiaki SHINOHARA
1991 Volume 57 Issue 535 Pages
849-854
Published: March 25, 1991
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Vortex shedding frequency was measured in the downstream of a circular cylinder in a pulsating flow. A hot-wire anemometer was used for the velocity measurement. The Strouhal number was calculated based on the measured shedding frequency. The constancy of the Strouhal number was also retained in the pulsating flow, though the Strouhal number itself was substantially higher than that in the steady flow.
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Toyohiko SUZUKI, Yoshitaka OCHIAI, Toshiaki SHINOHARA
1991 Volume 57 Issue 535 Pages
855-859
Published: March 25, 1991
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Vortex shedding frequency was measured downstream of the equilateral triangular cylinder in a pulsating flow. A hot-wire anemometer was used for the velocity measurement. The Strouhal number based on the shedding frequency was substantially higher than that for the steady flow. Spectral components other than basic shedding frequency were observed to show significant levels as the pulsation amplitude of the flow increased.
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Hideo KOGUCHI, Shoji TAKAMURA, Toshio YADA
1991 Volume 57 Issue 535 Pages
860-866
Published: March 25, 1991
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Unstable phenomena of the meniscus between two circular parallel plates in negative motion were theoretically and experimentally studied. In the present paper, a local capillary number was newly defined by using several parameters of the non-Newtonian property of a power-law fluid, and the relations between the local capillary number and the wave number of disturbance were theoretically derived on the basis of the linear stability theory. The theoretical relations under the condition of neutral stability and that of the maximum amplification for disturbance were compared with the experimental results, and the validity of the stability criterion was shown and the best agreement was obtained with the wave number of maximum amplification.
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Hideo KOGUCHI, Shoji TAKAMURA, Toshio YADA
1991 Volume 57 Issue 535 Pages
867-873
Published: March 25, 1991
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In the present paper, nonlinear growth of disturbance on the meniscus between two circular parallel plates in negative motion and the maximum load required for the separation of liquid were experimentally and theoretically studied. It was found from precise observation for a meniscus that a springing back of the free surface occurs at an early time of movement. A radius of the curvature, ρ, at the tip of the air finger was measured by digitizing a VTR of a meniscus in order to quantify the growth of disturbance. A relationship between ρ/R
Tip and ρh
0/R
0 h·, where R
Tip is a position of the tip of the measured disturbance, h
0 isinitial thickness of the liquid, R
0 the radius of the circular plate and h· the present thickness of liquid, was derived in a simple form. The load required for separating these plates increased with the velocity of plates due to stress overshoot, but decreased or became constant over a higher velocity.
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Fumio YOSHINO, Tsutomu HAYASHI, Syogo YOKOTA, Toyohiko SUZUKI
1991 Volume 57 Issue 535 Pages
874-881
Published: March 25, 1991
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Observation of the flow pattern and the measurement of water depth of the shallow water flow on a rotating circular cylinder were carried out. The results of the investigation showed that the roll wave which existed on a still cylinder did not exist on a rotating cylinder, and that the stationary centrifugal force wave (SC wave), the long-wave length wave (LW wave) and the ripple which started immediately downstream from the nozzle exit were generated when the flow velocity increased. The rotation of the cylinder strengthened the intensity of the waves which moved in the circumferential direction, and the SC and LW waves formed the cell structure in the downstream when a certain condition was satisfied. As a result, the extent of the regions of each flow pattern was obtained.
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Hiroshi SAKAMOTO, Hiroyuki HANIU, Shinobu MATUBARA
1991 Volume 57 Issue 535 Pages
882-890
Published: March 25, 1991
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The objective of this paper is to investigate the suppression of the fluid forces acting on a circular cylinder (called test cylinder) by controlling the flow around it. The control of the flow was established by introducing a fine circular cylinder (called control cylinder) in the neighbourhood of the test cylinder. Measurements were carried out by varying the position of the control cylinder in the ranges of G=0.2∼10mm (G is gap between two cylinders) and α=0°∼180° (α is angle along the circumference of the test cylinder). Then, the steady and unsteady fluid forces, vortex shedding frequency and flow pattern were systematically examined. Furthermore, such matters as the mechanism of control, the controlled wake structure and the relation between the characteristics of the controlled fluid forces and the behaviour of the flow were discussed in detail based on the results of the fluid forces, vortex shedding frequency and flow pattarn. In particular, it was found that the maximum reduction of the time-mean drag was 50%, and the maximum reduction in the fluctuating lift and drag was 85% by using the control cylinder with the diameter of 3mm, which is considerably small compared to the test cylinder with that of 49mm.
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Tohru FUKANO, Minoru FUKUHARA, Satoru MATSUO, Hidechito HAYASHI
1991 Volume 57 Issue 535 Pages
891-897
Published: March 25, 1991
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We have experimentally investigated the influence of the tip clearance between a flat-plate-type blade and a duct surface on the flow characteristics around a single rotating blade. The setting angle of the blade was limited within the range where the leading edge separation did not occur over the whole blade span. The local attack angle of the main flow to the blade became smaller toward the tip; the leading edge separation, however, began near the blade tip. The separated zone gradually extended toward the boss of the rotor as the blade setting angle became larger. This is due to the fact that the low-energy fluid in the dead flow region of the wake of the blade is accumulated near the blade tip and it causes the leading edge separation there. A typical periodic fluctuation of the wake flow due to Karman vortex shedding from the trailing edge of the blade was observed in the intermediate region of the blade at any time if the reattached main flow did not separate up to the trailing edge on the suction surface of the blade.
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Kazuo TANISHITA, Jyunichi SUZUKI, Naobumi OHISHI, Takeshi NARUSE
1991 Volume 57 Issue 535 Pages
898-904
Published: March 25, 1991
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Laser Doppler velocity measurements were performed on the entry flow of a strongly curved tube with the parabolic entry profile, in which a maximum curvature ratio, defined as the ratio of tube radius to the radius of curvature a/R, achieved is 1/2. Both axial and secondary velocities were measured, describing the fairly complete flow field. Intensified curvature effects cause the secondary flow, and the maximum secondary flow velocity went up to 90% of the cross-sectional averaged axial velocity in the curved tube with a/R = 1.2. Due to this enhanced secondary flow, separation of secondary flow is found near the inner wall.
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Hisanobu AZUMA, Kakuji OGAWARA, Sei-ichi IIDA
1991 Volume 57 Issue 535 Pages
905-913
Published: March 25, 1991
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The flow between concentric rotating cylinders, which is called the Taylor vortex flow, shows various flow modes. The flow is classified into three modes. One is called the primary mode which appears with the gradual increase of the inner cylinder's rotation, and the others are the secondary normal and secondary anomalous modes which appear with sudden increase. Unsteady three-dimensional numerical simulations considering an effect of the inner cylinder's acceleration have been performed, revealing that there are different processes of ocurrence between the primary normal and secondary normal modes. The bifurcation causing the above modes is observed at the same condition as with the experimental one. Transitions to wavy Taylor vortex flow from both modes appeared with increasing time. In addition, velocity and torque fluctuations, respectively, for a certain point in the field and for the inner cylinder are also shown.
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Motohiko NOUMI, Katsuhiro YAMAMOTO, Eisuke OUTA, Kiyohiro TAJIMA
1991 Volume 57 Issue 535 Pages
914-921
Published: March 25, 1991
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Pulsed water jets at the velocities of 300m/s to 500m/s produced by piston impact are examined by numerical analysis. Straight nozzles are used with the outlet diameters of 5 and 10mm. The two-step Lax-Wendroff method is employed for the unsteady axisymmetric two-phase flow in the nozzles using a Flux-Corrected Transport algorithm to limit artificial diffusion. After short transition, the flow in the nozzles arrives at a quasi-steady state. In the nozzle outlets, the contract flow and the separation with strong cavitation are formed. The vapor cavities also spread into the water column. Because of the short transition and contract flow, the jet speed of the straight nozzles is higher than that of the taper nozzles with the same nozzle outlet diameter. On the assumption that the flow in the nozzles is steady, the maximum jet speed can be approximated. It is illustrated that the nozzle shape affects the jet speed.
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Yoshinori UEKI, Ikuo NAKAMURA, Shintaro YAMASHITA
1991 Volume 57 Issue 535 Pages
922-929
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Spectrum tensor equations are derived for ψ
2, 1, ψ
2, 3, and ψ
1, 3, and the roles of terms in the equations are studied. Some terms can be explained by the same concept of spectrum tensor (i=j), but others play different roles. The production terms depending upon Coriolis force and metric force occur, and they are not due to mean flow tensor. Particularly, the production terms appearing in equations for ψ
2, 3 and ψ
1, 3 have opposite functions. The role of pressure-velocity terms is transport of spectrum components. Viscosity terms perform destruction, and they are not dissipated into heat. ψ
2, 1 is closely related to ψ
1, 1, ψ
2, 2 and ψ
3, 3. The relationship between ψ
2, 3, and ψ
1, 3 is also close due to production terms.
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Toshio MIYAUCHI, Manabu FUEKI
1991 Volume 57 Issue 535 Pages
930-934
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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The aim of this study is to clarify the coherent vortical structure in a turbulent mixing layer and the relation between pressure fields and vortical fields. To achieve this purpose, we simulated the spatially developing turbulent mixing layer by using a large eddy simulation. From these numerical simulations, the following conclusions are obtained: 1) Two-dimensional coherent vortical structure exists in a high Reynolds number turbulent mixing layer: 2) During the development of the mixing layer, two-dimensional coherent vortical structures merge and their scales become large: 3) Pressure fields are closely related to the vortical structure, and the negative pressure field relative to the mean value corresponds to the spanwise vortical structure.
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Nobuo OGAWA, Hiroshi MAKI, Kunio HIJIKATA
1991 Volume 57 Issue 535 Pages
935-942
Published: March 25, 1991
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From our previous reports, it is clarified that the fluctuations in the jet center have an important effect on opposed turbulent jet flow fields. In the jet center, where symmetrical flow fields are characterized, the turbulent structure will be different from those in other parts of the jet. In the turbulent opposed jet center, the fluctuating velocity plays role equal in importance to that of the mean velocity. The momentum which locates the impinging surface comprises three parts: that is, a mean velocity, a static pressure and a fluctuating velocity. The present paper deals with the influences of the variations of the fluctuating velocity, employing the turbulent lattice in the center of turbulent opposed jets, to the locations of the impinging surface.
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Moriyoshi TAMURA, Eiji HASEGAWA
1991 Volume 57 Issue 535 Pages
943-949
Published: March 25, 1991
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It is the purpose of the paper to investigate how the particles contained in the jet collide with the wall when a two-dimensional turbulent jet issuing from the nozzle impinges upon a wall normally. It is assumed that the interaction between particles is negligible, that the flow field is independent of the existence of the particle and that the particle is subjected to the interaction based on Stokes' drag law in the flow. Under these assumptions, the flow of the turbulent jet is numerically solved by means of the discrete vortex method and particle trajectories are numerically obtained as a function of the aspect ratio (the ratio of the distance between the nozzle and the wall to the nozzle width) and the Stokes number. The particle collision with the wall is divided into two types by the aspect ratio. When the aspect ratio is small, the fluid collides mainly with the wall in the portion of the potential core. Thus the position and the velocity with which particles collide with the wall are nearly identical with those in the case of the laminar jet. When the aspect ratio is large, the position of collision becomes close to the axis of the jet, and the velocity of collision becomes small compared with that of the case of the laminar jet. As the aspect ratio increases, the number of the collision particle decreases.
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Shinsuke MOCHIZUKI, Hideo OSAKA
1991 Volume 57 Issue 535 Pages
950-957
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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In order to control the turbulent energy production and transport processes due to the coherent vortices associated with the bursting phenomenon in a d-type rough wall turbulent boundary layer, longitudinal thin ribs were placed within the transverse grooves with a suitable spanwise spacing. Direct measurements of the local skin friction coefficient evidently show the effectiveness of drag reduction using the longitudinal ribs. Maximum drag reduction rates to d-type rough wall flow and to smooth wall flow are -10% and -3%, respectively. The drag reduction rate can be reasonably expressed in terms of the rib Reynolds number. Comparisons of some mean flow properties between the modified flow and the d-type rough wall flow provide evidence that the present passive control device reduces the turbulent energy production rate.
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Takatsune NARUMI, Tatsuo SEKINO, Tomiichi HASEGAWA
1991 Volume 57 Issue 535 Pages
958-965
Published: March 25, 1991
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Transmitting forces generated in a reverse squeezing film were measured and calculated when an upper spherical surface was caused to separate relative to a lower flat plate at a constant speed. The experimental results obtained were similar to those for normal squeezing flows, despite the opposite squeezing motion. Namely, no elastic effects were shown in the forces measured for PEO solutions. In the case of Separan solutions, however, the measured force overshoots the force estimated by consideration of viscous stress alone at the inception of reverse squeezing. In addition, the maximum rates of the overshoot were nearly equal to those obtained in normal squeezing under the same starting conditions expect for the direction of motion. A constitutive equation yielding the stress overshoot was used in the analysis of these flows under the condition where shear stress dominates. The analytical results approximately agree with the experimental ones for normal and reverse squeezing flows.
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Katsu'ine TABEI, Hiroyuki SHIRAI, Fumio TAKAKUSAGI
1991 Volume 57 Issue 535 Pages
966-970
Published: March 25, 1991
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By using the moire-schlieren method for symmetrical and asymmetrical flow fields, density distributions of underexpanded free jets of air from circular and square nozzles have been measured. Experimental moire image data of the flows, which show the integrated light deflection across the flow, were inverted to an internal density distribution by the numerical inverting method. The experiment was performed systematically by changing the pressure ratio across the nozzles from 4 to 13. It was found that the density profiles measured in the expanded free jets from a circular nozzle agreed with other experimental results on the whole, and that the results for a square nozzle showed complex flow configurations caused by the nozzle figure, nevertheless, the density distribution on the flow axis was very similar to that for a circular nozzle.
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Shigeru HINATA, Masayuki SAKURAI, Nobuhiro HIMENO, Hirotada IWADE
1991 Volume 57 Issue 535 Pages
971-976
Published: March 25, 1991
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The theoretical study was carried out to clarify the mechanism of bubble formation through a submerged nozzle in upward water flow. On the basis of the experimental results, a model of breakup of the air column in which the surface membrane is oscillating at the top of the nozzle due to the disturbance of flow was proposed. The size of the bubble generated from a nozzle in a stream ranging from Nozzle Reynolds number 1500 to 15000 was determined by applying the theory of the instability of a jet which was first analyzed by Lord Rayleigh. The proposed model is in good agreement with the experimental results.
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Michihisa TSUTAHARA, Takeyoshi KIMURA, Kiyoshi HASHIMOTO
1991 Volume 57 Issue 535 Pages
977-982
Published: March 25, 1991
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A new type of nozzle generating a two-phase high-speed water jet is presented. The structure is of simple convergent and divergent type. High pressure air is injected into the water flow through thin holes opened downstream of the throat. The increasing ratio of the momentum is higher than 10. As the pressure of the air increases, the speed of the jet increases, but the efficiency decreases. The nozzle with a small opening angle seems to be better, and the holes should be opened near the throat. The speed of the water phase is, in general, higher than that of the air phase. The pressure upstream of the nozzle is not necessarily high, so that this nozzle can work by itself for ship propulsion. The mechanism of generating the water jet is also considered qualitatively.
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Michihisa TSUTAHARA, Takeyoshi KIMURA, Kunio TAKAHASHI
1991 Volume 57 Issue 535 Pages
983-987
Published: March 25, 1991
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Characteristics of the pump in a square channel using the Weis-Fogh mechanism, which is the lift generation mechanism in the hovering flight of small insects, are studied in this paper. The wing motion of this mechanism is changed from the previous reciprocal type to a rotary type, which is considered to be simpler to apply to hydraulic machinery. A two-dimensional model of the above pump is proposed and the force on the wing is calculated by the singularity method. The pressure difference between the two points in front and behind the wings, the torque and the flow field around the wings are also shown. This model works as a pump or as a water turbine. The pressure rise increases as the number of wings or the flow coefficient increases.
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Jiande HUANG, Tomitaro TOYOKURA, Masanori AOKI
1991 Volume 57 Issue 535 Pages
988-994
Published: March 25, 1991
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In the previous report, it was pointed out that leakage flow through the comparatively large blade tip clearance of an open impeller considerably affects the flow just before the capacity at which an inlet reverse flow occurs. Then, in this paper, unsteady flows at the impeller entrance were measured for a small blade tip clearance impeller and a closed impeller. For the former, especially, static pressure distribution measurements on the casing surface outside of impeller blades and the flow visualization in the impeller were performed. The effect of blade number was also studied. As a result, the effects of the impeller blade tip clearance and the blade number on the inlet reverse flow starting point were clarified.
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Yoshinori SAITO, Shigeharu KABASHIMA, Kunio YOSHIKAWA, Kazumi TSUNODA, ...
1991 Volume 57 Issue 535 Pages
995-1001
Published: March 25, 1991
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Effects of total pressures on performances of a disk MHD generator were studied. Current-voltage characteristics, power outputs, distributions of both static pressure and Hall potential and swirl were measured at two different total pressures. The experimental results show that at the low total pressure, the current-voltage characteristics become steep, and as a result, the maximum power output is obtained at higher load resistances. It was observed that the enthalpy extraction rate was kept almost constant although the power output decreased at the low total pressure. These phenomena can be explained by the change of the Hall parameters, flow velocities and swirls in the MHD channel.
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Shigeru NOZU, Kouichi OZAKI, Hideo INABA, Hiroshi HONDA
1991 Volume 57 Issue 535 Pages
1002-1008
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Frictional pressure gradient and vapor phase mass transfer correlations were developed for condensation of nonazeotropic refrigerant mixture R114/R113 in the annuli of horizontal double tubes with an enhanced inner tube. The frictional pressure gradient data were correlated fairly well by a previously developed empirical equation for condensation of pure refrigerants. The vapor phase mass transfer correlation was based on the previous results for turbulent flow in smooth and rough tubes with and without surface suction. For given conditions of vapor and tube wall, the heat transfer coefficient can be calculated by using the correlations for the vapor phase mass transfer coefficient and the heat transfer coefficient for the condensate film. The calculated values agree with the measured data to a mean absolute deviation of 14.3%.
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Akira TAKIMOTO, Tsunenobu TERANISHI, Kanji HANEDA, Yujiro HAYASHI
1991 Volume 57 Issue 535 Pages
1009-1013
Published: March 25, 1991
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In order to clarify the condensation heat transfer mechanism of binary vapors of immiscible liquids, detailed experiments have been conducted with regard to the condensation of an azeotropic mixture of carbon tetrachloride and water on a vertical flat plate. The experimental results indicate that the condensation heat transfer coefficient of the mixture is larger than that of the pure organic vapor, and its mechanism can be explained to be in relation with the dynamic behavior of mixed condensate consisting of water droplets and organic liquid film flow.
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Akio NAKAYAMA, Matutaro KANO
1991 Volume 57 Issue 535 Pages
1014-1018
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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In order to elucidate the mechanism of saturated-Pool Nucleate boiling by interfered bubbles from the local viewpoint, as a first step, a flow visualization experiment of liquid motion caused by vapor bubble action was carried out. In this experiment, 2 hydrogen generating electrodes for supplying vapor bubbles were provided on the heating surface. Within the present study, the liquid motion was influenced by the vapor bubbling action coming from both electrodes. Moreover, the liquid speed was mainly decided by the liquid extrusion action due to vapor bubble growth and entailed flow effect after the separation of the vapor bubble.
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Mitsuhiro UEMURA, Shigefumi NISHIO, Ichiro TANASAWA
1991 Volume 57 Issue 535 Pages
1019-1024
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Enhancement of natural-convection boiling heat transfer by electric field is investigated experimentally. Boiling of a refrigerant R113 occurs on a flat surface under the atmospheric pressure, and a D.C. voltage up to 35kV is applied between the heat transfer surface and an electrode made of stainless steel wire mesh 10mm apart. The whole boiling curve is measured under different applied voltages. The orientation of the heat transfer surface can be varied from the horizontal facing up to the horizontal facing down. The results of experiment indicate that boiling heat transfer is enhanced by electric field. The film boiling heat transfer is greatly enhanced, especially when the surface faces horizontally downward. An enhancement ratio of film boiling heat transfer as high as 14 is obtained. The critical heat flux and the minimum heat flux are both increased with increasing electric field. As a result, in an electric field of high intensity, the boiling curve becomes almost independent of the orientation of the surface.
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Toshiyuki AMANO
1991 Volume 57 Issue 535 Pages
1025-1032
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Nucleate and film pool boiling heat transfers, critical heat fluxes, and minimum heat fluxes for nitrogen, tetrafluoromethane, and their mixtures have been measured on a fine thin wire. The orientation of wire was horizontal and vertical. Critical heat fluxes and minimum heat fluxes for mixtures were in concentrations larger than those for either pure component. The heat flux in nucleate boiling regime for mixtures was explained well by the experimental formula. Transition behavior from nucleate boiling to film boiling has been observed for step current heat input and rapid heating. It was found that there was no transition behavior for mixtures in comparision with the pure component. The nitrogen-tetrafluoromethane mixtures should be used for cryogens of oxide superconductors having critical temperature more than 110K.
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Kunio HIJIKATA, Kazutaka MINAMI, Takao NAGASAKI, Yoshiyuki AOYAMA
1991 Volume 57 Issue 535 Pages
1033-1037
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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The characteristics of turbulent flow and heat transfer have been experimentally investigated with a circular pipe in which a pair of twisted tapes were inserted as a promoter of convective and radiative heat transfer. The three-dimensional velocity and turbulence field, the friction factor, and the local heat transfer coefficient were measured. It was found that a secondary flow was induced by the present promoter, and the heat transfer was enhanced to about three times that of a smooth pipe. A marked increase of the local heat transfer coefficient was observed near the impinging region of the secondary flow on the wall. It was also found that a nearly isotropic and homogeneous turbulence field was caused by the promoter.
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Kunio HIJIKATA, Takao NAGASAKI, Kazutaka MINAMI
1991 Volume 57 Issue 535 Pages
1038-1043
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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The characteristics of heat transfer have been experimentally investigated for a circular pipe in which a pair of twisted tapes was inserted to enhance convective and radiative heat transfer. The local and average heat transfer coefficients, and pressure drop were measured for three kinds of pitch lengths. The performance of the present promoter was evaluated based on the area of heat transfer under the condition of the same flow rate, pressure drop and transferred heat. It was found in the case of room temperature that the heat transfer area can be reduced to about 30% less than a smooth pipe. In the case of high temperature, about 450°C, the heat transfer rate was further increased by a factor of 1.5 due to the effect of radiation between the pipe wall and the promoter.
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Hitoshi SUGIYAMA, Mitsunobu AKIYAMA, Katsuhiro SHIBATA
1991 Volume 57 Issue 535 Pages
1044-1050
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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A numerical analysis has been performed on three-dimensional developing turbulent flow in a square duct using a modified Reynolds stress equation model and transport equation model for turbulent flux. Special attention was paid to the relation between model constants and Reynolds stress distribution and the developing process of secondary flow of the second kind. Moreover, the method using a turbulent heat flux model was able to precisely predict the mean Nusselt number.
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Hiroyoshi KOIZUMI, Iwao HOSOKAWA
1991 Volume 57 Issue 535 Pages
1051-1056
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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This research aims at controlling the bouyancy-driven longitudinal rolls in a horizontal rectangular duct heated from below by properly setting the side wall temperature profile. Experiment for the Reynolds number ranging from 2400 to 12000 reveals time-averaged stable rolls which change their patterns depending on the Reynolds number and the side wall temperature profile. This result is extremely different from the previous one (Mori and Koizumi 1989) for the Reynolds number 220 which revealed unsteady flows with a time-averaged uniform temperature on the horizontal plane. A numerical calculation for high Reynolds number flow using the k-ε model, in which the Reynolds stresses in the cross section are approximated by the algebraic stress expressions, is performed for comparison with experiment.
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Kengo SASAGUCHI, Tetsuhiro UEMURA, Hiroyuki TAKEO
1991 Volume 57 Issue 535 Pages
1057-1064
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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The effect of Grashof number, Gr, on two-dimensional unsteady laminar natural convection in a rectangular cell surrounded by a vertical hot wall, a vertical insulated wall, and two horizontal conducting plates has been studied numerically using the SIMPLER algorithm. For Gr ranging from 10
3 to 10
5, transient velocity and temperature distributions, and timewise variation of averaged Nusselt number on the hotwall have been compared with those for an ordinary cell which has a hot wall and three insulated walls.
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Kazuhiko KUDO, Hiroshi TANIGUCHI, Hiroshi KANEDA, Ke-Hui GUO, Masahiko ...
1991 Volume 57 Issue 535 Pages
1065-1070
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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A computer program is developed to analyze two-dimensional coupled radiative and convective heat transfer in circulating fluidized bed boiler (CFBB). Based on bulk-density distribution obtained by solving one-dimensional gas and particle two-phase flow equations, radiative heat transfer in CFBB is analyzed by using a revised Monte Carlo method. Covective heat transfer between furnace walls and gas or particles are also considered by using Martin's model. The temperature profiles of gas and particles, and the wall heat flux distributions are obtained. The results approach to the Johnsson's experimental data when horizontal mixing of particles is considered. The effects of particle diameter on the bulk density and heat transfer in CFBB are also studied.
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Kazuhiko KUDO, Hiroshi TANIGUCHI, Toshio KOBAYASHI, Takeru FUKUCHI
1991 Volume 57 Issue 535 Pages
1071-1076
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Energy balance and its Reynolds number dependency are analysed in the recirculating zone behind a backward-facing step by using the standard k-ε model. By using a heat-line visualisation technique, the heat transfer between the main flow and the wall across the recirculating zone is shown to be divided into two processes: (1) heat transfer across the boundary layer formed by the backward flow along the wall and (2) heat transfer across the shear layer between the main flow and recirculating zone. Due to the difference between the Reynolds number dependency of these two mechanisms, the core temperature in the recirculating zone approaches the main flow temperature according to the increase of the Reynolds number.
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Hideo SUZUKI, Masahiko NAKAYAMA, Tomoya OTANI, Noriyuki KATAOKA, Kazuo ...
1991 Volume 57 Issue 535 Pages
1077-1083
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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The values of effective diffusivity for carbon dioxide and thermal conductivity have been measured in freshly excised respiring rat abdominal muscle in order to understand the heat and mass transport process occurring in the muscle tissue. The values of diffusivity increase with the decrease of the average partial pressure of CO
2, indicating the existence of significant facilitated diffusion. The thermal conductivity of the muscle tissue membrane in which the paritial pressure gradient of carbon dioxide was imposed was measured by the self-heated thermistor method. There appears to be a slight increase of diffusivity at the lower partial pressure and this finding indicates that there may exist some mechanism of simultaneous heat and mass transport in the muscle tissue.
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Shigenao MARUYAMA
1991 Volume 57 Issue 535 Pages
1084-1090
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Directional emission characteristics of various reflectors are compared by ray tracing analysis taking into account the directional reflectivity of mirror surfaces. For the case of a perfect reflector surface, the aperture of an involute reflector has an isotropic uniform distribution of radiant intensity. The hemispherical emissive power and directional radiant intensity of the involute reflector for metallic surfaces are slightly lower than the values for the ideal case. The distributions of emissive power and directional radiant intensity of conventional reflectors are signgficantly nonuniform compared with those of the involute reflector.
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Naoki MATSUNAGA, Morio HORI, Akira NAGASHIMA
1991 Volume 57 Issue 535 Pages
1091-1096
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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An apparatus for the measurement of the mutual diffusion coefficients of gases has been developed using the Taylor dispersion method. The present apparatus uses a thermistor TCD as the concentration detector, and it can be applied to oxygen-rich sample gases. The mutual diffusion coefficients of the H
2O-N
2, H
2O-O
2, H
2O-air, H
2O-CO
2 and H
2O-Ar systems have been measured at 150°C and 1atm. The result agrees well with reliable existing data for the H
2O-N
2 system. The uncertainty of the present results was estimated to be ±3%. The mutual diffusion coefficients of the H
2O-N
2, H
2O-O
2 and H
2O-air systems are found to be close to each other at 150°C.
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Seigo SAWADA
1991 Volume 57 Issue 535 Pages
1097-1100
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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Field experiments on utilizing the cold energy obtained during winter by storing it in the ground as artificial permafrost using heat pipes have been carried out over several years. Using the data obtained from the experiments, mumerical simulations were performed for the creation and degradation of a frozen underground zone. For predicting the temperature field, the finite difference method was used, and the latent heat associated with freezing or thawing of the soil water was treated as a heat sink (source). The simulations were performed using three kinds of soil: silt, clay and sand. The following fact became clear as a result of the simulations: if the two-dimensionality of the ground temperature is maintained under suitable soil conditions, it is possible to surround an area of 8m×8m with 4m-thick artificial permafrost using 72 lengths of heat pipe.
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Akira UMEMURA
1991 Volume 57 Issue 535 Pages
1101-1107
Published: March 25, 1991
Released on J-STAGE: March 28, 2008
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A physical model is developed to describe the phenomenon of bouncing which was observed in our previous two-body collision experiment for hydrocarbon liquid droplets. The repulsive forces acting between the colliding droplets are caused by the intervening air flow, which is analyzed on the basis of the lubrication theory taking into account the deformation of the droplets. The droplet bouncing takes place for a restricted range of the collision Weber number which depends on the droplet size and rheological properties. Its bounderies are identified in terms of the underlying elementary physics. In particular, the upper limit is proportional to the liquid viscosity, while the lower has little dependence, consistent with the experimental result.
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