Journal of Thermal Science and Technology
Online ISSN : 1880-5566
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Volume 2 , Issue 1
Showing 1-12 articles out of 12 articles from the selected issue
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Papers
  • A. S. HEGAZY
    Volume 2 (2007) Issue 1 Pages 1-12
    Released: February 02, 2007
    JOURNALS FREE ACCESS
    The present work is concerned with a new steam cycle proposed as a modification to the normal regenerative steam cycle. A steam ejector and an extra feed water heater are incorporated into the latter cycle. The motive steam of the ejector is bled from the steam turbine. The ejector entrains a portion of the saturated steam exiting the turbine and entering the condenser. Both amounts of motive and entrained steam are raised in pressure and used as heating steam in the first feed water heater. The saturated water getting out of this feed water heater is further heated in the second feed water heater and the cycle is then completed. Thermodynamic analyses of the proposed cycle are developed and used for predicting the characteristic performance of the proposed cycle. The results of the current work show clearly that the thermal efficiency of the proposed cycle is always greater than that of the normal regenerative steam cycle.
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  • Yutaka ABE, Yuichi ABE, Izuo AYA, Kenji YAMANE
    Volume 2 (2007) Issue 1 Pages 13-18
    Released: March 01, 2007
    JOURNALS FREE ACCESS
    The technology of the deep-ocean CO2 storage is expected to directly mitigate the source of the global warming. At deep-ocean condition above 4.45 MPa and below 283 K, the CO2 clathrate hydrate crystals are formed as membrane at the interface between the liquid-water phase and the liquid-CO2 phase. Since the strength and the thickness of the hydrate membrane are crucial to the storage period, it is important to experimentally measure the mechanical characteristics of the CO2 hydrate membrane and the hydrate droplet. In the present study, the CO2 hydrate membrane thickness is measured by using the laser-light interference method. It is clarified that the present method by using the beam light interference method is applicable to measure the CO2 hydrate membrane. The hydrate membrane thickness is estimated to be about 7 μm∼12μm at 10MPa and 275 K∼283 K. It is also clarified that thickness of the CO2 hydrate membrane is in proportion to the temperature.
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  • Isao TAGUCHI, Michio KURASHIGE
    Volume 2 (2007) Issue 1 Pages 19-30
    Released: March 01, 2007
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    Balloon compacts attract a great attention as a new class of lightweight materials. In the present paper, macroscopic thermal conductivity of uniaxially compacted and sintered balloons is evaluated for various compaction degrees and balloon's inner-outer diameter ratios. The compaction is modeled by making the balloons overlapped without balloon flattening, and the sintering by adding some appropriate amount of mass around overlapping necks; the whole mass is conserved in both of the modelings. The macroscopic conductivities are estimated using Kirchhoff's current law. The results are expressed in terms of the two microgeometrical parameters. It is found that the uniaxial compaction complicatedly affects the macroscopic conductivities and strength of induced anisotropy of the compacts.
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  • Tong-Bou CHANG
    Volume 2 (2007) Issue 1 Pages 31-42
    Released: March 14, 2007
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    This study applies the first and second laws of thermodynamics to investigate the problem of steady filmwise condensation on a finite-size horizontal disk. The boundary condition at the disk edge is obtained by applying the minimum mechanical energy principle. Closed form correlations for the Nusselt number and the dimensionless overall entropy generation number are established. For the case of without losing the condensation heat transfer coefficient, the present results suggest reducing the value of the parameter group BrGrψ to minimize the dimensionless overall entropy generation number. Finally, a formula is derived to establish the value of Ra/Ja which minimizes the dimensionless overall entropy generation number for a specified value of the parameter group BrGrψ.
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  • Yihua GU, Isao SATOH, Takushi SAITO, Tatsuya KAWAGUCHI
    Volume 2 (2007) Issue 1 Pages 43-54
    Released: April 10, 2007
    JOURNALS FREE ACCESS
    In this paper, segregation characteristics of fluidized particles, which were the mixture of two kinds of grains having different densities and sizes, and the temperature distributions within them were experimentally examined. The dominating heat transfer mechanism was discussed from the experimental results, in order to obtain fundamental information applicable for controlling the particle segregation and/or heat transfer in practical fluidized beds.
    The experimental results showed that the temperature segregation was dependent on the particle segregation and that the vertical heat transfer in the segregated fluidized bed was greatly resisted by the interface layer, which was located between the jetsam and flotsam layers and had a vertically changing particle concentration. The average vertical heat transfer coefficient or apparent thermal conductivity of the interface layer increased with the excess gas velocity. When the temperature segregation occurs, the apparent thermal conductivity of the interface layer was not only much lower than that of the vigorously fluidized flotsam layer, but even lower than that of the stagnant jetsam layer.
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  • Yihua GU, Isao SATOH, Takushi SAITO, Tatsuya KAWAGUCHI
    Volume 2 (2007) Issue 1 Pages 55-66
    Released: April 10, 2007
    JOURNALS FREE ACCESS
    In our previous paper, particle and temperature segregations in a fluidized bed of binary particle mixtures were experimentally examined, and heat transfer in the segregated fluidized bed was investigated. As the results, it was shown that the temperature segregation results mainly from low heat transfer coefficient through the interface layer, which exists between the flotsam-rich and jetsam-rich layers, and that the heat transfer coefficient increases rapidly with increasing the excess gas velocity.
    Following our previous paper, particle motion in the segregated fluidized bed was experimentally investigated in this paper, in order to make quantitative discussion on the relation between the heat transfer coefficient and particle motion in the interface layer. In the experiment, the Particle Imaging Velocimetry (PIV) method was applied to study the concentration and motion of particles in the segregated fluidized bed. A modified solid circulation model was built up to model the particle motion in the segregated fluidized bed.
    The experiment results showed that the vertical particle exchange rate of the interface layer increases with the excess gas velocity, and that the vertical heat transfer coefficient through the interface layer is mainly determined by the average particle exchange rate in the interface layer. Variations of the apparent thermal conductivity at different height in the particle layers were also determined by the vertical variation of the particle exchange rate. It was shown that the heat transfer coefficient or the thermal conductivity in the interface layer is influenced by the densities and specific heat capacities of the particles.
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  • Shin'ya OBARA
    Volume 2 (2007) Issue 1 Pages 67-78
    Released: April 24, 2007
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    Small kerosene diesel-engine power generators are introduced into an independent micro-grid (IMG) that connects 20 houses, and power and heat are supplied to them. A 3 kW engine generator is installed in six houses, and a boiler and a heat storage tank are also installed, and exhaust heat to make up for insufficiency is supplied. The boiler is installed in the house that does not install the engine generator, and heat is supplied to the demand side. Partial load operation of the engine generator has a large influence on power generation efficiency. Therefore, this paper discusses the system that controls the power of the engine generator by the power distribution control system using the genetic algorithm (GA), and the control system that changes the number of operations of the engine generators according to the magnitude of the power load. As a case study, the energy-demand model of the 20 houses in Sapporo was analyzed. As a result, the annual energy cost of the number of operations system and the power distribution control system is reducible with 16% and 8% compared with the conventional method, respectively. However, it depends for this cutback effect on the heat demand characteristic greatly, and when the proposed system is introduced into a community with little heat demand, effectiveness will decrease greatly.
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  • Amornrat KAEWPRADAP, Satoshi KADOWAKI
    Volume 2 (2007) Issue 1 Pages 79-89
    Released: May 02, 2007
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    Heat-loss effects on the chaotic behavior of cellular premixed flames generated by intrinsic instability were studied by two-dimensional unsteady calculations of reactive flows based on the compressible Navier-Stokes equation. The disturbance with the linearly most unstable wave number, i.e. the critical wave number, was superimposed on a planar flame. As the superimposed disturbance evolved, the cellular-flame front formed owing to intrinsic instability. The unstable behavior of cellular flames appeared at low Lewis numbers and became stronger as the heat-loss parameter increased. Owing to the unstable behavior, the burning velocity fluctuated with time. To study the characteristics of the unstable behavior, the power spectrum density of the fluctuation of the burning velocity was obtained. The power spectrum density had a sharp peak, whose frequency corresponded to the typical oscillation frequency of the unstable behavior, and the 1/f2 spectrum was found in low frequency range. Moreover, we performed the time series analysis on the burning-velocity fluctuation. We obtained the attractor and correlation dimension to study the characteristics of the chaotic behavior of cellular premixed flames. The characteristics depended strongly on the heat-loss parameter and Lewis number, i.e. on intrinsic instability. The results suggest that the present analysis is applicable to the diagnostics of the flame instability.
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  • Kazuhiro YAMAMOTO, Satoshi INOUE, Hiroshi YAMASHITA, Daisuke SHIMOKURI ...
    Volume 2 (2007) Issue 1 Pages 90-101
    Released: May 02, 2007
    JOURNALS FREE ACCESS
    The flow field in highly turbulent premixed combustion has been examined, using a cyclone-jet combustor. The shear-strain rate is obtained by PIV system. Results show that, in combustion field, mean axial velocity does not decay along center axis and RMS fluctuation velocity is much lower, compared with those in cold flow. The reaction zone detected by an ion probe well corresponds to region of large shear-strain rate. In combustion, turbulence is small around reaction zone to have the undiminished jet velocity, which leads to an increase in length of potential core, although the flame generated turbulence is observed through flow expansion.
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  • Yohei KOBAYASHI, Akira KUROKAWA, Takichi KOBAYASHI, Hisao HOJO, Hidehi ...
    Volume 2 (2007) Issue 1 Pages 102-110
    Released: May 18, 2007
    JOURNALS FREE ACCESS
    Quartz is used in various devices, since it can be easily vibrated by the piezoelectric effect and controlled in an electric circuit. The force, which acts on the vibrating body, follows the principles of fluid dynamics; this phenomenon is explained in detail by the Navier-Stokes equation that is a fundamental equation of motion of a flow system. The authors measured the drag acting on a vibrating body (i.e., a quartz oscillator) settled within a hydrogen-methane mixed gas. The quartz oscillator is sensitive to temperature, pressure, and viscosity. It was placed in a constant temperature bath to control the temperature accurately. A pressure gauge was also placed into the same bath, and the pressure inside the tube was controlled by using a piezo valve. This drag is measured and converted into a physical property by using an approximate solution of the Navier-Stokes equation. The drag changes depending on gas conditions, because the property of a gas differs under different conditions. If a quartz oscillator can detect this difference, it can be used as a sensor for a gas. In this study, the authors attempted to ascertain the possibility of using a quartz oscillator as a concentration sensor for a hydrogen-methane mixed gas. The large-scale project on hydrogen-methane mixed gas that has begun in Europe shows the increasing concern for devices using hydrogen-methane mixed gas among the countries because of environmental issues. Differences in the mixture ratio of the hydrogen-methane mixed gas were successfully determined by this sensor.
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  • Shin'ya OBARA, Shunsuke KITO, Akira HOSHI, Seizi SASAKI
    Volume 2 (2007) Issue 1 Pages 111-122
    Released: May 29, 2007
    JOURNALS FREE ACCESS
    The combustion exhaust heat of woody biomass engine using Stirling cycle is high temperature. This exhaust heat is used for the city gas reforming reaction of a proton exchange membrane fuel cell (PEM-FC) system. The woody biomass engine generator has the characteristic that the greenhouse gas amount of emission with power generation is greatly reducible. In this paper, the micro grid system that introduces PEM-FC/woody biomass engine hybrid cogeneration (PWHC) is proposed. It depends on the dynamic characteristics of the grid for the power quality at the time of load fluctuation being added to the micro grid. Especially, the dynamic characteristics of the independent micro grid are important on security of power quality. So, in this paper, the response characteristic of PEM-FC and woody biomass engine was investigated by the experiment and the numerical analysis. Furthermore, the response characteristic of the PWHC independent micro grid including auxiliary machinery was investigated by the numerical simulation. Moreover, an improvement of dynamic characteristics is proposed using the method of adding proportional-plus-integral control to PWHC. If woody biomass engine is introduced into a house, 10.2s will be required to stabilize power quality at the maximum. On the other hand, when woody biomass engine corresponds to a base load and PEM-FC corresponds to the load exceeding the base load, settling time is less than 1.6 s. In this study, relation between the system configuration of the PWHC micro grid and the dynamic characteristics of the power was clarified.
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  • Zhen-Zhe LI, Yun-De SHEN, Kwang-Su HEO, Jae-Woo LEE, Seoung-Yun SEOL, ...
    Volume 2 (2007) Issue 1 Pages 123-133
    Released: June 10, 2007
    JOURNALS FREE ACCESS
    A new method using thermal analysis database and optimization technique has been developed to substitute the original method what was based on trial and error. First, an original vacuum furnace was manufactured according to experiences. Modified baseline vacuum furnace which can be used in high temperature was produced from the original one by using experimental data and experiences. The results in 2 different conditions of nearly vacuum and argon ambient gas were investigated in order to define the worse but necessary condition between them. By comparing the analysis results with experimental results, the unknown thermal conductivity of insulator in high temperature has been found out. The calculated thermal conductivity of insulator has been applied to the process of thermal analysis database constructing under the condition of argon ambient gas which is the worse but necessary condition. In order to check the accuracy of constructed thermal analysis database, the interpolated results using constructed thermal analysis database have been compared with computational results. Finally, optimization study has been carried out to design an energy efficient, high temperature vacuum furnace which can fully satisfy user's design requirements by using the new method. Feasible optimal design has been obtained as a final product. With negligible computational cost, a high temperature vacuum furnace which has 31.9% reduction in the total heat was designed by using the new developed method.
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