Journal of Thermal Science and Technology
Online ISSN : 1880-5566
Volume 10 , Issue 2
Showing 1-8 articles out of 8 articles from the selected issue
  • Xinyu CHANG, Hosei NAGANO
    2015 Volume 10 Issue 2 Pages JTST0021
    Published: 2015
    Released: August 21, 2015
    In this study, mathematical models of multiple evaporators and condensers loop heat pipes (MLHP) were established, and several tests were conducted to identify the operating characteristics of MLHP. Flow regulators that can regulate the mass flow rate in each condenser according to each condenser's temperature were designed and applied. Pure acetone was chosen as the working fluid, and the temperature was measured by T-type thermocouples under different test conditions. Three types of tests were conducted in this study, and the corresponding mathematical models were established. When two evaporators were heated, the model reproduced the experimental data well, with the exception of the temperature of the vapor line; this difference was attributed to the effect of non-condensable gas. When one evaporator was heated, the model accurately reproduced the experimental data. Both test and calculation were performed for MLHPs operated with and without a flow regulator. When a flow regulator was employed, the compensation chamber temperature and the confluence of the liquid line were lower when MLHP was operated without a flow regulator, confirming the efficiency of the flow regulator. The ratio of mass flow rates on each side was also evaluated using the mathematical model.
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  • Shigenao MARUYAMA, Takeshi NAGAYAMA, Hiroki GONOME, Junnosuke OKAJIMA
    2015 Volume 10 Issue 2 Pages JTST0022
    Published: 2015
    Released: September 02, 2015
    Global warming is one of the most serious problems faced by humans. One method to decrease the Earth's temperature is to reduce solar irradiation by dispersing nanoparticles in the atmosphere. Submicron-diameter particles or aerosols scatter solar irradiation, whereas they are transparent to long-wavelength infrared radiation emitted by the Earth. This phenomenon has received attention in the discussions of the nuclear winter, which is an uncontrolled cooling of the global temperature. The objective of the present work is to examine the first-order approximation of the feasibility of controlling the global temperature without reducing the emission of greenhouse gases. We propose the controlled dispersion of nanoparticles into the stratosphere at an altitude of 30 km. A precise analysis of the radiative properties of particles in the solar spectrum and IR regions is conducted, and radiative transfer through the stratosphere-dispersed nanoparticles is approximated using a one-dimensional single-scattering model. Several types of nanoparticles are considered. The optimum size of the nanoparticles determined using the model is 350-450 nm. The dispersion of nanoparticles with a total mass of 3×107 tons into the stratosphere will reduce 3% of the solar irradiation. The blockage can be maintained by launching 10-ton projectiles 19 times per day from 100 launch sites.
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  • Haie HUO, Chengjun JING, Haibo HUO
    2015 Volume 10 Issue 2 Pages JTST0023
    Published: 2015
    Released: September 11, 2015
    The effect of natural ventilation on yearly transmission load and optimum insulation thickness of different orientation external walls is studied in this paper. In addition, the effects of insulation location and life-cycle cost analysis (LCC) model on optimum insulation thickness are also investigated. The research is performed for four cities in hot summer and cold winter zone in China. Expanded Polystyrene (EPS) is selected as the insulation material. A FORTRAN code developed by an implicit finite difference method is applied to calculate yearly cooling and heating transmission loads. A LCC method, which is according with the reality, is applied to determine optimum insulation thickness. Results show that insulation location almost has no effect on total yearly transmission load while natural ventilation plays a significant role in reducing the yearly cooling transmission load for all orientation walls. Moreover, it is found that natural ventilation results in obvious decrease of optimum insulation thickness and different LCC models lead to significant distinction in optimum insulation thickness. Research indicates that the effect of orientation on optimum insulation thickness cannot be ignored. At last, a sensitivity analysis on optimum insulation thickness is carried out and the results show that insulation price is the most sensitive factor.
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  • Hirofumi NOGE, Yoshiyuki KIDOGUCHI, Wira JAZAIR YAHYA, Yoko IMAI, Kazu ...
    2015 Volume 10 Issue 2 Pages JTST0024
    Published: 2015
    Released: September 11, 2015
    Water-in-diesel emulsion fuel (W/O) operated in diesel engines, shows a significant reduction of particulate matter (PM). In this paper, PM reduction characteristics by thermal decomposition of W/O10 and W/O20 (10vol.% and 20vol.% of water in W/O respectively) are identified in diesel combustion atmosphere using a plug flow reactor with a co-flow diffusion burner. To analyze initial thermal decomposition at diesel diffusion combustion, the W/O fuels are thermally decomposed in the plug flow reactor first, then the thermally decomposed W/O fuels are introduced into a co-flow diffusion burner as fuel and PM are generated. In high temperature atmosphere without oxygen in the reactor, W/O10 and W/O20 are thermally decomposed and both of them almost produce light hydrocarbons (LHCs) higher than a diesel fuel, which means thermal decomposition before combustion are encouraged by the W/O. Excitation-emission matrix (EEM) method shows that polycyclic aromatic hydrocarbons (PAHs) are produced by both W/O fuels and diesel fuel during the thermal decomposition period but some W/O fuels oxidize a huge amount of PAHs in the later diffusion combustion. CO, CO2 measurements after the combustion of the thermal decomposed substances in the diffusion burner via high temperature reactor reveal that diffusion combustion of W/O fuels contribute to Soluble Organic Fraction (SOF) and Solid reduction which leads to reduction of CO and increase of CO2 respectively.
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  • Noritsune KAWAHARADA, Daisaku SAKAGUCHI, Hironobu UEKI, Masahiro ISHID ...
    2015 Volume 10 Issue 2 Pages JTST0025
    Published: 2015
    Released: October 22, 2015
    A laser 2-focus velocimeter (L2F) was used for the measurement of diesel fuel sprays. Temporal and spatial changes in the number, velocity and size of droplets inside sprays were investigated near the nozzle orifice and were correlated with the needle valve lift of the injector nozzle. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3μm, and the distance between two foci was 17μm. The data sampling rate of the L2F system was markedly high as 15MHz. Fuel sprays were injected intermittently into the atmosphere by using a common rail injector. The orifice diameter of the injector nozzle was 0.112mm and the rail pressure was 40MPa. The periods of solenoid energizing was set at 2.0ms. Measurement positions were located at 10mm downstream from the exit of the nozzle orifice. The results show that droplets mainly existed in the region off the spray center in the early injection period and concentrated at the spray center in the middle of injection period. Temporal changes in the number of droplets near the spray center were strongly affected by the needle lift and there in the relatively wide region were affected by the injection rate. Temporal changes in the droplet velocity near the spray center were strongly affected by the injection rate. The luminance distribution of the spray image was similar to the distribution of the number of droplets multiplied by the square of droplet size.
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  • Chungpyo HONG, Yasuhiro YOSHIDA, Shinichi MATSUSHITA, Ichiro UENO, Yut ...
    2015 Volume 10 Issue 2 Pages JTST0026
    Published: 2015
    Released: December 09, 2015
    The experimental investigations on the phenomenon of supersonic flow at the exit of straight micro-tubes with diameters ranging from 150 to 530 μm were conducted. The successive incident and reflected shock wave on supersonic and under-expanded flow were visualized by the Shadowgraph and Schlieren methods. The pressure and Mach number of the under-expanded supersonic flow were determined by the angle of the shock wave generated from the needle tip. It was found that the Mach number at the exit of straight micro-tubes is beyond unity because shock waves are generated from the needle tip at the micro-tube exit. Additionally, numerical simulations based on ALE (Arbitrary-Lagrangian-Eulerian) were performed with the same conditions as the experiments to validate their results. The LB1 turbulence model was used for the turbulent flow. The compressible momentum and energy equations with the assumption of ideal gas were solved. The computational domain extends to the downstream region. The two results are in excellent agreement. The Mach number at the exit ranges from 1.16 to 1.27. The flow characteristics of the under-expanded supersonic gas flow in a straight micro-tube were revealed.
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  • Haruka YASUOKA, Tomohiko IMAE, Masayuki KANEDA, Kazuhiko SUGA
    2015 Volume 10 Issue 2 Pages JTST0027
    Published: 2015
    Released: December 22, 2015
    Nonequilibrium molecular dynamics simulations are performed for force-driven argon gas nanochannel flow to investigate the effect of the nanoscopic wall structure on the gas flow characteristics. The monoatomic molecule argon is first used for both the fluid and wall molecules. A face-centered cubic wall structure is first investigated. It is confirmed that the fcc (111) surface structure induces the fastest flow, followed by the fcc (100) and (110) surface structures. Unlike liquid flow in a nanochannel, the density of the monolayer adsorbed on the wall surface greatly depends on the wall configuration. A lattice wall configuration that allows stronger adsorption of molecules induces higher velocity flow. From simulations with different wall molecule bond lengths, the gas flow is affected more by the surface roughness than adsorption of gas molecules to the wall. Because the density close to the wall surface is affected by the surface configuration, the relationship between gas molecule density and the velocity profile is analytically investigated in the early transition regime. The results suggest that the magnitude of the adsorbed monolayer density partially causes a kink in the velocity profile. Other wall molecule configurations are also investigated, such as silicon, diamond, and graphite. It is found that the diamond structure can induce a much larger density peak than silicon owing to the high wall density. This strong adsorption to the wall disrupts the motion of fluid molecules near the wall, which results in less slippage and lower bulk velocity. The graphite structure is comparable to the diamond structure. Finally, the wall-fluid interaction of the graphite wall and argon gas is considered using different interatomic potentials for the wall and the gas. Adsorption becomes weaker and the slippage velocity is significant because the wall surface roughness becomes the dominant factor affecting the flow.
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  • Hiroyuki NISHIKAWA, Kazuyuki MATSUMURA, Shigeki OKINO, Takashi WATANAB ...
    2015 Volume 10 Issue 2 Pages JTST0028
    Published: 2015
    Released: December 28, 2015
    An experiment and a time series analysis have been made on the flow in a rectangular natural convection loop. It was found that the flow reversal occurs in a certain range of the heat flux and Reynolds number, which depends on the cooling water temperature. Based on time series temperature data of the system, an attractor in a state space has been reconstructed. Geometrical structures and orbital instability for this attractor were evaluated by the recurrence plot analysis and a nonlinear prediction by the method of local linear approximation. A nonlinear prediction was applied to the turbulence time series. As a result, a recurrence plot of the predicted time series obtained from the turbulence data has characteristics similar to those of the measured of the unstable flow. This fact suggests that, even when an apparent turbulent flow is observed, a transition to the unstable flow may occur. In order to confirm this conjecture, we have performed another experiment with the addition of a disturbance to the loop. The experimental results are consistent with the chaos analysis. We have successfully shown the validity of the nonlinear prediction and its recurrence plot as a means to evaluate dynamical flow instability.
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