Journal of Thermal Science and Technology
Online ISSN : 1880-5566
Volume 9 , Issue 2
Showing 1-10 articles out of 10 articles from the selected issue
Papers
  • Toshiaki HANAOKA, Yukihiko OKUMURA
    2014 Volume 9 Issue 2 Pages JTST0006
    Published: 2014
    Released: July 04, 2014
    JOURNALS FREE ACCESS
    The effects of Fe and K contents of Fe- and K-loaded chars containing 0-23% Fe and 0-20% K, respectively, with negligible amounts of poisoning elements, on the CO2 gasification behavior (C + CO2 2CO) were investigated in the temperature range of 750-1050°C. For 23% Fe-loaded char at gasification temperatures of 900 and 1000 °C, the CO2 gasification rate constants (Kp) were respectively 3.3 times and ~ 8 times higher than those of the char without Fe. At 900 °C, the Kp value increased with an increase in the Fe content up to 10% and remained almost constant above 10% Fe. For K-loaded chars, the Kp value of the char loaded with 10% K had a maximum value of 5.4 min−1at 900 °C; this value was ~ 300 times that of the char without K loading and ~ 90 times higher than the corresponding Kp values of Fe-loaded chars at 900 °C. The addition of excess K (upon loading greater than 10%) to bio-char decreased the Kp because of the decrease in the number of active sites on the char surface.
    Download PDF (786K)
  • Shung-Wen KANG, Chun-Hsien HUANG, Yu-Tang CHEN
    2014 Volume 9 Issue 2 Pages JTST0007
    Published: 2014
    Released: July 28, 2014
    JOURNALS FREE ACCESS
    A prototype two-phase loop thermosyphon (TPLT) was built and tested for thermal performance. This experimental study simultaneously investigated the evaporator resistance and flow visualization in operating the TPLT under sub-atmospheric pressure. To facilitate the visualization of flow regime in the evaporator, a transparent glass window was attached to the evaporator. Evaporators with 1-mm-thick sintered copper powder wicks (average diameter, 100 μm) were used. Temperature distribution and evaporator resistance were measured while increasing the input power in a series of 11 steps (20, 60, 100, 120, 140, 160, 180, 200, 220, 240, and 260 W) until the sintered wicks reached completely dried out. Temperature fluctuations and instabilities in the vapour and liquid lines were observed. Heat leakage from the evaporator and intermittent motion in the flow regime were significant factors in generating the implicit boiling instability. As the input power was increased, onset of pool boiling, nucleate boiling, as well as slug and bubbles were observed successively when the liquid level was above the surface of the wicks. When the net input power reached 236 W, the water film suddenly receded toward the wick surface. The process of the meniscus receding during the film evaporation, and the dynamics from the initial condition until dryout on the sintered copper wicks were observed and documented.
    Download PDF (1659K)
  • Adetayo Samuel EEGUNJOBI, Oluwole Daniel MAKINDE
    2014 Volume 9 Issue 2 Pages JTST0008
    Published: 2014
    Released: August 14, 2014
    JOURNALS FREE ACCESS
    This paper investigates numerically the entropy generation rate in an transient variable viscosity Couette flow between two concentric pipes. The nonlinear governing equations for momentum and energy balance are obtained and solved using semi-discretization finite difference method coupled with Runge-Kutta-Fehlberg integration scheme. The velocity and the temperature profiles are obtained and used to determine the entropy generation rate. Graphical results are presented to depict the effects of various embedded parameters on velocity profiles, temperature profiles, entropy generation rate and the Bejan number.
    Download PDF (748K)
  • Hirotatsu WATANABE, Yutaka SHOJI, Takuma YAMAGAKI, Jun HAYASHI, Fumite ...
    2014 Volume 9 Issue 2 Pages JTST0009
    Published: 2014
    Released: August 14, 2014
    JOURNALS FREE ACCESS
    The study aims to visualize droplet behaviors of emulsified fuel in secondary atomization in a flame stabilized in a laminar counterflow field. To study secondary atomization characteristics in the flame, direct photography of the flame using a color high-speed video camera (7,000 fps) and magnified shadow imaging of spray droplets using a monochrome high-speed video camera (180,064 fps) were used. Frequencies of secondary atomization in the flame were also discussed. As a result, “bright spots,” which were of similar or higher luminosity than the surrounding area were observed by direct photography around the luminous flame of the emulsified fuel, whereas the frequency of occurrence of “bright spots” was almost negligible when n-dodecane was used. Observations indicated that the droplet flame rapidly expanded. This expansion was linked to secondary atomization phenomena such as puffing (i.e., vapor eruption from the droplet surface), partial micro-explosion (i.e., where a large portion of a droplet bursts), and micro-explosion (i.e., where the entire droplet bursts), which were visualized in the flame by magnified shadow imaging. It was suggested that secondary atomization caused rapid evaporation and spread of fuel vapor. The magnified shadow imaging technique provided a clear description of droplet behavior in the flame. Numerous puffing and micro-explosion were observed regardless of the flame emissions. In addition, it was observed that vapor blowout in secondary atomization accelerated droplet velocity, and led to the random movement of spray droplet. It was shown that the frequencies of secondary atomization increased in the downstream region where the luminous flame was formed. Secondary atomization occurred in droplets of various sizes in the downstream region, whereas it occurred in only small droplets in the upstream region where the luminous flame was not formed.
    Download PDF (694K)
  • Ken TERAKAWA, Tatsuya SAITO, Yuji NAKAMURA, Tsuneyoshi MATSUOKA, Harun ...
    2014 Volume 9 Issue 2 Pages JTST0010
    Published: 2014
    Released: August 20, 2014
    JOURNALS FREE ACCESS
    Flame spread and counterflow diffusion flame experiments are widely conducted to investigate the combustibility of solid fuels. Although the use of the gas phase Damköhler number to organize the flame spread rate or regression rate of a solid fuel is effective under constant pressure, some research point out the possibility that the combustion pressure may be an independent factor in determining the regression rate. This research employs a counterflow diffusion flame to investigate the effects of combustion pressure on regression rate, and clarifies the deviation of results using the classical Damköhler number under varying pressures. First, a numerical flow analysis was conducted to determine the oxidizer velocity gradient near the fuel surface, which is an essential factor in evaluating the non-dimensional regression rate. Next, using an enclosed combustion chamber with independently variable oxidizer flux and pressure, experiments with a quasi two-dimensional flame were conducted with polyethylene solid fuel and nitrogen diluted oxygen oxidizer, and the regression rate was measured for two experiment series, constant pressure, and constant oxidizer flux. By comparing the two series, the effect of pressure on non-dimensionalized regression rate is clarified. The results suggest that contrary to the theoretical reaction rate of the gas phase, the non-dimensional regression rate increases when the combustion pressure is decreased, even in the thermal regime. This suggests that the classic method of organizing the regression rate with Damköhler number in thermal regime could not be implemented with varying pressure conditions, possibly due to the change in diffusion rates involved with varying pressures.
    Download PDF (2816K)
Short Paper
  • Slawomir BLASIAK, Jakub Emanuel TAKOSOGLU, Pawel Andrzej LASKI
    2014 Volume 9 Issue 2 Pages JTST0011
    Published: 2014
    Released: September 09, 2014
    JOURNALS FREE ACCESS
    The simulations conducted for non-contacting face seals show that performance-related parameters greatly affect the distribution of temperature in the fluid film causing thermal deformations of the sealing rings. The results indicate that the thermal deformations of the rings should be taken into account at the design stage, especially when non-contacting face seals are to be used in high-performance systems. The mathematical model of heat transfer used for the simulations consists of a system of coupled differential equations with partial derivatives, including heat equations and an energy equation with precisely defined boundary conditions. The calculated distributions of temperature were used to determine the values of thermal deformations of the sealing rings.
    Download PDF (1213K)
Papers
  • Haiqiang LIU, Lin LU, Zhongjun WANG
    2014 Volume 9 Issue 2 Pages JTST0012
    Published: 2014
    Released: October 06, 2014
    JOURNALS FREE ACCESS
    The performance of the two-stroke engine depends on the scavenging process, which affects air-fuel mixture and combustion. This paper presents results from experiments in which the timing of exhaust valve opening and closing was varied in two-stroke marine diesel engine during shop testing, and reveals the effect on performance and emission, as well as the corresponding concept analysis. A simulation model was then developed based on AVL BOOST and experimental results, its validity was confirmed by actual measurements. This simulation enables a more thorough investigation into engine performance features and the scavenging process. In particular it provides a detailed examination of how changes in EVO and EVC timing impact the scavenging process and ultimately engine performance. These results are summarized, and based on these results, optimal EVO and EVC settings are suggested for balancing the scavenging process, and also the engine performance and NOx emissions.
    Download PDF (822K)
  • Shin'ya OBARA, Takuya KANAI, Kenji ISHIZAWA, Jorge Morel
    2014 Volume 9 Issue 2 Pages JTST0013
    Published: 2014
    Released: November 25, 2014
    JOURNALS FREE ACCESS
    A small-scale energy network present at the Antarctic Syowa Base (Syowa Base microgrid, SBMG) has issues related to the amount of fuel transported from Japan and the environmental impact from emissions. Therefore, the Syowa Base is considering the introduction of photovoltaics (PV) and wind power generations to drastically increase the local supply and consumption of energy. After the introduction of a type of heat supply system, heat pump system, using engine exhaust heat and an electric storage heater hybrid system into SBMG, the reduced introductory rate of renewable energy and fuel consumption at the Syowa Base was investigated. Results confirmed a reduction in fuel consumption of the base by heat storage using renewable energy, following the introduction of a heat pump and electric storage heater hybrid system. However, for the electric storage heater to function year round, extensive wind power generation was required. The heat pump and electric storage heater hybrid system reduced fuel consumption of the Syowa Base by 15 % in January. On the other hand, hybrid systems reduced fuel consumption to about half of the present system. Fuel reduction was not observed in July and October because these months had a much greater heat demand. Reduction in fuel consumption of the whole base required an increase in the amount of wind power generation, which was influenced very little by the seasonal changes, and an optimization of the electric storage heater operation.
    Download PDF (1669K)
  • Reiko KURIYAMA, Yohei SATO
    2014 Volume 9 Issue 2 Pages JTST0014
    Published: 2014
    Released: December 17, 2014
    JOURNALS FREE ACCESS
    The present study proposes a velocity measurement based on thermal tracing by Raman imaging and investigates its applicability focusing on the error in temperature measurement, towards the establishment of a non-intrusive and micro-scale velocimetry. In order to realize fluorescence-free measurement, two-wavelength Raman imaging was employed to measure the temperature field in a channel flow. This technique exploits the contrasting temperature dependencies of hydrogen-bonded (HB) and non-hydrogen-bonded (NHB) OH stretching Raman bands of liquid water, and enables the determination of planar temperature distributions from the intensity ratio of the HB to NHB images. A calibration experiment showed a linear relationship between the temperature and the Raman intensity ratio in the range 293-333 K with temperature sensitivity of -0.56% K-1. It was also confirmed that the spatial variation of the intensity ratio led to a large measurement error (approximately 9.1 K). Afterwards Raman images were acquired with various measurement conditions, and the influence of each parameter on the measurement error was quantitatively investigated. The apparent temperature variance was considerably reduced by increasing electron-multiplying gain and binning factor for spatial averaging, whereas an increase in the size of the measurement area resulted in a quadratic increase in the temperature variance due to the inhomogeneous excitation intensity. Finally, the requirements of the thermal flow conditions for the present methodology to be applied were quantitatively examined according to the measurement results.
    Download PDF (2239K)
  • Saiful HASMADY, Kazuyoshi FUSHINOBU
    2014 Volume 9 Issue 2 Pages JTST0015
    Published: 2014
    Released: December 17, 2014
    JOURNALS FREE ACCESS
    This paper reports a numerical study on the effects of CO contamination towards the distribution of chemical species, surface coverage, current density and temperature inside a PEMFC using a kinetics-transport bridging model. Bridging is done by linking macro-scale, macro-homogeneous transport phenomena models with micro-scale contamination kinetics model via conversion of the surface concentration of the reactants on the rough electrocatalyst into surface site coverage of the participating adsorbates using Langmuir-Freundlich isotherm. The effects of CO contamination is investigated by solving the bridged model iteratively under steady state, single phase and non-isothermal conditions in three-dimensions. The effect of CO-ad presence on the electrocatalyst surface towards distribution of chemical species, current density and temperature is discussed at cell temperature of 70°C and two nominal current densities of 0.5 and 1.0 A/cm2. The results show that the region under the ribs at anode catalyst layer registered higher magnitude of current density due to blockage from CO-ad under channel. The anode catalyst layer also shows an increase in local temperature comparable to the cathode catalyst layer that can aggravate dehydration of the membrane, which in turn affect its durability in long-term operation.
    Download PDF (2712K)
feedback
Top