Thermal Science and Engineering
Online ISSN : 1882-2592
Print ISSN : 0918-9963
ISSN-L : 0918-9963
Volume 16 , Issue 1
Showing 1-6 articles out of 6 articles from the selected issue
  • Kazuma HIROSAKA, Korakot YUVAMITRA, Akira ISHIKAWA, Tatsuya HASEGAWA
    2008 Volume 16 Issue 1 Pages 1-9
    Published: 2008
    Released: May 08, 2008
    JOURNALS FREE ACCESS
    Wet biomass is hard to handle as a fuel for power plants because it contains high moisture and its drying process needs more energy input than it produces. Hydrothermal oxidation could be one of the promising technologies to overcome this problem because this process does not need drying process at all. We focus on recovery of thermal energy produced by hydrothermal oxidation of wet biomass. Two kinds of power plant are investigated, a direct type and an indirect type. In the direct type power plant, reactant is oxidized in a reactor and directly flowed into a turbine. In the indirect type power plant, reactant is oxidized in a reactor and the reaction heat is conveyed to the main water, which is flowed into a turbine. The amount of electric power and the energy conversion efficiency are calculated by using ethanol, glucose and peat solutions as reactants. In both type of power plant, one steam turbine is employed for generating electricity with the maximum turbine inlet temperature of 650 °C. As ethanol concentration increased, the amount of electric power and the energy conversion efficiency become higher. The maximum efficiency for the direct type power plant using ethanol solution is about 26.4 % for 17.6 wt% at the reactor pressure of 10 MPa. The efficiency of the indirect type power plant is much lower than that of the direct type, but by pressurizing main water up to 4 MPa, the efficiency becomes higher up to 20.9 %. For glucose solution, the maximum efficiency for the direct type is about 25.5 % for 34.5 wt% at the reactor pressure of 5 MPa. The maximum efficiency of the indirect type at the main water pressure of 4 MPa is about 21.1 % for 40.7 wt%. For peat solution, only the indirect type is investigated. The maximum efficiency at the main water pressure of 4 MPa is about 20.8 % for 36.8 wt%.
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  • Yukihiro YONEMOTO, Tomoaki KUNUGI
    2008 Volume 16 Issue 1 Pages 11-29
    Published: 2008
    Released: May 08, 2008
    JOURNALS FREE ACCESS
    A gas-liquid interface contains various complex physics and unknown phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. Therefore, a modeling of gas-liquid interface is one of key issues of the numerical research on multiphase flows. Currently, the Continuum Surface Force model (CSF) is popular to model a gas-liquid interface in computational fluid dynamics. However, the CSF model cannot explain the physics of the gas-liquid interface because it is derived through a mechanical energy balance at the interface. In this study, by assuming a gas-liquid interface as a fluid-membrane with a thin but finite thickness, we develop a new gas-liquid interface model based on thermodynamics via mathematical approach. In particular, we derive an equation of free energy based on a lattice gas model including the effect of the electric double layer caused by a contamination on the interaction between the bubble interfaces. Finally, we derive a set of new governing equations for fluid motion based on a mesoscopic concept. The free energy is incorporated into the Navier-Stokes equation as new terms by using Chapman-Enskog expansion. Moreover, by using the new governing equation, we derive the jump condition at the gas-liquid interface based on thermodynamics. Then, we compare the obtained thermodynamic jump condition with the conventional one. As a result, we reveal that the conventional jump condition is true under a specific condition and that thermodynamic jump condition provides more general formalism than the conventional one.
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  • Masanori FUJIMOTO, hiro TOCHITANI
    2008 Volume 16 Issue 1 Pages 31-40
    Published: 2008
    Released: May 08, 2008
    JOURNALS FREE ACCESS
    This paper deals with the stabilization of the formation of conic waves on a liquid-liquid interface under electric field. It is known that the interface becomes unstable when the electric field is perpendicularly applied to the interface, and the conic waves that are sometimes called Taylor cone are formed. The liquid drops are generated from these waves. In this study, the stabilization of the interface behavior has been achieved by setting up the metal-net of square mesh or rectangular mesh which restrains the movement of the interface, so that the wave is periodically generated in mesh. Distilled water and silicone oil are used in the experiment. A positive electrode of 80 mm×80 mm is set in the oil, and a negative one in water. Pictures of the phenomena of the interface are taken with the video camera of normal-speed or high-speed, and analyzed precisely on the monitor. As a result, the waves and drops formed are steady and uniform. The size of the mesh influences the formation period of the waves. When the size increases, the period lengthens. The mechanism of the drop formation divides into two types. One type is generated from the tip of the conic wave generated in a mesh. In the other type, the liquid column which results from the growth of the conic wave disintegrates, and becomes drops of comparatively large diameter. It is also shown that a liquid column can be formed by composing two reflection waves in a rectangular mesh.
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  • Takanari MIZUSHIMA, Takaaki INADA, Fumio TAKEMURA, Akira YABE, Hiroshi ...
    2008 Volume 16 Issue 1 Pages 41-48
    Published: 2008
    Released: May 08, 2008
    JOURNALS FREE ACCESS
    Clathrate hydrate of tetra n-butyl ammonium fluoride (TBAF) is a promising thermal storage material, because this clathrate can be produced from TBAF solutions at temperatures between 0 and 27 °C under the atmospheric pressure. In this study, melting characteristics of the TBAF clathrate hydrate were investigated by using a differential scanning calorimeter (DSC). Four types of endothermic peaks were observed in DSC curves during melting, when the TBAF clathrate was produced from TBAF solutions at initial concentrations between 10 and 55 wt%. One of these peaks cannot be explained by the existing phase diagram. This endothermic peak suggests an unknown crystal structure of TBAF clathrate that coexists stably with TBAF solutions at a concentration higher than 50 wt%. X-ray diffraction data of TBAF clathrate also supported the existence of this unknown crystal structure. Enthalpy changes corresponding to the four types of endothermic peaks in DSC curves were evaluated. The results showed that the TBAF clathrate can be used as a thermal storage material at 29 °C, which is nearly equal to the congruent melting point of TBAF clathrate.
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  • Yukihiro YONEMOTO, Tomoaki KUNUGI
    2008 Volume 16 Issue 1 Pages 49-60
    Published: 2008
    Released: May 08, 2008
    JOURNALS FREE ACCESS
    The Young’s equation describes the interfacial equilibrium condition of a liquid droplet on a smooth solid surface. This relation is derived by Thomas Young in 1805. It has been discussed until today after his work. In general, the Young’s equation is discussed from the viewpoint of thermodynamics and derived by minimizing the total free energy of the system with intensive parameters in the total free energy kept constant, i.e., the variation of the total free energy is zero. In the derivation, the virtual work variations in the horizontal and vertical directions of the droplet on the smooth solid are considered independently. However, the virtual work variation at the droplet surface depends on the variation of the horizontal and vertical directions. This point has been overlooked in the past studies. In this study, by considering this directional dependency, we derived the modified Young’s equation based on the thermodynamics. Finally, we evaluated the modified Young’s equation by comparing the analytical solution of the relationship between a contact angle and the contact line radii of the droplet with some experimental data. Moreover, we investigated the line tension itself.
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  • 2008 Volume 16 Issue 1 Pages 61-62
    Published: 2008
    Released: May 08, 2008
    JOURNALS FREE ACCESS
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