Journal of Power and Energy Systems
Online ISSN : 1881-3062
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  • Yoichi UTANOHARA, Yukinori NAGAYA, Akira NAKAMURA, Michio MURASE, Koic ...
    2013 Volume 7 Issue 3 Pages 138-147
    Published: 2013
    Released: September 03, 2013
    JOURNALS FREE ACCESS
    Flow accelerated corrosion (FAC) thinning rate downstream from an orifice was measured under different velocity conditions in a high-temperature water test loop to understand the effects of flow velocity on FAC thinning rate. The FAC tendency differed downstream and upstream from the orifice. The metal loss increased linearly with time downstream from the orifice, though metal loss rate gradually decreased with time upstream. FAC rate increased as flow velocity increased, particularly from 1D to 3D. The maximum FAC thinning rate increased in proportional to the 0.51th power of the mean cross-sectional velocity in this experiment. The root mean square (RMS) of wall shear stress predicted by large eddy simulation (LES) had a clear relationship with FAC thinning rate. This result indicated that FAC thinning rate can be described as a function of the wall shear stress. Additionally, the mass transfer coefficient estimated from the RMS of wall shear stress had an almost linear correlation with FAC thinning rate.
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  • Yasushi MUTO, Yasuyoshi KATO
    2013 Volume 7 Issue 3 Pages 148-161
    Published: 2013
    Released: September 11, 2013
    JOURNALS FREE ACCESS
    The supercritical CO2 gas turbine cycle can achieve high cycle thermal efficiency by reducing compressor work near the critical point. The achievable cycle thermal efficiency value is strongly dependent on the recuperator performance. Values of the achievable cycle thermal efficiency are calculated by assuming a value of average recuperator temperature-effectiveness of 91%. The turbine inlet pressure is 20 MPa. The effects of turbine inlet temperature are examined. The calculations are conducted both for the non-intercooling cycle and the intercooling cycle. Results show that the non-intercooling cycle is preferred to the intercooling cycle up to 600°C because of its simplicity. However, the latter is preferred to the former at temperatures greater than 600°C attributable to its approximately 2% higher efficiency. For the typical temperature of 527°C and also 650°C, the diagrams of mass and heat balance are given. The maximum cycle thermal efficiencies are, respectively, 43.4% and 48.9% for 527°C and 650°C. The effects of pressure are examined and 20 MPa is justified as an optimal value. Finally, the effects of recuperator effectiveness on the cycle thermal efficiency are examined, which are revealed to be linear and the cycle thermal efficiency increases about 0.5% for a 1% increase of the recuperator effectiveness.
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  • Luis A. R. QUADRANTE, Yoshiki NISHI
    2013 Volume 7 Issue 3 Pages 162-176
    Published: 2013
    Released: November 15, 2013
    JOURNALS FREE ACCESS
    We conducted an experiment to quantify the increase in efficiency of energy extraction from a constant flow that can be obtained by attaching a pair of tripping wires to an elastically mounted cylinder under influence of vortex-induced vibrations. Free oscillation tests were carried with three different cylinder configurations: smooth, with tripping wires positioned at angular positions equal to 60° and 75°. The Reynolds number varied from 2.9×103 to 2.2×104. We measured the amplitude of oscillation and the output voltage to calculate the power generated and conversion efficiency. The maximum power generation occurred when tripping wires were positioned at 60° and reduced velocity was 12, but only a 2.88% efficiency was achieved at this case. The maximum efficiency obtained was 12.47% and occurred when tripping wires were positioned at 75°, with reduced velocity 6.5. The maximum efficiency with tripping wires attached was about four times larger than the maximum efficiency obtained on smooth cylinder case. The presence of tripping wires also widen the lock-in region and when they were placed at 75° an almost constant power generation was obtained within reduced velocity ranging from 6 to 8.5, meaning that it is possible to design a system that generates the same amount of power even with variations on flow speed.
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