• Title/Summary/Keyword: Water Channels

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Limitations of the Transition State Variation Model. Part 8. Dual Reaction Channels for Solvolyses of 3,4-Dimethoxybenzenesulfonyl Chloride

  • Koo, In-Sun;Kwon, Eun-Ju;Choi, Ho-June;Yang, Ki-Yull;Park, Jong-Keun;Lee, Jong-Pal;Lee, Ikc-Hoon;Bentley, T. William
    • Bulletin of the Korean Chemical Society
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    • v.28 no.12
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    • pp.2377-2381
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    • 2007

  • Solvolyses of 3,4-dimethoxybenzenesulfonyl chloride (DSC) in water, D2O, CH3OD, and in aqueous binary mixtures of acetone, acetonitrile, 1,4-dioxane, ethanol, methanol, and 2,2,2-trifluoroethanol (TFE) have been investigated at 25.0 oC. Kinetic solvent isotope effects (KSIE) in water and in methanol and product selectivities in alcohol-water mixtures are also reported. The Grunwald-Winstein plot of first-order rate constants for the solvolyic reaction of DSC with YCl shows marked dispersions into separated lines for various aqueous mixtures. With use of the extended Grunwald-Winstein equation, the l and m values obtained are 1.12 and 0.58 respectively for the solvolyses of DSC. The relatively large magnitude of l is consistent with substantial nucleophilic solvent assistance. From Grunwald-Winstein plots the rate data are dissected approximately into contributions from two competing reaction channels. This interpretation is supported for alcohol-water mixtures by the trends of product selectivities, which show a maximum for ethanol-water mixtures. From the KSIE of 1.45 in methanol, it is proposed that the reaction channel favored in methanolwater mixtures and in all less polar media is general-base catalysed and/or is possibly (but less likely) an addition-elimination pathway. Also, the KISE value of 1.35 for DSC in water is expected for SN2-SN1 processes, with minimal general base catalysis, and this mechanism is proposed for solvolyses in the most polar media.

  • https://doi.org/10.5012/bkcs.2007.28.12.2377 인용 PDF KSCI

Counter-Current Gas-Liquid Two-Phase Flow in Narrow Rectangular Channels with Offset Strip Fins (휜이 있는 협소 사각 유로에서 대향류 기/액 2상 유동)

  • Sohn, B.H.;Kim, B.J.;Jeong, S.
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.229-234
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    • 2001

  • An adiabatic counter-current vertical two-phase flow of air and water in narrow rectangular channels with offset strip fm was investigated experimentally. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.06 m/s and 0 to 2.5 m/s ranges, respectively. Two-phase flow regimes were classified by examining the video images of flow patterns in transparent test sections of 760 mm long and 100 mm wide channel with gaps of 3.0 and 5.0 mm. The channel average void fraction was measured by the quick-closing valve method. Unlike the flow regimes in the channels without fin, where bubbly, slug, chum, and annular flow were identified, only bubbly and chum flow regimes were found for the channels with offset strip fin. However the existence of fin in the channels showed negligible effects on the void fraction. Instead counter-current flow limitations were found to happen at lower air superficial velocity once offset strip fin was introduced in narrow rectangular channels.

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The Flow Field of Undershot Cross-Flow Water Turbines Based on PIV Measurements and Numerical Analysis

  • Nishi, Yasuyuki;Inagaki, Terumi;Li, Yanrong;Omiya, Ryota;Hatano, Kentaro
    • International Journal of Fluid Machinery and Systems
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    • v.7 no.4
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    • pp.174-182
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    • 2014

  • The ultimate objective of this study is to develop a water turbine appropriate for low-head open channels to effectively utilize the unused hydropower energy of rivers and agricultural waterways. The application of a cross-flow runner to open channels as an undershot water turbine has been considered and, to this end, a significant simplification was attained by removing the turbine casing. However, the flow field of an undershot cross-flow water turbine possesses free surfaces, and, as a result, the water depth around the runner changes with variation in the rotational speed such that the flow field itself is significantly altered. Thus, clear understanding of the flow fields observed with free surfaces to improve the performance of this turbine is necessary. In this study, the performance of this turbine and the flow field were evaluated through experiments and numerical analysis. The particle image velocimetry technique was used for flow measurements. The experimental results reflecting the performance of this turbine and the flow field were consistent with numerical analysis. In addition, the flow fields at the inlet and outlet regions at the first and second stages of this water turbine were clarified.

  • https://doi.org/10.5293/IJFMS.2014.7.4.174 인용 PDF KSCI