• Title/Summary/Keyword: Friction Multiplier

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Experimental Study of Interfacial Friction in NaBH4 Solution in Microchannel Dehydrogenation Reactor (마이크로채널 탈수소 화학반응기에서 수소화붕소나트륨 수용액의 계면마찰에 대한 실험연구)

  • Choi, Seok Hyun;Hwang, Sueng Sik;Lee, Hee Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.2
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    • pp.139-146
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    • 2014
  • Sodium borohydride ($NaBH_4$) is considered as a secure metal hydride for hydrogen storage and supply. In this study, the interfacial friction of two-phase flow in the dehydrogenation of aqueous $NaBH_4$ solution in a microchannel with a hydraulic diameter of $461{\mu}m$ is investigated for designing a dehydrogenation chemical reactor flow passage. Because hydrogen gas is generated by the hydrolysis of $NaBH_4$ in the presence of a ruthenium catalyst, two different flow phases (aqueous $NaBH_4$ solution and hydrogen gas) exist in the channel. For experimental studies, a microchannel was fabricated on a silicon wafer substrate, and 100-nm ruthenium catalyst was deposited on three sides of the channel surface. A bubbly flow pattern was observed. The experimental results indicate that the two-phase multiplier increases linearly with the void fraction, which depends on the initial concentration, reaction rate, and flow residence time.

Boiling Heat Transfer in a Narrow Rectangular Channel with Offset Strip Fins (오프셋 스트립 휜이 있는 협소 사각유로의 비등열전달)

  • Kim Byong Joo;Jeong Eun Soo;Sohn Byong Hu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.10
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    • pp.977-983
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    • 2004
  • An experimental study on saturated flow boiling heat transfer of R113 was peformed in a vertical narrow rectangular channel with offset strip fins. Two-phase pressure gradients and boiling heat transfer coefficients in an electrically heated test section were measured in the range of quality $0{\sim}0.6$, mass flux $17{\sim}43kg/m^{2}s$, and heat flux of $500{\sim}3,000W/m^2$ Two-phase friction multipliers were determined as a function of Lockhart-Martinelli parameter. Local boiling heat transfer coefficients were analysed in terms of mass flux, heat flux and local vapor quality. Correlation for boiling heat transfer coefficients was proposed, which was in good agreement with experimental data.

Prediction of Reactor Coolant Pump Performance Under Two-Phase Flow Conditions (이상유동시 원자로 냉각재 펌프의 성능 예측)

  • Lee, S.;Bang, Y.S.;Kim, H.J.
    • Nuclear Engineering and Technology
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    • v.26 no.2
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    • pp.179-189
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    • 1994
  • A performance of reactor coolant pump in two-phase flow is examined using the pump geometric conditions and the performance of the pump in single-phase flow. Wall friction loss of the reactor coolant pump in single-phase flow is prdicted using the Truckenbrodt boundary layer theory, and the head loss in two-phase flow is predicted with calculated well friction loss and separation loss coefficients. The analysis results are compared with the Combustion Engineering pump test data. The effect of two-phase multiplier on the peak clad temperature in Loss-of-Coolant Accident is also examined using the RELAP5 and the results indicate the importance of its accuracy.

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Pressure Drop due to Friction in Small Rectangular Channel (미소 사각 채널에서의 마찰 압력 강하)

  • Lim, Tae-Woo;Choi, Jae-Hyuk;Kim, Jun-Hyo;Choi, Yong-Suk
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.18 no.5
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    • pp.461-467
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    • 2012
  • An experimental study was carried out to measure frictional pressure drop in flow boiling to deionized water in a microchannel having a hydraulic diameter of $500{\mu}m$. Tests were performed in the ranges of heat fluxes from 100 to $400kW/m^2$, vapor qualities from 0 to 0.2 and mass fluxes of 200, 400 and $600kg/m^2s$. The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. From the experimental results, it is found that the two phase multiplier decreases with an increase in mass flux. Measured data of pressure drop are compared to a few available correlations proposed for macroscale and mini/microscale. The homogeneous model well predicted frictional pressure drop within MAE of 29.4 % for the test conditions considered in this work.

Anisotropic Version of Mohr-Coulomb Failure Criterion for Transversely Isotropic Rock (횡등방성 암석의 강도해석을 위한 이방성 Mohr-Coulomb 파괴조건식)

  • Lee, Youn-Kyou;Choi, Byung-Hee
    • Tunnel and Underground Space
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    • v.21 no.3
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    • pp.174-180
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    • 2011
  • An anisotropic version of Mohr-Coulomb failure criterion is proposed in order to provide a strength criterion for transversely isotropic rock. The concept of fabric tensor introduced by Pietruszczak & Mroz (2001) is employed to define the friction angle and cohesion as scalar functions of the fabric tensors. The anisotroy in these two strength parameters are calculated in association with the consideration of the relative rotation between the principal stress coordinate and the principal material triad. The critical plane on which the anisotropic function maximized is found by an optimization technique based on the Lagrange multiplier method. To demonstrate the performance of the anisotropic failure criterion, conventional triaxial tests on the samples having various inclinations of weakness plane are simulated and the resulting triaxial strength and dip angle of failure plane are discussed.

Frictional Pressure Drop of a Capillary Tube Flow of Pure HFC Refrigerants and Their Mixtures (HFC 순수냉매 및 혼합냉매의 모세관내에서 마찰에 의한 압력강하)

  • Chang, S.D.;Ro, S.T.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.7 no.4
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    • pp.589-599
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    • 1995
  • The frictional pressure drop of a capillary tube flow is experimentally investigated for pure refrigerants such as R32, R125, and R134a and refrigerant mixtures such as R32/R134a(30/70 by mass percent), R32/R125(60/40), R125/R134a(30/70), and R32/R125/R134a(23/25/52). The binary interaction parameters for the calculation of viscosities of refrigerant mixtures are found based upon the data in the open literature. Several homogeneous flow models predicting the viscosity of two-phase region are compared to select the best model. Cicchitti's equation is known to be the most adequate for the prediction of the viscosity for refrigerant mixtures, which is used in the analysis of adiabatic capillary flows. A model for the prediction of the frictional pressure drop of single and two-phase flow is developed for refrigerant mixtures in this study. This model may be used to design and analyze the performance of a capillary tube in the refrigerating system.

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Experimental Study about Two-phase Damping Ratio on a Tube Bundle Subjected to Homogeneous Two-phase Flow (균질 2상 유동에 놓인 관군에 작용하는 감쇠비에 대한 실험적 연구)

  • Sim, Woo Gun;Dagdan, Banzragch
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.3
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    • pp.171-181
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    • 2017
  • Two-phase cross flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. The drag force acting on a tube bundle subjected to air/water flow is evaluated experimentally. The cylinders subjected to two-phase flow are arranged in a normal square array. The ratio of pitch to diameter is 1.35, and the diameter of the cylinder is 18 mm. The drag force along the flow direction on the tube bundles is measured to calculate the drag coefficient and the two-phase damping ratio. The two-phase damping ratios, given by the analytical model for a homogeneous two-phase flow, are compared with experimental results. The correlation factor between the frictional pressure drop and the hydraulic drag coefficient is determined from the experimental results. The factor is used to calculate the drag force analytically. It is found that with an increase in the mass flux, the drag force, and the drag coefficients are close to the results given by the homogeneous model. The result shows that the damping ratio can be calculated using the homogeneous model for bubbly flow of sufficiently large mass flux.