• Title/Summary/Keyword: recirculation flow

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Examination on High Vibration of Recirculation System for Feed Water Piping in Combined Cycle Power Plant (복합 발전소 주급수 재순환 배관계의 고진동 현상 및 대책)

  • Kim, Yeon-Whan;Kim, Jae-Won;Park, Hyun-Gu
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.04a
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    • pp.648-654
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    • 2011
  • The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

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Slurry Flow Simulation in the Separation Stage of Screw Decanter (스크류 데칸트 분리단 내부에서의 유동 해석)

  • Baek, Yeong-Su;Na, Eun-Su;Park, Jae-Deok
    • 연구논문집
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    • s.31
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    • pp.53-63
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    • 2001
  • Numerical investigation based on the control-volume using finite-difference method has been made by the development of computer program in order to figure out the pattern of the flow field inside screw decanter. The typical flow pattern inside screw decanter is characterized by the two strong recirculation zones separated by the main stream from slurry discharge hole to exit. These recirculation regions and flow pattern are strongly influenced by the centrifugal force and the change of the value of slurry viscosities, that is,500, 1,000 and 3,000cp respectively. The wear of screw decanter appeared experimentally in two spots; one is near the circumferential area of the slurry discharge hole and the other is on the decanter blades at a certain height from the bottom to a different degree after the continuous long-term operation. These wears are partly explained by the flow pattern and the strong turbulence intensity near the recirculation attachment region.

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The Influences of LiBr Solution Recirculation in Absorber on the Absorption Chiller Performance (흡수기 용액 재순환이 흡수식 냉동기 성능에 미치는 영향)

  • Jeong, Jong-Su;Jin, Seong-Min;Park, Chan-U;Choe, Seung-Hak;Jeong, Bong-Cheol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.5
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    • pp.733-741
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    • 2002
  • If a part of the poor solution from the absorber outlet is recirculated to the absorber inlet, the solution temperature at the solution spray pump can be reduced, and the solution flow rate in the absorber is increased. We have performed the experiments on the influences of the absorption chiller performance according to the ratio of the recirculation, defined as the ratio of the recirculation flow rate to the total solution flow rate at the absorber outlet. As increasing the ratio of the recirculation, the absorption capacity of the solution can be deteriorated. On the other hand, due to the increasing flow rate, the heat transfer rate can be enhanced. As a result, the performance of the absorber and the cooling capacity of the absorption chiller have nothing to do with the recirculation ratio, and the lifetime of the spray pump will be maintained.

A study on the flow characteristics in a MILD combustion waste incinerator with the change of flue gas recirculation inlet location (MILD 연소 폐기물 소각로에서 배기가스 재순환 흡입구 위치에 따른 유동 특성 연구)

  • Ha, Ji Soo;Shim, Sung Hun;Jung, Eung Ho
    • Journal of Energy Engineering
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    • v.23 no.3
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    • pp.51-57
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    • 2014
  • A MILD(Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow position of hot exhaust gas to the combustion furnace. A numerical analysis was accomplished to elucidate the flow characteristics in the MILD combustion incinerator for several cases with or without exhaust gas recirculation. It could be seen from the result of the present numerical study that the flow recirculation could be observed in the upper region over the vertical dividing wall for the case without exhaust gas recirculation. The optimal position of exhaust gas recirculation position was derived by the comparison of %RMS of x directional velocity for the cases with exhaust gas recirculation. The case with the exhaust gas recirculation position at the upper right of free board was the most effective with the smallest value of 57.4% RMS.

A Study on the Numerical Analysis of Internal Flow in a Cone Type Valve (Cone Type 밸브 내부유동 수치해석에 관한 연구)

  • Chin, Do-Hun
    • Journal of the Korean Society of Industry Convergence
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    • v.23 no.2_2
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    • pp.199-207
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    • 2020
  • These days, many different types of valves are developed in the industrial area according to their use purpose. Multiple kinds of valves are installed to control a flow and pressure of the pipe conveying fluid. Valves serve as critical roles in land plants such as power plants. The performance of equipment varies depending on valve characteristics. In this study, the internal flow analysis on Cone-type valve is conducted to analyze flow field and secure a value of the flow coefficient Cv. According to the internal flow analysis, when the flow distribution of the middle cross-section of valve was open 100%, flow field was relatively and smoothly taken out. If it was open 50%, flow recirculation region increased and a little complex flow field occurred. Unlike ball valve or butterfly valve, this valve had flow recirculation in its outlet depending on a valve opening amount. Therefore, it was found that there was no flow recirculation in the outlet of Cone-type valve.

A COMPUTATIONAL ANALYSIS FOR OUTLET SHAPE DESIGN TO SUPPRESS FLOW RECIRCULATION IN A ROTATING-DISK CVD REACTOR (회전원판형 CVD 장치의 유동 재순환을 억제하는 출구부 형상 설계를 위한 전산해석)

  • Park, J.J.;Kim, K.;Kwak, H.S.
    • Journal of computational fluids engineering
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    • v.18 no.4
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    • pp.74-81
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    • 2013
  • A numerical design analysis is conducted to search for an optimal shape of outlet in a rotating-disk CVD reactor. The goal is to suppress flow recirculation that has been found in a reactor having a sudden expansion of flow passage outside of the rotating disk. In order to streamline gas flow, the sidewall at which the flow in the Ekman layer is impinged, is tilted. The axisymmetric laminar flow and heat transfer in the reactor are simulated using the incompressible ideal gas model. For the conventional vertical sidewall, the flow recirculation forming in the corner region could be expanded into the interior to distort the upstream flow. The numerical results show that this unfavorable phenomenon inducing back flow could be dramatically suppressed by tilting the sidewall at a certain range of angle. The assessment of deviation in deposition rate based on the characteristic isotherm illustrates that the sidewall tilting may expand the domain of stable plug-like flow regime toward higher pressure. A physical interpretation is attempted to explain the mechanism to suppress flow recirculation.

Flow Dynamics of Gas Turbine Swirl Nozzle

  • Moriai, Hideki;Fujimoto, Yohei;Miyake, Yoshiaki
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.63-65
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    • 2008
  • CFD cold-flow analysis results of the air-blast swirl nozzle for the small aircraft engine combustor are shown. Two major recirculation zones are observed near the nozzle. The centerline recirculation zone velocity profile of CFD is compared with the experimental results.

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Flow analysis of the Hydrogen Recirculation System for Fuel Cells (연료전지 수소 재순환 시스템의 유동해석)

  • Kim, Jae-Choon;Lee, Yong-Taek;Chung, Jin-Taek;Kim, Yong-Chan;Hwang, In-Chul
    • 유체기계공업학회:학술대회논문집
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    • 2005.12a
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    • pp.759-764
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    • 2005
  • In this paper, numerical analysis of hydrogen recycle system has been conducted in order to enhance the efficiency of automotive fuel cell. Generally, the excess hydrogen is provided in the automotive fuel cell. Since the non-reaction hydrogen reduces automotive fuel cell efficiency, reuse of the non-reaction hydrogen can be helpful to improve the fuel cell performance. In case of PEM FC, the water vapor is provided to hydrogen from the cathode so that the mixture experiences phase change depending on the changes of pressure and temperature. The internal flow of the mixture in the hydrogen recirculation system of fuel cell was investigated for real flow conditions. The variation of performance, properties and mass fractions of mixture, hydrogen and water-vapor were investigated. This study was performed based on 80KW level automotive fuel cell's recycling system.

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A Study on the Flow Characteristics of the Flue Gas Recirculation with the Change of Venturi Tube Shape (벤튜리관 형상에 따른 배기가스 재순환 유동 특성에 관한 연구)

  • Ha, Ji Soo;Shim, Sung Hun;Kim, Dae Yeon
    • Journal of the Korean Institute of Gas
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    • v.23 no.1
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    • pp.12-18
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    • 2019
  • Exhaust gas recirculation method is widely used among various methods for reducing nitrogen oxides in automobile engines and incinerators. In the present study, the computational fluid dynamic analysis was accomplished to derive the optimal location of air nozzle exit position by changing its position in a venturi tube for the maximum flue gas recirculation effect. In addition, the flue gas recirculation characteristics with a cone at the exit of air nozzle was elucidated with flue gas recirculation flow rate ratio and mixed gas exit temperature. When the air nozzle exit position was changed from the start position (z = 0) to the end position (z = 0.6m) of the exhaust gas recirculation exit pipe, the change of streamline and temperature distribution in the venturi tube was observed. The exhaust gas recirculation flow rate and the average temperature at the mixed gas exit position was quantitatively compared. From the present study, the optimal location of air nozzle exit position for the maximum flue gas recirculation flow rate ratio and maximum mixed gas exit temperature is z = 0.15m (1/4L). In addition, when the cone is installed at the outlet of the air nozzle, the velocity of the air nozzle outlet is increased, the flue gas recirculation flow rate was increased by about 2 times of the flow rate without cone, and the mixed gas exit temperature is increased by $116^{\circ}C$.

A Computational Study of the Fuel-Cell Ejector System (연료전지 이젝터 시스템에 관한 수치해석적 연구)

  • Lee, Jun-Hee;Lee, Hae-Dong;NamKoung, Hyuck-Joon;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3191-3196
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    • 2007
  • The present study addresses a method to operate a fuel-cell system effectively using a recirculation ejector which recycles wasted hydrogen gas. Configuration of a recirculation ejector is changed to investigate the flow behavior through it under varying operating conditions, and how such conditions affect the fuel-cell hydrogen cycle. The numerical simulations are based on a fully implicit finite volume scheme of the axisymmetric, compressible, Reynolds-Averaged, Navier-Stokes equations for hydrogen gas, and are compared with available experimental data for validation. The results show that a hydrogen recirculation ratio is effectively controlled by a configurational alteration within the operational region in which the recirculation passage doesn't plugged by a sonic line.

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