• Title/Summary/Keyword: Backflow

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Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

  • Yamamoto, Kazuyoshi;Tsujimoto, Yoshinobu
    • International Journal of Fluid Machinery and Systems
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    • v.2 no.1
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    • pp.40-54
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    • 2009
  • Cavitation instabilities in turbo-machinery such as cavitation surge and rotating cavitation are usually explained by the quasi-steady characteristics of cavitation, mass flow gain factor and cavitation compliance. However, there are certain cases when it is required to take account of unsteady characteristics. As an example of such cases, cavitation surge in industrial centrifugal pump caused by backflow vortex cavitation is presented and the importance of the phase delay of backflow vortex cavitation is clarified. First, fundamental characteristics of backflow vortex structure is shown followed by detailed discussions on the energy transfer under cavitation surge in the centrifugal pump. Then, the dynamics of backflow is discussed to explain a large phase lag observed in the experiments with the centrifugal pump.

A Study on Backflow Simulation of Rainwater for Automotive Body (자동차 차체에서 빗물의 역류 모사에 관한 연구)

  • Lee, Jung-Woon;Yun, Jea-Deuk;Park, Sung-Bae;Jung, Yoong-Ho
    • Korean Journal of Computational Design and Engineering
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    • v.16 no.5
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    • pp.323-330
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    • 2011
  • Large number of part design such as for aircraft and automotive development is preceded by functional or sectional design groups for efficiency. With the assembly development of large number of parts, interferences and gaps can be found when the parts and sub-assemblies by those design groups are to be assembled. When rainwater come into the space among parts and is not be drained sufficiently, rainwater within the structure can backflow to gaps or unexpected outlets, which may cause severe problems of part corrosion and electric shock. This research has developed a method and a program to simulate backflow of rainwater within space among parts, which can find unexpected outlets and gaps as in real situation. The developed program can not only simulate up and downstream of liquid, but also the flow with multiple channels of division and joining. The developed method can also be applied to aircraft and ship design process.

A Study On Effectiveness of Prevent Smoke Backflow in Apartment (계단식 공동주택 방연풍속 실효성에 대한 연구)

  • Lee, Kwang­Soo;Yoon, Myong­O;Lee, Jun
    • Journal of the Society of Disaster Information
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    • v.17 no.1
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    • pp.1-9
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    • 2021
  • Purpose: The purpose of this study is to analyze the differential pressure and velocity to prevent smoke backflow of Stairways Apartment House fire, and verified the effectiveness of smoke velocity standards proposed by NFSC 501A. Method: The smoke control design of the stairways apartment house of the real model and the performance of the velocity to prevent smoke backflow according to the window opening conditions of the living room were analyzed using the CONTAM program. Result: Although the differential pressure performance of the apartment's smoke control system was satisfactory, it was found that Performance of velocity to prevent smoke backflow did not come out according to the opening condition of the living room window. Conclusion: In the case of Stairways Apartment House, it is necessary to review the method of making exceptions to the 'velocity to prevent smoke backflow' standard required by the National Fire Safety Codes(NFSC 501A)

A Study for Regulating Flow Fluctuation and Preventing Backflow of Peristaltic Pump (연동펌프의 유량맥동 조절과 역류현상을 방지하는 장치에 대한 연구)

  • Jeong, Yoo-seok;Lee, Cheol-Soo;Lee, Tae-Kyung
    • The KSFM Journal of Fluid Machinery
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    • v.19 no.5
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    • pp.28-34
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    • 2016
  • Though a peristaltic pump is a crucial element in miniaturized drug delivery systems, it has some intrinsic disadvantages such as backflow and flow fluctuation. To overcome these limitation, we have developed valve-less peristaltic pump system including orifice and stagnation chamber. we measured flow rate to investigate the performance of rotary peristaltic pump with three rollers and an elastomeric tube pumping a viscous fluid. The flow fluctuations and the backflow happen as a result from the disengagement of the contact interaction between the rollers and the tubes. Stagnation chamber installed in front of orifice plate was composed of rubber tube and gas chamber. By changing orifice hole diameter with stagnation chamber flow rate and pressure in the tube was regulated. The obtained maximum reduction ratio of flow fluctuation is 96.79%.

Large Eddy Simulation of the Dynamic Response of an Inducer to Flow Rate Fluctuations

  • Kang, Dong-Hyuk;Yonezawa, Koichi;Ueda, Tatsuya;Yamanishi, Nobuhiro;Kato, Chisachi;Tsujimoto, Yoshinobu
    • International Journal of Fluid Machinery and Systems
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    • v.2 no.4
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    • pp.431-438
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    • 2009
  • A Large Eddy Simulation (LES) of the flow in an inducer is carried out under flow rate oscillations. The present study focuses on the dynamic response of the backflow and the unsteady pressure performance to the flow rate fluctuations under non-cavitation conditions. The amplitude of angular momentum fluctuation evaluated by LES is larger than that evaluated by RANS. However, the phase delay of backflow is nearly the same as RANS calculation. The pressure performance curve exhibits a closed curve caused by the inertia effect associated with the flow rate fluctuations. Compared with simplified one dimensional evaluation of the inertia component, the component obtained by LES is smaller. The negative slope of averaged performance curve becomes larger under unsteady conditions. From the conservations of angular momentum and energy, an expression useful for the evaluation of unsteady pressure rise was obtained. The examination of each term of this expression show that the apparent decrease of inertia effects is caused by the response delay of Euler's head and that the increase of negative slope is caused by the delay of inertial term associated with the delay of backflow response. These results are qualitatively confirmed by experiments.

Preventing Freezing of Condensate inside Tubes of Air-Cooled Condenser (공랭식 응축기 관내 응축수 동결 방지에 관한 연구)

  • Joo, Jeong-A;Hwang, In-Hwan;Cho, Young-Il;Lee, Dong-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.8
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    • pp.811-819
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    • 2012
  • An air-cooled condenser is a device that is used for converting steam into condensate by using ambient air. The air-cooled condenser is prone to suffer from a serious explosion when the condensate inside the tubes of a heat exchanger is frozen; in particular, tubes can break during winter. This is primarily due to the structural problem of the tube outlet of an existing conventional air-cooled condenser system, which causes the backflow of residual steam and noncondensable gases. To solve the backflow problem in such condensers, such a system was simulated and a new system was designed and evaluated in this study. The experimental results using the simulated condenser showed the occurrence of freezing because of the backflow inside the tube. On the other hand, no backflow and freezing occurred in the advanced new condenser, and efficient heat exchange occurred.

The Reduced Model Test for the Determination of Ventilation Velocity to Prevent Backflow in Uni-directional Road Tunnel during a Fire Disaster (일방향 도로터널내 화재 발생시 역류를 막는 환기속도결정에 관한 축소모형실험)

  • 유영일;이희근
    • Tunnel and Underground Space
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    • v.8 no.2
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    • pp.107-117
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    • 1998
  • In the case of a fire disaster in a uni-directional road tunnel, it is important to determine the critical ventilation velocity to prevent the backflow travelling toward the tunnel exit where vehicles are stopped. The critical ventilation velocity is horizontal velocity to prevent hot smoke from moving toward the tunnel exit. According to Froude modelling, the model tunnel whcih was 300mm in diameter and 21 m in length was made of acryl tubes. Inner section of acryl tubes was clothed with polycarbonate. 1/20 scaled model vehicles were installed to simulate the situation that vehicles are stopped in the tunnel exit. Methanol in a pool type burner was burned in the middle of tunnel to simulate a fire hazard. In this study, the basis of determining the critical ventilation velocity is the ventilation flow rate that is able to maintain the allowable CO concentration in the tunnel section. We assumed that the allowable CO concentration was backflow dispersion index. Futhermore, We intended to find out CO distribution and temperature distribution according as we changed ventilation velocity. The results of this study were that no backflow happened when ventilation velocity was 0.52 m/s in the case of 5.75 kW. If we adapt these results of a fire disaster releasing 10MW heat capacity in real tunnel which is 400m in length, no backflow happens when ventilation velocity is 2.31m/s. After we figured out dimensionless heat release rate and dimensionless ventilation velocity of model test and those of real test to verify experimental correctness, we tried to find out correlation between experimental results of model tunnel and those of real tunnel.

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An Interal Flow Analysis of Turbo Pump Inducer (터보펌프 인듀서의 내부 유동 해석)

  • Shim, Chang-Yeul;Kang, Shin-Hyoung
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.631-636
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    • 2001
  • The internal flow in the rocket pump inducer of LE-7 engine for H-II rocket was predicted at design and off-design flow rates using CFD code, CFX- Tascflow. In this numerical study, the performance curve of inducer coressponding to flow rates variation and the internal flow in the front of blade leading edge show good agreement between the calculations and the measurements. Backflow is appeared at suction side of leadinge edge tip, and this region is extended to upstream as flowrate decrease. Because of backflow, pressure loss coressponding to meridinal coordinate occupy 50% from inlet domain to leading edge. By this phenomena, pressure loss in front of blade leading edge take a great effect to inducer performance.

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