• 제목/요약/키워드: friction Factor

검색결과 966건 처리시간 0.025초

A Sensitivity Analysis of Centrifugal Compressors Empirical Models

  • Baek, Je-Hyun;Sungho Yoon
    • Journal of Mechanical Science and Technology
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    • 제15권9호
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    • pp.1292-1301
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    • 2001
  • The mean-line method using empirical models is the most practical method of predicting off-design performance. To gain insight into the empirical models, the influence of empirical models on the performance prediction results is investigated. We found that, in the two-zone model, the secondary flow mass fraction has a considerable effect at high mass flow-rates on the performance prediction curves. In the TEIS model, the first element changes the slope of the performance curves as well as the stable operating range. The second element makes the performance curves move up and down as it increases or decreases. It is also discovered that the slip factor affects pressure ratio, but it has little effect on efficiency. Finally, this study reveals that the skin friction coefficient has significant effect on both the pressure ratio curve and the efficiency curve. These results show the limitations of the present empirical models, and more resonable empirical models are reeded.

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맥동압력조건에서 재생기를 통한 왕복유동의 압력강하 특성에 대한 연구 (Investigation on the pressure drop characteristics of oscillating flow through regenerator under pulsating pressure conditions)

  • 최성열;남관우;정상권
    • 한국초전도저온공학회:학술대회논문집
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    • 한국초전도저온공학회 2003년도 학술대회 논문집
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    • pp.21-27
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    • 2003
  • This paper proposes a new model of the pressure drop for more accurate description of oscillating flow through regenerator under pulsating pressure conditions in contrast to an existing model based on steady flow. For the universal uses of the oscillating flow model, non-dimensional parameters, which consist of Reynolds number, Valensi number gas domain length ratio, oscillating flow friction factor and phase angle of pressure drop, are derived from the capillary tube model of the regenerator. Two correlation equations of the model are obtained from the experiments for the twill square screen regenerators under various operating frequencies and inlet mass flow rates. The oscillating friction factor is a function of only the Reynolds number and the phase angle of pressure drop is a function of the Valensi number and the gas domain length ratio. Experiment is also performed to examine the effects of the shape of screens.

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발포 알루미늄이 삽입된 환형관에서의 압력손실 및 강제대류 열전달 (Pressure Loss and Forced Convective Heat Transfer in an Annulus Filled with Aluminum Foam)

  • 노주석;이계복;이충구
    • 설비공학논문집
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    • 제17권9호
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    • pp.855-862
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    • 2005
  • An experimental investigation has been carried out for aluminum foam heat sink inserted into the annulus to examine the feasibility as a heat sink for high performance forced water cooling in the annulus. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 13.6, 18.9, 25.1, 31.4 $kw/m^2$ and Reynolds number ranged from 120 to 2000. Experimental results show that the friction factor is higher than clear annulus without aluminum foam, while the significant augmentation in Nu is obtained. This technique can be used for the compactness of the heat exchanger.

거친외벽면을 가진 동심환형관내에서 완전히 발달된 유동의 난류구조 (Structure of turbulence of fully developed flow in concentric annuli with rough outer wall)

  • 안수환
    • 설비공학논문집
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    • 제11권1호
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    • pp.1-9
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    • 1999
  • For roughened annular pipes with diameter ratios of 0.26, 0.39, and 0.56 and with Reynolds numbers ranging 13,000 to 67,000, friction factor, autocorrelation coefficients, power spectral density functions, and integral length scales for each flow condition using X-type hot wire anemometry system are experimentally investigated. Distributions of these quantities show that the times which the streamwise autocorrelation coefficients become zero first increase with decreasing the radius ratios of concentric annuli and Reynolds numbers, however the power spectra density functions increase with increasing the radius ratios and Reynolds number.

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전난류에서의 파마찰계수 (Wave Friction Factor far Rough Turbulent Flow)

  • 유동훈
    • 한국해안해양공학회지
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    • 제5권2호
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    • pp.51-57
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    • 1993
  • 포텐셜 이론으로 구해지는 해저면 유속은 일반적으로 난류경계층에서의 파유속과 같다고 가정한다. 해저면 가까이에서 파운동에 의한 유속분포를 해석하기 위한 최근의 이론과 수치모형에서 발견되는 실험결과와의 오차는 주로 이 가정의 문제점으로부터 연유하는 것으로 사료된다. 경계층 최상점에서의 유속에 대한 이론치와 실유속치와의 관계식을 본고에서 제의하였다. 이 관계식을 이용하여 Jonsson(1967)과 Fredsoe(1984)가 각각 개발한 기존 이론식을 수정하였으며, 수정된 이론을 이용하여 파마찰계수를 산정한 결과, 발표된 실험치들과 비교하여 상당한 향상을 얻을 수 있었다.

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응축기의 설계조건에서 공기측 열전달계수 및 압력강하 산출 (Evaluation of Air-side Heat Transfer and Friction Characteristics on Design Conditions of Condenser)

  • 김창덕;전창덕;이진호
    • 설비공학논문집
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    • 제15권3호
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    • pp.220-229
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    • 2003
  • An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150~250 kg/$m^2$s with air flows at velocity ranges from 0.6 m/s to 1.6 m/s.

Numerical Analysis on the Effect of Parameters that Affect the Flow Rate through the Tunnel with Jet Fan Ventilation System

  • Kim, Sa-Ryang;Hur, Nahmkeon;Kim, Young-Il;Kim, Ki-Jung
    • International Journal of Air-Conditioning and Refrigeration
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    • 제11권4호
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    • pp.178-187
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    • 2003
  • In this study, ventilation flow rate and pressure rise through a tunnel are simulated numerically using computational fluid dynamics (CFD) for various conditions such as roughness height of the surface of tunnel, swirl angle and hub/tip ratio of jet fan, and entrance and exit effects. By using a modified wall function, friction factor can be predicted with respect to the Moody chart within 10% of error for the circular pipe flow and 15% for the present tunnel. For more accurate design, the effect of the swirl angle and hub/tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan needs to be considered.

하수관거의 최저유속 (Minimum Velocity of Sewerage Pipes)

  • 유동훈;이정영
    • 한국수자원학회논문집
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    • 제32권4호
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    • pp.469-478
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    • 1999
  • 한수관내 침전물의 퇴적을 방지하기 위하여는 최저유속과 에너지경사, 관경을 산정하여 제시하여야 되는데 이들 수치를 바로 결정하는 양해법 산정식들을 개발하였다. 이를 위하여 토사의 임계전단력과 상용관 마찰계수 산정을 위하여 지수형 산정식들을 도입하였으며, 이들 지수형 산정식들은 기존 실험관측자료를 이용하여 개발되었다. 제시된 수치들의 적합성을 판별하기 위하여 여러 예들을 본 연구에서 개발된 산정식들을 적용하여 검토하였다.

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냉간단조용 금형 수명에 미치는 공정 변수의 영향 (Process variables and die life for cold forging)

  • 이영선;최석탁;권용남;임영목;이정환
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2005년도 춘계학술대회 논문집
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    • pp.215-218
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    • 2005
  • For the production of cold forged parts with near-net-shape attributes, the quality of the tool system is responsible for an essential portion of costs fer the finished components. Therefore, a tool lift is one of the important issues on cold forging industry. There are many complicated variables related with tool life, such as material, heat-treatment, coating, lubricant, process design. In this study, heat-treatment of tool material and lubricant are investigated to improve the tool life. Deep cryogenic treatment of tool steel is very efficient to improve the wear resistance due to the fine carbide. And, friction factor of lubricants for cold forging are measured by the ring compression test. Zinc-Phosphate and $MoS_2$ lubricant is effective to sustain the friction factor under 0.1.

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Explicit Design of Uniformly Rough Pipe

  • Yoo, Dong-Hoon
    • Korean Journal of Hydrosciences
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    • 제7권
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    • pp.107-124
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    • 1996
  • Pipe design normally requires pump power, discharge or pipe diameter for each condition given. Due to several investigators the pipe friction factor con now be estimated by explicit way for a wide range of flow condition. In various problems of pipe design, however, the flow condition cannot be pre-determined even for a uniformly rough pipe. In these cases a lot of iterations are often required to have an accurate solution with ordinary approach. This paper presents the direct computation method of discharge and pipe diameter without any iteration process. Introducing the power law of friction factor, various non-dimensional physical numbers are derived such as power-diameter number, power-discharge number, diameter-slope number and discharge-slope number. One of the physical numbers concerned with discharge or pipe diameter can be related to a combination of the other in an explicit way.

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