• 제목/요약/키워드: momentum flux parameters

검색결과 20건 처리시간 0.019초

A Dispersion and Characteristic Analysis for the One-dimensional Two-fluid Mode with Momentum Flux Parameters

  • Song, Jin-Ho;Kim, H.D.
    • Nuclear Engineering and Technology
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    • 제33권4호
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    • pp.409-422
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    • 2001
  • The dynamic character of a system of the governing differential equations for the one- dimensional two-fluid model, where the momentum flux parameters are employed to consider the velocity and void fraction distribution in a flow channel, is investigated. In response to a perturbation in the form of a'traveling wave, a linear stability analysis is peformed for the governing differential equations. The expression for the growth factor as a function of wave number and various flow parameters is analytically derived. It provides the necessary and sufficient conditions for the stability of the one-dimensional two-fluid model in terms of momentum flux parameters. It is demonstrated that the one-dimensional two-fluid model employing the physical momentum flux parameters for the whole range of dispersed flow regime, which are determined from the simplified velocity and void fraction profiles constructed from the available experimental data and $C_{o}$ correlation, is stable to the linear perturbations in all wave-lengths. As the basic form of the governing differential equations for the conventional one-dimensional two-fluid model is mathematically ill posed, it is suggested that the velocity and void distributions should be properly accounted for in the one-dimensional two-fluid model by use of momentum flux parameters.s.

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소형로켓엔진에 적용된 스월 동축형 인젝터의 형상변수와 기체-액체 운동량 플럭스 비에 따른 분무특성 (Spray Characteristics According to the Variation of Design Parameters and Gas-liquid Momentum-flux Ratio in a Swirl-coaxial Injector Applied to Small Rocket Engine)

  • 안현종;강윤형;김정수
    • 한국추진공학회지
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    • 제27권1호
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    • pp.27-36
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    • 2023
  • 소형로켓엔진에 적용되는 기체-액체 스월 동축형 인젝터의 분무성능을 파악하고자 형상변수와 추진제의 공급조건을 변화시켜 수류시험을 수행하였다. 인젝터의 형상변수인 스월 챔버의 직경 및 수축부의 각이 증가할수록 스월 강도가 증대되어 분무성능이 향상되었다. 또한, 기체-액체의 운동량 플럭스 비가 증가함에 따라 기체 유동이 액적 일부를 분무액막에서 이탈시켜, 분무시트의 중심부에서 gas-droplet mixture core가 형성되었다.

An Improved Mechanistic Model to Predict Critical Heat Flux in Subcooled and Low Quality Convective Boiling

  • Kwon, Young-Min;Chang, Soon-Heung
    • Nuclear Engineering and Technology
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    • 제31권2호
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    • pp.236-255
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    • 1999
  • An improved mechanistic model was developed to predict a convective boiling critical heat flux (CHF) in the vertical round tubes with uniform heat fluxes. The CHF formula for subcooled and low quality boiling was derived from the local conservation equations of mass, energy and momentum, together with appropriate constitutive relations. The model is characterized by the momentum balance equation to determine the limiting transverse interchange of mass flux crossing the interface of wall bubbly layer and core by taking account of the convective shear effect due to the frictional drag on the wall-attached bubbles. Comparison between the present model predictions and experimental CHF data from several sources shows good agreement over a wide range of How conditions. The present model shows comparable prediction accuracy with the CHF look-up table of Groeneveld et al. Also the model correctly accounts for the effects of flow variables as well as geometry parameters.

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Numerical study of direct contact membrane distillation process: Effects of operating parameters on TPC and thermal efficiency

  • Zamaniasl, Mohammadmehdi
    • Membrane and Water Treatment
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    • 제10권5호
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    • pp.387-394
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    • 2019
  • Membrane distillation (MD) is one of the water treatment processes which involves the momentum, heat and mass transfer through channels and membrane. In this study, CFD modeling has been used to simulate the heat and mass transfer in the direct contact membrane distillation (DCMD). Also, the effect of operating parameters on the water flux is investigated. The result shows a good agreement with the experimental result. Results indicated that, while feed temperature is increasing in the feed side, water flux improves in the permeate side. Since higher velocity leads to the higher mixing and turbulence in the feed channel, water flux rises due to this increase in the feed velocity. Moreover, results revealed that temperature polarization coefficient is rising as flow rate (velocity) increases and it is decreasing while the feed temperature increases. Lastly, the thermal efficiency of direct contact membrane distillation is defined, and results confirm that thermal efficiency improves while feed temperature increases. Also, flow rate increment results in enhancement of thermal efficiency.

Empirical Correlations for Penetration Height of Liquid Jet in Uniform Cross Flow - A Review

  • No, Soo-Young
    • 한국분무공학회지
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    • 제16권4호
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    • pp.176-185
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    • 2011
  • The empirical correlations for the prediction of penetration height of liquid jet in crossflow are reviewed and classified in this study. Around thirty different correlations had been proposed by many investigators. It has generally known that the penetration height of a liquid jet in a cross-flow is a function of the liquid to air momentum flux ratio and the normalized downstream distance from the injector. However, several researchers incorporated the Weber number, liquid-to-water or air viscosity ratio, pressure ratio or Reynolds number, temperature ratio in the empirical correlations. The existing correlations can be grouped as correlations in a power-law, logarithmic, and exponential forms, respectively. Correlations in a power-law form can be further classified as three groups such as basic form, Weber number form and other parameters form. It should be pointed out that correlations in a logarithmic form in terms of Weber number or any other parameters could not be found. Universal correlation has still not been established due to the significant discrepancies between various correlations suggested to date. Several of the studies reported the significant discrepancies of predicted values by the existing correlations. The possible reasons for discrepancies will be summarized as measurement technique, assumptions made in defining terms in the liquid to air momentum flux ratio, difficulties in defining the boundaries of the liquid jets, and nozzle/injector geometry. Evaluation of validity for the correlations proposed recently by several investigators is essentially required. Those include eight power-law forms, two logarithmic forms, and one exponential form.

양측벽면에 반복돌출형 거칠기가 있는 이중관통로내의 난류유동과 열전달 (Turbulent Flow and heat Transfer in the Annular Passage with Repeated-Ribbed Roughness on Both Walls)

  • 안수환;김덕현
    • Journal of Advanced Marine Engineering and Technology
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    • 제20권1호
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    • pp.1-12
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    • 1996
  • The fully developed tubulent momentum and heat transfer induced by the square- ribbed roughness elements on both the inner and outer wall surfaces in the concentric annuli are studied analytically based on a modified turbulence model. Heat transfer coefficients for two conditions, i.e, a) inner wall heated as constant heat flux and outer wall insulated b) inner wall insulated and outer wall heated as constant heat flux, are investigated. The analytical results of the fluid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity profiles and friction factors, and etc. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Nusselt number and Prandtl number.

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운동량 플럭스 비의 변화에 따른 기체 중심 스월 동축형 분사기의 기체 가진 동특성 연구 (A Study on Dynamic Characteristics of Gas Centered Swirl Coaxial Injector with Acoustic Excitation by Varying Momentum Flux Ratio)

  • 이정호;박구정;윤영빈
    • 한국분무공학회지
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    • 제20권3호
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    • pp.168-174
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    • 2015
  • Combustion instability is critical problem in developing liquid rocket engine. There have been many efforts to solve this problem. In this study, the method was sought through the injector as part of these efforts to suppress combustion instability. If the injector can suppress the disturbance coming from the supply line as a kind of buffer it will serve to reduce combustion instability. Especially we target at gas propellant oscillation in gas-centered swirl coaxial injector. The phenomenon is simulated with acoustic excitation of speaker. The film thickness response at injector exit was measured by using a liquid film electrode. Also the response of spray to the disturbance was observed by high-speed photography. Gas-liquid momentum flux ratio and the frequency of feeding gas oscillation were changed to investigate the effect of these experimental parameters. The trend of response by varying these parameters and the cause of weak points was studied to suggest the better design of injector for suppressing combustion instability.

분사조건에 따른 기체/액체 동축형 인젝터의 분무특성에 관한 연구 (A Study on Characteristics of Gas/Liquid Coaxial Sprays Under Varying Flow Conditions)

  • 정원호;김동준;임지혁;윤영빈
    • 한국항공우주학회지
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    • 제33권1호
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    • pp.54-61
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    • 2005
  • 기체와 액체 추진제를 사용하는 동축형 분사기의 분무특성을 조사하기 위하여 shadow graph와 mechanical patternator, PDPA를 이용한 실험을 수행하였다. 차원해석 방법을 도입하여 운동량 플럭스 비(M)와 레이놀즈 수(Re)를 기체/액체 동축형 분무의 주요 변수로 설정하였고, 실험을 통하여 전단 및 스월 동축형 분무의 특성을 거시적 및 미시적 관점에서 비교분석하였는데, 기체 추진제의 영향력이 커지는 분사조건에서 전단 및 스월 동축형 분무의 거시적 특성이 유사해짐을 확인할 수 있었다. 또한, 본 연구에서는 미시적 분무특성에 대한 분석 결과로서 분무액적 크기와 분사조건 사이의 관계식도 제시하였다.

衝突水噴流에 의한 高溫面의 沸騰熱流束에 관한 硏究 (A study on the boiling heat flux on high temperature surface by impinging water jet)

  • 이기우;김유
    • 대한기계학회논문집
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    • 제12권1호
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    • pp.81-94
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    • 1988
  • 본 연구에서는 표면상태가 다양한 고온면을 충돌온류에 의하여 냉각하는 방식이 광범위하게 응용되고 있는 점에 유의하여 표면조도, 노즐직경 및 분류속도를 변화시키고 노즐끝에 전열면의 직경과 동일한 원형판을 부착하여 비철액체를 막고 문극내에 온류액체를 강제유동시킴으로써 열전달에 미치는 모든 영향을 실험에 의해 고찰하고 고찰하고 포화수온류에 의한 열류속의 무차원관계식을 도출하는 것을 본 연구의 목적으로 하였다.

전천 카메라와 페브리-페로 간섭계 자료를 이용한 한반도 상공 중간권 중량파의 고유파동계수 및 운동량 플럭스 산출 (ESTIMATION OF INTRINSIC WAVE PARAMETERS AND MOMENTUM FLUXES OF MESOSPHERIC GRAVITY WAVES OVER KOREA PENINSULA USING ALL-SKY CAMERA AND FABRY-PEROT INTERFEROMETER)

  • 정종균;김용하;원영인;지건화
    • Journal of Astronomy and Space Sciences
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    • 제24권4호
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    • pp.327-338
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    • 2007
  • 보현산($36.2^{\circ}\;N,\;128.9^{\circ}\;E$)의 전천카메라로 관측한 OI 557.7nm 밤대기광 방출선에 나타난 단주기 중량파의 운동량 플럭스가 산출되었다. 중량파의 고유위상속도($C_{int}$), 고유주기(${\tau}_{int}$), 그리고 수직파장(${\lambda}_z$)는 전천 화상에서 도출된 수평파장(${\lambda}_h$), 관측파동주기(${\tau}_{ob}$), 진행방향(${\phi}_{ob}$), 관측위상속도(${\upsilon}_{ob}$)와 일본 Shigaraki($34.8^{\circ}\;N,\;13.1^{\circ}\;E$) 페브리-페로 간섭계로부터 관측된 중성바람으로부터 유도되었다. 2002년부터 2006년까지 두 관측소의 기상 및 관측 장비 상태를 고려한 결과 총 5일이 분석 가능일로 선택되었다. 중량파 고유파동계수의 평균값은 $({\tau}_{int})\;=\;12.9\;{\pm}\;6.1m/s,\;({\lambda}_z)\;=\;12.9\;{\pm}\;6.5,\;(C_{int})\;=\;40.6\;{\pm}\;11.6min$으로 나타났다. ${\lambda}_z\;<\;6km$인 경우를 제외하고 4일에 대한 계산된 운동량 플럭스의 값은 $12.0{\pm}15.2m^2/s^2$이다. 중간권 중량파의 전형적인 운동량 플럭스를 획득하기 위하여 전천 카메라와 중성바람을 측정할 수 있는 장비와의 장기간에 걸친 연계관측이 요구된다.