• 대한기계학회논문집
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• 제12권3호
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• pp.534-540
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• 1988

본 연구에서는 디이젤분무 주위기체의 유동특성중에서 유동속도에 관하여 보 고 하였다. 본모에서는 분무기간중 분사압력의 시간경과특성이 상이한 두 종류의 분 사계를 사용하여 생성된 분무와 주위 기체와의 유동방향의 시간경과 및 유입시기, 정 상유입속도 도달시간등을 분무의 축방향과 반경방향에 대하여 상세한 측정결과를 얻었 기에 보고한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.490-495
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• 2003

In steel-making process of iron and steel industry, the purity and quality of steel can be dependent on the amount of CO contained in the molten metal. Recently, the supersonic oxygen jet is being applied to the molten metal in the electric furnace and thus reduces the CO amount through the chemical reactions between the oxygen jet and molten metal, leading to a better quality of steel. In this application, the supersonic oxygen jet is limited in the distance over which the supersonic velocity is maintained. In order to get longer supersonic jet propagation into the molten metal, a supersonic coherent jet is suggested as one of the alternatives which are applicable to the electric furnace system. It has a flame around the conventional supersonic jet and thus the entrainment effect of the surrounding gas into the supersonic jet is reduced, leading to a longer propagation of the supersonic jet. In this regard, gasdynamics mechanism about why the combustion phenomenon surrounding the supersonic jet causes the jet core length to be longer is not yet clarified. The present study investigates the major characteristics of the supersonic coherent jet, compared with the conventional supersonic jet. A computational study is carried out to solve the compressible, axisymmetric Navier-Stokes equations. The computational results of the supersonic coherent jet are compared with the conventional supersonic jets.

• Nuclear Engineering and Technology
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• 제56권7호
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• pp.2545-2556
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• 2024

In the present study, we investigated the velocity distribution, temperature distribution and condensation characteristics of steam jet issuing from four different orifice nozzles with a Reynolds number of approximately 79,000 using the phase Doppler particle analyzer system and a K-type thermocouple. The steam jet discharged from the orifice nozzle has a wider jet width compared to pipe nozzle because of the vena-contracta which can enhance the mixing of steam jet with the ambient air. Therefore, the orifice jet showed less condensation due to its wideness, resulting in small velocity decay rate and large temperature decay rate due to momentum conservation and decreased latent heat release compared to pipe nozzle, respectively. Also, the wider jet width of the orifice jet resulted in larger velocity and temperature spread rate compared to the pipe jet. In addition, the increase in the aspect ratio of the orifice jet led to more condensation and larger velocity spread rate and temperature spread rate due to both the vena-contracta and axis-switching effect, resulting in the increase of jet entrainment.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.254-259
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• 1996

Phase Doppler particle analyze. (PDPA) is a instrument which can be used to obtain simultaneous size and velocity measurements in a multiphase flow. In this study, the size of the water droplets entrained from a bubbling surface of a stagnant liquid column is measured by PDPA with a specially designed transmitter of long focal length and large beam diameter. The test section tube is made of acryle with 18 mm I.D. and 900 mm length. The experimental data are obtained for the air superficial velocity between 0.7 m/s to 3.4 m/s at atmospheric pressure. The experimental results show that there exists large difference in the entrainment mechanism between the churn-turbulent flow and annular flow. Through the present study, the phase Doppler analyzer system is shown to be successfully applied to measure particle sizes larger than $2,000\mu\textrm{m}$ if a transmitter of long focal length is utilized.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제23회 KOSCO SYMPOSIUM 논문집
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• pp.17-26
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• 2001

Self flue gas recirculation flow is an effective method for low NOx emission in the regenerative low NOx burner. The object of this study is to analyze the self flue gas recirculating flow by varying jet velocity of the combustion air. Fuel and air flow rates are fixed and combustion air jet nozzle diameters are 13, 6.5 and 5mm. The stoichiometric line is obtained from the concentration of the fuel using an acetone PLIF technique. It is found that the self flue gas recirculating flow is entrained into that line using a two color PIV technique. As the jet velocity of combustion air is increased, the flue gas entrainment rate into the stoichiometric line is increased. This result suggests that NOx emission can be reduced due to the effects of flue gas which is lowering the flame temperatures.

• 한국가시화정보학회지
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• 제5권2호
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• pp.48-55
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• 2007

Flow structure inside a refrigerating compartment of a scale-down display cooler model was investigated experimentally by using PIV (particle image velocimetry) method, a reliable velocity field measurement technique, in the present study. In addition, we also carried out flow visualization regarding flow structure and particle movement inside a display cooler by using a tracer method. As a result, the mean velocity field measurement shows a large scale vortical flow structure inside a refrigerating compartment due to strong entrainment flow, going through a base plate open gaps.

• 설비공학논문집
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• 제15권7호
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• pp.557-562
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• 2003

Flue gas from apartment heating gas boiler is exhausted outside through an exhaust duct mounted horizontally in a vertical row on the wall. The flue gas includes nitrogen-oxides (NOx) and carbon monoxide. To investigate the possible entrainment of the flue gas into the apartments through the windows, a large eddy simulation (LES) based numerical method is utilized. Distribution of the velocity intensity and temperature around the exhaust ducts is presented for three numerical parameters: exhaust velocity, temperature of the flue gas, and exhaust duct length. The flow field visualized with particles inserted at the ends of the ducts is also presented. The results clearly show that the exhausted flue gas may flow into the apartments when the windows are open.

• 한국연소학회지
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• 제6권1호
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• pp.20-28
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• 2001

Self flue gas recirculation flow is an effective method for low NOx emission in a regenerative low NOx burner. The object of this study is to analyze self flue gas recirculating flow by varying the jet velocity of the combustion air. Fuel and air flow rates are fixed and combustion air jet nozzle diameters are 13, 6.5 and 5mm. The stoichiometric line is obtained from the concentration of fuel using the acetone PLIF technique. It is found that self flue gas recirculating flow is entrained into that line using the two color PIV technique. As the jet velocity of combustion air is increased, the flue gas entrainment rate into the stoichiometric line is increased. This result suggests that NOx emission can be reduced due to the effects of flue gas lowering the flame temperature.

• 한국지반공학회논문집
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• 제32권10호
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• pp.17-29
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• 2016

본 연구에서는 지반침식 및 연행작용을 고려한 토석류 해석을 위한 모델을 개발하였으며, 이를 대변형 3차원 유한요소 해석을 통해 거동을 분석하였다. 지반침식 및 연행작용을 고려한 토석류 해석 모델은 토석류에 의한 지반의 변형속도에 따른 전단강도 감소를 고려하였으며, 대변형 해석은 Coupled Eulerian-Lagrangian (CEL)기법을 이용하였다. 모델의 적정성을 확인하기 위하여 지반침식 및 연행작용을 고려한 실내실험(Mangeny et al., 2010)을 모사하여 거동을 비교하였으며, 또한 실제 발생한 우면산 래미안 유역의 토석류를 대상으로 연행작용을 고려한 해석과 고려하지 않은 해석 결과를 비교함으로써 연행작용에 따른 토석류의 거동 및 피해영향 범위를 분석하였다. 그 결과, 실내 모형실험의 결과를 적절히 모사할 수 있었으며, 실제 유역규모의 해석에서도 토석류의 흐름에 의해 원지반의 침식 및 연행작용을 모사할 수 있었으며 연행작용으로 인해 유하부로 흘러내려오는 토석류의 체적과 속도가 증가하는 것을 확인하였다. 이로 인하여 본 연구에서 제안한 해석 모델은 지반의 침식 및 연행작용을 고려하여 토석류의 속도, 토석류의 규모 및 피해 면적을 적절히 예측할 수 있을 것으로 판단된다.

• 한국수자원학회논문집
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• 제56권spc1호
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• pp.1049-1058
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• 2023

보와 저낙차 댐과 같은 하천횡단구조물을 통과하는 흐름은 도수 현상을 동반하는 급변류가 지배적이다. 구조물 하류에서 도수로 인한 유속과 수면의 강한 비정상성은 수공구조물의 안정에 영향을 줄 수 있다. 특히, 높은 Froude 수 조건에서 발생하는 정상도수는 공기연행이 현저하게 발생하여 흐름 특성은 더욱 복잡해진다. 이 연구에서는 Froude 7.3 조건에서 발생하는 정상도수를 모의하기 위해서 큰와모의 기법과 하이브리드 VoF 기법을 이용한 수치모의를 수행하였다. 수치모의 결과는 구조물 하류 바닥면에서 계측된 순간최대압력과 시간평균압력 분포를 유사하게 재현하는 것으로 나타났다. 단, 구조물 직하류에서의 순간최소압력 분포는 대상으로 하는 실험 계측값과 반대의 양상을 보이지만, 유사한 다른 시험과는 같은 양상을 보임으로써 본 연구에서 수행한 수치모의는 합리적으로 압력변동을 예측하는 것으로 판단된다. 도수 중앙부에서의 연직방향 유속분포와 공기농도분포는 유사한 조건의 실험 결과들과 자기상사성을 보이면서 양호하게 일치하는 것으로 나타났다. 이러한 결과는 본 연구에서 적용한 큰와모의 기법과 하이브리드 VoF 기법이 높은 Froude 수 조건에서 강한 공기연행을 동반하는 도수현상을 양호하게 재현할 수 있음을 보여준다.