• 설비공학논문집
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• 제26권8호
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• pp.366-374
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• 2014

Experimental mass transfer data, which were obtained for the $CO_2$-water slug flows in vertical tubes with 2, 5, and 8mm diameters, were analyzed in comparison with the penetration theory. It was found that a penetration model with molecular diffusion coefficient cannot predict the experimental data accurately. An effective diffusion coefficient, which considers enhancement effect of interfacial waves, was suggested to improve prediction. Another empirical factor was also suggested to consider the effect of non-uniform interface velocity. A modified penetration model was found to be capable of predicting the experimental data reasonably well.

• 대한기계학회논문집B
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• 제39권7호
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• pp.557-566
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• 2015

본 논문에서는 $600{\times}600{\mu}m$ 사각 마이크로 채널에서의 기-액체 테일러(슬러그) 흐름의 특성을 실험을 통해 살펴보았다. 실험 유체로는 질소와 물을 사용하였으며, 액체 및 기체 겉보기 속도는 각각 0.01 ~ 3 m/s, 0.1 ~ 3 m/s 의 범위에서 테일러 흐름이 나타나는 구간에서만 데이터를 얻었다. 기포 길이, 액체 슬러그 길이, 기포 속도 그리고 기포 생성 주파수를 고속 카메라를 사용하여 이미지 분석을 통해 측정하였다. 제시된 측정값(기포 길이, 액체 슬러그 길이, 기포 속도)과 이전 문헌에서 제안된 경험적 모델의 비교결과 대부분 오차가 50% 이상으로 나타났다. 따라서 기포와 액체 슬러그 길이 그리고 기포 속도에 대한 개선된 모델을 제시하였고, ${\pm}20%$ 이내의 비교적 우수한 결과를 볼 수 있었다. 또한 기포 생성 주파수는 기포 길이, 액체슬러그 길이 그리고 기포 속도의 관계를 이용하여 ${\pm}20%$ 이내에서 예측가능함을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제31권6호
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• pp.618-630
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• 1999

An analytical model that includes the steam condensation effect has been derived and a parametric study has been performed. In addition, a series of experiments were performed and a total of 34 experimental data for the onset of CCFL in nearly horizontal countercurrent two-phase How have been obtained for various flow rates of water. Comparisons of the present CCFL data with slug formation models show that the agreement between the present as well as the existing model and the data is about the same. However, the deviation between the Taitel and Dukler's model predictions and the data is the largest when if j$_{f}$<0.04 m/s. A parametric study of the effect of the steam condensation using the present model shows that, when all local conditions are similar, the model predicted local gas velocities that cause the onset of flooding are slightly lower when condensation occurred. Based on the visual observation and the evaluation of the present work, it has been concluded that the criterion derived for the onset of slug flow can be directly used to predict the onset of inner flooding in nearly horizontal two-phase flow within the experimental ranges of the present work.

• 대한기계학회논문집B
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• 제36권1호
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• pp.83-88
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• 2012

관내 2상 유동의 기공률을 효과적으로 측정할 수 있는 3-ring 임피던스미터를 이용하여 실제 슬러그류 및 기포류를 측정하였다. 먼저, 임피던스미터의 신호와 기공률 사이의 보정곡선을 구하였다. 임피던스미터는 동일한 기공률을 갖는 슬러그류와 기포류에 대해 각각 다른 보정곡선을 나타내는 특성을 보였다. 임피던스미터는 유동패턴에 따라 두 보정 곡선 중 하나를 선택해야 하며, 기공률 측정 결과로 부터 유동 패턴을 판단할 수 있었다. 두 개의 임피던스미터를 통해 측정된 기공률 변화 곡선으로부터 기포의 이동 속도, 크기를 효과적으로 측정할 수 있었다.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1507-1519
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• 2003

The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 1998년도 공동 심포지엄 및 추계학술발표회
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• pp.32-37
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• 1998

In this paper, the role of intermediate cover soils with respect to the leachate and gas flow is investigated from various field investigations and the hydraulic conductivity of the disposed waste is obtained using pumping and slug tests. From the results of field investigations, it was found that the flow of leachate and gas is prevented by the buried cover soils. The hydraulic conductivities of field pumping test and slug tests are well matched and stayed in the range of hydraulic conductivities of well compacted wastes in the literature.

• Nuclear Engineering and Technology
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• 제28권3호
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• pp.299-310
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• 1996

A two-step approach has been used to obtain a new criterion for the onset of slug formation : (1) In the first step, a more general expression than the existing models for the onset of slug flow criterion has been derived from the analysis of singular points and neutral stability conditions of the transient one-dimensional two-phase flow equations of two-fluid model. (2) In the second step, introducing simplifications and incorporating a parameter into the general expression obtained in the first step to satisfy a number of physical conditions a priori specified, a new simple criterion for the onset of slug flow has been derived. Comparisons of the present model with existing models and experimental data show that the present model agrees very closely with Taitel & Dukler's model and experimental data in horizontal pipes. In an inclined pipe ($\theta$ =50$^{\circ}$), however, the difference between the predictions of the present model and those of existing models is appreciably large and the present model gives the best agreement with Ohnuki et al.'s data.

• 설비공학논문집
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• 제25권5호
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• pp.246-254
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• 2013

Some characteristics of nitrogen-water slug flow were optically measured, in vertical acrylic tubes of 2, 5 and 8 mm diameter. Bubble velocity, bubble and unit cell lengths were measured, by analyzing the light intensity signals from two sets of dot laser-infrared sensor modules mounted along the transparent tubes. Optical images of the bubbles were also taken and analyzed, to measure bubble shapes and liquid film thickness. It was found that the measured bubble velocities were in good agreement with the empirical models in the literature, except for those measured under high superficial velocity condition in the 2 mm tube. Bubble length was found to be the longest in the 2 mm tube, being 4 to 5 times those of the other tubes. Liquid film was found to have developed early in the 2 mm tube, which made the blunt shape of the bubble head. Liquid film thickness in the 8 mm tube was measured at almost twice those of the other tubes.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.368-373
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• 1997

The transition from a statified wavy to a slug flow has been analyzed considering the mechanistic forces acting on the wave crest in a nearly horizontal air-water countercurrent flow. To verify the results of the analysis, a series of experiments have been performed changing the inclination angle of the test section. Comparisons of the theoretical predictions with experimental data show a good agreement and the results show that the present model gives similar results of Taitel and Dukler's in the case of inclined pipes. However, at high superficial liquid velocity, the results of present work agree more closely with data than that of Taitel and Dukler's. Also, predictions of the present model gives a very close agreement with the experimental data for various tube sizes obtained by others.

• 동력기계공학회지
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• 제16권1호
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• pp.30-37
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• 2012

공기 양수 펌프는 재생 에너지 분야, 부식 및 마모 특성의 유체의 활용 등 높은 신뢰성과 낮은 유지보수 비용을 필요로 하는 분야에서 그 사용이 증대되고 있다. 본 연구에서는 소형 공기 양수 펌프의 성능 평가 및 기초 데이터를 얻기 위한 연구로, D=0.012~0.019m, L=0.933m인 배관의 침수 깊이(${\beta}$=0.55,0.60,0.65,0.70)에 따른 수치해석을 수행하였다. 수치 해석 및 실험 결과는 유사성을 뛰었으며, 펌프의 사양과 효율은 공기의 질량 유속 비, 침수 깊이 비와 양수 배관의 길이에 관한 함수로 나타났다. 그리고 최대 물과 공기 질량 유속의 비는 각 배관에서 서로 다른 침수 깊이의 비로 나타났으며, 공기 양수 펌프의 최대 효율이 발생되는 운전조건은 슬러그(slug)와 슬러그 교반 정도(slug-churn flow regime)에 따라 나타남을 알 수 있었다.