• Title/Summary/Keyword: Slug Flow

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CFD Modeling of Unsteady Gas-Liquid Flow in a Small Scale Air-Lift Pump (소형 공기 양수 펌프의 불규칙한 가스-액체 흐름의 CFD 모델링)

  • Li, X.S.;Jeong, H.M.;Chung, H.S.
    • Journal of Power System Engineering
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    • v.16 no.1
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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.

Study on The Oxygen Transfer Properties of Airlift Pump (에어리프트 펌프의 산소 전달 특성에 관한 연구)

  • OH Se-Kyung
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.30 no.3
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    • pp.451-458
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    • 1997
  • The oxygen transfer coefficient was not significantly affected by either flow pattern, initial bubble size or the wastes present in the water studied. Surface active substances in the water did however influence the transition from bubble to slug flow. Airlift with length to diameter ratios less than 50 suffered from considerable losses in efficiency. When properly designed, airlift pumping efficiencies were comparable to those of conventional centrifugal pumps and the oxygen transfer efficiency were as high as or higher than those of diffused aeration systems.

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Effect of Gas- and Liquid-injection Methods on Formation of Bubble and Liquid Slug at Merging Micro T-junction (마이크로 T자형 합류지점에서 기체 및 액체의 주입 방법이 기포 및 액체 슬러그 생성에 미치는 영향)

  • Lee, Jun Kyoung;Lee, Chi Young
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.4
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    • pp.227-236
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    • 2016
  • In the present experimental study, the effect of gas- and liquid-injected methods on the formation of bubble and liquid slug at the merging micro T-junction of a square microchannel with dimensions $600{\mu}m{\times}600{\mu}m$ was investigated. Nitrogen and water were used as test fluids. The superficial velocities of the liquid and gas were in the range of 0.05 - 1 m/s, and 0.1 - 1 m/s, respectively, where the Taylor flow was observed. The bubble length, liquid slug length, bubble velocity, and bubble generation frequency were measured by analyzing the images captured using a high-speed camera. Under similar inlet superficial velocity conditions, in the case of gas injection to the main channel at the merging T-junction (T_gas-liquid), the lengths of the bubble and liquid slug were longer, and the bubble generation frequency was lower than in the case of liquid injection to the main channel at the merging T-junction (T_liquid-gas). On the other hand, in both cases, the bubble velocity was almost the same. The previous correlation proposed using experimental data for T_liquid-gas had predicted the present experimental data of bubble length, bubble velocity, liquid slug length, and bubble generation frequency for T_gas-liquid to be ~24%, ~9%, ~39%, ~55%, respectively.

A Study on the River Discharge Measurement Techniques (하천유량 측정기법에 관한 연구)

  • 김성원;지홍기
    • Journal of Environmental Science International
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    • v.7 no.6
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    • pp.793-801
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    • 1998
  • In this study, the Dilution Method is used to measure river discharge through the hydraulic model test. the dilution method is divided into Constant-Rate-Infection Method and Slug-Injection Method in the river discharge measurement techniques. When the dilution method is applied in the hydraulic model flume, it is analyzed that the estimated error of constant-rate-injection method is less than that of the slug-in-jection method, and the result shows that floodflow analysis is more efficient than lowflow analysis as compared observed discharge with calculated discharge. The result of statistical error analysis shows that the constant-rate-injection method is appropriate technique for the measurement of the river discharge. Therefore, the dilution method among the river discharge measurement techniques can be applied for the river basin which can't be measured with current meter or unsteady-flow regime in the urban-small drainage or hydraulic structure equipment area and can be obtained more exact results than any other discharge measurement techniques.

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Valve actuation effects on discrete monopropellant slug delivery in a micro-scale fuel injection system

  • McDevitt, M. Ryan;Hitt, Darren L.
    • Advances in aircraft and spacecraft science
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    • v.1 no.4
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    • pp.409-425
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    • 2014
  • Converging flows of a gas and a liquid at a microchannel cross junction, under proper conditions, can result in the formation of periodic, dispersed microslugs. This microslug formation phenomenon has been proposed as the basis for a fuel injection system in a novel, 'discrete' monopropellant microthruster designed for use in next-generation miniaturized satellites. Previous experimental studies demonstrated the ability to generate fuel slugs with characteristics commensurate with the intended application during steady-state operation. In this work, numerical and experimental techniques are used to study the effect of valve actuation on slug characteristics, and the results are used to compare with equivalent steady-state slugs. Computational simulations of a valve with a 1 ms valve-actuation cycle show that as the ratio of the response time of the valve to the fully open time is increased, transient effects can increase slug length by up to 17%. The simulations also demonstrate that the effect of the valve is largely independent of surface tension coefficient, which is the thermophysical parameter most responsible for slug formation characteristics. Flow visualization experiments performed using a miniature valve with a 20 ms response time showed less than a 1% change in the length of slugs formed during the actuation cycle. The results of this study indicate that impulse bit and thrust calculations can discount transient effects for slower valves, but as valve technology improves transient effects may become more significant.

Leachate Behavior within the Domestic Seashore Landfill(I)- Hydrogeologic Property Identification through In-situ Tests - (폐기물 매립지 내에서의 침출수 거동(I)- 현장조사를 통한 수리지반 특성 -)

  • 장연수;조용주
    • Journal of the Korean Geotechnical Society
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    • v.15 no.6
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    • pp.99-109
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    • 1999
  • In the case of domestic general waste landfills, cumulated leachate level is often formed in the landfill due to the waste of high moisture content and it becomes important to characterize the hydraulic properties of the disposed waste. Although many hydrologic studies have been peformed for leachate barriers and pheriperal subsurface environments, few studies have been done to investigate the hydraulic property of the disposed waste and cover soils and to analyse the leachate flow behavior within landfills. In this paper, the geotechnical properties of the waste and buried cover soils are identified through the field experiment including pumping and slug tests. The results of various tests show that the field density of the cover soils is somewhat higher than the maximum laboratory density of cover soils and the vertical flow of leachate and gas in the landfill 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.

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Modification of Bouwer and Rice Method to Evaluate Hydraulic Conductivity of Cutoff Wall Considering Filter Cake Development (수정 Bouwer and Rice 법을 이용한 필터케이크가 존재하는 연직차수벽의 현장 투수계수 산정법)

  • Nguyen, The-Bao;Lee, Chul-Ho;Kwak, Tae-Hoon;Choi, Hang-Seok
    • Journal of the Korean Geotechnical Society
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    • v.25 no.12
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    • pp.47-55
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    • 2009
  • As a conventional line-fitting method, the Bouwer and Rice method has been popularly adopted to estimate the hydraulic conductivity of an aquifer through a slug test. Because a vertical cutoff wall is usually very compressible and features a small wall thickness, the Bouwer and Rice method should be carefully applied to analyzing slug test results to estimate the hydraulic conductivity of vertical cutoff walls. In addition, a relatively impermeable layer, called a filter cake, formed at the interface between the cutoff wall and the natural soil formation makes it difficult to use the Bouwer and Rice method directly. In order to overcome such limitations, the original Bouwer and Rice method has been modified by incorporating the concept of the flow net method. In this modification, the geometry condition of cutoff walls including the filter cake is effectively considered in evaluating the hydraulic conductivity of a vertical cutoff wall.

Flow Patterns of Gas-Liquid Two-phase Flow under Microgravity (미소중력하의 기액이상류의 유동양식)

  • 최부홍
    • Journal of Advanced Marine Engineering and Technology
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    • v.27 no.3
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    • pp.460-465
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    • 2003
  • Microgravity experiments were conducted to determine the effect of liquid and gas superficial velocities on flow behaviors. Flow behaviors observed under microgravity conditions can be classified into five flow patterns: bubble. Taylor bubble, slug, semi-annular and annular flows. Transition boundary between four flow patterns could be determined by drift-flux model. It was also found that the effect of gravity and pipe inclination on flow pattern transition was not significant in the inertia dominant region.

A comparative study on the flow patterns in closed loop pulsating heat pipe charged with various working fluids (다양한 작동유체로 충전된 폐쇄 루프 맥동 히트파이프 내부 유동패턴 비교)

  • Kang, Seok Gu;Kim, Seong Keun;Ahmad, Hibal;Jung, Sung Yong
    • Journal of the Korean Society of Visualization
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    • v.17 no.3
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    • pp.52-58
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    • 2019
  • Thermal performance and flow patterns inside the closed loop pulsating heat pipe (CLPHP) were experimentally investigated. For investigating the effect of working fluids, CLPHP was filled with various working fluids including methanol, acetone and ethanol. The thermal resistance was calculated by temperatures in evaporator and condenser and flow patterns were visualized by a digital camera. The thermal resistances for all fluids were decreased as the heat increases. Flow patterns change from static slug to elongated slug flows, bulk circulation and annular flows as the heat increases. Dry-out occurs after annular flows. For reasonable comparison of thermal performances, normalized CHF, Kutateladze number (Ku), was compared. Even though ethanol has smallest CHF, Ku of ethanol is similar with that of methanol. In addition, acetone has the highest Ku that means CLPHP with acetone provides the higher thermal performance compared with CLPHP with other fluids.

KAIST-CIWH Computer Code and a Guide Chart to Avoid Condensation-Induced Water Hammer in Horizontal Pipes

  • Chun, Moon-Hyun;Yu, Seon-Oh
    • Nuclear Engineering and Technology
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    • v.32 no.6
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    • pp.618-635
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    • 2000
  • A total of 17 experimental data for the onset of slugging, which is assumed to be the precursor of the condensation-induced waterhammer (CIWH), have been obtained for various How rates of water Incorporating the most recent correlations of interfacial heat transfer and friction factor developed for a circular geometry and using an improved criterion of transition from stratified to a slug flow, two existing analytical models to predict lower and upper bounds for CIWH have been upgraded. Applicability of the present as well as existing CIWH models has been tested by comparison with two sets of CIWH data. The result of this comparison shows that the applicability of the present as well as existing models is reasonably good. Based on the present models for CIWH, a computer code entitled as“KAIST-CIWH”has been developed and sample guide charts to find CIWH free regions for a given combination of major flow parameters in a long horizontal pipe have been presented along with the results of parametric studies of major parameters (D, P, $T_{f,in}$, and L/D) on the critical inlet water flow rate($W_{f,in}_crit$ for both lower and upper bounds. In addition, two simple formulas for lower and upper bounds that can be used in an emergency for quick results have been presented.

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