• Title/Summary/Keyword: Fully Developed Flow

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Solid-liquid 2phase flow in a concentric annulus with rotation of the inner cylinder (안쪽축이 회전하는 동심환형관내 고-액 2상 유동연구)

  • Kim, Young-Ju;Han, Sang-Mok;Woo, Nam-Sub;Hwang, Young-Kyu
    • Journal of Energy Engineering
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    • v.18 no.2
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    • pp.87-92
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    • 2009
  • An experimental investigation is conducted to study a 2-phase vertically upward hydraulic transport of solid particles by water and non-Newtonian fluids in a slim hole concentric annulus with rotation of the inner cylinder. Rheology of particulate suspensions in viscoelastic fluids is of importance in many applications such as particle removal from surfaces, transport of proppants in fractured reservoir and cleaning of drilling holes, etc. In this study, a clear acrylic pipe was used in order to observe the movement of solid particles. Annular velocities varied from 0.3 m/s to 2.0 m/s. The mud systems included fresh water and CMC solutions. Main parameters considered in the study were inner-pipe rotation speed, fluid flow regime and particle injection rate. A particle rising velocity and pressure drop in annulus have been measured for fully developed flows of water and of aqueous solutions. For both water and 0.2% CMC solutions, the higher the concentration of the solid particles is, the larger the pressure gradients become.

Prediction of Combined Forced and Natural Turbulent Convection in a Vertical Plane Channel with an Elliptic-Blending Second Moment Closure (타원-혼합 2차모멘트 모형에 의한 강제와 자연대류가 복합된 수직 평판 난류유동의 예측)

  • Shin, Jong Keun;An, Jeong Soo;Choi, Young Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.11 s.242
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    • pp.1265-1276
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    • 2005
  • The elliptic conceptual second moment models for turbulent heat fluxes, which are proposed on the basis of elliptic-blending and elliptic-relaxation equations, are applied to calculate the combined forced and natural turbulent convection in a vertical plane channel. The models satisfy the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also have the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. Also the models are closely linked to the elliptic blending model which is used for the prediction of Reynolds stress. In order to calibrate the heat flux models, firstly, the distributions of mean temperature and scala flux in fully developed channel flow with constant wall difference temperature are solved by the present models. The buoyancy effect on the turbulent characteristics including the mean velocity and temperature, the Reynolds stress tensor, and the turbulent heat flux vector are examined. In the opposing flow, the turbulent transport is greatly enhanced with both the Reynolds stresses and the turbulent heat fluxes being remarkably increased; whereas, in the aiding flow, the opposite change is observed. The results of prediction are directly compared to the DNS to assess the performance of the model predictions and show that the behaviors of the turbulent heat transfer in the whole flow region are well captured by the present models.

Numerical Study on Flow and Heat Transfer Characteristics of Pipes with Various Shapes (파이프 형상에 따른 내부 열유동 특성과 성능에 관한 수치해석적 연구)

  • Park, Sang Hyeop;Kim, Sang Keun;Ha, Man Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.11
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    • pp.999-1007
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    • 2013
  • The present work reports numerical results of the pressure drop and heat transfer characteristics of pipes with various shapes such as circular, elliptical, circumferential wavy and twisted using a three-dimensional simulation. Numerical simulations are calculated for laminar to turbulent flows. The fully developed flow in pipes was modeled using steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations. The friction and Colburn factor of each pipe are compared with those of a circular tube. The overall flow and heat transfer calculations are evaluated by the volume and area goodness factor. Finally, the objective of the investigation is to find a pipe shape that decreases the pressure loss and increases the heat transfer coefficient.

A Rapid Assessing Method of Drug Susceptibility Using Flow Cytometry for Mycobacterium tuberculosis Isolates Resistant to Isoniazid, Rifampin, and Ethambutol

  • Lee, Sun-Kyoung;Baek, Seung-Hun;Hong, Min-Sun;Lee, Jong-Seok;Cho, Eun-Jin;Lee, Ji-Im;Cho, Sang-Nae;Eum, Seok-Yong
    • Tuberculosis and Respiratory Diseases
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    • v.85 no.3
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    • pp.264-272
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    • 2022
  • Background: The current conventional drug susceptibility test (DST) for Mycobacterium tuberculosis (Mtb) takes several weeks of incubation to obtain results. As a rapid method, molecular DST requires only a few days to get the results but does not fully cover the phenotypic resistance. A new rapid method based on the ability of viable Mtb bacilli to hydrolyze fluorescein diacetate to free fluorescein with detection of fluorescent mycobacteria by flow cytometric analysis, was recently developed. Methods: To evaluate this cytometric method, we tested 39 clinical isolates which were susceptible or resistant to isoniazid (INH) or rifampin (RIF), or ethambutol (EMB) by phenotypic or molecular DST methods and compared the results. Results: The susceptibility was determined by measuring the viability rate of Mtb and all the isolates which were tested with INH, RIF, and EMB showed susceptibility results concordant with those by the phenotypic solid and liquid media methods. The isolates having no mutations in the molecular DST but resistance in the conventional phenotypic DST were also resistant in this cytometric method. These results suggest that the flow cytometric DST method is faster than conventional agar phenotypic DST and may complement the results of molecular DST. Conclusion: In conclusion, the cytometric method could provide quick and more accurate information that would help clinicians to choose more effective drugs.

Three-Dimensional Flow Characteristics and Wave Height Distribution around Permeable Submerged Breakwaters; PART II - with Beach (잠제 주변의 파고분포 및 흐름의 3차원 특성; PART II-해빈이 있을 경우)

  • Hur, Dong-Soo;Lee, Woo-Dong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.1B
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    • pp.115-123
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    • 2008
  • In the present study, a three dimensional hydrodynamic characteristics around the fully submerged dual breakwaters with a sand beach has been investigated numerically using a 3-D numerical scheme, which can determine the eddy viscosity with LES turbulence model and is able to consider wave-structure-seabed interaction in 3-dimensional wave field (LES-WASS-3D), recently developed by Hur and Lee (2007). Based on the numerical experiments, strong vortices can be generated fore and aft edges of the structures, and propagate lee sides. Thus relatively large circulation flows are occurred around submerged breakwaters. The 3-D flow hydrodynamic characteristics have been examined by mean flows and mean vortices for various x-y, x-z sections and y-z layers. Wave height distribution and wave set-up around and over submerged breakwaters, and breaking point migration toward shore side is discussed in detail.

Numerical Analysis of Chamber Flow and Wave Energy Conversion Efficiency of a Bottom-mounted Oscillating Water Column Wave Power Device (고정식 진동수주형 파력 발전장치의 챔버 유동 및 파에너지 변환효율 해석)

  • Koo, Weon-Cheol;Kim, Moo-Hyun;Choi, Yoon-Rak
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.3
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    • pp.388-397
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    • 2010
  • A two-dimensional time-domain, potential-theory-based fully nonlinear numerical wave tank (NWT) was developed by using boundary element method and the mixed Eulerian-Lagrangian (MEL) approach for free-surface node treatment. The NWT was applied to prediction of primary wave energy conversion efficiency of a bottom-mounted oscillating water column (OWC) wave power device. The nonlinear free-surface condition inside the chamber was specially devised to represent the pneumatic pressure due to airflow velocity and viscous energy loss at the chamber entrance due to wave column motion. The newly developed NWT technique was verified through comparison with given experimental results. The maximum energy extraction was estimated with various chamber-air duct volume ratios.

Verification of Prediction Technique of Wave-making Resistance Performance for a Ship attached with a Vertical Blade (수직날개를 부착한 선박의 조파저항 성능 추정 기법의 검증)

  • Choi, Hee-Jong;Park, Dong-Woo
    • Journal of Navigation and Port Research
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    • v.37 no.1
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    • pp.1-7
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    • 2013
  • In this paper the developed prediction technique of wave-making resistance performance for a ship attached with a vertical blade had been verified. Numerical analysis program as a prediction technique had been developed using the Rankine source panel method and the vortex lattice method(VLM). The nonlinearity of the free surface conditions was fully taken into account using the iterative method and the trim and the sinkage of the ship were also considered in the numerical analysis program. Panel cutting method was applied to get hull surface panels. Numerical computations were carried out for a 4000TEU container carrier and the vertical blade was attached 6 different locations astern. To investigate the validity of the numerical analysis program the commercial viscous flow field analysis program FLUENT was used to obtain the viscous flow field around the ship and the model test was performed. The model test results were compared with the numerical analysis results.

An Experimental Investigation on the Airside Performance of Fin-and-Tube Heat Exchangers Having Sinusoidal Wave Fins (사인 웨이브 휜-관 열교환기의 공기측 성능에 관한 실험연구)

  • Kim, Nae-Hyun;Cho, Jin-Pyo;Yoon, Baek
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.4
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    • pp.355-367
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    • 2004
  • The heat transfer and friction characteristics of the heat exchangers having sinusoidal wave fins were experimentally investigated. Twenty-nine samples having different waffle heights (1.5 mm and 2.0 m), fin pitches (1.3mm to 1.7mm) and tube rows (one to three) were tested. Focus was given to the effect of the waffle configuration (herringbone or sinusoidal) on the heat transfer and friction characteristics. Results show that the sinusoidal wave geometry provides higher heat transfer coefficients and friction factors than the herringbone wave geometry, and the difference increases as the number of row increases. The i/f ratios of the herringbone wave geometry, however, are larger than those of the sinusoidal wave geometry. Compared to the herringbone wave geometry, the sinusoidal wave geometry yielded a weak row effect, which suggests a superior heat transfer performance at the fully developed flow region. Possible explanation is provided considering the flow characteristics in wavy channels. Within the present geometric range, the effect of the waffle height on the heat transfer coefficient was not prominent. The effect of the fin pitch was also negligible. Existing correlations highly overpredicted both the heat transfer coefficients and friction factors. A new correlation was developed using the present data.

Cumulative Distributions and Flow Structure of Two-Passage Shear Coaxial Injector with Various Gas Injection Ratio (2중 유로형 전단 동축 분사기의 기체 분사율에 따른 유동 및 입도분포)

  • Lee, Inchul;Kim, Dohun;Koo, Jaye
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.7
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    • pp.675-682
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    • 2013
  • To verify the effect of inner- and outer-stage gas jets, a shear coaxial injector was designed to analyze the axial velocity profile and breakup phenomenon with an increase in the measurement distance. When the measurement position was increased to Z/d=100, the axial flow showed a fully developed shape due to the momentum transfer, aerodynamic drag effect, and viscous mixing. An inner gas injection, which induces a higher momentum flux ratio near the nozzle, produces the greater shear force on atomization than an outer gas injection. Inner- and Outer-stage gas injection do not affect the mixing between the inner and outer gas flow below Z/d=5. The experiment results showed that the main effect of liquid jet breakup was governed by the gas jet of an inner stage. As the nozzle exit of the outer-stage was located far from the liquid column, shear force and turbulence breaking up of the liquid jets do not fully affect the liquid column. In the case of an inner-stage gas injection momentum flux ratio within 0.84, with the increase in the outer gas momentum flux ratio, the SMD decreases. However, at an inner-stage gas jet momentum flux ratio over 1.38, the SMD shows the similar distribution.

Experimental study on the spray characteristics of a dual-manifold liquid-centered swirl coaxial injector

  • Lee, Ingyu;Yoon, Jungsoo;Park, Gujeong;Yoon, Youngbin
    • International Journal of Aeronautical and Space Sciences
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    • v.15 no.4
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    • pp.444-453
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    • 2014
  • A throttleable rocket engine enables operational possibilities such as the docking of spacecraft, maneuvering in a certain orbit and landing on a planet's surface, altitude control, and entrance to atmosphere-less planets. Thus, throttling methods have long been researched. However, dual-manifold injectors, which represent one throttling method, have been investigated less than others. In this study, dual-manifold and single-manifold injectors were compared to determine the characteristics of dual-manifold injectors. Also, the effects of gas injection were investigated with various F/O ratios. To investigate the characteristics, mass flow rate, spray pattern, spray angle, and droplet size were measured. The spray angle and droplet size were captured by indirect photography. About 30 images were taken to assess the spray patterns and spray angle. Also, 700 images were analyzed to understand the droplet distribution and targeting area, moving to the right from the centerline with 1.11-cm intervals. The droplet size was obtained from an image processing procedure. From the results, the spray angle showed two transition regions, due to swirl momentum in the swirl chamber regardless of the F/O ratio. The droplet size showed similar trends in both dual-manifold and single-manifold injectors except in the low mass flow rate region. In the case of the dual- manifold injector, the spray cone was not fully developed in the low mass flow rate region due to low angular momentum in the swirl chamber.