• Title/Summary/Keyword: Re-entrainment

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Jet Entrainment Effect in Buoyant Jet and Iso-Thermal Fire Modeling (부력제트의 주위공기 유입효과 및 등온기체 모델링)

  • Lee, Eui-Ju
    • Fire Science and Engineering
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    • v.23 no.6
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    • pp.111-115
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    • 2009
  • Acetone LIF and Rayleigh scattering measurements were performed to identify the entrainment of ambient air in the buoyant jet qualitatively. The air entrainment near nozzle exit was enhanced with increasing both an axial distance and Reynolds number. The results supported that the air entrainment had to be considered in isothermal model for the development of its accuracy. Also, this paper provided an isothermal model based on the ideal plume, of which radiative heat loss fraction was assumed to 0.35 and the entainment of isothermal jet was considered. This simple model could be used in compartment or semi-enclosure fires such as tunnel, and it is more reliable because of introducing entrainment effect in isothermal jet.

Performance improvement of wave plate mist eliminator through geometry modification (Wave plate 습분제거기의 형상 변경을 통한 성능 개선)

  • Jung-Hun, Noh;Min-Cheol, Cho;Seung-Jong, Lee
    • Particle and aerosol research
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    • v.18 no.4
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    • pp.97-107
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    • 2022
  • The geometry of popular wave plate type mist eliminator for the wet flue gas desulfurization process was improved, fabricated, and experimentally evaluated. A Mist eliminator is a type of inertial particle collector which collection efficiency is proportional to the velocity of the gas phase. However, as the amount of re-entrainment is also proportional to the gas phase velocity, there is a limitation for the gas phase flow rate. Re-entrainment is one of the most important issues in a mist eliminator and is likely to occur as the input of the liquid phase and flow rate of the gas phase increase. In order to resolve this problem, the projection angle of the improved mist eliminator is set to 30° from the conventional one while maintaining the cross-section. With low flow rate conditions, the modified mist eliminator showed a similar pressure drop and overall collection efficiency. However, with conditions in which re-entrainment is obviously occurring, the modified mist eliminator showed better performance in draining droplets than the conventional one. As a result, the modified mist eliminator showed higher overall collection efficiency.

A Study of the Transient Flow Characteristics of a Vacuum Ejector-Diffuser System.

  • Rajesh, G.;Kim, H.D.
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2769-2774
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    • 2007
  • In vacuum ejector-diffuser systems where a finite volume secondary chamber is used, the secondary jet exhibits transient characteristics during start-up. A steady state is achieved after some time in which mass entrainment prevails indefinitely inside the ejector, though there is no flow from the secondary chamber. An attempt is made in this work to study the infinite entrainment of secondary jet into the primary jet from a finite secondary chamber, with the help of a computational fluid dynamics method. The present study is also intended to identify the operating range of vacuum ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the only condition in which an infinite mass entrainment is possible is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point. Steady flow assumption is valid only after this point.

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A Study on the Transient Flow Process in a Vacuum Ejector-Diffuser System (진공 이젝터-디퓨져 시스템내의 비정상 유동 과정에 관한 연구)

  • Vincent, Lijo;Kim, Heuy-Dong;Setoguchi, T.
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.05a
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    • pp.299-302
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    • 2009
  • The objective of the present study is to analyze the transient flow through theejector system with the help of a computational fluid dynamics (CFD) method. An attempt is made to investigate the interesting and conflicting phenomenon of the infinite entrainment into the primary stream without an infinite mass supply from the secondary chamber. The results obtained show that the one and only condition in which an infinite mass entrainment can be possible in such types of ejectors is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium of pressures at the onset of the recirculation zone. A steady flow in the ejector system is valid only after this point.

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Comparison of Tangential and Axial Flow Cyclones for Small Dust Collectors (소형 집진기용 접선식 및 축류식 사이클론 성능비교)

  • Lee, Sungwon;Lee, Chungmin;Yoon, Jong-Hwan
    • Journal of the Korean Society of Visualization
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    • v.16 no.2
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    • pp.45-52
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    • 2018
  • The tangential and axial cyclones were fabricated using a 3D printer and the total collecting efficiency, cut-diameter, and pressure drop characteristics of the two types of cyclones with the same inlet area were investigated experimentally. The results show that the total collecting efficiency tends to increase as the inlet velocity increases. However, at a 20m/s condition of the tangential cyclone, the collected particles were re-entrained to the ascending vortex flow, resulting in a decrease of the total collecting efficiency. In the axial cyclone, the cross-sectional area is designed to increase at the inlet and the velocity is reduced, so that the re-entrainment effect does not appear in this study. The pressure loss of the tangential cyclone was larger than that of the axial cyclone. The cut-diameter tends to decrease with increasing the inlet velocity in two types of cyclones, except for the 20m/s condition of the tangential cyclone.

Velocity Field Measurements of a Vertical Turbulent Buoyant Jet Using a PIV Technique (PIV 기법을 이용한 비등온 부력제트의 유동구조에 관한 연구)

  • Sin, Dae-Sik;Yun, Jeong-Hwan;Lee, Sang-Jun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.5
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    • pp.611-618
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    • 2001
  • The flow characteristics of a turbulent buoyant jet were experimentally investigated using a single-frame PIV system. The Reynolds number based on the nozzle exit velocity and nozzle diameter was about Re=5$\times$10$^3$. The instantaneous velocity fields in the streamwise plane passing the jet axis were measured in the near field X/D <11 with and without the temperature gradient. By ensemble averaging the instantaneous velocity fields, the spatial distributions of mean velocity, vorticity, and higher-order statistics up to third order were obtained. The temperature difference of 10$\^{C}$ does not affect a significant influence to the flow structure in the near field, but the total entrainment rate is increased slightly. The entrainment rate shows a linear variation with the streamwise distance in the region after X/D=5.0.

Physically-based Soil-water Erosion Model - Based on Hairsine and Rose's Concept - (물리적인 기반의 토양침식모델 개발)

  • 김성준
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.39 no.4
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    • pp.82-89
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    • 1997
  • A physically-based soil-water erosion model with simple hydrology and Rose & Hairsine's erosion concept is described, and was implemented in the form of computer program. The model derived from the concept of stream power(Bagnold, 1977) considers settling velocity characteristics of the soil and distinguishes between the processes of entrainment and re-entrainment. It deals separately with rill flow and sheet flow, handles vegetation in terms of soil contact cover, and has the ability to simulate soil movement on nonuniform slopes. The model predicted sediment concentrations reasonably with the results of Mclsaac et al. (1990). It showed a capability to quantitatively predict the movement of soil on uniform and nonuniform slopes. Among the model parameters, soil depositability $({\phi})$ was the most sensitive from the sensitivity analysis.

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SPIV Flow Analysis of Turbulent Jet with Triangular Multi-Tabs (삼각형 멀티 탭이 부착된 난류제트에 대한 SPIV 유동해석 연구)

  • Jang Young Gil;Lee Sang Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.5 s.236
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    • pp.561-567
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    • 2005
  • The effect of triangular multi-tabs attached at the perimeter of jet nozzle on flow structure in the near field was investigated experimentally. A stereoscopic PIV(SPIV) system was employed to measure three orthogonal velocity components of the 3-D turbulent jet. In this study, two different types of sharp-edged jet nozzle having 4, 8 tabs were tested at the Reynolds number of Re=10,000. SPIV measurements were carried out at 5 cross-sectional planes. Six hundred instantaneous velocity fields were measured for each experimental condition and they were ensemble averaged to get spatial distributions of turbulent statistics such as mean velocity and turbulence intensity. Entrainment rate of surrounding fluid into the tabbed jets was estimated using the measured 3-D velocity field data. The strong vortex structure was induced for the jet flow with 4 tabs, increasing entrainment rate.

An Experimental Study on the Variable Sonic Ejector System (가변형 음속 이젝터 시스템에 관한 실험적 연구)

  • Lee, Jun-Hee;Jung, Sung-Jae;Kim, Heuy-Dong;Koo, Byoung-Soo
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.2035-2040
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    • 2004
  • A cone cylinder is used to obtain variable operation conditions for the sonic ejector-diffuser system. The cone cylinder is designed to move upstream and downstream to change the ejector throat area ratio, thus obtaining variable mass flow rates. The present study investigates the effects of ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream for the variable sonic ejector system. In experiment, the ejector throat area is varied in the range from ${\psi}=11.88$ to 66.69, and the operating pressure ratio from $p_{0p}/p_a=1.25$ to 9.0. The results show that the variable sonic ejector system is suitable for a required entrainment ratio of secondary stream by altering the ejector throat area ratio and operating pressure ratio.

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EFFECTS OF GRID SPACER WITH MIXING VANE ON ENTRAINMENTS AND DEPOSITIONS IN TWO-PHASE ANNULAR FLOWS

  • KAWAHARA, AKIMARO;SADATOMI, MICHIO;IMAMURA, SHOGO;SHIMOHARAI, YUTA;HIRAKATA, YUDAI;ENDO, MASATO
    • Nuclear Engineering and Technology
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    • v.47 no.4
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    • pp.389-397
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    • 2015
  • The effects of mixing vanes (MVs) attached to a grid spacer on the characteristics of air-water annular flows were experimentally investigated. To know the effects, a grid spacer with or without MV was inserted in a vertical circular pipe of 16-mm internal diameter. For three cases (i.e., no spacer, spacer without MV, and spacer with MV), the liquid film thickness, liquid entrainment fraction, and deposition rate were measured by the constant current method, single liquid film extraction method, and double liquid film extraction method, respectively. The MVs significantly promote the re-deposition of liquid droplets in the gas core flow into the liquid film on the channel walls. The deposition mass transfer coefficient is three times higher for the spacer with MV than for the spacer without MV, even for cases 0.3-m downstream from the spacer. The liquid film thickness becomes thicker upstream and downstream for the spacer with MV, compared with the thickness for the spacer without MV and for the case with no spacer.