• Title/Summary/Keyword: crossflow

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Fundamentals of Particle Fouling in Membrane Processes

  • Bhattacharjee Subir;Hong Seungkwan
    • Korean Membrane Journal
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    • v.7 no.1
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    • pp.1-18
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    • 2005
  • The permeate flux decline due to membrane fouling can be addressed using a variety of theoretical stand-points. Judicious selection of an appropriate theory is a key toward successful prediction of the permeate flux. The essential criterion f3r such a decision appears to be a detailed characterization of the feed solution and membrane properties. Modem theories are capable of accurately predicting several properties of colloidal systems that are important in membrane separation processes from fundamental information pertaining to the particle size, charge, and solution ionic strength. Based on such information, it is relatively straight-forward to determine the properties of the concentrated colloidal dispersion in a polarized layer or the cake layer properties. Incorporation of such information in the framework of the standard theories of membrane filtration, namely, the convective diffusion equation coupled with an appropriate permeate transport model, can lead to reasonably accurate prediction of the permeate flux due to colloidal fouling. The schematic of the essential approach has been delineated in Figure 5. The modern approaches based on appropriate cell models appear to predict the permeate flux behavior in crossflow membrane filtration processes quite accurately without invoking novel theoretical descriptions of particle back transport mechanisms or depending on adjust-able parameters. Such agreements have been observed for a wide range of particle size ranging from small proteins like BSA (diameter \~6 nm) to latex suspensions (diameter \~1μm). There we, however, several areas that need further exploration. Some of these include: 1) A clear mechanistic description of the cake formation mechanisms that clearly identifies the disorder to order transition point in different colloidal systems. 2) Determining the structure of a cake layer based on the interparticle and hydrodynamic interactions instead of assuming a fixed geometrical structure on the basis of cell models. 3) Performing well controlled experiments where the cake deposition mechanism can be observed for small colloidal particles (< 1μm). 4) A clear mechanistic description of the critical operating conditions (for instance, critical pressure) which can minimize the propensity of colloidal membrane fluting. 5) Developing theoretical approaches to account for polydisperse systems that can render the models capable of handing realistic feed solutions typically encountered in diverse applications of membrane filtration.

Near-Field Hydrodynamic Analysis of the Submerged Thermal Discharge Using CFD Model (CFD 모델을 이용한 수중방류 온배수의 근역 동수역학 해석)

  • Hwang, In-Tae;Kim, Deok-Ho
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.23 no.6
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    • pp.466-473
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    • 2011
  • The buoyancy and initial momentum fluxes make near-field dominated by buoyant jet when thermal discharge releases underwater. In order to estimate prediction capabilities of those near-field phenomena, non-hydrostatic RANS applied CFD(Computational Fluid Dynamic) model was used. Condition of model was composed based on past laboratory experiments. Numerical simulations carried out for the horizontal buoyant jet in the stagnant flow and vertical buoyant jet into crossflow. The results of simulation are compared with the terms of trajectory and dilution rate of laboratory experiments and analytic model(CorJET) results. CFD model showed a good agreement with them. CFD model can be appropriate for assessment of submerged thermal discharge effect because CFD model can resolve the limitations of near-field analytic model and far-field quasi 3D hydrodynamic model. The accuracy and capability of the CFD model is reviewed in this study. If the computational efficiency get improved, CFD model can be widely applied for simulation of transport and diffusion of submerged thermal discharge.

A Comparative Study of 2-Dimensional Turbulence Models for Thermal Discharge (2차원 온배수 난류모형의 비교연구)

  • Choi, Hung-Sik
    • Journal of Korea Water Resources Association
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    • v.32 no.3
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    • pp.225-235
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    • 1999
  • For a comparative evaluation of three turbulence models in the analyses of thermal discharge behavior into a crossflow, a 2-dimemsional near-field numerical model is developed. The selected models are k-ε and k-ι turbulence models as a 2-equation turbulence model and a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate for the consideration of buoyancy production and turbulent heat flux terms are added to a k-ε turbulence model. The developed models are applied to a steady flow in an open channel with simple geometry and the numerical results agree with the existing experimental data. Numerical results of buoyancy induced gravitational lateral spreading by 4-equation turbulence model agree with the experimental data better than those of 2-quation turbulence models. The flow patterns by 4 and 2-equation turbulence models are similar.

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Initial and Near-field Dilution at the Ocean Outfall of Masan-Changwon Municipal Wastewater Treatment Plant(II) (마산ㆍ창원 하수종말 처리장의 해양방류 처리수에 대한 초기ㆍ근역 희석연구(II))

  • Kang See Whan;You Sung-Hyup;Oh Byung-Cheol;Park Kwang-Soon
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.3 no.1
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    • pp.35-44
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    • 2000
  • The winter case of the near-field dilution at the Masan outfalls has been studied by field measurements and CORMIX model simulations. Dilution rates of the wastewater discharge in winter were obtained by a salinity deficit method using the field data observed in the neap tidal period of February, 1999. The observed dilution rates in winter season were found to be very high in the range of 90~130 due to the isopycnal mixing of ambient density compared with the summer range of 30~40 under weak neap tidal currents. The results of CORMIX model simulations also show that the winter dilution rates under a weak ambient current(Ua=6.0ms/s) were increased by 3-fold of the summer dilution rates. However, the difference between two seasons becomes small by 30% under a strong current(Ua=15.5cm/s). This result indicates that the dilution and hydrodynamic mixing process of the effluents are more influenced by ambient crossflow condition than by ambient density stratification at the outfalls site.

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Spray Characteristics of Jet According to Position of Injector Hole in Cross Flow (횡단유동내 인젝터 홀의 위치에 따른 제트의 분무 특성)

  • Choi, Myeung Hwan;Shin, DongSoo;Radhakrishna, Kanmaniraja;Son, Min;Koo, jaye
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.905-911
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    • 2017
  • Effects of injector position and momentum flux ratio on a vertical jet in a cross flow field were studied qualitatively and shown by using air and water. The experiment was carried out by fixing the momentum flux ratio and varying the position of the injector hole. Conversely, the injector hole position was fixed and the momentum flux ratio was varied. Image visualization was performed by a Shadowgraph technique using a high speed camera. The visualized images were compared for finding differences in spraying through Density Gradient Magnitude Image. It is observed that as the x/d of the apparatus increased the jet break up height decreases and the spray angle also decreases. When x/d is 0, the spray reaches the floor and ceiling at any momentum flux ratio.

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Energy-saving potential of cross-flow membrane emulsification by ceramic tube membrane with inserted cross-section reducers

  • Albert, K.;Vatai, Gy.;Giorno, L.;Koris, A.
    • Membrane and Water Treatment
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    • v.7 no.3
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    • pp.175-191
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    • 2016
  • In this work, oil-in-water emulsions (O/W) were prepared successfully by membrane emulsification with 0.5μm pore size membrane. Sunflower oil was emulsified in aqueous Tween80 solution with a simple crossflow apparatus equipped with ceramic tube membrane. In order to increase the shear-stress near the membrane wall, a helical-shaped reducer was installed within the lumen side of the tube membrane. This method allows the reduction of continuous phase flow and the increase of dispersed phase flux, for cost effective production. Results were compared with the conventional cross-flow membrane emulsification method. Monodisperse O/W emulsions were obtained using tubular membrane with droplet size in the range 3.34.6μm corresponded to the membrane pore diameter of 0.5μm. The final aim of this study is to obtain O/W emulsions by simple membrane emulsification method without reducer and compare the results obtained by membrane equipped with helix shaped reducer. To indicate the results statistical methods, 3p type full factorial experimental designs were evaluated, using software called STATISTICA. For prediction of the flux, droplet size and PDI a mathematical model was set up which can describe well the dependent variables in the studied range, namely the run of the flux and the mean droplet diameter and the effects of operating parameters. The results suggested that polynomial model is adequate for representation of selected responses.

A Study on Flow-Induces Vibration of Tube Array in Uniform Crossflow(I) (균일 유동장내 튜브 배열의 유동관련 진동에 관한 연구 (I))

  • 이기백;김봉환;양장식;김문경;장석상
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.5
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    • pp.924-932
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    • 1992
  • This paper presents the results of an experimental study on the characteristics of the vortex- induced vibration of an elastically supported circular cylinder in the cross air flow. For a range of velocities, power spectral densities of the signals from a hot-wire anemometer placed in the wake of an oscillating circular cylinder and gap sensors placed in the both ends of a circular cylinder were obtained to determine vortex-shedding frequencies, natural frequencies and vibrating frequencies of a cylinder. The effects of slots in the test section on vortex shedding and cylinder oscillation were investigated. The present study covered the reduced velocity range 1.0 .leg. Ur .leg. 64.6. The response characteristics of the cylinder has been shown to vary extensively, depending on the slots in the test section as well as on the reduced velocity. For an elastically supported cylinder, a purely translation mode oscillation was observed at a low velocity, however a rotation mode oscillation was often superposed for higher velocities. These two oscillating frequencies were equal to their natural frequencies irrespective of the changes of free stream velocities.

Experimental Study on the Backflushing for Ultrafiltration Treatment of Alkaline Cleaner Containing Cutting Oils (오일 함유 세척수의 한외여과 처리에서의 역세척에 관한 실험연구)

  • 김종표;정명석;김재진;정건용;전성덕
    • Membrane Journal
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    • v.8 no.2
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    • pp.94-101
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    • 1998
  • The oil separation is effectively performed from the oil containing alkaline cleaner solution by using a backflushed ultrafiltration system, where hollow fibers commercially made by polyacrylonitrile copolymer are bundled. Backflushing to reduce membrane fouling during crossflow ultrafiltration is investigated. Experimental observations allow us to understand the behavior of permeate flux according to the relative operating conditions, and determine the optimum condition of normal operation and backflushing. The maximum improvement of net permeate flux owing to backflushing was found to be about 23 % with the condition of 10 min/40 sec for the cycle of normal/backflushing operations. Note that, however, the maintenance of stable permeate flux is lost as the duration of normal operation is increased. The permeate flux depends on both the backflushing pressure and the feed flow rate. It is obvious that there is a critical velocity of feed flow, in which permeate flux is practically independent of backflushing pressure. Above this critical value, the permeate flux is proportional to an appropriate power of the backflushing pressure, ΔPbackn, where exponent n is enhanced with increasing feed velocity.

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Visualization of Microfiltraton Membrane Fouling by High Speed Video System (고속 비디오 시스템을 이용한 정밀여과 막오염의 시각화)

  • 정건용;김래현
    • Membrane Journal
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    • v.13 no.3
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    • pp.174-181
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    • 2003
  • In this study the formation of the particle layer near the membrane surface was observed for the crossflow micro filtration module by the high speed video system. The microfiltration membrane of 0.2 {\mu}m$ nominal pore size and the 0.05 wt% solution of the polyacryl-copolymer particle distributed between 100 and 180 {\mu}m$ were used for the experiment. The feed rates were changed to 0.5, 0.75, 1.0, 1.25 and 1.5 cm/sec while the permeate rates were maintained at 20±3 of the feed rates, respectively, It was observed that the particles were accumulated rapidly on the membrane surface as the feed flow rate increased, but the particles were not accumulated at 0.5 cm/sec, Also, it was confirmed that almost all of the particles in the layer already formed during filtration were removed within 30 seconds as the feed flow rate increased to 1.88 cm/sec.

Spray Characteristics of Liquid Jets in Acoustically-Forced Crossflows (음향가진된 횡단류 유동장 내 액체제트의 분무특성)

  • Song, Yoonho;Hwang, Donghyun;Ahn, Kyubok
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.2
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    • pp.1-10
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    • 2018
  • This study investigated the acoustic forcing effects on the liquid column breakup length and the trajectory of liquid jets in crossflows. Cold-flow tests with a single hole circular nozzle injector were carried out by changing the injection pressure and acoustic forcing amplitude. Additionally, spray images were obtained at 12 phase angles to investigate the influence of the phage angle. The results revealed that the liquid column breakup lengths generally decreased under the acoustic forcing conditions, in comparison to those under the non-acoustic forcing conditions. However, they were not affected by the variation in the phase angles. On the contrary, it was found that the acoustic forcing hardly influenced the liquid column trajectories.