• Title/Summary/Keyword: Taylor Vortex

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Effects of Corrugation Angle on Local Heat/Mass Transfer in Wavy Duct of Heat Exchanger (열교환기 내부 유로의 꺾임각 변화에 따른 국소 열/물질전달 특성 고찰)

  • Jang, In-Hyuk;Hwang, San-Dong;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.7
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    • pp.789-799
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    • 2004
  • An experimental study is conducted to investigate the effects of duct corrugation angle on heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewalls are determined by using a naphthalene sublimation technique. The corrugation angles(${\alpha}$) of the wavy ducts are 145$^{\circ}$, 130$^{\circ}$, 115$^{\circ}$ and 100$^{\circ}$. And the Reynolds numbers based on the duct hydraulic diameter vary from 300 to 3,000. The results show that at the low Re(Re $\leq$1000), the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, high heat/mass transfer regions are formed on both pressure-side and suction-side walls. At the high Re(Re $\geq$ 1000), these secondary flows are vanished with helping flow transition to turbulent flow and the regions which show high heat/mass coefficients by flow reattachment are formed on suction side. As corrugation angle decreases, the local peak Sh induced by Taylor-Gortler vortices increase at Re $\leq$1000. At high Re(Re $\geq$ 1000), by the existence of different kind of secondary flows called Dean vortices, non-uniform Sh distribution appears along spanwise direction at the narrow corrugation angle (${\alpha}$=100$^{\circ}$). Average Sh also increase by the enhanced effect of secondary vortices and flow reattachment. More pumping power (pressure loss) is required with the smaller corrugation angle due to the enhancement of flow instability.

The Onset of Tayler-Görtler Vortices in Impulsively Decelerating Circular Flow

  • Cho, Eun Su;Kim, Min Chan
    • Korean Chemical Engineering Research
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    • v.53 no.5
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    • pp.609-613
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    • 2015
  • The onset of instability induced by impulsive spin-down of the rigid-body flow placed in the gap between two coaxial cylinders is analyzed by using the energy method. In the present stability analysis the growth rate of the kinetic energy of the base state and also that of disturbances are taken into consideration. In the present system the primary flow is a transient, laminar one. But for the Reynolds number equal or larger than a certain one, i.e. $Re{\geq}Re_G$ secondary motion sets in, starting at a certain time. For $Re{\geq}Re_G$ the dimensionless critical time to mark the onset of vortex instabilities, ${\tau}_c$, is here presented as a function of the Reynolds number Re and the radius ratio ${\eta}$. For the wide gap case of small ${\eta}$, the transient instability is possible in the range of $Re_G{\leq}Re{\leq}Re_S$. It is found that the predicted ${\tau}_c$-value is much smaller than experimental detection time of first observable secondary motion. It seems evident that small disturbances initiated at ${\tau}_c$ require some growth period until they are detected experimentally.

Interrelationship Between Topological Structures and Secondary Vortices in the Near Wake of aCircular Cylinder (실린더 근접후류에서 위상학적 구조와 2차 와류의 상호 관계)

  • Seong, Jae-Yong;Yu, Jeong-Yeol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.10
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    • pp.1355-1364
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    • 2001
  • Characteristics of secondary vortices is topologically investigated in the near-wake region of a circular cylinder, where the Taylor's hypothesis does nut hold. The three-dimensional flow fields in the wake-transition regime were measured by a time-resolved PIV for various planes of view. The convection velocities of the Karman and secondary vortices are evaluated from the trajectory of the vortex center. Then, saddle points are determined by applying the critical point theory. It is shown that the inclination angle of the secondary vortices agrees well with the previous experimental data. The flow fields in a moving frame of reference have several critical points and the mushroom-like structure appears in the streamline patterns of the secondary vortices. Since the distributions of fluctuating Reynolds stresses defined by triple decomposition are closely related with the existence of secondary vortices, the physical meaning of them is explained in conjunction with the vortex center and saddle point trajectories.

Modeling of Wall Impingement Process of Hollow-Cone Fuel Spray according to Wall Geometry (벽면 형상에 따른 중공 원추형 분무의 벽 충돌 과정 모델링)

  • Shim, Young-Sam;Choi, Gyung-Min;Kim, Duck-Jool
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3467-3472
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    • 2007
  • The effects of the wall geometry on the spray-wall impingement process of a hollow-cone fuel spray emerging from a high-pressure swirl injector of the Gasoline Direct Injection (GDI) engine were investigated by means of a numerical method. The ized Instability Sheet Atomization (LISA) & Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model for spray atomization process and the Gosman model were applied to model the atomization and wall impingement process of the spray. The calculation results of spray characteristics, such as a spray development process and a radial distance after wall impingement, compared with the experimental ones by the Laser Induced Exciplex Fluorescence (LIEF) technique. It was found that the radial distance of the cavity angle of 90$^{circ]$ after wall impingement was the shortest and the ring shaped vortex was generated near the wall after spray-wall impingement process.

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Precise Estimations on Vorticities using a Hybrid PTV-PIV Algorithm (하이브리드 PTV-PIV알고리듬에 의한 고정밀 와도 추정)

  • Doh, Deog-Hee;Cho, Gyong-Rae;Lee, Jae-Min
    • Journal of the Korean Society of Visualization
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    • v.8 no.4
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    • pp.26-30
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    • 2010
  • A PTV algorithm was constructed using a linear transformation, in which the merits of the conventional PIV and PTV were adopted. In PIV calculations, the obtained velocity vectors are affected by the filtering effects by its calculation principle. PTV techniques are widely used for their excellences of measuring small scaled flows, such as nano and bio flows. However, PTVs produce vector errors due to interpolation process. To overcome these problems, a hybrid PTV algorithm was constructed by combining PTVs' and PIVs' benefits using a linear transformation. The Taylor-Green vortex flows were generated for the tests of vorticity calculations. The conventional gray-level cross-correlation PIV technique and 2-Frame PTV technique were tested for the same flows for comparisons with those obtained by the constructed hybrid algorithm. The excellence of the constructed hybrid algorithm was validated through an actual experiment on the cylinder wake.

수처리용 분리막 모듈 설계 및 오염 방지

  • 정건용
    • Proceedings of the Membrane Society of Korea Conference
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    • 1997.04a
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    • pp.87-109
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    • 1997
  • Reverse osmosis(R/O), ultrafiltration(UF) and microfiltration (MF) processes are widely used for water treatment. In the seminar, characteristics of typical membrane modules including tubular, hollow fiber, plate and frame and spiral wound types will be discussed in detail. The design methods based on hydrodynamics for hollow fiber and spiral wound modules will be introduced analytically. Concentration polarization (CP) and membrane fouling mechnism as well as the techniques for CP reduction will be handled. The CP control techniques contain chemically modified membrane surface, pretreatment of feed water, operation of low trans-membrane pressure, chemical or physical cleaning methods and artificial production of various fluid turbulences near the membrane surface, etc. In especially, the recent commercial membrane modules for CP control including module rotation, vibration and Taylor or Dean vortex system will be introduced and discussed in detail.

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Study on Cake Resistance and Microfiltraion Performance of Rotating Membrane Filters (회전막 정밀여과기에서 케이크 저항과 여과성능에 대한 연구)

  • 박원철;최창균;김재진;박진용
    • Proceedings of the Membrane Society of Korea Conference
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    • 1998.04a
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    • pp.105-109
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    • 1998
  • 1. Introduction : In microfiltration the transport, deposition and removal of particles control cake formation on a filter. In this connection a new model on cake formation, based on the wall shear stress, was tested here in comparison with experiments of fine particle slurry under Taylor-vortex flow. The model expresses the deposition process for particles as two first-order steps in series of mass transfer and adhesion, and their removal process as a linear relation to the wall shear stress. This embraces characteristics of both dead-end and crossflow filtration. The correlation resulting from fitting to experimental data represented the experimental data reasonably well. This study will be helpful in analyzing fouling in heat exchangers.

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Effects of Natural Convection Instability on Membrane Performance in Dead-end and Cross-flow Ultrafiltration

  • Youm, Kyung-Ho;Anthony G. Fane
    • Proceedings of the Membrane Society of Korea Conference
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    • 1995.04a
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    • pp.6-10
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    • 1995
  • An inevitable problem feature of membrane processing is concentration polarization (CF) which is a result of the accumulation of retained solutes at the membrane surface. In ultrafiltration (UF), this accumulation can lead to fouling due to the irreversible deposition of macromolecules both at the membrane surface and in the membrane pores. To reduce or control CP and folding, many possible methods have been considered [1]. One of the most effective approaches is to induce fluid instability near the membrane surface by using pusation flow [2, 3], Taylor [4] and Dean [5, 6] vortex flows. Winzeler and Belfort [6] have comprehensively reviewed several possible attempts to use fluid instabihties for improved membrane performance.

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Effects of Aspect Ratio on Local Heat/Mass Transfer in Wavy Duct (열교환기 내부 유로 종횡비 변화에 따른 국소 열/물질전달 특성 고찰)

  • Jang In Hyuk;Hwang Sang Dong;Cho Hyung Hee
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.6
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    • pp.569-580
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    • 2005
  • The present study investigates the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger. The effects of duct aspect ratio and flow velocity on the heat/mass transfer are investigated. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The aspect ratios of the wavy duct are 7.3, 4.7 and 1.8 with the corrugation angle of $145\Omega$. The Reynolds numbers, based on the duct hydraulic diameter, vary from 300 to 3,000. The results show that at the low Re(Re $\leq$ 1000) the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, non-uniform heat/mass transfer coefficients distributions appear. As the aspect ratio decreases, the number of cells formed by secondary vortices are reduced and secondary vortices and comer vortices mix due to decreased aspect ratio at Re$\leq$1000. At Re >1000, the effects of corner vortices become stronger. The average Sh for the aspect ratio of 7.3 and 4.7 are almost same. But at the small aspect ratio of 1.8, the average Sh decreases due to decreased aspect ratio. More pumping power (pressure loss) is required for the larger aspect ratio due to the higher flow instability.

Investigation on Boundary Conditions of Fractional-Step Methods: Compatibility, Stability and Accuracy (분할단계법의 경계조건에 관한 연구: 적합성, 안정성 및 정확도)

  • Kim, Young-Bae;Lee, Moon-J.;Oh, Byung-Do
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.410-415
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    • 2001
  • An analytical and numerical examination of second-order fractional-step methods and boundary condition for the incompressible Navier-Stokes equations is presented. In this study, the compatibility condition for pressure Poisson equation and its boundary conditions, stability, and numerical accuracy of canonical fractional-step methods has been investigated. It has been found that satisfaction of compatibility condition depends on tentative velocity and pressure boundary condition, and that the compatible boundary conditions for type D method and approximately compatible boundary conditions for type P method are proper for divergence-free velocity for type D and approximately divergence-free for type P method. Instability of canonical fractional-step methods is induced by approximation of implicit viscous term with explicit terms, and the stability criteria have been founded with simple model problems and numerical experiments of cavity flow and Taylor vortex flow. The numerical accuracy of canonical fractional-step methods with its consistent boundary conditions shows second-order accuracy except $D_{MM}$ condition, which make approximately first-order accuracy due to weak coupling of boundary conditions.

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