• Title, Summary, Keyword: Large Bubble

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Holdup Characteristics of Small Bubbles in a Viscous Slurry Bubble Column (점성슬러리 기포탑에서 작은 기포의 체류량 특성)

  • Jin, Hae-Ryong;Song, Yang-Ho;Kang, Yong;Jung, Heon;Lee, Ho-Tae
    • Korean Chemical Engineering Research
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    • v.49 no.1
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    • pp.83-88
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    • 2011
  • Holdup characteristics of small bubbles were investigated in a viscous slurry bubble column. The phase holdup of small bubbles was obtained from the knowledge of total bubble(gas) holdup and large bubble holdup, which were measured by mean of static pressure drop method and dual resistivity probe method, respectively. Effects of gas velocity, viscosity of continuous liquid phase and solid fraction in the slurry phase on the small bubble holdup as well as holdups of total bubble(gas) and large bubble in a viscous slurry bubble column. The small bubble holdup increased with increasing gas velocity but decreased with increasing liquid viscosity or solid fraction in the slurry phase. In addition the fraction of small bubble in the total bubble(gas) holdup increased with increasing gas velocity but decreased with increasing liquid viscosity or solid fraction in the slurry phase. It was revealed that the rising velocity of large bubble did not related to the holdup of small bubble in a viscous slurry bubble column.

Nonlinear Behaviors of a Gas-filled Bubble Oscillator with Large Amplitude of Excitation (큰 압력 진폭에 의해 구동되는 기포진동체의 비선형 거동 특성)

  • 김동혁
    • Journal of the Korean Society of Marine Engineering
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    • v.26 no.1
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    • pp.116-124
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    • 2002
  • The bubble model by Keller and Prosperetti is adapted to solve the nonlinear oscillation of a gas bubble. This formulation leads to accurate results since it introduces the energy equation instead of the polytropic assumption for the bubble interior. The numerical method used in this study is stable enough to handle large amplitude of bubble oscillation. The numerical results show some interesting nonlinear phenomena fur the bubble oscillator. The excitation changes the natural frequency of the bubble and makes some harmonic resonances at $f/f_0=1/2, 1/3$ and so on. The natural frequency of a bubble oscillator decreases compared with the linear case result, which means that the nonlinear bubble oscillation system is a "softening"system. In addition, the frequency response curve jumps up or down at a certain frequency. It is also found that there exist multi-valued regions in the frequency response curve depending on the initial conditions of bubble. The dependency of the bubble motion on the initial condition can generate extremely large pressure and temperature which might be the cause of the acoustic cavitation and the sonoluminescence.inescence.

Constitutive Equations for Dilute Bubble Suspensions and Rheological Behavior in Simple Shear and Uniaxial Elongational Flow Fields

  • Seo Dongjin;Youn Jae Ryoun
    • Fibers and Polymers
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    • v.6 no.2
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    • pp.131-138
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    • 2005
  • A theoretical model is proposed in order to investigate rheological behavior of bubble suspension with large deformation. Theoretical constitutive equations for dilute bubble suspensions are derived by applying a deformation theory of ellipsoidal droplet [1] to a phenomenological suspension theory [2]. The rate of deformation tensor within the bubble and the time evolution of interface tensor are predicted by applying the proposed constitutive equations, which have two free fitting parameters. The transient and steady rheological properties of dilute bubble suspensions are studied for several capillary numbers (Ca) under simple shear flow and uniaxial elongational flow fields. The retraction force of the bubble caused by the interfacial tension increases as bubbles undergo deformation. The transient and steady relative viscosity decreases as Ca increases. The normal stress difference (NSD) under the simple shear has the largest value when Ca is around 1 and the ratio Of the first NSD to the second NSD has the value of 3/4 for large Ca but 2 for small Ca. In the uniaxial elongational flow, the elongational viscosity is three times as large as the shear viscosity like the Newtonian fluid.

Large-Scale Vortical Structure of Turbulent Separation Bubble Affected by Unsteady Wake (비정상 후류가 난류박리기포의 응집구조에 미치는 영향)

  • Jeon, Se-Jong;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.9
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    • pp.1218-1225
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    • 2002
  • Large-scale vortical structure of a turbulent separation bubble affected by unsteady wake is essential to understand flow mechanisms in various fluid devices. A spoked-wheel type of wake generator provides unsteady wake, which modifies the turbulent separation bubble significantly by changing rotation directions and passing frequencies. A detailed mechanism of vortex shedding from the separation bubble with unsteady wake is analyzed by taking a conditional average with spatial box filtering, which spatially integrates measured signals at pre-determined wavelength. A convecting nature of the large-scale vortical structure is analyzed carefully. Spatial evolution of the large-scale vortical structure with frequency variance is also exemplified.

Size Verification of Small and Large Bubbles in a Bubble Column (기포탑에서 작은기포와 큰기포의 크기 구별)

  • Seo, Myung Jae;Jin, Hae-Ryong;Lim, Dae Ho;Lim, Ho;Kang, Yong;Jun, Ki-Won
    • Korean Chemical Engineering Research
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    • v.50 no.2
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    • pp.304-309
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    • 2012
  • Size verification of small and large bubbles in a bubble column was investigated by employing the dynamic gas disengagement (DGD) method and dual electrical resistivity probe (DRP) method, simultancously. The holdups of large and small bubbles in the bubble column in a given operating condition were obtained by means of the DGD method by measuring the pressure drop variation in the column with a variation of time after stopping the gas input into the column. The size and frequency of bubbles were measured by the DRP method in the same operating condition, from which the bubble holdup of each range of size was obtained. The verification of size in determining the large or small bubbles was decided by comparing the holdups of large or small bubbles measured by the DGD method with that measured by the DRP method. Filtered compressed air and tap water were used as a gas and a continuous liquid medium. The diameter and height of the bubble column were 0.102 m and 1.5 m, respectively. The demarcation size between the large and the small bubbles in the bubble column was 4.0~5.0 mm; the demarcation size was about 5.0 mm when the gas velocity was in the relatively low range, but about 4.0 mm when the gas velocity was in the relatively high range, within this experimental conditions.

Noise Reduction Effect of an Air Bubble Layer on an Infinite Flat Plate Considering the Noise of Multi-bubbles (다중기포 발생소음을 고려한 무한평판 주위에 형성된 수중 기포층의 방사소음 감소 효과)

  • Kim, Jong-Chul;Heo, Bo-Hyun;Cho, Dae-Seung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.11
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    • pp.1222-1230
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    • 2009
  • A theoretical model was developed to compute the effect of a bubble layer in reducing the radiation noise generated by a force applied on an infinite flat plate considering the noise of multi-bubbles. Using the model, the effectiveness of a bubble layer in reducing the structure-borne noise of the plate was evaluated to consider various parameters such as the source noise levels, the thickness of bubble layers, the volume fractions and the frequency characteristics of bubbly fluids. Considering the noise of multi-bubbles, the actual reduction effect of radiation noise using a bubble layer was expected in cases of high source levels, high volume fractions of bubbles and large thickness of the bubble layer above the resonance frequency of the bubble layer. Accordingly, it is recommended that the thickness of a bubble layer, the source noise level and the characteristics of bubbly fluids should be optimized cautiously to maximize noise reduction effects.

Analysis of Controlling the Size of Microbubble in DAF (DAF에서 기포의 크기제어 및 영향분석)

  • Dockko, Seok;Kwak, Dong-Heui;Kim, Young-Hwan
    • Journal of Korean Society of Water and Wastewater
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    • v.18 no.2
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    • pp.235-241
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    • 2004
  • The dissolved air flotation (DAF) process has been widely used for removing suspended solids with low density in water. It has been known as measuring the size of microbubbles precisely which move upward rapidly in contact zone is difficult. In this study particle counter monitoring (PCM) method is used to measure the rising microbubble after injection from a nozzle. Size and distribution curve of microbubbles are evaluated at different conditions such as pressure drop at intermediate valve, length of pipeline between saturation tank and nozzle and low pressure. And the efficiency is also checked when it collides with different size floc. The experimental results show the following fact. As the final pressure drop occurred closer to a nozzle, the bubble size became smaller. And small bubble collides with large floc as well as small one because of its physical characteristic. However large bubble collides well with large floc rather than small one since hydrodynamic flow in streamline interferes to collide between two. With performing computational process by mathematical model we have analyzed and verified the size effect between bubble and floc. Collision efficiency is the highest when P/B ratio shows in the range of 0.75 < P/B ratio ($R_{particle/Rbubble}$) < 2.0.

Improvement and validation of a flow model for conical vortices

  • Ye, Jihong;Dong, Xin
    • Wind and Structures
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    • v.19 no.2
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    • pp.113-144
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    • 2014
  • Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

The Effect of Heat Transfer from the Bubble Growing on the $B\dot{e}nard$ Convection Flow in a Square Cavity ($B\dot{e}nard$ 대류가 형성된 사각공동내의 상단 평판에서 기포의 성장이 열전달에 미치는 영향)

  • Eom, Yong-Kyoon;Kwon, Seung-Hye;Kwon, Gi-Han
    • Proceedings of the KSME Conference
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    • pp.211-216
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    • 2001
  • Flow motion and variation of thermal field around a bubble which attached at the upper cooled solid wall in a $B\dot{e}nard$ convection flow is studied experimentally using thermo-sensitive liquid-crystal tracers and image processing for flow visualization and analysis. The air is injected gradually by $0.1m\ell$ to make the bubble. As the growing of the bubble in a $B\dot{e}nard$ convection flow, the variation of temperature field and surface tension along the bubble, which in turn cause to change the thermal field patterns and the flow direction and patterns. 6 cells flow pattern is transformed into diverse flow pattern. At the large size of a bubble, it's only conduction mechanism under the region of the bubble because of low Ra number 1137, but the convection flow both sides of the bubble leads to another convection flow in the bubble influence area which has been remained stable stagnation.

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Deformation characteristics of spherical bubble collapse in Newtonian fluids near the wall using the Finite Element Method with ALE formulation

  • Kim See-Jo;Lim Kyung-Hun;Kim Chong-Youp
    • Korea-Australia Rheology Journal
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    • v.18 no.2
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    • pp.109-118
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    • 2006
  • A finite-element method was employed to analyze axisymmetric unsteady motion of a deformable bubble near the wall. In the present study a deformable bubble in a Newtonian medium near the wall was considered. In solving the governing equations a structured mesh generator was used to describe the collapse of highly deformed bubbles with the Arbitrary Lagrangian Eulerian (ALE) method being employed in order to capture the transient bubble boundary effectively. In order to check the accuracy of the present FE analysis we compared the results of our FE solutions with the result of the collapse of spherical bubbles in a large body of fluid in which solutions can be obtained using a 1D FE analysis. It has been found that 1D and 2D bubble deformations are in good agreement for spherically symmetric problems confirming the validity of the numerical code. Non-spherically symmetric problems were also solved for the collapse of bubble located near a plane solid wall. We have shown that a microjet develops at the bubble boundary away from the wall as already observed experimentally. We have discussed the effect of Reynolds number and distance of the bubble center from the wall on the transient collapse pattern of bubble.