• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.571-576
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• 2011

Characteristics of bubble driven wakes were investigated in a simulated GTL process(0.102 m ${\times}$ 1.5 m in height) with viscous liquid medium. Effects of gas velocity(0.04 ~ 0.12 m/s) and liquid viscosity(0.001 ~ 0.050 $Pa{\cdot}s$) on the wake characteristics such as rising velocity, frequency, size and holdup were determined by employing a resistivity probe method. The wake phase formed behind the rising multi-bubbles as well as single bubbles were detected effectively from the conductivity fluctuations measured by the probe. Compressed, filtered and regulated air and aqueous solutions of Carboxy Methyl Cellulose(CMC) were used as a dispersed gas phase and a continuous liquid medium, respectively. It was found that the rising velocity and size of wake phase increased with an increase in gas velocity or liquid viscosity. The holdup and frequency of wake phase increased with increasing gas velocity due to the increase of gas input into the process with increasing gas velocity. However, the values of holdup and frequency of wake phase decreased with increasing liquid viscosity, since the size of bubbles and thus that of wakes increased with increasing liquid viscosity. The ratio of wake holdup to that of gas phase, which was in the range of 0.25 ~ 0.48, increased with an increase in liquid viscosity but decreased with gas velocity. The wake characteristics were well correlated in terms of operating variables within this experimental conditions.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.41-46
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• 2017

Control of mixing and transport processes are the key areas that can be benefited by understanding the hydrodynamics in gas-liquid two-phase flows. In particular, the enhanced bubble-induced liquid-phase mixing is known to be a function of void fraction distribution, gas phase velocity and so on. To further our insight on the characteristics of the liquid-phase mixing induced by the bubbles, in the present study, we experimentally investigate the mixing performance of a rectangular bubble column while changing the void fraction from 0.006 to 0.075%. A shadowgraphy technique is used to measure the gas-phase properties such as void fraction and size/velocity of bubbles. On the other hand, we use dye visualization with low diffusive buoyant dye to directly measure the level of mixing. Finally, we confirm that the time taken for full mixing scales with the inverse of volume void fraction.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.598-605
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• 1997

In recent years, the number of vehicle fires, as well as the number of motor vehicles, has been increasing rapidly. Therefore, several types of automatic fire suppression systems for the engine compartment of automobiles have been developed to extinguish automobile fires, and most of these systems use halon 1301 as a fire extinguishing agent. Due to environmental concerns, the phase-out of halons has been announced, so now there is a need to replace halon 1301. For this, a 1,1,1,2,3,3,3-heptaflouropropane (HFC-227ea, FM-$200^{TM}$) gas-filled Aqueous Film- Forming foam (known as AFFF) extinguisher was devised even though air foam extinguishers could be used. This is because the air in the foam bubbles is a source of oxygen required for the combustion reaction. It can be surmised that it is possible to increase the fire extinguishing efficiency of AFFF by filling in foam bubbles with a gaseous extinguishing agent. The best choice is the FM-$200^{TM}$ gas-filled AFFF, Which has the maximum expansion ratio of 62:1. This makes it possible for the expanded foam to rapidly fill the engine compartment.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.2
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• pp.195-203
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• 2018

Among the techniques of reducing the drag to increase the speed of underwater moving bodies, we studied on the drag reduction method by gas injection. Researches on gas injection method have been paid much attention to reduce the drag of vessels or pipe inner walls. In this study, we used a sintered metal mesh that can uniformly distribute fine bubbles by gas injection method, and applied it to a cylindrical underwater moving body. Using the KRISO medium-sized cavitation tunnel, we measured both the bubble size on the surface of the sintered mesh and the bubble distribution in the boundary layer. Then, drag reduction tests were performed on the cylinder type underwater moving models with cylindrical or round type tail shape. Experiments were carried out based on the presence or absence of tail jet injection. In the experiments, we changed the gas injection amount using the sintered mesh gas injector, and changed flow rate accordingly. As a result of the test, we observed increased bubbles around the body and confirmed the drag reduction as air injection flow rate increased.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1703-1705
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• 2014

Bubble column reactors are considered the reactor of choice for numerous applications including oxidation, hydrogenation, waste water treatment, and Fischer-Tropsch (FT) synthesis. They are widely used in a variety of industrial applications for carrying out gas-liquid and gas-liquid-solid reactions. In this paper, the computational fluid dynamics (CFD) model is used for predicting the gas holdup and its distribution along radial and axial direction are presented. Gas holdup increases linearly with increase in gas velocity. Gas bubbles tends to concentrate more towards the center of the column and follows a wavy path.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.16-27
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• 2002

A level-set method is used for analyzing the behaviors of gas bubbles in two fluids incompressible viscous flow domain. The governing equations are solved by using a finite volume method. The numerical results are verified by comparing with the experimental and other computational results. Computations for the deformations and motions of one or multi-bubbles in the flow domain with the initial undisturbed free interface are conducted. It can be seen that numerical results for different surface tension and density ratio arise very different behaviors of bubbles. When bubbles rise near the free interface, the free interface gives some great influence on the behaviors of bubbles. The present results computed by a level-set method give useful information about the properties of bubble motions and deformations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1446-1452
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• 2009

The behavior of bubbles in a centrifugal fluidized bed with a 340mm inner diameter, 195mm high was observed by photographs using 10.5${\mu}m$and 21.5${\mu}m$mean diameter of $Al_2O_3$particles as bed materials at each of 400rpm, 600rpm, 800rpm, and 1000rpm number of rotations of the rotor. At these experimental ranges, the experimental results clearly proved the effect of number of rotations of the rotor on the behavior of bubbles in the centrifugal fluidized bed. As the number of rotations of the rotor increased, the gas velocity at which bubbles begin to be formed also increased but diameter of bubbles decreased. And sizes of the bubbles were relatively small.

• 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.

• Korean Chemical Engineering Research
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• v.43 no.2
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• pp.272-277
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• 2005

Characteristics of bubbling behavior and bubble properties were investigated in a gas-liquid countercurrent bubble column of in diameter 0.152 m and 3.5 m in height, respectively. Effects of gas and liquid velocities and bubble distribution mode(even, wall-side, central or asymmetric distribution) on the bubble properties such as chord length, frequency, rising velocity and holdup in the reactor were measured and examined by means of dual resistivity probe method. The bubble size, frequency and holdup increased with increasing gas($U_G$) or liquid velocity($U_L$). The rising velocity of bubbles increased with increasing $U_G$, whereas decreased with increasing $U_L$. The uniformity of bubble size distribution and bubble holdup decreased when the distribution mode of bubbles at the gas distributor was changed from even to wall-side, central or asymmetric. The central distribution of bubbles was better than asymmetric mode but worse than wall-side distribution, in considering the bubble holdup and uniformity of distribution.

• Nuclear Engineering and Technology
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• v.45 no.2
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• pp.203-210
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• 2013

The objective of this conducted research is to study the iodine removal efficiency in a self-priming venturi scrubber for submerged and non-submerged operating conditions experimentally and theoretically. The alkaline solution is used as an absorbent, which is prepared by dissolving sodium hydroxide (NaOH) and sodium thiosulphate ($Na2S_2O_3$) in water to remove the gaseous iodine ($I_2$) from the gas. Iodine removal efficiency is examined at various gas flow rates and inlet concentrations of iodine for submerged and non-submerged operating conditions. In the non-submerged venturi scrubber, only the droplets take part in iodine removal efficiency. However, in a submerged venturi scrubber condition, the iodine gas is absorbed from gas to droplets inside the venturi scrubber and from bubbles to surrounding liquid at the outlet of a venturi scrubber. Experimentally, it is observed that the iodine removal efficiency is greater in the submerged venturi scrubber as compare to a non-submerged venturi scrubber condition. The highest iodine removal efficiency of $0.99{\pm}0.001$ has been achieved in a submerged self-priming venturi scrubber condition. A mathematical correlation is used to predict the theoretical iodine removal efficiency in submerged and non-submerged conditions, and it is compared against the experimental results. The Wilkinson et al. correlation is used to predict the bubble diameter theoretically whereas the Nukiyama and Tanasawa correlation is used for droplet diameter. The mass transfer coefficient for the gas phase is calculated from the Steinberger and Treybal correlation. The calculated results for a submerged venturi scrubber agree well with experimental results but underpredicts in the case of the non-submerged venturi scrubber.