• Journal of the Society of Naval Architects of Korea
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• v.53 no.4
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• pp.300-306
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• 2016

The gas ventilated by supercavitation splits into smaller bubbles and follows the water passage of the cavitation tunnel. The bubbles quickly return to the test section by rather high speed flow, and interrupt the observation of the supercavitation. To secure clear observation in the test section, the bubble collecting section(settling chamber) of large volume is prepared to collect bubbles in the water passage ahead of the test section. The bubble collecting section should provide enough buoyancy effect to the bubbles for proper bubble collecting. However, rather high-speed oncoming flow produces non-uniform velocity distribution and deteriorates buoyancy effect in the bubble collecting section. In the present study, the bubble collecting space and three porous plates are designed and analyzed through numerical methods, and the bubble collecting function is experimentally validated by 1/10-scaled model in terms of the formation of uniformly low velocity distribution in the bubble collecting section.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.582-587
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• 2011

Holdup characteristics of bubble, wake and continuous liquid phases were investigated in bubble columns with viscous liquid media. Effects of column diameter(0.051, 0.076, 0.102 and 0.152 m ID), gas velocity($U_G$=0.02~0.16 m/s) and liquid viscosity(${\mu}_L$=0.001~0.050 $Pa{\cdot}s$) of continuous liquid media on the holdups of bubble, wake and continuous liquid phases were discussed. The three phase such as bubble, wake and continuous liquid phases were classified successfully by adapting the dual electrical resistivity probe method. Compressed filtered air and water or aqueous solutions of CMC(Carboxy Methyl Cellulose) were used as a gas and a liquid phase, respectively. To detect the wake as well as bubble phases in the bubble column continuously, a data acquisition system(DT 2805 Lab Card) with personal computer was used. The analog signals obtained from the probe circuit were processed to produce the digital data, from which the wake phase was detected behind the multi-bubbles as well as single bubbles rising in the bubble columns. The holdup of bubble and wake phases decreased but that of continuous liquid media increased, with an increase in the column diameter or liquid viscosity. However, the holdup of bubble and wake phases increased but that of continuous media decreased with an increase in the gas velocity. The holdup ratio of wake to wake to bubble phase decreased with an increase in the column diameter or gas velocity, however, increased with an increase in the viscosity of con-tinuous liquid media. The holdups of bubble, wake and continuous liquid media could be correlated in terms of operating variables within this experimental conditions as: ${\varepsilon}_B=0.043D^{-0.18}U_G^{0.56}{\mu}_L^{-0.13}$, ${\varepsilon}_W=0.003D^{-0.85}U_G^{0.46}{\mu}_L^{-0.10}$, ${\varepsilon}_C=1.179D^{0.09}U_G^{-0.13}{\mu}_L^{0.04}$.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.184-189
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• 1997

A prompt fission gas release model incorporating the resistance to gas flow in the gap was developed and the effects of gap resistance and failure location on prompt fission gas release from the cladding breach were assessed. The process of prompt fission gas release from the plenum and gap into the coolant was modeled in accordance with three major phenomena: (1) transient gas flow in the gap, (2) the growth of the fission gas bubble while it is still attached to the breach, and (3) the detachment of the fission gas bubble from the breach and mixing with the coolant. The cumulative mass release fraction by the present model was calculated for the case of Young-Gwang 3 & 4 nuclear fuel rod as a typical example. The results showed that the release behavior of prompt fission gas with time was different from the frictionless model which has frequently been used in a simplified approach, and that the location of cladding failure was another key factor for the prompt fission gas release process due to the resistance in the gap.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.11a
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• pp.39-43
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• 2007

In this paper the experiments of breakdown characteristics $SF_6$ liquid ($LSF_6$) in model GIS(Gas Insulated Switchgear) were described. From the experiments results, The ability of $LSF_6$ insulation is higher than high-pressurized $SF_6$ gas. The breakdown characteristics of $LSF_6$ were produced by bubble formed evaporation of $LSF_6$ and bubble caused by high electric emission. It is considered in this paper that the results are fundamental data for electric insulation design of superconductor and cryogenic equipments machinery which will be studied and developed in the future.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.335-338
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• 2003

A finite element-based, integrated process model has been developed and applied to predict the detailed, three-dimensional aspects of the thermo-mechanical behavior occurring in the slab caster considering inclusion removal from molten steel by argon bubble flotation. Gas bubbles are simulated using the dispersion model calculating the volume fraction, and the bubble capture effect is included by a source term in the transport equation for particles. The process model is applied to the investigation of the effect of various process parameters on the inclusion removal in the molten steel.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.876-879
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• 2009

Fischer-Tropsch 합성 반응과 같은 slurry bubble column reactor에서는 반응 속도를 증진시키기 위해서는 서로 다른 상간의 접촉 면적을 최대화함으로써 물질 전달을 원활하게 유지하여야 한다. 특히 Fischer-Tropsch 합성 반응에서는 반응물인 기체가 촉매로서 기능하는 고체 표면으로의 external mass transfer가 효과적으로 이루어져야 하기 때문에 반응기 내의 기체의 거동뿐만 아니라 고체인 촉매의 분포에 대한 연구가 활발하게 이루어지고 있다. 따라서 본 연구에서는 반응기 내에 기체의 superficial velocity를 변화시키면서 기체의 hold up 뿐만 아니라 고체 입자의 분포특성에 대하여 관찰하였다. Superficial velocity가 증가함에따라 gas hold up의 경우, 일정하게 증가하다가 6 cm/sec 이상에서 그 증가폭이 감소하였다. 즉 6 cm/sec이상에서 turbulent flow regime을 형성하였다. 또한 고체입자의 분포 역시 기체의 superficial velocity가 증가함에따라 보다 균일하게 되는 것을 확인할 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.167-169
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• 2003

This paper presents a theoretical study concerning multibubble dynamics in a sound field and the numerical validation for it by employing our new CFD code MTS-DiCUP. In recent papers, the author has shown theoretically that an unknown characteristic frequency, named 'transition frequency,' exists in a multibubble system. For a N -bubble case, up to 2N -1 transition frequencies per bubble have been predicted, only N ones of them correspond to the natural frequencies of the system. The transition frequencies that do not correspond to the natural frequencies give rise to the phase reversal of bubbles' pulsation without resonant response. In this paper, it has been suggested theoretically that those transition frequencies may cause the sign reversal of the secondary Bjerknes force, which is an interaction force acting between acoustically coupled gas bubbles. This theoretical result has been validated by the direct numerical simulation, at least in a qualitative sense.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.252-253
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• 2007

In this paper the experiments of breakdown characteristics $SF_6$ liquid ($LSF_6$) in model GIS(Gas Insulated Switchgear) were described. From the experiments results, The ability of $LSF_6$ insulation is higher than high-pressurized $SF_6$ gas. The breakdown characteristics of $LSF_6$ were produced by bubble formed evaporation of $LSF_6$ and bubble caused by high electric emission. It is considered in this paper that the results are fundamental data for electric insulation design of superconductor and cryogenic equipments machinery which will be studied and developed in the future.

• Journal of the Korean Society of Visualization
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• v.15 no.2
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• pp.48-58
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• 2017

To analyze bubbles generated by an ABB (Air Bubble Barrier), we developed image processing procedure and statistical analysis method. Air was discharged from 5 mm nozzle as swarm form at the bottom of 1 m3 water tank. Flow rates of discharged air are ranged from 2 L/min to 20 L/min and these are corresponding to Reynolds number of 1766-17663. Rise velocity of bubble is extracted by using image process pretending intrusive method. Mean equivalent velocity was calculated using void fraction weighting factor. Bubble diameter is obtained and compared with correlations in the literature. Also, we present a correlation according to the result of this study. Mean velocity and mean diameter of bubbles increase with increasing gas Reynolds number. But these parameters show an asymptotic trend when they approach to high Reynolds number.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.5
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• pp.246-254
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• 2013

Some characteristics of nitrogen-water slug flow were optically measured, in vertical acrylic tubes of 2, 5 and 8 mm diameter. Bubble velocity, bubble and unit cell lengths were measured, by analyzing the light intensity signals from two sets of dot laser-infrared sensor modules mounted along the transparent tubes. Optical images of the bubbles were also taken and analyzed, to measure bubble shapes and liquid film thickness. It was found that the measured bubble velocities were in good agreement with the empirical models in the literature, except for those measured under high superficial velocity condition in the 2 mm tube. Bubble length was found to be the longest in the 2 mm tube, being 4 to 5 times those of the other tubes. Liquid film was found to have developed early in the 2 mm tube, which made the blunt shape of the bubble head. Liquid film thickness in the 8 mm tube was measured at almost twice those of the other tubes.