• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.85-88
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• 2002

In order to visually analyze the flow characteristics, gas was injected into the liquid bath through nozzle installed at the center of bottom of the bath. When gas was injected into the liquid bath, several flow patterns were observed bubble-liquid plumb, the spout flow that occurred at the free surface, liquid circulation flow by bubble's behavior, etc. Various bubbles, from small bubbles to Taylor bubbles, consisted of the bubble-liquid plumb. In the pure liquid region, the large and small several vortices were formed and irregularly circulated. These irregular repetition and circulation play a important role of mixing in the bath. The vortices were developed in the upper and the side wall regions and the movement of flow in the low region was very small. It is known as 'dead zone'.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.67-73
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• 2022

Underwater environmental pollution caused by microplastic particles is considered to be one of the most serious problems in many oceans and countries nearby. Previous academic studies or field technologies tried to remove the micro-sized particles are often energy-consuming and costly, so it is hard to be employed for the actual uses. In this study, the mechanism of removal of micro-sized polyethylene spheres (size in order of 100㎛) using a rising bubble is experimentally investigated. It is found that the particles are either affected by bubble wake, thus translocated close to the water surface, or pushed far away by the surrounding fluid flow, depending on their initial position relative to the bubble. By scrutinizing the visualized behaviors of bubble-particle interaction, we draw the governing parameter, i.e., the polar angle between the particle and the bubble, to determine the effective capturing of the particles with a rising bubble.

• Wind and Structures
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• v.11 no.3
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• pp.221-240
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• 2008

The spanwise flow structure around a rigid smooth circular cylinder model in cross-flow has been investigated based on the experimental data obtained from a series of wind tunnel tests. Surface pressures were collected at five spanwise locations along the cylinder over a Reynolds number range of $1.14{\times}15^5$ to $5.85{\times}10^5$, which covered sub-critical, single-bubble and two-bubble regimes in the critical range. Separation angles were deduced from curve fitted to the surface pressure data. In addition, spanwise correlations and power spectra analyses were employed to study the spatial structure of flow. Results at different spanwise locations show that the transition into single-bubble and two-bubble regimes could occur at marginally different Reynolds numbers which expresses the presence of overlap regions in between the single-bubble regime and its former and later regimes. This indicates the existence of three-dimensional flow around the circular cylinder in cross-flow, which is also supported by the observed cell-like surface pressure patterns. Relatively strong spanwise correlation of the flow characteristics is observed before each transition within the critical regime, or formation of first and second separation-bubbles. It is also noted that these organized flow structures might lead to greater overall aerodynamic forces on a circular cylinder in cross-flow within the critical Reynolds number regime.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.499-504
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• 2012

Characteristics of overall heat transfer were investigated in a three-phase slurry bubble column with relatively low surface tension media, which has been frequently encountered in the fields of industry. The heat transfer phenomena was examined in the system which was composed of a coaxial vertical heater and a proper of bubble column. The heat transfer coefficient was estimated from the measured mean value of temperature difference between the heater surface and the column proper at the steady state condition. Effects of gas velocity ($U_G$), solid fraction in the slurry phase ($C_S$) and surface tension (${\sigma}_L$) of continuous liquid media on the overall heat transfer coefficient (h) in the bubble column were determined. The mean value of temperature difference was estimated from the data of temperature difference fluctuations with a variation of time. The amplitude and mean value of temperature difference fluctuations with respect to the elasped time appeared to decrease with decreasing the surface tension of liquid phase. The overall heat transfer coefficient between the immersed heated and the bubble column increased with an increase in the gas velocity or solid fraction in the slurry phase, but it decreased with an increase in the surface tension of continuous liquid media. The overall heat coefficient in the slurry bubble column with relatively low surface tension media was well correlated in term of operating variables and dimensionless groups within this experimental conditions.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2771-2788
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• 2020

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces nonuniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

• The Journal of the Acoustical Society of Korea
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• v.19 no.2
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• pp.46-53
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• 2000

In coastal bay waters, bubbles are generated by relatively heavy ship-traffic, breaking waves due to man-made structures and biological activities. Therefore, the bubble-generating mechanism as well as the bubble density distribution in the bay are quite different from the open ocean where breaking waves are major contributor for bubble density distribution. High frequency surface-backscattered signals were obtained in the coastal bay waters and they were analyzed to compare with those from the open waters in terms of the sea-surface backscattering strength at various grazing angles, the reverberation characteristics in the sub-surface layer and spectral spreading of the scattered signals. The results show that, the surface scattered signals have an irregular distribution of amplitude in time and the width of the spectral spreading is wider than that of the open sea with rough surface. Furthermore, the amplitude distribution of the reverberation signals is not following the Rayleigh distribution, that is eon to be a typical pattern for the open ocean. The results of our analysis imply that the bubble size and the bubble density in the bay are quite different from those observed in the open waters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1107-1116
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• 2006

The droplet ejection process driven by an evaporating bubble in a thermal inkjet printhead is investigated by numerically solving the conservation equations for mass, momentum and energy. The phase interfaces are tracked by a level set method which is modified to include the effect of phase change at the interface and extended for multiphase flows with irregular solid boundaries. The compressibility effect of a bubble is also included in the analysis to appropriately describe the bubble expansion behaviour associated with the high pressure caused by bubble nucleation. The whole process of bubble growth and collapse as well as droplet ejection during thermal inkjet printing is simulated without employing a simplified semi-empirical bubble growth model. Based on the numerical results, the jet breaking and droplet formation behaviour is observed to depend strongly on the bubble growth and collapse pattern. Also, the effects of liquid viscosity, surface tension and nozzle geometry are quantified from the calculated bubble growth rate and ink droplet ejection distance.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.7
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• pp.77-83
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• 2022

When carbon dioxide in a liquid becomes supersaturated, carbon dioxide gas bubbles are generated in the liquid, and they ascend to the surface as they develop further. At this time, the inner wall of the cup with carbon gas attached is known as the entrapped gas cavity (EGS); once an EGS is established, it does not disappear and will continuously create carbon bubbles. This bubbling phenomenon can be activated or suppressed by changing the properties of the solid surface in contact with the carbonated liquid. In this study, the foaming of carbonated liquid is promoted or suppressed by modifying the wettability of the surface. A micro/nano surface structure is formed on the surface of an aluminum cup to produce a superhydrophilic surface, and a superhydrophobic surface similar to a lotus leaf is synthesized via fluorination. Experiment results show that the amount of carbon dioxide bubble generated differs significantly in the first few seconds depending on the surface, and that the amount of gas generated after it enters the stabilization period is the same regardless of the wettability of the cup surface.

• Resources Recycling
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• v.29 no.6
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• pp.104-113
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• 2020

Bubble size in froth flotation has long been recognized as a key factor which affects the bubble residence time, the bubble surface area flux (Sb) and the carrying rate (Cr). This paper presents method of bubble size measurement, relationship between operating variables and gas dispersion properties in flotation column. Using high speed camera and image analysis system, bubble size has been directly measured as a function of operating parameters (e.g., superficial gas rate (Jg), superficial wash water rate (Jw), frother concentration) in flotation column. Relationship compared to measured and estimated bubble size was obtained within error ranges of ±15~20% and mean bubble size was 0.718mm. From this system the empirical relationship to control the bubble size and distribution has been developed under operating conditions such as Jg of 0.65~1.3cm/s, Jw of 0.13~0.52cm/s and frother concentration of 60~200ppm. Surface tension and bubble size decreased as frother concentration increased. It seemed that critical coalescence concentration (CCC) of bubbles was 200ppm so that surface tension was the lowest (49.24mN/m) at frother concentration of 200ppm. Bubble size tend to increase when superficial gas rate (Jg) decreases and superficial wash water rate Jw and frother concentration increase. Gas holdup is proportional to superficial gas rate as well as frother concentration and superficial wash water rate (at the fixed superficial gas rate).

• Journal of computational fluids engineering
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• v.13 no.4
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• pp.126-134
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• 2008

We developed a three dimensional Navier-Stokes code based on the level set method to simulate two phase flows with high density ratio. The Navier-Stokes equations with consideration of the surface tension effects are solved by using SIMPLE algorithm on a non-staggered grid. The present code is validated by simulating two test problems. First one is to simulate a rising bubble inside a cube. The thickness of the interface of the bubble is shown to affect the pressure distribution around the interface. As the thickness decreases, the pressure field around the interface becomes more oscillatory. As the bubble rises, a ring vortex is shown to form around the interface and the bubble eventually develops into an ellipsoidal shape. Merge of two bubbles inside a container is secondly tested to show the robustness of the present code for two phase flow simulation. Numerical results show stable and reliable behavior during the process of merging of two bubbles. The velocity and pressure fields around the interface of bubbles are shown oscillation free during the merging of two bubbles.