• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.255-267
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• 2022

In this paper, noise characteristics of bubbles created by an orifice-type bubble generator are studied. In order to understand the overall bubble noise characteristics, the bubble noise spectra proposed by Strasberg and Blake, respectively, are examined, and an air injection experiment was performed in the large cavitation tunnel of KRISO to measure the bubble noise. The experiments were performed under a quiescent condition and flow conditions using 5 types of air bubble generator. From the measurement results, the characteristics of the bubble noise spectrum according to the experimental conditions are observed, and the effect of each parameter on bubble noise is analyzed by regression analysis. Finally, empirical models based on the regression analysis for bubble noise are presented, and it is confirmed that the estimated bubble noise is in good agreement with the measured results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.10
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• pp.667-672
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• 2016

The goal of this study was to develop a venturi-type air bubble generator with a porous material throat. Using the two-phase multi-flow CFD analysis for the venturi tube, researchers determined the optimal design of major dimensions, such as the venturi throat length and diameter, in order to control the performance of the air bubble supply through the porous material throat in a venturi tube. Researchers then determined the relationship between the flow rate of supply water and the major design dimensions of the venturi-type air generator for maximizing the performance of the air bubble supply through the porous material throat in a venturi tube.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.54-64
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• 1996

It seems that blowing air bubble out of the bulb surface of a ship of flat bottom will reduce the frictional resistance, since wetted area of the hull surface is reduced owing to air bubble staying close to the surface. To as certain this concept, at first, the limiting streamlines around the bow was observed, and local distribution of pressure and shear stress, due to the change of air-blowing position, air supply pressure, and the model speed, was investigated. It was found that the local friction was reduced near the bulb and air-bubble formations also play an important role as a drag component. This paper can be considered as a preliminary study on the drag reduction of conventional ships by the micro-bubble injection.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.190-197
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• 2006

It is well known that the acoustic characteristics of the sea are significantly affected by bubbles which have their own inherent characteristics at the undersea. In this study, the shape and acoustic characteristics of air bubbles generated by an underwater nozzle are calculated numerically, and are measured with a high speed camera and a hydrophone at various air flow rates in the experimental apparatus. As a result of analysis, the shape calculated numerically well matched with measured values at low flow rates, but in case of relatively higher flow rates. the use of correction coefficient is needed for more accurate estimation of the bubble shape. And also the rising velocity of a single bubble is constant regardless of both the bubble size and the flow rate. and the acoustic signal generated when the bubble is produced by an underwater nozzle has the same characteristic of natural frequency of the bubble pulsation, and is agreed with Minnaert's equation if the correction coefficient is considered in accordance with the flow rate.

• Environmental Engineering Research
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• v.11 no.2
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• pp.91-98
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• 2006

There is a possibility of the production of the air bubbles in membrane pores due to the reduction in pressure during membrane filtration. The effect of fine air bubbles from dissolved gases on microfiltration was investigated in the submerged membrane bio-reactor (SMBR). The $R_{air}$ (air bubble resistance) was defined as the filtration resistance due to the air bubbles formed from the gasification of dissolved gases. From the results of filtration tests using pure water with changes in the dissolved oxygen concentration, the air bubbles from dissolved gases were confirmed to act as a foulant and; thus, increase the filtration resistance. The standard pore blocking and cake filtration models, SPBM and CFM, respectively, were applied to investigate the mechanism of air bubble fouling on a hollow fiber membrane. However, the application of the SPBM and CFM were limited in explaining the mechanism due to the properties of air bubble. With a simple comparison of the different filtration resistances, the $R_{air}$ portion was below 1% of the total filtration resistance during sludge filtration. Therefore, the air bubbles from dissolved gases would only be a minor foulant in the SMBR. However, under the conditions of a high gasification rate from dissolved gases, the effect of air bubble fouling should be considered in microfiltration.

• 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.

• Journal of the Korean Society of Visualization
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• v.8 no.3
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• pp.41-48
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• 2010

A visualization study to evaluate bubble motion in a tab water filled cylindrical tank with a varying flow rate of compressed air is conducted. The flow rate of compressed air varies from 1 to 5 L/min. Time resolved images are acquired by a high speed camera in 10 bit gray level at 100 fps and the measurement volume is irradiated by a 230 W halogen lamp. It is observed that there are three different regions; the bubble formation region, the rising bubble region and the free surface region. During the rise of bubble, the shape is changed as if an elastic body. Based on the binarized bubble image, the mean diameters of rising bubbles are estimated at beneath of the free surface. As the gas flow rate increases, the mean diameter is increased and the rising velocity also increases with buoyancy force.

• The Korean Journal of Community Living Science
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• v.24 no.2
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• pp.187-194
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• 2013

The purpose of this study was to define the optimal boxthorn berries washing method for developing the boxthorn berries cleaner. We analyzed the rate of removal of residual pesticides according to washing methods; 1st - habitual washing method, 2nd - drum rotation washing method, 3th - drum rotation and air bubble washing method, 4th - drum rotation and nozzle spray washing method, 5th - drum rotation and air bubble and nozzle spray washing method. A rate of removal of residual pesticides of 88% was detected in the drum rotation and air bubble and nozzle spray washing method, and a rate of 82% was detected in the habitual washing method. The drum rotation and air bubble and nozzle spray washing method appeared to be the best good washing effect compared to the habitual washing method(about 6% compared to 82.0% higher). Clothianidin Triadimefon, Triforine ingredients, the drum rotation and air bubble and nozzle spray washing method efficiency was lower compared to the habitual washing method removal efficiency.

• Journal of Plant Biotechnology
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• v.31 no.3
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• pp.249-253
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• 2004

The type of air lift bioreactor affected the root growth in ginseng adventitious root cultures. Among bioreactors used in this experiment, bulb type bubble bioreactor (BU) was the best to increase root growth (41.92 g dry weight). The kLa value representing the oxygen transfer capacity from medium to explants (6.98 h$^{-1}$ ) in BU with 5 cm bubble column was higher than other bioreactors. On the other hand, cylindric tube bioreactor (CT) without bubble column resulted in minimum root growth (38.55 g dry weight) and kLa value (5.25 h$^{-1}$ ). Furthermore, the root growth (50.30 g dry weight) in BU with 10 cm bubble column more increased than 5 cm bubble column. However, the kLa value do not affected the secondary metabolite such as ginsenosides. These results show that the bubble column in air lift bioreactor increase kLa value and increased kLa value stimulate the growth of ginseng adventitious roots.

• Journal of the Korean Society of Safety
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• v.18 no.1
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• pp.14-18
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• 2003

The structural development of air-water bubble plumes has been measured under different condition on air flow rate in a cylindrical bath. The time-averaged structure of plumes has been measured with an oscilloscope and an electro-conductivity probe. The temperature of bubbles was also obtained by a thermal-infrared camera. Gas volume fraction and bubble frequency were high since bubbles concentrated on the nozzle. In general, their axial and radial values tended to decrease with increasing distance. Bubble temperature reached water temperature within a short time. The present study showed that thermal equilibrium between bubbles and water was completed before bubbles flow became stable.