• Journal of the Korean Society of Visualization
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• v.20 no.2
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• pp.55-62
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• 2022

We experimentally investigate a rising toroidal bubble impacting a free surface. The toroidal bubble is created by releasing pulsed air. By adjusting the volume and circulation of the toroidal bubble, the characteristics of interactions between the toroidal bubble and the free surface are identified. Because of the impact by the toroidal bubble, the free surface is convexly deformed upwards above the center point of the toroidal bubble, while the edge of the deformed free surface is pulled down. When the circulation of the bubble becomes stronger, the surface which was pulled down breaks eventually, and air above the free surface is entrained into water, forming an unstable toroidal bubble. The deformations at the center and edge of the free surface are in a linear relationship with the Froude number and the Weber number, respectively.

• Korean Journal of Food Science and Technology
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• v.19 no.3
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• pp.220-224
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• 1987

The concentration ranges forming surface excess of bovine serum albumin(BSA) and ovalbumin solutions were determined, and the factors affecting the foam separation of BSA were investigated. The surface tension of BSA solution decreased from 72 to 61 dynelcm, when the concentration changed from $5{\times}10^{-3}$ to $3{\times}10^{-2}%$, and the critical micelle concentration was appeared to be at 0.03% of BSA. At the isoelectric point (pH 4.9) of BSA, the foamate volume was maximum, but enrichment ratio was minimum, resulting in the maximum recovery rate. When the pH deviated from the isoelectric point, the foamate volume decreased and the enrichment ratio increased. The enrichment ratio increased, while the foamate volume decreased drastically as the temperature was elevated above $20^{\circ}C$, resulting in the decrease in recovery rate. As the gas flow rate increased, the enrichment ratio decreased and the foamate volume increased. When $(NH_4)_2SO_4$ was added, the enrichment ratio decreased, but the maximum foamate was obtained at ionic strength 7. The concentration to form the surface excess of ovlbumin, which has lower surface hydrophobicity than BSA, was 200 times higher than that of BSA. This fact indicates the possibility of selective foam separation by hydrophobicity difference of proteins.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.19-19
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• 2011

수중방전은 다양한 라디칼을 직접 물 속에서 발생시키기 때문에 수처리 공정에 다양한 응용이 가능하다. 특히, 최근에 선박평형수 등의 살균이 국제적인 이슈가 되고 있고, 2017년까지는 모든 선박에 살균을 위한 수처리 설비가 의무화된다. 본 연구에서는 염분이 있는 수체에서의 방전공정을 연구하고 이를 수처리공정에 적용할 수 있는 방법에 대해 연구하였다. 해수의 경우 전도도가 53mS로 자유로운 전하의 이동이 가능하기 때문에 일반적인 민물방전의 전원과 전극 등으로는 방전을 할 수 없다. 이에 세라믹과 금속의 이중구조로 되어 있는 모세관전극을 개발하여 전도성이 있는 수체에서의 방전을 이루었다. 전원장치로는 60 Hz, 380 V를 1차측에 인가하여 2차측에서 약 3 kV, 10 kW의 파워가 발생하는 12위상차 교류전원장치를 개발하여 사용하였다. 모세관 내부에 전압이 인가되면 전류가 발생하여 joule heating에 의하여 모세관 내부에 기포가 형성된다. 이 때, 전류의 단락이 이루어지면서 고전압쪽에 전하가 축적되며 기포내부의 E-field가 상승한다. 이후 기포 내에서 방전이 개시되며 각종 라디칼을 생성한다. 방전에 의해 생성되는 산화제로는 오존, OH라디칼, 과산화수소 등이 있으며, 해수에서는 Cl-의 결합에 의하여 Cl2 가스가 발생한다. 약 30,000 J/L의 체적에너지에 대하여 생성되는 총염소의 농도는 2.5 mg/L이다. 수중방전의 적용대상으로 선박평형수, 멤브레인과의 결합, 용존기포부상법을 선정하여 적용가능성을 연구하였다. 먼저 선박평형수 살균처리를 위해 해수의 처리유량을 20 lpm으로 유지하고 대장균, 바실러스, 조류(테트라셀미스) 등을 투입하여 전극 12개가 삽입된 12위상차 플라즈마 반응기를 통과시켰더니, 약 30,000 J/L의 체적에너지에 대하여 1일 후의 살균력이 각각 99.99, 99.99, 99.9%의 살균력을 나타내었다. 이는 국제해사기구에서 권장하는 살균수준인 99.9%를 초과하는 수치이다. 플라즈마를 이용한 해수살균공정의 안정적 운전을 위해 후단에 UF멤브레인을 추가하여 잔류생존 미생물을 제거할 수 있다. 이를 위해 플라즈마가 후단의 멤브레인 운전에 미치는 영향을 평가하였다. 카올린과 탄산칼슘을 오염원으로 각각 투입하여 멤브레인으로 처리를 하였을 때, 방전 직후 멤브레인에 걸리는 막간압력차가 약 30% 감소하였는데, 이는 막에 형성된 파울링이 방전에 의해 제거된 것으로 평가할 수 있다. 수중방전은 다양한 산화제를 생성함과 동시에 미세기포를 발생시키는데 이는 수중유기물의 부상분리에 적용될 수 있다. 방전모세관전극의 내부직경을 1 mm로 유지하고, 60 Hz, 교류전원으로 방전한 결과 평균입경 44 um의 기포를 발생시켰고, 이는 일반적으로 용존공기부상법에 사용되는 기포의 크기와 일치한다.

• Journal of Korea Soil Environment Society
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• v.4 no.1
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• pp.49-55
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• 1999

The treatment of petroleum contaminated soil requires various physico-chemical remediation technologies which are efficient in time and can reduce the possibility of secondary contamination by themselves In this study, an innovated soil washing process was proposed to treat the diesel-contaminated soil. Micro-bubbles, which were generated by hydrogen peroxide, deserted and floated the contaminants. Soils less than #60(0.25mm) were artificially contaminated by 6,500mg TPH/kg dry soil initially. The process was examined for pH, the soil to water mixing ratio, concentration of $H_2O$$_2$, and contacting times. In the case of less than #60 soil, maximum removal efficiency(60%) was obtained at pH 12. 1.0% hydrogen peroxide, and 1 : 5 soil to water mixing ratio for 1 hour.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.216-223
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• 2019

The objective of this study is to propose a reliable stress-strain model in compression for lightweight concrete using bottom ash aggregates and air foam(LWC-BF). The slopes of the ascending and descending branches in the fundamental equation form generalized by Yang et al. were determined from the regression analyses of different data sets(including the modulus of elasticity and strains at the peak stress and 50% peak stress at the post-peak performance) obtained from 9 LWC-BF mixtures. The proposed model exhibits a good agreement with test results, revealing that the initial slope decreases whereas the decreasing rate in the stress at the descending branch increases with the increase in foam content. The mean and standard deviation of the normalized root-square mean errors calculated from the comparisons of experimental and predicted stress-strain curves are 0.19 and 0.08, respectively, for the proposed model, which indicates significant lower values when compared with those(1.23 and 0.47, respectively) calculated using fib 2010 model.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.772-779
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• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.9
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• pp.513-520
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• 2016

It is well known that volatile compounds including disinfection by-products as well as emissive dissolved gas in water can be removed effectively by air stripping. The micro-bubbles of flotation unit are so tiny as microns while the diameter of fine bubbles applied to air stripping is ranged from hundreds to thousands of micrometer. Therefore, the micro-bubbles in flotation can supply very wide specific surface area to transfer volatile matters through gas-liquid boundary. In addition, long emission time also can be gained to emit the volatile compound owing to the slow rise velocity of micro-bubbles in the flotation tank. There was a significant difference of the THMs species removal efficiency between air stripping and flotation experiments in this study. Moreover, the results of comparative experiments on the removal characteristics of THMs between air stripping and flotation revealed that the mass transfer coefficient, $K_La$ showed obvious differences. To overcome the limit of low removal efficiency of dissolved volatile compounds such as THMs in flotation process, the operation range of bubble volume concentration is required to higher than the operation condition of conventional particle separation.

• Korean Chemical Engineering Research
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• v.48 no.2
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• pp.185-192
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• 2010

The chemical-looping combustion(CLC) has advantages of no energy loss for separation of $CO_2$ without $NO_x$ formation. This CLC system consists of oxidation and reduction reactors where metal oxides particles are circulating through these two reactors. In the present study, the reaction kinetic equations of iron oxide oxygen carriers supported on bentonite have been determined by the shrinking core model. Based on the reactivity data, design values of solid circulation rate and solids inventory were determined for the rector. Two types of interconnected fluidized bed systems were designed for CLC application, one system consists of a riser and a bubbling fluidized bed, and the other one has a riser and two bubbling fluidized beds. Solid circulation rates were varied to about $30kg/m^2s$ by aeration into a loop-seal. Solid circulation rate increases with increasing aeration velocity and it increases further with an auxiliary gas flow into the loop-seal. As solid circulation rate is increased, solid hold up in the riser increases. A typical gas leakage from the riser to the fluidized bed is found to be less than 1%.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.373-374
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• 2010

This study is to search for recycling method of the WCP(waste concrete powder). From the experiment analysis on the chemical composition, we confirmed that $SiO_2$ was occupied about 60% of WCP. To investigate the applicability of WCP as replacement material of Quartz, we tested the properties of autoclaved light weight concrete containing WCP. As a results, when increasing the replacement of WCP, compressive strength decreased and pore diameter did not change. On the other hand, when increasing curing times, compressive strength and pore diameter increased.

• Journal of the Korean Society of Visualization
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• v.10 no.2
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• pp.14-19
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• 2012

An optical fiber probe system for measuring the local void fraction in the air-water two-phase flow was developed with a 1550 nm light source. Air was injected through a nozzle placed in the center of the bottom wall of a water-filled cylindrical tank. The optical fiber probe having a diameter of $125{\mu}m$ was sufficiently thin to resolve the air-water interface of the bubbly flows. To verify the performance of the optical fiber probe, the synchronized high speed visualization study using a high speed camera was carried out. Comparison between the optical signals and the instantaneous bubble diffraction images confirms that the optical fiber probe is very accurate to measure the void fraction in two-phase flows. The estimated bubble diameter and the rising velocity by the optical fiber probe have 1% and 5% of accuracy, respectively.