• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.10
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• pp.817-824
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• 2015

Experiments were carried out to investigate the flow and mass transfer characteristics of an orifice nozzle. Measurements of primary and suction flow rates, dissolved oxygen concentration, and electric power were obtained. Vertically injected mixed-jet images were captured by a direct visualization technique with a high speed camera unit. The mass ratio, volumetric mass transfer coefficient, and mass transfer performance were calculated using the measured data. As the primary flow pressure increases, the mass ratio decreases slightly, while the volumetric mass transfer coefficient and electric power increase. As the primary flow pressure increases and the mass ratio decreases, the mass transfer rate increases because of the fine bubbles and wider distribution of the bubbles.

• Microbiology and Biotechnology Letters
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• v.17 no.4
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• pp.277-282
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• 1989

Xanthan gum is a biopolymer produced by Xanthomonas campestris. In xanthan gum fermentation, the fermentation broth changes to highly viscous non-Newtonian fluid as xanthan gum concentration increases. Maximum xanthan gum concentration is limited by high viscosity of the broth since mass transfers of nutrient and oxygen are inhibited. Int this study the mass transfer effects were investigated in batch and fed-batch fermentations at various agitation speeds and by separate oxygen transfer experiments. Xanthan gum production rate was observed to be largely dependent on oxygen transfer coefficient; while cell growth rate was not affected highly by this factor.

• Journal of Power System Engineering
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• v.3 no.4
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• pp.45-50
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• 1999

기포 펌프는 물과 공기 사이의 접촉 면적을 증가시켜 공기로부터 물로의 산소 용해를 높이는 기능을 가지고 있다. 이 연구에서는 기포 펌프에서 여러 가지 흐름 패턴을 설정하고, 이것을 근거로 하여 슬립모델을 확립하여, 기포 펌프의 산소 용해 특성을 조사하였다. 이 연구에서 수행한 실험 결과로부터, 산소 전달 계수는 흐름 패턴(기포 흐름, 기포-슬러그 흐름, 슬러그 흐름)에는 상당한 영향을 받았으나, 시료수의 오염 정도에 따른 영향은 그다지 크지 않음을 확인하였다. 그리고, 산소 전달양은 레이놀즈 수에 비례하여 증가하며, 산소 전달면을 증가시키기 위해서는 에어 스톤이나 디퓨저의 이용이 매우 효과적임을 확인하였다. 또한, 표면 활성 물질은 물의 오염 정도나 흐름 패턴에 관계없이 산소 전달에 큰 영향을 미침을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.61-69
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• 2015

The objective of this study is to experimentally investigate the mixed flow behaviors and oxygen transfer characteristics of a vertical orifice ejector. The experimental apparatus consisted of an electric motor-pump, an orifice ejector, a circulation water tank, an air compressor, a high speed camera unit and control or measurement accessories. The mass ratio was calculated using the measured primary flow rate and suction air flow rate with experimental parameters. The visualization images of vertically injected mixed jet issuing from the orifice ejector were qualitatively analyzed. The volumetric oxygen transfer coefficient was calculated using the measured dissolved oxygen concentration. At a constant primary flow rate, the mass ratio and oxygen transfer coefficient increase with the air pressure of compressor. At a constant air pressure of the compressor, the mass ratio decreases and the oxygen transfer coefficient increases as the primary flow rate increases. The residence time and dispersion of fine air bubbles and the penetration of mixed flow were found to be important parameters for the oxygen transfer rate owing to the contact area and time of two phases.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.640-646
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• 2011

Dissolved oxygen (DO) refers to the volume of oxygen that is contained in water, and is a major indicator of water quality. The objective of this paper was to investigate the effect of salinity on the dissolved oxygen characteristics in an ejector-aerator. An experimental aeration system composed of a motor-pump, an ejector, a motor-blower, a set of aeration and recirculation tank and a control panel. The dissolved oxygen concentrations decreased with the water salinity. The volumetric mass transfer coefficient increased with increasing the water salinity.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.318-318
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• 2011

자연수를 가압(4~5기압)하면서 물과 공기의 비를 4:1~3:1로 혼합하면 수체 내 초미세기포(Diameter $3{\sim}10{\mu}m$)가 발생하는데 이를 산소용해수라 하며 수질정화시설 또는 양식장 등에 널리 사용되고 있다. 산소용해수의 특징은 기포의 비표면적이 넓고 10시간 이상 포화 농도를 유지하여 수체에 잔류하는 시간이 길기 때문에, 일반 산기석을 활용한 포기나 순산소 용해 등의 타 방법과 구별된다. 산소용해수의 산소전달효율은 기존 방법과 큰 차이를 보이기 때문에 실제 적용시에는 대상수를 이용하여 산소전달계수($K_{L}a$)를 사전에 산정할 필요가 있다. 본 연구에서는 한국건설기술 연구원의 안동 수자원 환경실험센터 내 실외형 콘크리트 사각반응수조에 산소용해장치 및 확산장치를 결합한 일체형 시스템을 적용시켜 2010년 9월~2011년 1월의 5개월간 결과를 분석, 본 장치의 $K_{L}a$를 산정 후 수질정화의 활용 면에서 검토하였다. $K_{L}a$의 산정에는 다양한 방법이 이용되나 용존 산소 농도의 제어에 한계가 있는 실외 대형실험장에 적합한 Lewis and Whitman의 Two-film 이론에 근거한 정상포기법을 적용하였다. 체적 $80m^3$의 수조 내에서 현장 유지용수를 대상으로 실험한 결과 산소전달계수는 $0.324\pm0.050$/min, 포화농도는 8.64 mg $O_2$/L, 도달시간은 11 /min이 산정되었으며, 이는 기존 산기석 포기의 산소전달계수 범위인 $0.105\pm0.019$ /min보다 약 3.1배 높은 결과를 보였다. 또한, 확산장치의 수류 순환 방향 및 정도를 검토하기 위하여 실험수조에서 1m단위로 격자를 구성한 후 초음파 유속계로 실측한 결과 0.0~2.5 m/s 의 평면적 유속범위를 도출하였다. 그리고 전체 순환을 고려했을 때 용존산소는 약 8시간 후 8.64 mg $O_2$/L 값에 도달하여 안정화 되었으며, 강한 수류순환과 산소용해수에 의해 하상에 존재하는 퇴적물들의 이송 및 산화촉진을 유도하였다. 이를 근거로 실험수조의 체적과 기준 가동시간인 8시간을 적용시켰을 때, 실험구 수질은 대조구와 비교하여 COD, T-N, T-P가 모두 25~35% 개선되었다. 이 결과는 여과공정 없이 단순 순환만을 고려한 물리적 수질정화 방법의 단독 활용 가능성을 나타내며, 기존 연구에서 나타난 SOD (Sediment oxygen demand) 저감 능력을 감안할 때 향후 폐쇄성 수역의 수질관리에도 효율적으로 활용할 수 있음을 시사한다.

• Applied Chemistry for Engineering
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• v.10 no.2
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• pp.310-318
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• 1999

The concentration breakthrough curves were examined to predict mass transfer coefficients of nitrogen and oxygen in adsorption column for design data of PSA process. Experimental breakthrough curves for bulk gas flow were compared with theoretical simulation results. For quantitative analysis of the adsorption, coupled Langmuir isotherm was considered and LDF model was used to describe the mass transfer effect. In the experimental and theoretical results, it was found that mass transfer coefficient was not affected by flow rate but strongly affected by pressure. As a result of this tendency, mass transfer resistance in this system was proved to belong to the macropore diffusion controlling region and the mass transfer coefficients could be expressed by exponential functions of pressure change. The mass transfer coefficients for one component, nitrogen or oxygen, were successfully applied to breakthrough curves for bulk mixed gases. The experimental curves were reasonably in consistent with the theoretical curves and the error time was less than 5 percent.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.9
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• pp.847-854
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• 2013

The objective of this study is to experimentally investigate the mixed flow and oxygen transfer characteristics of a horizontally injected aeration process using an annular nozzle ejector. The flow rate ratio, pressure ratio and ejector efficiency are calculated using the measured flow rate and pressure with the experimental parameters of the ejector pitch and primary flow rate. The visualization images of mixed flow issuing from the ejector are analyzed qualitatively, and the volumetric oxygen transfer coefficients are calculated using the measured dissolved oxygen concentration. The mixed flow behaves like a buoyancy jet or horizontal jet owing to the momentum of primary flow and air bubble size. The buoyancy force of the air bubble and the penetration of mixed flow are found to be important parameters for the oxygen transfer rate owing to the contact area and time of two phases.

• Nuclear Engineering and Technology
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• v.27 no.4
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• pp.619-625
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• 1995

발전소 계통의 부식의 원인은 여러가지가 있으나 그 중 용존산소에 의한 덴팅이나 점식등은 증기발생기에 심각한 영향을 줄 수 있다. 용존산소를 제거하는 방법은 기계적 방법과 환원제를 사용하는 화학적 방법, 그리고 촉매를 이용하는 방법등이 있는데 이중 촉매를 이용하는 방법이 우수한 것으로 평가되고있다. 본 연구는 촉매탑을 이용하여 용존산소를 제거하는 공정에 있어서 여러가지 촉매를 사용하여 용존산소가 제거되는 것을 실증하였고 각 촉매의 성능을 비교하였다. 그 결과 Lewatit OC-1045 촉매가 가장 우수한 성능을 보였다. 촉매탑 실험시 물질전달 계수를 측정하고 이 값과 촉매탑 모델링을 이용하여 실제 발전소 계통에 부착시켜 응용할 수 있는 촉매탑 설계를 수행하였다.