• 한국식품저장유통학회지
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• 제23권5호
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• pp.605-613
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• 2016

세절 도라지의 선도 연장을 위한 연구로 세절 도라지를 마이크로버블을 처리함과 동시에 $55^{\circ}C$ 물에 열수처리하고 저장 기간 연장을 조사하기 위하여 고산소/고이산화탄소 MAP를 처리한 후 10일간 저장하면서 미생물수, 색상 및 관능적 품질 변화를 조사하였다. 마이크로버블-열수처리는 세절 도라지의 일반세균수, 진균류수, 장내세균수, 대장균군수의 감소를 보였으며 특히 장내세균수와 대장균군수는 2 log CFU/g 이상의 감소 효과를 나타냄으로써 미생물 제어 효과가 뚜렷이 나타났다. 저장 중 고산소/고이산화탄소 MAP 포장은 호기성균의 성장은 억제하는 것으로 나타났으나 혐기성균에 속하는 장내세균과 대장균군은 저장기간이 증가할수록 증식하는 것으로 확인되었다. 시판 도라지와 동일한 방법으로서 침지 후 PP 포장한 세절 도라지와 본 연구에서 제안한 OMH 처리 후 고산소/고이산화탄소 MAP 처리한 세절 도라지의 저장 중 표면 색도를 분석한 결과 황색도 b값이 유의적인 변화를 보여주었으며 OMH-MAP 처리한 세절 도라지의 b값은 저장 10일째의 수준이 일반 포장 도라지의 4일째 수준과 유사하였다. 또한 관능적 평가에서, OMH-MAP 처리한 세절 도라지에 대한 관능적 평가에서 향과 종합적 기호도의 변화는 Control 처리구 보다 낮아 품질의 신선도가 기존의 세절 도라지 세척 및 포장방법과 비교하여 3일 이상 연장됨을 확인하였다. 이상의 품질 변화 특징을 종합하여 $5^{\circ}C$에서 저장한 세절 도라지의 기호도와 가장 높은 상관관계를 가지는 인자를 분석한 결과, 향과 대장균군이 가장 높은 상관도를 보였고 OMH-MAP 처리한 세절 도라지의 기호도는 향과 대장균군으로 전체 모형의 94%와 76%를 설명할 수 있었다. 결론적으로 마이크로버블-열수 세척을 하여 세절 도라지를 고산소/고이산화탄소 MAP 포장하는 것이 세절 도라지의 저장유통 중 품질 유지에 효과적임을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제22권2호
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• pp.139-147
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• 2021

가축분뇨는 고액분리 후 액상 가축분뇨를 호기생물반응조에서 충분히 부숙시켜 화학비료를 대체한 유기질비료(액비)로 이용하고 있다. 그러나 액비는 작물 생장 중인 여름철에는 토양 살포가 제한되기 때문에 액비 처분 문제가 반복 발생되고 있다. 액비를 추비(웃거름)로 이용하기 위해서는 액비 내 슬러지 저감, 병원성 미생물에 대한 안정성 문제가 확보되어야 한다. 본 연구에서는 가축분뇨 액비의 추비 이용을 위해 부유물질(SS) 제거와 살균 효과가 있다고 알려져 있는 마이크로버블 장치(FeMgO 촉매 삽입)의 액비 내 부유물질과 대장균군의 저감효과를 알아보고 마이크로 필터 장치를 연계한 시스템의 부유물질 제거 효율 향상 여부를 확인하였다. 마이크로버블 장치의 부상분리 과정을 거치면서 액비 내 부유물질은 57.9% 제거되었으며, 대장균군은 검출되지 않았다(16,200 MPN/100mL → 0 MPN/100mL). 마이크로 버블 장치와 마이크로 필터 연계 시스템의 수리학적 체류시간 최적화을 통해 액비 내 부유물질 제거 효율은 수리학적 체류시간이 0.1h 조건에서 92.9%까지 향상된 것을 확인하였다. 같은 조건에서 처리수의 성상을 확인한 결과 유기오염물질은 64.5%(TCOD), 70.1%(SCOD) 제거되었으며 인산염인(PO4-P)과 총질소(TN)의 농도도 각각 54.9%와 51.5%까지 감소되었다. 이러한 연계 시스템으로부터 처리된 유출수는 기존 액비의 조성보다 부유물질 및 오염물질 농도 감소, 대장균군이 포함되지 않아 추비로 직접 이용이 가능할 것으로 판단된다.

• 대한기계학회논문집B
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• 제27권2호
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• pp.236-242
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• 2003

Thermal bubbles find their diverse application areas in the MEMS (MicroElectroMechanial Systems) technology, including bubble jet printers, microactuators, micropumps, etc.. Especially, microactuators and micropumps, which use a microbubble growing by a controlled heat input, frequently involve mechanical and thermal interaction of the bubble with a solid structure, such as a cantilever beam and a membrane. Although the concept is experimentally verified that an internal pressure of the bubble can build up high enough to deflect a thin solid plate or a beam, the physics of the entire process have not yet been thoroughly explored. This work reports the experimental study of the growth of a thermal bubble while deflecting a thin cantilever beam. A physical model is presented to predict the elastic response of the cantilever beam based on the experimental measurements. The scaling law constructed through this work can provide a design guide for micro- and nano-systems that employ a thermal bubble for their actuation/pumping mechanism.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2005년도 추계학술대회 논문집
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• pp.17-22
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• 2005

An experimental study was carried out to investigate the effect of local ultrasonic forcing on a turbulent boundary layer. Stereoscopic particle image velocimetry (SPIV) was used to probe the characteristics of the flow. A ultrasonic forcing system was made by adhering six ultrasonic transducers to the local flat plate. Cavitation which generates uncountable minute air-bubbles having fast wall normal velocity occurs when ultrasonic was projected into water. The SPIV results showed that the wall normal mean velocity is increased in a boundary layer dramatically and the streamwise mean velocity is reduced. The skin friction coefficient ($C_{f}$) decreases $60\%$ and gradually recovers at the downstream. The ultrasonic forcing reduces wall-region streamwise turbulent intensity, however, streamwise turbulent intensity is increased away from the wall. Wall-normal turbulent intensity is almost the same near the wall but it increases away from the wall, In tile vicinity of the wall, Reynold shear stress, sweep strength and production of turbulent kinetic energy were decreased. This suggests that the streamwise vortical structures are lifted by ultrasonic forcing and then skin friction is reduced.

• 한국전산유체공학회지
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• 제21권4호
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• pp.46-53
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• 2016

Direct numerical simulation is conducted to observe the behavior of microbubbles in isotropic turbulence. Navier-Stokes equation and the motion of equation for microbubbles are solved with periodic boundary condition in a cube domain. Vorticity contour, enstrophy ratio, relative reduction of bubble rise velocity, and the closest distance of particles are investigated for various Stokes numbers and gravity factors to understand clustering of microbubbles. Also, clustering due to the effect of the lift force is investigated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.483-486
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• 2002

Injection of microbubbles and/or polymer solution has been known to be a promising method for the reduction of frictional drag of water-borne vehicles. Naval Architects have been interested in friction drag reduction technology, since the friction drag of a commercial ship can be over $70{\%}$ of total resistance. The reduction of friction drag is also important for autonomous underwater vehicles and naval submarines to improve their durability and survivability In this study two sets of experiments were carried out for the friction drag reduction of 2-D channel wall and flat plate in the circulating water channels in Chungnam National University. Preliminary results from the experiments are presented and discussed.

• 한국환경과학회지
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• 제23권1호
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• pp.97-104
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• 2014

The sludge flotation/thickening apparatus equipped a micro-bubble generating pump was used to investigate micro-bubble generating properties on operational parameters. We evaluated micro-bubble generating properties as results to be operated the apparatus by operational parameters which are pump discharge pressure, air/water ratio(A/W ratio), air flow rate, and water flow rate. Micro-bubble generating efficiencies in pumps without recycling flow and with 50% of recycling flow was found to be very efficient on optimum A/W ratio from 1.06 to 3.62% and optimum A/W ratio from 1.05 to 4.06%, respectively. In condition of 3.6% of A/W ratio, we showed that the apparatus could be generated 36,000 ppm of micro-bubble concentration to be optimum treatment efficiency in sludge thickening process.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.585-590
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• 2000

Problems involved in the numerical analysis on the forced oscillation of nonlinear oscillators such a microbubble oscillation under ultrasound and Duffing oscillator were discussed. One of the problems is proper choice of the time scale of the driving force. which is related to the numerical artifacts due to the mismatch between the natural frequency of an oscillator(or bubble) and the characteristic frequency of the applied force. Such problem may occur in a nonlinear oscillator whose behavior is crucially dependent on the frequency of the applied force. The artificial resonance problem during the numerical evaluation of such nonlinear systems was also discussed.

• 상하수도학회지
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• 제18권2호
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• pp.247-253
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• 2004

Major species of Lake Deganuma has varied depending on the season. Namely, there are Micractinium pusillum, chlorella., Scenedesmus sp. shown up in spring season, Microcystis aeruginosa, Microcystis wesenbergii, Anabena spiroides in summer and autumn season and Cyclostephanos invisitatus, Diatoma in winter season in the Lake. As the number of plankton increased, the zeta potential on their surface of them decreased. For this reason, they were dispersed in the lake though the population increased. Zeta potential of M. aeruginosa showed -20mV when their outer size got smaller. As for coagulant dosing in DAF, large amount of coagulant was effective to get lots of sludge during water treatment.

• 상하수도학회지
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• 제18권2호
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• pp.228-234
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• 2004

Dissolved air flotation (DAF), in which suspended solids are removed from water by means of micro-size air bubbles raising slowly up in water and lifting solids from water (smaller than those) attached onto the micro-bubbles as well as those (larger than solids) being attached on these, have been used in water and wastewater since 1920s. The dissolved air flotation technology was originally based on the laminar flow conditions prevailing in water to be treated, but the latest development in that technology has led now to a situation, in which the flow conditions may also be turbulent ones in the modem dissolved air flotation units. Despite of that, the flotation phenomenon used in this unit operation for removal suspended solids from water or wastewater is still the same.