• 한국기계가공학회지
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• 제14권1호
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• pp.98-104
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• 2015

This experiment was a study of a Vortex nozzle designed to produce micro-bubbles due To investigate air self-suction and the generation of micro-bubble by the Vortex nozzle, the dimensions of air intake region, the nozzle shape, and the nozzle exit diameter ($d_n=5,7,9.2,12.3mm$)werevaried. The air self-suction rate was ~1,000 to 2,000 cc/min at the orifice nozzle (7 mm), and ~100 and ~22 cc/min at the sector nozzles (9.2 and 12.3 mm, respectively). The most bubbles were detected in the orifice nozzle, but bubbles less than $50{\mu}m$ were found in the 12.3-mm sector nozzle. The dissolved oxygen in the tank water was much greater in Case 2 than in Case 1, at both the orifice and sector nozzles. Moreover, the reduction rate of dissolved oxygen was found to be less at the sector nozzles, than at the orifice nozzle.

• Journal of Ship and Ocean Technology
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• 제8권1호
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• pp.1-9
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• 2004

Experiments on friction drag reduction by injecting polymer (Polyethylene oxide) solution or micro-bubbles were carried out in the cavitation tunnel of KRISO. Two different drag reduction mechanisms were applied to a slender axi-symmetric body to measure the total drag reduction. And then the amount of friction drag reduction was estimated under the assumption that the reduction mechanisms were effective only to the friction drag component. As the result of the tests, polymer solution drag reduction up to 23％ of the total drag was observed and it corresponds to about 35％ of the estimated friction drag of the axi-symmetric body. This result matched reasonably well to that of the flat plate test "(Kim et al, 2003)". The normalization of the controlling parameters was tried at the end of this paper. Micro-bubble drag reduction was within 1％ of its total drag. This unexpected result was quite different from that of the flat plate case "(Kim et at, 2003)" The possible reasons were discussed in this paper.

• 상하수도학회지
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• 제25권5호
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• pp.659-666
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• 2011

Although DAF(Dissolved Air Flotation) has been successfully accepted for water and wastewater treatment, the fundamental characteristics of the process have not been fully investigated. Water is saturated with compressed air to dissolve the air into the water at high pressure in saturation tank. Then the water containing dissolved air is released into a floatation tank at a lower pressure, generating micro-bubbles that rise gently through the water and carry the suspended matter to the surface. This study investigated the removal of sewage using automatic mixture type DAF pump and non-powered flotation tank. Characteristics of two devices were compared and analyzed with samples. The results showed that the PAC exhibited higher performance than other coagulants. When air dosage was 2.5ml/l/min, treatment was stable in operation. In the DAF pump with a pressure of 4 atm., the average size of bubbles was 36.2${\mu}m$. Removal efficiency of SS was 80%. At this time removal efficiency of COD was about 80%, of T-N was 30% and T-P was 70% in stable operation. It was concluded that DAF pump system with micro bubble performed higher efficiencies compared to general DAF system for treating wastewater.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2648-2653
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• 2007

Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• 한국전산유체공학회지
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• 제12권3호
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• pp.41-46
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• 2007

Dynamic behavior of immiscible gas bubble attached to the wall in channel flow plays very important role in many engineering applications. Special attention has been paid to micro direct methanol fuel cell(${\mu}$DMFC) where surface tension becomes dominant factor with minor gravitational effect due to its reduced size. Therefore, displacement of $CO_2$ bubble generating on a cathode side in ${\mu}$DMFC can be very difficult and efficient removal of $CO_2$ bubbles will affect the overall machine performance considerably. We have focused our efforts on studying the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We used Level Contour Reconstruction Method(LCRM) which is the simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• 한국환경과학회지
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• 제16권10호
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• pp.1189-1195
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• 2007

Small gas bubbles are used in many environmental and industrial processes for solid-liquid separations or to facilitate heat and mass transfer between phases. This study examines some of the factors that affect the bubble volume and size processed in the EF (electroflotation) process. The effect of electrode material, NaCl dosage, current and electrode distance were studied. The results showed that the generated bubble volume with electrode material lay in: Pt/Ti ${\fallingdotseq}$ Ru/Ti ${\fallingdotseq}$ Ir/Ti > Ti electrode. The more NaCl dosage was high, the smaller bubble was generated due to the low electric power. Bubble generation was increased with increase of current. With the increase of NaCl dosage, bubble generation was increased at same electric power (16.2 W). Generated bubble volume was not affected by electrode distance. However, no clear trends in bubble size as a function of these parameters were evident.

• 수산해양기술연구
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• 제30권2호
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• pp.109-115
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• 1994

This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into near the buffer layer of turbulent boundary layer on flat plate. The concentrations of micro bubble distribution in the boundary was calculater by eddy viscosity equations in the governing equations. When near region of the buffer layer of turbulent boundary layer is filled with micro-bulle of air and viscous of the region is kept low, the velocity profile in the near region should be changed substantially. Then the Reynolds stress in the region becomes less, which guide to lower velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.519-523
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• 2009

In this study, the base mixing ratio was determinated to estimate the optimal mixing ratio of material with a change of mixing ratio of micro cement, sand, foaming agent, plasticizer by testing the unconfined compressive strength test. The unconfined compressive strength test was performed to grasp a engineering characteristics of with a change of micro cement, bubble. The results of test, the unconfined compressive strength increased with a micro cement's increase and bubble's decrease. In the future, it will be secured that is reliable datas from laboratory of various condition and in-situ tests to develop optimal lightweight foamed concrete.

• 한국수소및신에너지학회논문집
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• 제24권6호
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• pp.518-523
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• 2013

This paper describes the reduction of a hydrogen sulfide ($H_2S$) generated from a biogas plant. Micro bubble system is adopted to supply air into the water in the reaction chamber, which can increase the contact area of the supplied air to the reserving water. Two stage reaction chambers having two reaction rooms are designed and manufactured to enhance the reduction rate of a hydrogen sulfide. Sodium hydroxide (NaOH) is also considered to get rid of a hydrogen sulfide. Air volume rate to the water in a reaction chamber is maintained between 0.5 and $1.0m^3/min$. Throughout experimental measurement of the concentration of a hydrogen sulfide by changing the volume of supplied air into the water, reduction rate of a hydrogen sulfide increases as air volume increases. Adding sodium hydroxide to the water with the air supply can reduce effectively a hydrogen sulfide up to 99.5% from biogas. It is noted that a hydrogen sulfide generated by a biogas plant can reduce by supplying micro bubble air and sodium hydroxide effectively.

• 대한기계학회논문집A
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• 제36권12호
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• pp.1643-1651
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• 2012

현재 생활문화 수준의 향상과 소득 증대에 따라 환경오염에 대한 관심이 증가하고 있다. 또한, 수질오염에 대한 규제가 강화되어 수질오염 방지 및 하수처리 효율 향상을 위한 연구가 지속적으로 수행되고 있다. 하수처리 효율을 향상시키는 방법 중 하나는 수처리조 내에서 용존산소량을 늘려주는 것이다. 본 연구에서는 용존산소량을 늘려주고, 산소 발생기에서 발생되는 버블의 크기를 작게 만들 수 있는 설계 방안을 제시한다. 마이크로버블 발생노즐로 유입되는 물과 공기의 유동 형태에 따라 선회 및 충돌을 생성시켜 버블의 크기를 미세하게 만들었다. 본 해석결과에서 충돌 방식의 경우 버블의 크기는 목표치를 만족하지 못하였다. 반면 선회를 이용한 노즐에서는 $0{\sim}50{\mu}m$ 사이의 버블이 79.3%를 차지하고 있는 것으로 나타났다. 본 연구를 통해 개발된 마이크로버블 발생노즐은 하수처리 효율을 증대시킬 수 있을 것이다.