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

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.3
• /
• pp.22-29
• /
• 2015

In this study, we tested to develop and apply structural insulation performance improvement concrete to field, which had compressive strength in 24 MPa and thermal conductivity twice as much as normal concrete. After experiment about slump and air contents, combination product of Plain and calcined diatomite powder showed reduction of slump and air contents and combination product with micro foam cell admixture, we cannot find result of slump and air contents reduction. Unit weight of combination product with insulation performance improvement materials decreased more than that of Plain. In the test of compressive strength, compressive strength of insulation performance improvement concrete decreased more than that of Plain but was content with 24 MPa. thermal conductivity of insulation performance improvement concrete tended to decrease. Freezing and thawing resistance of insulation performance improvement concrete was similar to that of Plain. In carbonation resistance test, combination product with calcined diatomite powder showed the result which was similar to that of Plain. In carbonation resistance test, combination product with micro foam cell admixture showed a increase compared to that of Plain and length variation of combination product generally increased.

• Journal of the Society of Naval Architects of Korea
• /
• v.40 no.3
• /
• pp.1-8
• /
• 2003

For the experiment of the friction drag reduction by microbubble injection, a drag reduction water tunnel was specifically designed and made. Experimental apparatus and procedures were devised and developed for measuring the change of wall friction drag with microbubble injection. For fully-developed channel flows. the change of friction drag with important parameters of microbubble injection is investigated and the experimental data and results obtained are presented. The amount of friction drag reduction up to 25% is observed in the present study.

• Korean Chemical Engineering Research
• /
• v.54 no.4
• /
• pp.543-547
• /
• 2016

Bubble properties such as size (chord length) and rising velocity were investigated in a bubble column with electrolyte solutions, of which diameter was 0.152m and 2.5m in height, respectively. The size and rising velocity of bubbles were measured by using the dual electrical resistivity probe method. Effects of gas and liquid velocities and ionic strength of liquid phase on the size and rising velocity of bubbles were determined. The bubble size increased with increasing gas velocity but decreased with increasing liquid velocity or ionic strength of liquid phase. The rising velocity of bubbles increased with increasing gas velocity and decreased with increasing ionic strength of liquid phase, however, it showed a slight maximum value with varying liquid velocity. The size and rising velocity of bubbles were well correlated with operating variables.

• Korean Chemical Engineering Research
• /
• v.48 no.3
• /
• pp.359-364
• /
• 2010

Three kinds of functional regions such as continuous slurry(${\varepsilon}_f$), bubble(${\varepsilon}_b$) and wake(${\varepsilon}_w$) regions were identified, and the individual phase holdups of each functional region were determined in a three-phase slurry bubble column of 0.152 m ID. The holdups of bubble and wake were measured by adopting the electrical resistivity probe method. Effects of gas velocity and solid concentration in the slurry phase on the individual holdups of functional regions in the column were discussed. The holdup of continuous slurry phase decreased but that of bubble or wake increased, with an increase in the gas velocity in the column. The increase of solid content in the slurry phase could lead to the increase in the holdup of continuous slurry phase but decrease in the bubble or wake holdup. The portion of wake holdup was in the range of 15~40% of the bubble holdup, which decreased with increasing gas velocity or solid content in the slurry phase. The individual holdups of three functional regions were well correlated with operating variables within this experimental conditions.

• Korean Chemical Engineering Research
• /
• v.49 no.1
• /
• pp.83-88
• /
• 2011

Holdup characteristics of small bubbles were investigated in a viscous slurry bubble column. The phase holdup of small bubbles was obtained from the knowledge of total bubble(gas) holdup and large bubble holdup, which were measured by mean of static pressure drop method and dual resistivity probe method, respectively. Effects of gas velocity, viscosity of continuous liquid phase and solid fraction in the slurry phase on the small bubble holdup as well as holdups of total bubble(gas) and large bubble in a viscous slurry bubble column. The small bubble holdup increased with increasing gas velocity but decreased with increasing liquid viscosity or solid fraction in the slurry phase. In addition the fraction of small bubble in the total bubble(gas) holdup increased with increasing gas velocity but decreased with increasing liquid viscosity or solid fraction in the slurry phase. It was revealed that the rising velocity of large bubble did not related to the holdup of small bubble in a viscous slurry bubble column.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.241-241
• /
• 2011

최근들어 저온플라즈마를 이용한 생물학적 응용분야가 각광을 받고 있다. 특히 전기전도도를 가진 전해질 내에서 형성된 액상 플라즈마는 열손상없이 암, 세균 및 비정상 장기조직의 제거가 가능하다는 점에서 기존 시술들이 가지는 문제를 해결할 수 있다. 허리통증을 유발하는 탈출 수핵을 대용량으로 제거하기위한 플라즈마발생 전극에 관한 연구가 수행되었다. 수핵 분해량을 늘리기 위해서는 플라즈마를 통하여 다량의 수산화기 라디컬을 형성, 수핵표면에 조사해야 한다. 이를 위하여 6개의 텅스텐 전극표면에서 기포를 발생시켜 플라즈마 발생면적을 넓힐 수 있었다. 텅스텐 전극들은 캡톤코딩과 세라믹 스페이서를 통하여 분리되었고, 전극의 후방에는 SUS 재질의 환형 접지전극을 배치하여 6개의 텅스텐 전극표면에서 모두 기포가 발생할 수 있도록 하였다. 시술적용시 플라즈마 및 전극이 가지는 제한 조건은 단백질 변성을 막기위한 섭씨 45도 이하의 온도 상승과 조직에 대한 기계적인 손상 방지를 위한 2.5 mm 이하의 전체 전극 굵기이다. 이를 만족하는 가운데 수산화기 라디컬 형성을 증대할 수 있는 전극의 구조를 결정하기 위하여 1-D 전기 열유체 모델 도입하였다. 모델에서 도출된 기포의 두께를 바탕으로 다중전극간의 거리 조절을 통하여 플라즈마 방전구조를 전극 - 전극 (기포두께${\times}2$ > 전극간 거리)과 전극 - 기포표면 (기포두께${\times}2$ < 전극간 거리)으로 통제하였다. 형성된 플라즈마의 소모전력, 전자 밀도및 수산화기 라디컬의 회전온도를 분석하기 위하여 0.9% 염화나트륨 수용액, 1.6 S/m, 전해질에서 플라즈마 형성를 형성하고 전기신호 및 광학신호를 관측하였다. 전극에 인가된 전압은 340 VRMS이며 운전주파수는 380 kHz이다. 실험 결과, 전극 - 기포표면 방전구조는 전극 -전극 방전구조에 비하여 전해질의 저항역할로 인하여 방전전류가 3.4 Ipp에서 1.6 Ipp로 감소하였으나, 기포표면에서의 물분자의 분해로 인하여 수산화기 라디컬에서의 발광세기는 약 4배 증가하였다. 또한 수산화기의 회전온도 분포상에서도 전극 - 기포표면 방전은 주변 물분자의 열교환으로 인하여 전극 -전극간 방전의 1500K 에 비하여 낮은 400K를 보였다. 이는 전극-기포표면 방전구조의 전극이 낮은 온도의 수산화기를 다량으로 형성할 수 있음을 시사하며, 카데바를 이용한 실험에서 220초에 걸쳐 약 87%의 수핵을 기계적 손상 및 단백질 변형없이 효과적으로 제거함을 확인하였다.

• Cement Symposium
• /
• no.17
• /
• pp.15-21
• /
• 1989

시멘트 모르타르에 EVAc 에멀젼 및 계면활성제(Sodium Dodecylbenzenesulfonate)를 첨가하여 압축강도, 흡수율, 화학적 저항성, 수화발열속도, 전자현미경 등으로 그 물성을 관찰하였다. EVAc를 시멘트에 첨가할 경우 5-15wt$\%$, SDBF는 0.03wt$\%$를 첨가하고 혼수량을 flow value로써 기준하는 것이 최적조검임을 알 수 있었다. 그리고 EVAc emulsion을 첨가함으로써 혼수량 및 흡수율의 감소 효과를 거둘 수가 있었으며 또한 화학적 저항성도 증가되었다. EVAc emulsion을 과다 첨가할 경우에는 기포가 많이 형성되어 강도가 저하하나, 여기에 계면활성제(Sodium Dodecylbenzenesulfonate)를 가하면 강도가 증가하였으며, 한편 수화 속도는 지연되었다.

• Korean Chemical Engineering Research
• /
• v.43 no.2
• /
• pp.272-277
• /
• 2005

Characteristics of bubbling behavior and bubble properties were investigated in a gas-liquid countercurrent bubble column of in diameter 0.152 m and 3.5 m in height, respectively. Effects of gas and liquid velocities and bubble distribution mode(even, wall-side, central or asymmetric distribution) on the bubble properties such as chord length, frequency, rising velocity and holdup in the reactor were measured and examined by means of dual resistivity probe method. The bubble size, frequency and holdup increased with increasing gas($U_G$) or liquid velocity($U_L$). The rising velocity of bubbles increased with increasing $U_G$, whereas decreased with increasing $U_L$. The uniformity of bubble size distribution and bubble holdup decreased when the distribution mode of bubbles at the gas distributor was changed from even to wall-side, central or asymmetric. The central distribution of bubbles was better than asymmetric mode but worse than wall-side distribution, in considering the bubble holdup and uniformity of distribution.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.565-568
• /
• 2008

Domestic area of most be happened chloride deicer damage. Because daily mean temperature is below 0$^{\circ}C$ from the area of domestic most. Concrete durability influence Air Content. Presently, We used to AE(air-entraining agent) for increase freeze-thaw durability. So, on concrete Air Spacing ratio used $200{\mu}m{\sim}230{\mu}m$ in Canada and under $250{\mu}m$ in Japan institution. Use of Air content has been and will continue to be a major part of concrete durability and scaling. Chloride-containing chemicals such as calcium chloride or rock salt are main deicers for the road. The prepared optimum mix concrete in this study show that freeze-thaw and scaling resistance of Non-AE(air content 1.5%) and AE (air content 4.5%, 7.2%). Solution concentrations of deicing agent were good result, and the pore system and change of hydration products is not difference comparing before freeze-thaw test.