• Fire Science and Engineering
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• 제10권3호
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• pp.29-40
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• 1996

The AFFF(Aqueous Film Forming Foam : 3M Company's Light Water) agent are synthetic compounds that foams which are similar to those produced by protein based materials. The foam extinguishing agent was used In the extinguisher was the AFFF agent. We sought, however, to make other foams by using halon 1301 (CF$_3$Br) and halon alternatives, such as HCFC Blend A($CHCIF_2$ 82%, $CF_3$CHCIF 9.5%m $C_{10}$$H_{16}$ 3.75%), HFC-227ea ($CF_3$ $CHFCF_3$) We selected these alternatives instead of air in order to raise the expansion ratio of the AFFF agent. By these means we discovered that it is possible to increase the expansion ratio of the AFFF agent up to 44:1 and up to 24:1 when HFC-227ea was used as a halon alternatives. Therefore our new foam extinguishing agents can be used in a portable extinguish agents can be used in a portable extinguishers.

• Proceedings of the Materials Research Society of Korea Conference
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.57.1-57.1
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• 2012

금속을 용해 응고시킬 때 생성되는 소위, 주조 결함이나 소결금속 내의 기공은 재료의 성능이나 강도를 현저하게 낮추는 결함으로서 예전부터 기피되어 왔다. 또한, 재료공정에 있어서도 여하의 기공이나 기포가 없는 치밀한 고강도 및 고기능성 재료를 개발하는 것에 최대한의 주의와 관심을 기울여 왔다. 반면에 자연계의 천연물이나 인공물을 둘러보면 그 대부분이 다공질임을 쉽게 눈치챌 수 있다. 예를 들어 목재, 지엽 등의 생물을 시작해서 콘크리트 등의 인공물, 우리 체내의 뼈도 전형적인 다공질구조로 구성되어 있다. 이러한 구조로부터 재료의 재질제어 이외에 구조제어라는 새로운 어프로치를 고려할 수 있고, 최근 들어, 금속재료에 있어서도 이러한 다공질 구조에 관한 연구가 활성화되어 충격흡수재, 생체재료, 베어링재료 등의 다양한 응용이 전개되고 있다. 원주상의 방향성 기공을 갖는 로터스 금속의 제조 원리는 용융금속의 높은 가스용해도와 고체금속의 낮은 가스고용도의 차이를 이용하여 응고할 때 고용되지 않는 가스원자가 기포를 형성시키는 것이다. 수소용해도는 모든 금속에 있어서 온도상승에 따라 증가하지만 융점에 있어서 용해도의 불연속적 증가를 나타내며 응고할 때 고액계면에서 다량의 가스를 방출하고 기공 생성을 야기한다. 특히, 고 액상에 있어서 수소용해도 차가 큰 마그네슘, 니켈, 철, 동 등은 기포를 생성하기 쉽다. 또한 기공의 배열구조를 제어하기 위해 일방향응고법를 이용하여 기공에 방향성을 부여한다. 외관상 기공구조가 연근뿌리를 닮은 것으로 부터 로터스 금속이라는 명칭이 널리 알려져 있다. 이와 같은 제조방법에 의해 로터스 금속은 기공 방향, 기공크기, 기공률을 자유롭게 제어할 수 있고 우수한 기계적 성질이 기존의 발포금속, 소결금속과 전혀 다른 특성을 가지고 있다. 이러한 기공구조는 용해온도, 응고속도, 분위기 가스압, 불활성가스와의 혼합체적비 등의 제어를 통해서 조절할 수 있다. 이와 같이 제조한 방향성 다공질금속은 BT (인플란트, 생체적합성, 저탄성, 경량), ST (초음속기엔진부품, 경량), IT (고성능수냉모듈), ET(고온촉매, 필터)의 분야로의 응용을 기대한다.

• Journal of the Korean Society of Visualization
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• 제6권2호
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• pp.14-19
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• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble flow in a rectangular water tank is studied. The Time-resolved PIV technique is adopted for the quantitative visualization and analysis. 532 nm Diode CW laser is used for illumination and orange fluorescent particle images are acquired by a PCO 10bit high-speed camera. To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is changed from 2 l/min to 4 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by the POD analysis technique. It is observed that the large scale counterclockwise rotation and main vortex is generated in the upper half depth from the free surface and one quarter width from the sidewall. When the flow rates are increased, the main vortex core is moved to the side and bottom wall direction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제23권5호
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• pp.414-422
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• 2013

As structure-borne sound, the floor impact sound is one of the serious noises in residential building. Most of heating system applied to the typical Korean residential building is floor heating system which is called ondol. The ondol usually consists of finishing material, mortar with heating coil, light-weight aerated concrete and reinforced concrete. This study focused on the isolation of heavy-weight impact sound and modification of mortar and light-weight aerated concrete. Specifically the glass foam aggregate was added on light-weight aerated concrete. Also, water-cement ratio and amount of cement on mortar were revised. The sound pressure level of heavy-weight impact was measured in reverberation chamber using both bang-machine and impact ball. The size of specimen was 1 m by 1 m. Substitution ratio of glass foam aggregate on light-weight aerated concrete shows relationship with heavy-weight impact sound pressure level. In addition, heavy-weight impact sound pressure level was decreased with increment of water-cement ratio and amount of cement on mortar.

• Journal of Korean Society of Water and Wastewater
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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.

• Journal of the Korean Society of Visualization
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• 제6권1호
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• pp.41-46
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• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble stream in a rectangular water tank is studied. The time-resolved PIV technique is adopted for the quantitative visualization and analysis. 488 nm Ar-ion CW laser is used for illumination and orange fluorescent ($\lambda_{ex}=540nm,\;\lambda_{em}=560nm$) particle images are acquired by a PCO 10bit high-speed CCD camera (1280$\times$1024). To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is 3 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by time-resolved POD analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortex structures moving along with large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.468-474
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• 2010

최근 국내에서 연약지반개량을 위하여 적극 도입되기 시작한 차세대 지반처리기술인 경량혼합토공법의 배합설계에 대한 고찰을 하였다. 경량혼합토는 건설잔토나 준설토 및 현장에서 발생하는 점토나 실트질 흙을 사토처리 하지 않고 현장에서 유용할 수 있는 매우 경제적이고 환경적인 공법으로서 일본에서는 지난 10여년에 연간 수백만톤의 경량혼합토를 생산하여 건설현장에 적용한 실적을 보유하고 있다. 특히 폐자원(폐타이어가루, 왕겨)을 경량혼합토에 첨가하여 건설재료 재활용을 위한 역학적 실험을 수행하였다. 본 연구에서는 경량혼합토를 제작하기 위해 필요한 배합설계변수인 원료토의 중량, 함수비 및 기포재와 첨가할 물의 양, 그리고 강도를 발현하기 위하여 필요한 고화재로서 시멘트첨가량에 대한 최적의 배합설계에 대한 분석을 하였다. 지금까지 제안된 시멘트함유량은 초기의 경량혼합토 목표강도가 주어지면 원료토의 조건에 따라 원하는 비중과 강도를 토대로 적절하게 현장에 적합하게 결정하는 단계에 있으나 일부 현장에서 지나친 목표강도 설정으로 과대한 시멘트를 사용하는 사례가 많아 국가적으로 막대한 손실을 초래하고 있다. 본 논문에서는 경량혼합토의 목표강도을 분석하고 그에 따른 최적의 시멘트함유량을 제시하고자 한다.

• Journal of the Society of Disaster Information
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• 제8권3호
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• pp.204-212
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• 2012

Lightweight soils are very economical and environment friendly materials that are valuable in field without wasting construction materials, dredged soils and clay/ silty soils during construction. Recently, the research of lightweight soils mixed with recycled material (recycled tire powder, rice husks) have been investigated. In this study the mix design factors (i.e., weight of soil, water content, foaming agent and added water) were analyzed and optimized mix design was suggested using cement content for revealing strength. For the analysis the stress-strain behavior, strength with respect to time, and experimental strength for the component of recycled material were analyzed. Finally, target strength was determined to calculate reasonable and economical mix ratio and the optimized cement content was suggested.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제39권1호
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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.

• Applied Chemistry for Engineering
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• 제9권6호
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• pp.901-906
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• 1998

Gas and liquid flow characteristics were investigated in an internal circulation airlift reactor using a single nozzle for a gas distributor. In three reactors with different diameters of the downcomer and heights of the riser, the gas holdup in the individual flow zone and the impulseresponse curve of tracer for an air-water system were measured for various gas velocities and reactor heights. Experimental results showed that the flow behavior of bubbles in the riser was the slug flow due to strong coalescences of bubbles and that the bubble flow pattern in the downcomer was the transition bubble flow for the smaller diameter of the downcomer, however, it was the homogeneous bubble flow for the larger one. And mean gas holdups in the individual flow zone and the reactor were greatly increased with decreasing the diameter of the downcomer for the equal ratio of height of the top section to that of the riser. Also, the mixing time was much effected by the height of the top section of reactor and for the equal ratio of height of top section to that of the riser, it was increased with increasing the diameter of the downcomer and the height of the riser. Flow characteristics of liquid were mainly varied with the bubble flow pattern in the downcomer and the size of the top section of reactor. And circulation velocities of liquid in the riser were increased with increasing gas velocities and the size of the top section of reactor, and for the equal ratio of height of top section to that of the riser, they were increased with increasing the diameter of the downcomer and the height of the riser.