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나노유체 : 수조비등 환경에서 나노입자 코팅두께에 따른 임계열유속 결과의 실험적 연구
박성대 ( Seong Dae Park ),문성보 ( Sung Bo Moon ),방인철 ( In Cheol Bang ) 한국액체미립화학회 2012 한국액체미립화학회 학술강연회 논문집 Vol.2012 No.-
Since nanofluids, which are colloidal dispersions of nanoparticles in a base fluid such as water, were known as a way to significantly enhance the CHF, the pool boiling CHF test was conducted in a variety conditions depending on the material, the concentration etc. The concentration is the factor which influences the amount the coating materials on the heater surface. In most papers which are reporting the results of the pool boiling CHF test for nanofluids, the exact heating time is not described according to the heat flux level. The heating time is also an important factor that determines the amount of coated material. Alumina nanofluid is prepared by dispersing nanoparticles into the distilled water as a base fluid. The concentration of nanofluid is 0.01Vol%. Pre-coating process was carried out from 1 to 180 minutes at 600kW/m2. Heating time affects CHF positively in the region of a relatively short pre-coating time. The trend of CHF change is slowly decreased as pre-coating time is incrased. When more nanoparticles are coated on the heater surface but not heat transfer area is limited, the heat resistance which is disturbing the heat flow is increasing. The static contact angle was measured for sessile droplets of pure water (1μl) at 25℃ in air on the clean and nanoparticles coated surfaces boiled in nanofluids. The dramatic decrease of contact angle was observed on the coated heater surface. The results of contact angle are not uncovering the slight decrease of CHF in high pre-coating region. Hydrodynamic instability theory has been known as model of Zuber who proposed initially. The nanoparticle-coated surface has a shorter average distance compared with a bare surface. A case of high pre-heating time has a short wavelength in this work. A short wavelength allows to the vapor to prevent the formation of bulk vapor by venting the vapor equally across the heater surface. But the results of wavelength are not similarly uncovering the slight decrease of CHF in high pre-coating region. Coating thickness was measured by analyzing the SEM images. The thickness is continually increased but the gradient is becoming gentle. Reversely, porosity is decreased as the pre-boiling time is longer. It means that the coating layer formed by nanoparticles is becoming dense. It is clear the coating layer functions as a heat transfer resistance.
유명재,박성대,임호선,이우성,Yoo, Myong-Jae,Park, Seong-Dae,Lim, Ho-Sun,Lee, Woo-Sung 한국마이크로전자및패키징학회 2012 마이크로전자 및 패키징학회지 Vol.19 No.1
Currently due to increasing integration of various electronic devices and need of multi-functions, more and more heat is produced and for electronic devices to achieve maximum performance with optimum life time, heat dissipation is critical. A solution to such problems is use of high heat dissipative insulating sheet. In this paper status of current products are introduced and several technology aspects to meet the demand of increased heat dissipation needs is introduced.
미립화 및 분무장치 2 : 수력학적 캐비테이션을 모의 크러드 침전층 제거 실험
김성만 ( Seong Man Kim ),이승원 ( Seung Won Lee ),박성대 ( Seong Dae Park ),방인철 ( In Cheol Bang ) 한국액체미립화학회 2012 한국액체미립화학회 학술강연회 논문집 Vol.2012 No.-
Axial Offset Anomaly (AOA) referring to an unexpected neutron flux depression is also known as Crud Induced Power Shift (CIPS). Fuel assemblies removed from an AOA core has shown a thick porous deposition layer of crud on fuel clad surface. Hydrodynamic cavitation generates shock pressure of a few tens MPa due to bubble collapse like the cavitation generated by Ultrasonics. It is well known that the cavitation can erode the metal surface. The idea of the current study is that such energetic cavitation bubble collapses could help to remove the crud from the fuel assembly. Therefore, the current study first investigates effects of hydrodynamic cavitation occurred from a single hole orifice fundamentally. The orifice can be easily occurred the cavitation. In addition to common cavitation, effect of swirl was measured and quantified using sensitive film. The purpose of this study is to optimize the effect of cavitation erosion. For investigate the cavitation effect, effect of cavitation was measured by film. The film was discolored by the pressure with a measurement range of its own. It is individual to reflect the value stored pressure as the disposable film. For investigate of removal effect, CRUD was coated by nanoparticle. CRUD consists primarily of magnetite, nickel ferrite, cobalt ferrite, and so on. For only checking the cavitation effects in this work, however, specimens made of SS316L, alloy of Cr, Ni and Fe are simply deposited by silicon carbide nanoparticles since the nanoparticles with the CRUD porous layer. It shows a CRUD-like deposition structure. Weight change of sample was measured the through each coated sample for analyzing the removal effect on each cavitation number. The result of pressure in two flows, higher pressure level is observed in case of using swirl flow. The samples were exposed to cavitation during the same time, and it was compared the result between using only orifice and using both orifice and line static mixer. Maximum shock pressure was recorded at swirl flow caused by line static mixer.
폐쇄성 대장암 환자에서 스텐트 삽입술 후 발생한 복부구획 증후군
백성규(Seong Kyu Baek),배옥석(Ok Suk Bae),박성대(Sung Dae Park) 대한외과학회 2008 Annals of Surgical Treatment and Research(ASRT) Vol.75 No.5
Colonic stenting has been suggested as an acceptable therapeutic option for the palliation of malignant colorectal obstruction or to achieve bowel decompression and preparation. It is effective as a bridge to surgery that is useful as an option to avoid emergency colostomy. However, it is associated with complications such as intestinal perforation, stent migration, bleeding, and failure of bowel decompression. Of all the complications, intestinal perforation and failure of bowel decompression are most serious and require surgical treatment. Here we report a case of abdominal compartment syndrome after stent insertion for obstructive colon cancer. The main causative factors for abdominal compartment syndrome were bowel distension associated with endoscopic gas inflation and failure to achieve bowel decompression.
가공면미세결함의 나노 인프로세스 측정을 위한 AFM시스템의 개발
권현규,최성대,박무훈,Gwon, Hyeon-Gyu,Choe, Seong-Dae,Park, Mu-Hun 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.3
This paper examines a new in-process measurement system for the measurement of micro-defects on the surfaces of brittle materials by using the AFM (Atomic Force Microscopy). A new AFM scanning stage that can also perform nano-scale bending of the sample was developed by adding a bending unit to a commercially available AFM scanner. The bending unit consists of a PZT actuator and sample holder, and can perform static and cyclic three-point bending. The true bending displacement of the bending unit is approximately 1.8mm when 80 volts are applied to the PZT actuator. The frequency response of the bending unit and the stress on the sample were also analyzed, both theoretically and experimentally. Potential surface defects of the sample were successfully detected by this measurement system. It was confirmed that the number of micro-defects on a scratched surface increases when the surface is subjected to a cyclic bending load.
Reactions of Aryl Halides with Phenoxides and Alkoxides by Phase Transfer Catalysis
조봉래,박성대,Jo, Bong Rae,Park, Seong Dae Korean Chemical Society 1984 Bulletin of the Korean Chemical Society Vol.5 No.3
The reaction of aryl halides with phenoxides and alkoxides were investigated under phase transfer catalytic conditions. 2,4-Dinitro- and 4-nitrohalobenzenes reacted readily with phenoxides in NaOH(aq)-benzene in the presence of Bu4N+Br, affording the products quantitatively. Although the aryl halides did not react with alkoxides under the same condition, the reactions were completed within 2 hours at room temperature when conducted under solid-liquid phase transfenr catalytic condition. The reactivity of aryl halides was in the order, Ar = 2,4-dinitrophenyl > 4-nitrophenyl, and X = F > Cl, consistent with the SNAr mechanism. The reactivity of oxyanions increased with the change of reaction condition from liquid-liquid to solid-liquid phase transfer catalysis. The results were explained with the concentration and the degree of hydration of the anion in benzene.
다층 구조를 적용한 Dual band 방향성 결합기 개발에 관한 연구
유명재,유찬세,박성대,이우성,강남기,Yoo Myong Jae,Yoo Joshua,Park Seong Dae,Lee Woo S.,Kang Nam K. 한국마이크로전자및패키징학회 2004 마이크로전자 및 패키징학회지 Vol.11 No.2
전력 결합기 및 전력 배분기는 마이크로파 수동 소자의 일종으로 전력을 결합하거나 나눌 때 쓰이는 것이다. 최근의 정보통신 시스템의 추세를 보아 수동 소자의 집적화 및 소형화가 요구된다. 본 연구에서는 이러한 추세를 감안하여 2012 크기의 다층 구조를 적용한 양대역 방향성 결합기를 저온 동시소성 기술을 활용하여 제작하였다. DCS(Digital communication system)와 EGSM(European global system for mobile) 대역에서 각기 원하는 커플링을 얻기 위해서 수직 결합 패턴들을 다층 구조에 적용하였다. 제작된 방향성 결합기의 결합성, 삽입 손실, 격리성 및 방향성 등의 특성들을 측정하였고 시뮬레이션 결과들과 비교 고찰하였다. A coupler or divider is a microwave passive component used for power coupling or dividing. Regarding the trend of current telecommunication systems monolithic integration of passive components is highly desirable. In this study by the LTCC(Low temperature co-fired ceramics) technology a 2012 size type dual band coupler with multi-layer structure was fabricated. To achieve the desired coupling values for both DCS and EGSM bands, broad side coupled patterns were used with multi-layer structure. Its characteristics such as coupling, insertion loss, isolation and directivity values were measured and compared with simulation results.