• 한국입자에어로졸학회지
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• 제9권2호
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• pp.89-102
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• 2013

24-hr $PM_{2.5}$ samples were collected from January 19 through February 27, 2009 at an urban site of Gwangju and analyzed to determine the concentrations of organic and elemental carbon(OC and EC), water-soluble OC(WSOC), eight ionic species($Na^+$, $NH^{4+}$, $K^+$, $Ca^{2+}$, $Mg^{2+}$, $Cl^-$, ${NO_3}^-$ and ${SO_4}^{2-}$), and 22 elemental species. Haze phenomena was observed during approximately 29%(10 times) of the whole sampling period(35 days), resulting in highly elevated concentrations of $PM_{2.5}$ and its chemical components. An Asian dust event was also observed, during which $PM_{2.5}$ concentration was 64.5 ${\mu}g/m^2$. Crustal materials during Asian dust event contributed 26.6% to the $PM_{2.5}$, while lowest contribution(5.1%) was from the haze events. OC/EC and WSOC/OC ratios were found to be higher during haze days than during other sampling days, reflecting an enhanced secondary organic aerosol production under the haze conditions. For an Asian dust event, enhanced concentrations of OC and secondary inorganic components were also found, suggesting the further atmospheric processing of precursor gases during transport of air mass to the sampling site. Correlations among WSOC, EC, ${NO_3}^-$, ${SO_4}^{2-}$, and primary and secondary OC fractions, which were predicted from EC tracer method, suggests that the observed WSOC could be formed from similar formation processes as those of secondary organic aerosol, ${NO_3}^-$ and ${SO_4}^{2-}$. Results from principal component analysis indicate also that the observed WSOC was strongly associated with formation routes of the secondary organic and inorganic aerosols.

• 한국추진공학회지
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• 제5권1호
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• pp.18-25
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• 2001

2차 가스 분사 추력벡터 제어 성능 해석을 위한 체계적인 수치계산을 수행하였다. 분사위치와, 노즐 팽창각이 압력비, 추력비, 비추력비 및 축추력 증대와 같은 전체 성능 파라미터에 미치는 2차 분사의 효과를 고찰하였다. 2차 제트 분사에 의한 복잡한 노즐 배기 유동에 대한 수치 해석은 Baldwin-Lomax 난류 모델을 포함하는 비정상 3차원 레이놀즈 평균 Navier-Stokes 방정식을 이용하여 수행하였고, 팽창 팽착반각이 $9.6^{\cire}$인 로켓 노즐에서의 2차 공기분사에 대해 적용, 실험값과 비교, 검증 하였다. 전체 성능 파라미터에 대한 결과로서 주 노즐의 하류에 2차 분사구를 위치시키는 것이 반사 충격파의 발생을 방지하며, 넓은 적용범위에 대하여 효율적이고 안정한 추력 방향제어에 적합한 것으로 나타났다.

• 한국대기환경학회지
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• 제31권5호
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• pp.437-448
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• 2015

The purpose of this study is to present the source contribution of the fine particles ($PM_{2.5}$) in Chungju area using the CMB (chemical mass balance) method throughout the four seasons in Korea. The Chungju's annual average level of $PM_{2.5}$ was $48.2{\mu}g/m^3$, which exceeded two times higher than standard air quality. Among these particles, the soluble ionic compounds represent 54.2% of fine particle mass. Additionally, the OC concentration in Chungju stayed similar to other domestic cities, while the EC concentration decreased significantly compared to other domestic/international cities. The concentration of sulfur represented the highest composition (8%) among the fine particle compounds. According to the CMB results, the general trend of the $PM_{2.5}$ mass contributors was the following: secondary aerosols (50.5%: ammonium sulfate 26.5% and ammonium nitrate 24.0%) > gasoline vehicle (18.3%) > biomass burning (11.0%) > industrial boiler (6.0%) > diesel vehicles (4.4%). The contribution of the secondary aerosols was the main cause than others. This impact is assumed to be emitted from air pollutants of urban cities or neighbor countries such as China.

• 오토저널
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• 제14권6호
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• pp.67-73
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• 1992

This paper describes Hyundai's research and development work on a flexible fuel vehicle (FFV). The work on FFV has been conducted to evaluate its potential as an alternative to the conventional gasoline vehicle. Hyundai FFV described here can be operated on M85, gasoline, or any of their combinations, in which the methanol concentration is measured by an electrostatic type fuel sensor. For that operation, a special FFV ECU(Eletronic Control Unit) has been developed and incorporated in the FFV. The characteristics affecting FFV operation, such as FFV ECU control strategy and injector flow rate, have been investigated and optimized through the experiment. And various development tests have been performed in view of engine performance, durability, cold startability, and exhaust emissions reduction. The exhaust gas aftertreatment system consisting of manifold type catalyst and secondary air injection system shows good emission reduction performance including formaldehyde, and finally, the possibility of the FFVs as the low emission vehicles is evaluated by presenting NMOG(Non-Methane Organic Gases) levels with respect to M0 and M85. With these results, it is concluded that FFV can be a candidate for the low emission vehicles, but more works on its durability improvement is required.

• 한국연소학회지
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• 제13권2호
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• pp.7-13
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• 2008

The aim of this work is to identify application of ultra low NOx and CO combustor. To achieve this, we developed the premixed oxidizer-staging combustor using a cyclone flow. Various factors such as equivalence ratio for the combustion condition and swirl type for secondary air injection have been tested experimentally for flame stability and NOx, CO emission characteristics. Before to do this, we had been tested cyclone premixed combustor in advance. it is similar to first combustor of premixed oxidizer-staging combustor. As a result, cyclone premixed flame shows the very high flame stability and low NOx emission. however, it can be identified that there were some problems such as a little high CO emission and thermal resistance of combustor wall. Cyclone premixed oxidizer-staging combustor can resolve those of problems. In our combustor, we can found out optimal condition that the secondary air injection method is swirl type, swirl direction is co-swirl and equivalence ratio of first combustor is 1.3. Quantitatively, we can achieve 10.8 ppm for NOx and 30.2 ppm for CO emissions respectively. Form this result, we can identified that cyclone premixed oxidizer-staging combustor can apply to ultra low NOx and CO combustor.

• 한국세라믹학회지
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• 제53권2호
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• pp.134-138
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• 2016

Porous $Co_3O_4$ spheres with bimodal pore distribution (size: 2-3 nm and ~ 30 nm) were prepared by ultrasonic spray pyrolysis of aqueous droplets containing Co-acetate and polyethylene glycol (PEG), while dense $Co_3O_4$ secondary particles with monomodal pore distribution (size: 2-3 nm) were prepared from the spray solution without PEG. The formation of mesopores (~ 30 nm) was attributed to the decomposition of PEG. The responses of a porous $Co_3O_4$ sensor to various indoor air pollutants such as 5 ppm $C_2H_5OH$, xylene, toluene, benzene, and HCHO at $200^{\circ}C$ were found to be significantly higher than those of a commercial sensor using $Co_3O_4$ and dense $Co_3O_4$ secondary particles. Enhanced gas response of porous $Co_3O_4$ sensor was attributed to high surface area and the effective diffusion of analyte gas through mesopores (~ 30 nm). Highly sensitive porous $Co_3O_4$ sensor can be used to monitor various indoor air pollutants.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권3호
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• pp.27-35
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• 2001

Heat transfer characteristics of a heat exchanged for low temperature waste heat recovery using oscillating capillary tube heat pipe (OCHP) were evaluated against the charging ratio variation of working fluid and various working fluids. R-l42b, R-22 and R-290 were used as working a 2.6mm in outside diameter, 1.44mm in inside diameter with 101m length and 140 turns. Charging ratio of working fluid was 40% and 50%. water was used as secondary fluid. Inlet temperature and mass velocity for each secondary fluid were 297 K, 280 K and 9~27 $4kg/m^2s$, respectively. From experimental results, it was found that heat transfer performance of R-22 was higher than those of R-142b and R-290 and it was proportional to Figure of Merit for thermosyphon. As a result, it was thought that R-22 was the most reasonable working fluid of waste heat recovery for low temperature waste heat recovery.

• 설비공학논문집
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• 제12권7호
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• pp.659-666
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• 2000

Heat transfer characteristics of a heat exchanger for low temperature waste heat recovery using oscillating capillary tube heat pipe were evaluated against the charge ratio variation of working fluid and various working fluids. R-l42b, R-22 and R-290 were used as working fluids. The heat exchanger was composed of heat pipe with capillary tube bundles, having a 2.6mm in outer diameter, 1.4mm in inner diameter with 101m long, and 40 turns. Charge ratio of working fluid was 40% and 50%. Water was used as secondary fluid. Inlet temperature and mass velocity for each secondary fluid were 297 K, 280 K and9~27 kg /$m^2s$,, respectively. From experimental results, it was found that heat transfer performance of R-22 was higher than those of R-l42b and R-290 and it was proportional to Figure of merit for thermosyphons. As a result, it was thought that R-22 was the most suitable working fluid of waste heat recovery for low temperature waste heat recovery.

• 전자공학회논문지SC
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• 제45권3호
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• pp.80-85
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• 2008

기존의 캡슐형 내시경은 공간적 제약으로 인해 약 30mW 용량의 1차 전지를 사용한다. 그러나 1차 전지를 사용하는 방식은 배터리 용량의 한계와 1회용 소모품으로 가격이 비싸다. 이러한 문제를 해결하기 위해 신체 외부에서 캡슐형 내시경에 무선으로 에너지를 전송 방식을 제안하였다. 제안된 방식은 송 수신측 양단에 LC공진 회로를 이용하여 $10{\sim}20cm$의 공극을 통해 송신측 코일에서 캡슐형 내시경으로 에너지를 전달하는 방식이다. 위치와 방향성에 상관없이 에너지 효율의 증가를 위해 수신측 코일은 페라이트 코어를 이용한 3축 권선 방식을 이용하였다. 실험에 의한 측정 결과 제안된 방식은 수신측 회로에 안정적으로 30mW의 전력을 공급할 수 있음을 확인하였다.

• 동력기계공학회지
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• 제16권4호
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• pp.51-59
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• 2012

The computational flow analysis using LES technique was carried out to investigate the flow characteristics of a sirocco fan under the maximum flowrate condition. The commercial SC/Tetra software was used for this unsteady and three-dimensional numerical analysis. In consequence, because a flow is unstable within the range of about 50% of a housing depth from a bellmouth around the cutoff region, the passing flow through the blade cascade occurred on the X-Y plane is a slow or a reverse with approaching to the housing inlet. Also, the secondary flow shows on the radial plane of a housing, and its vortex center exists within about 33% of a housing depth from a bellmouth except the cutoff region. Moreover, the flow occurring on the exit plane of a sirocco fan shows a complex secondary flow.