• 대한기계학회논문집
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• 제18권3호
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• pp.662-669
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• 1994

In the combustion system, the optimum spray conditions reduce the pollutant emission of exhaust gas and enhance the fuel efficiency. The spray characteristics-the drop size, the drop velocity, the number density and the mass flux, become increasingly important in the design of combustor and in testifying numerical simulation of spray flow in the combustor. The purposes of this study are to clarify the spray characteristics of twin-fluid nozzle and to offer the data for combustor design and the numerical simulation of a spray flow. Spatial drop diameter was measured by immersion sampling method. The mean diameter, size distribution and uniformity of drop were analyzed with variations of air/liquid mass flow ratio. The results show that the SMD increases with the liquid supply flow rate and decreases with the air supply velocity. The radial distribution of SMD shows the larger drops can diffuse farther to the boundary of spray. And the drop size range is found to be wider close to the spray boundary where the maximum SMD locates.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1229-1237
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• 1998

Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.

• 대한기계학회논문집B
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• 제23권2호
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• pp.262-271
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• 1999

A study of aerosol dynamics has been done to obtain axially and radially varying size distributions of particles generated in the Modified Chemical Vapor Deposition process. Heat and mass transfer have also been studied since particle generation and deposition strongly depend on the temperature field in a tube. Bimodal size distributions of particles have been obtained both in the particulate flow and in the deposited particle layer for the first time using the sectional method to solve aerosol dynamics. Variations of geometric mean diameter, geometric standard deviation have been studied for various parameters; flow rates and maximum wall temperature. The comparison between one-dimensional and two-dimensional approaches has also been made.

• 한국대기환경학회지
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• 제16권6호
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• pp.573-583
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• 2000

In order to investigate the characteristics of PM(sub)2.5 in the background area, the following pollutant were measured from February 1996 to June 1999 in Kanghwa: PM(sub)2.5 mass, sulfate, nitrate, chloride, ammonium, sodium, calcium, magnesium and potassium. The mean concentration of PM(sub)2.5 mass was 25.8$\pm$1.2$\mu\textrm{g}$/㎥(range 5.18~85.74). This value was higher than the annual PM(sub)2.5 US NAAQS(15$\mu\textrm{g}$/㎥) and the total number of samples higher than the 24-h PM(sub)2.5 US NAAQS(65$\mu\textrm{g}$/㎥) was seven. PM(sub)2.5 masses also showed temporal variations both yearly and seasonally. Total water soluble ions constituted about 45% of PM(sub)2.5 miss, and sulfate, nitrate and ammonium were main components in water soluble ions. Compared with the literature data from other areas, the measured PM(sub)2.5 concentrations were relatively high.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.869-874
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• 2003

The atomization characteristics were investigated through the influence of the change of GLR and the change of working fluid on droplet size distribution and mean diameter of drop produced by effervescent atomizer. For simultaneous injection of water and high viscous waste vegetable oil, effervescent atomizer with two aerator tubes was specially designed. From the experimental results, regardless of mass fraction of vegetable oil in working fluids, it is expected that effervescent atomizer will exhibit excellent atomization performance at the high GLR conditions.

• 대한기계학회논문집
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• 제18권11호
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• pp.3021-3031
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• 1994

Experiments have been performed to find out the effect of the mixing port length of Y-jet atomizers on the spray performance, using air and water as the test fluids. Water and air flow rates and drop sizes were measured at each injection pressure condition for different mixing port length. The air flow rate was almost unaffected by the change of the mixing port length. However, the water flow rate was relatively susceptible to the change of the mixing port length. The mixing point pressure was very much influenced by the mixing port length. Variations of spatial distribution of Sauter Mean Diameter (SMD, $D_{32}$) and the cross-section-averaged SMD ($D_{32,m}$) with different mixing port length and air/water mass flow rate ratio were examined. Generally, when the mixing port length was reduced, the mean drop size decreased and became spatially even.

• 한국지구과학회지
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• 제22권5호
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• pp.415-422
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• 2001

대류권과 성층권의 대기대순환에 관한 연구는 전지구 규모의 기후변동에 대한 인간활동의 영향을 이해하는 데에 있어서 매우 중요하다. 최근, 상부대류권과 성층권의 대기대순환에 있어서의 일년주기의 존재가 많은 연구에 의하여 보고되어졌다. 이 연구에서는 10년간(1985년 12월${\sim}$1995년 11월)의 자료에 대하여, 변형오일러평균방정식계의 운동방정식과 연속방정식을 이용하여 잔차평균자오면순환을 구하고, 그 순환과 100hPa면을 가로지르는 질량 플럭스들의 장기변동을 조사한다. 그 장기변동을 정량적으로 파악하기 위하여 중회귀통계모델을 사용한다. 특히, 이 연구에서는 이상기상과 전지구 규모의 기후변동의 원인으로서 알려진 엘니뇨현상과 관련한 대류권과 성층권의 평균자오면순환에 초점을 맞춘다. 연구의 결과는, 전지구 규모의 대류권-성층권 평균자오면순환은 엘니뇨현상과 준2년주기진동의 동풍 위상 동안에 강화되어지고, 라니냐현상과 준2년주기진동의 서풍 위상 동안에 약화되어진다는 사실을 보인다. 그리고, 1991년 6월에 있었던 피나투보 화산 폭발의 신호가 얻어진다. 그 화산 폭발 때문에 전지구 규모의 대류권-성층권 평균자오면순환은 급격히 강화되어진다.

• 한국기계가공학회지
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• 제20권6호
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• pp.114-120
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• 2021

This study is focused on the root mean square and peak-to-valley based on the injection conditions of the f-theta lens, one of the main components of laser printers and laser scanning systems. The f-theta lens of an aspherical plastic lens requires ultra-preaction. Injection molding is typically used for the mass production of aspherical plastic lenses. In the injection-molding method, the resin in the lens shape is filled with the resin after melting the plastic pellets at a constant temperature and then cooled. It is necessary to maintain a uniform injection molding system to produce high-quality lenses. These injection-molding systems are influenced by different factors, such as pressure, speed, temperature, mold, and cooling. It is possible to obtain a lens that exhibits the optical characteristics required to achieve harmony. We investigated the root mean square and peak-to-valley caused by variations in temperature, a critical parameter in the melting and cooling of plastic resins generated inside and outside the injection mold.

• 대기
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• 제22권3호
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• pp.331-344
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• 2012

The changes in the Hadley circulation during the second half of the 20th century were examined using observations and the 20C3M (Twentieth Century Climate in Coupled Models) simulations by the 21 IPCC AR4 models. Multi-model ensemble (MME) mean shows that the mean features of the Hadley circulation, such as the intensity, magnitude, and the seasonal variations, are very realistically reproduced, compared to the ERA40 reanalysis. But the long-term trends of the Hadley circulation in 20C3M MME are quite different to those of observations. The observed intensity of the Hadley cell is persistently enhanced, particularly during boreal winter. In comparison, the meridional overturning circulations reproduced in the MME mean remains invariant in time, and even weakened in boreal summer. This discrepancy between the ERA40 and 20C3M MME is consistently shown in the overall structure of the Hadley circulations, such as mass streamfunction, the velocity potential, the vertical shear of meridional wind, and the vertical velocity in the tropical region. This results indicate that the current climate models are skill-less to capture the long-term trend of Hadley circulation yet, and should be improved in simulation of the large-scale features to enhance the confidence level of future climate change projection.

• 한국대기환경학회지
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• 제29권6호
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• pp.701-712
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• 2013

The purpose of this study is to determine concentrations and compositions of $PM_{2.5}$ and their characteristic variations at Ieodo Ocean Research Station in the East China Sea and to examine the influence of air pollutants transported from Asia continents. $O_3$ and meteorological parameters were measured since June 2003 and $PM_{2.5}$ filter samples were collected from June 2004 to June 2008. In total, 244 samples were analyzed for water soluble ions and carbonaceous compounds. The mean mass concentration of $PM_{2.5}$ and $O_3$ were $21.8{\pm}14.9{\mu}g/m^3$ and $51.6{\pm}16.1$ ppb, respectively. The average concentrations (mass fractions) of sulfate and ammonium were $6.26{\mu}g/m^3$ (28.74%) and $1.59{\mu}g/m^3$ (7.31%), respectively. Nitrate was considered to be lost through evaporation due to long stay at the station. The mean concentrations of EC and OC were $1.01{\mu}g/m^3$ and $2.34{\mu}g/m^3$, respectively, from June 2006 to June 2008. The average OC/EC ratio was 2.31. The organic matter converted from OC by multiplying 2.1 and elemental carbon constituted 22.60% and 4.66% of $PM_{2.5}$ mass, respectively.