• 한국재료학회지
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• 제13권5호
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• pp.323-327
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• 2003

Properties of nanoparticles synthesized during gas phase reaction were studied in terms of particle behaviors using real-time particle characterization method. For this study, $TiO_2$ nanoparticles were synthesized in the chemical vapor condensation process(CVC) and their in-situ measurement of particle formation and particle size distribution was performed by scanning mobility particle sizer(SMPS). As a result, particle behaviors in the CVC reactor were affected by both of number concentration and thermal coagulation, simultaneously. Particularly, growth and agglomeration between nanoparticles followed two different ways of dominances from coagulations by increase of number concentration and sintering effect by increased temperature.

• 한국추진공학회지
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• 제23권4호
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• pp.35-41
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• 2019

비행운은 차가운 대기환경에서 항공기가 운항할 때 엔진 배기의 수증기가 응축하여 발생하는 구름을 뜻한다. 비행운은 환경적, 군사적으로 악영향을 끼치는 요소로 지목되고 있으며, 이에 따라 비행운을 저감시키기 위한 다양한 연구가 선진국에서 진행되었다. 본 연구에서는 비행시험 없이 지상에서 진행할 수 있는 Lab-scale 비행운 발생 장치를 설계하고, 이를 활용하여 기존 연구에서 제시된 비행운 저감 기법을 실험적으로 검증하는 데 그 목적이 있다. 연구를 통해 과열증기와 저온풍동을 사용하는 비행운 발생 장치를 제작하였으며, 이를 통해 기존 문헌에 제시된 에탄올 및 유화제가 비행운 저감에 효과가 없음을 실험적으로 확인하였다.

• 설비공학논문집
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• 제7권4호
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• pp.600-610
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• 1995

When combustion gas is cooled down below the dew point of sulfuric acid vapor in the heat recovery systems, condensation occurs. Since the condensed sulfuric acid solution causes low-temperature corrosion in materials, it is important to measure the SOx dew point by electric measurement. In this study, two kinds of probes having electric gaps of 1mm or 2mm were used. and experiments were carried out by the parameters of sulfuric acid vapor and water vapor concentration. The changes of electric current caused by sulfuric acid condensed on the surface of probe according to the cooling rate and the probe head surface temperature were sudied. The opimum cooling rate was decreased with the increasing of water vaper concentration regardless of sulfuric acid concentration. The sensitivity of electric current is improved for the narrower gap(1mm) of ring electrodes, but it rarely affects the SOx dew point measuring of different probes according to the change of cooling rate.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.625-626
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• 2006

In the present study, the focus is on the synthesis of nanosized WC powder by the chemical vapor condensation proces. The synthesized W-C system powder by the CVC process shows W2C, W, WO3 phases and can not shows WC phase. After recarburization heat treatment under mixture gas atmosphere of argon and hydrogen gases, the synthesized W-C system powder fully transformed to the pure WC. The synthesized WC powder after recarburization heat treatment has an average particle size of 20 nm. The nano-sized WC powder can be prepared by the combination of the CVC process and heat treatment methods.

• 한국표면공학회지
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• 제32권3호
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• pp.297-302
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• 1999

In situ measurement of infrared absorption spectra has been performed during low-temperature plasma-enhanced chemical vapor depositiion of silicon-oxide films using tetramethoxysilane as a silicon source. Several absorption bands due to the reactant molecules are clearly observed before deposition. In the plasma, these bands completely disappear at any oxygen mixing ratio. This result shows that most of the tetramethoxysilane molecules are dissociated in the rf plasma, even C-H bonds. Existence of Si-H bonds in vapor phase and/or on the film surface during deposition has been found by infrared diagnostics. We observed both a decrease in Si-OH absorption and an increase in Si-O-Si after plasma off, which means the dehydration condensation reaction continues after deposition. The rate of this reaction is much slower than the deposition ratio of the films.

• 설비공학논문집
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• 제17권11호
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• pp.981-989
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) are measured on a low fin tube and Turbo-C tubes at the saturated vapor temperature of $30^{\circ}C$, $39^{\circ}C$, and $50^{\circ}C$ for R22, R410A, R407C and R134a with the wall subcooled at $3{\~}8^{\circ}C$. The HTCs of all refrigerants decreased as increasing the saturation temperature from $30^{\circ}C$ to $50^{\circ}C$. This trend is due to better thermodynamic properties of the liquid phase at low temperature Beatty and Katz's prediction yielded a $20.0\%$ deviation for the low fin tube data. The heat transfer enhancement factors for the 26 fpi low fin tube and Turbo-C tubes are 4.0${\~}$5.5 and 3.0${\~}$8.1 respectively for the refrigerants tested. Finally the performance of Turbo-C tube is better than that of the low fin tube.

• 한국입자에어로졸학회지
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• 제9권4호
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• pp.247-252
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• 2013

Removal of water contents in a gas is needed in industrial field of gas processing related on energy production/conversion, and environmental treatment. Inertial separators are economic devices for separating droplets from the gas stream. For design and incorporation of inertial pre-treatment separator, characteristics of removal of water contents with various operation conditions are needed. In this study, removal efficiency of water droplets at various flowrates (5-14 SCMM) and relative humidity (R.H.) conditions (40%, and 90%) has been investigated. At low R.H. condition, the removal characteristic is similar to the removal of solid particles. But, droplet growth resulting from the condensation of water vapor at high R.H. condition, is significant and it made increase in removal efficiency of droplet phase of water contents. For rapid removal of water contents, an effective method to enhancing condensation growth of water droplets is highly needed.

• 대한기계학회논문집B
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• 제28권12호
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• pp.1535-1548
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• 2004

Condensation heat transfer experiments were conducted with the oblong shell and plate heat exchanger without oil in a refrigerant loop using R-l34a, R-407C and R-410A. An experimental refrigerant loop has been developed to measure the condensation heat transfer coefficient h$_{r}$ and frictional pressure drop $\Delta$p$_{f}$ of the various refrigerants in a vertical oblong shell and plate heat exchanger. The effects of the refrigerant mass flux(40∼80kg/$m^2$s), average heat flux(4∼8kW/$m^2$), refrigerant saturation temperature(30∼4$0^{\circ}C$) and vapor quality of refrigerants on the measured data were explored in detail. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. A comparison of the performance of the various refrigerants revealed that R-410A had the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. The pressure drops were also reported in this paper. The pressure drops for R-410A were approximately 45% lower than those of R-l34a. R-407C had 30% lower pressure drops than R-l34a. Experimental results were compared with several correlations which predicted condensation heat transfer coefficients and frictional pressure drops. Comparison with the experimental data showed that the previously proposed correlations gave unsatisfactory results. Based on the present data, empirical correlations of the condensation heat transfer coefficient and the friction factor were proposed.tor were proposed.sed.

• 한국세라믹학회지
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• 제36권7호
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• pp.742-750
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• 1999

화학기상응축법을 이용한 TiO2 나노분말합성시 전구체 주입속도 및 산소 반응기체유량의 변화에 따른 나노입자의 형성과정을 분말특성의 관점에서 조사하였다. 기상합성반응의 주요 열역학, 동역학적 인자인 과포화도, 충돌율, 체류시간의 상기 두 공정변수에 대한 의존성을 이론적으로 평가하였고, 이를 0.376, 0.742 m//min의 두 전구체 주입속도 조건에서 산소유량을 1에서 2slm까지 변화시키며 합성한 TiO2 나노분말의 특성과 관련하여 분석하였다 모든 조건에서 합성된 TiO2 분말은 20~30 nm의 크기를 갖는 미세한 anatase 상과 극소량의 rutilc상이 혼합되어 서로 느슨한 결합을 하고 있었다 전구체 주입속도가 0.376m//min의 경우, 전반적인 입도와 응집도는 0.742 m//min에 비해 작았으며, 산소유량이 증가할수록 체류시간과 충돌율이 감소하여 형성된 TiO2 분말의 입도는 감소하였다. 또한 산소유량 증가에 따른 과포화도의 감소는 분말형성과정과 기구에 영향을 미치는 것으로 판단되나, 정확한 분석을 위해서는 각각의 독립적인 열역학 및 동역학적 변수 조건하에서의 면밀한 고찰이 요구되었다.

• 생물환경조절학회지
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• 제22권1호
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• pp.35-41
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• 2013

본 연구는 우리나라 온실 피복재의 결로 발생을 억제하는데 필요한 기초자료를 제공하기 위하여 토마토 재배용 실험온실의 포차변화 및 피복재에 발생하는 결로량의 변화를 분석하였으며 결과를 요약하면 다음과 같다. 실험온실의 경우 포차가 병 발생을 유발하기 쉬운 한계포차인 0.2kPa보다 더 크게 유지되어 온습도환경이 양호한 것으로 판단되었고 제습여부 결정을 위한 임계포차인 0.5kPa보다는 작게 나타나 제습은 필요한 것으로 판단되었다. 내부피복재의 표면온도는 외부온도와 커튼상부온도의 평균값 보다 약간 더 큰 것으로 나타났으며, 대체로 외부온도의 변화에 비례하여 변화하는 것으로 나타났다. 외부의 온도 및 습도 변화에 상관없이 커튼 상부의 습도는 거의 100%에 가까운 상대습도를 유지하여 결로 발생이 용이한 조건인 것으로 나타났다. 커튼하부의 습도는 내부습도의 큰 변화에도 불구하고 75~90% 정도로 안정된 값을 유지하였으며, 이는 온풍난방을 실시하여 온도를 $15^{\circ}C$로 유지하였기 때문으로 판단된다. 실험조건 및 피복재의 종류에 따라 결로 발생량은 많은 차이가 있는 것으로 알려져 있다. 실험온실의 결로 발생량은 Seginer와 Kantz(1986)의 연구결과와 가장 잘 일치하는 것으로 나타났으나 다른 온실실험 결과들과는 약간의 차이를 보여주고 있기 때문에 앞으로 실험을 통해서 더 자세한 검증을 거친다면 우리나라 온실 피복재에 발생하는 결로량을 분석하는데 유용하게 활용될 수 있을 것으로 기대된다.