• 대한기계학회논문집
• /
• 제15권5호
• /
• pp.1763-1773
• /
• 1991

본 연구에서는 포화수증기와 공기의 혼합기내에서 분무수적으로의 열 및 질량 전달률을 계산하기 위하여 수적의 부분혼합모형과 비혼합모형에 대하여 수적내 과도온 도분포의 해석해를 적용성이 보장되면서도 계산상의 어려움이 수반되지 않는 형태로 구하기 위하여 수적내부의 열전도해석에 있어서 적분법을 적용하였다. 적분법으로 얻어지는 과도온도분포의 해는 유한차의 다항식으로 표시되어 비혼합모형인 경우 각시 간 구간의 경계에서의 온도분포가 연속성을 유지하면서 물성치들의 온도에 대한 종속 성이 쉽게 고려되고 계산도 용이한 형태이다. 본 보에서 제시하는 해석결과의 적용 성을 조사하기 위하여 완전혼합모형을 포함하는 세가지 수적모형들에 대한 계산결과들 로부터 얻어진 시간변화에 따른 수적의 무차원 체적평균온도변동을 유효한 실험결과들 과 비교, 검토하였으며, 부분혼합모형에 대하여 혼합기의 압력, 수적의 초기온도, 혼 합기 속에 포함되어 있는 수증기의 체적분율, 수적의 초기크기, 수적의 초기속도 및 분사각도가 주위혼합기로부터 수적으로 전달되는 열 및 질량전달에 미치는 영향을 조] 사하고 도출된 대표적인 검토 결과를 제시하였다.

• 한국대기환경학회지
• /
• 제26권4호
• /
• pp.380-391
• /
• 2010

Airborne in-situ measurements of aerosol/cloud number concentrations were analyzed to investigate the effects of aerosols on warm cloud formation in the Pacific Dust Experiment (PACDEX) during April and May 2007. In the air masses originating from the Asian continent, high concentrations of fine particles including black carbon (BC) were observed when compared to other regions. A strong correlation (r=0.88) between condensation nuclei (CN) having sizes ranging from 0.1 to 1.0 mm ($CN_{0.1-1.0}$) and cloud condensation nuclei (CCN) at 0.4% supersaturation ($CCN_{0.4%}$) suggests that most of the $CN_{0.1-1.0}$ can contribute to cloud formation. The possibility of a cloud droplet formation by BC particles was expected at the high water vapor mixing ratio (WVMR) and the abundance of water-soluble components at the low altitude less than 3 km.

• 한국항공우주학회지
• /
• 제31권4호
• /
• pp.1-7
• /
• 2003

습공기에 포함된 수증기가 상(Phase)변화를 일으킬 때 잠열이 발생하고 이 잠열은 익형 주위의 압축성 유동 상태량들을 변화시키므로, 이러한 열 증가가 유동에 끼치는 영향에 대하여 수치해석을 통하여 연구 수행하였다. 수치해석은 Rusak 과 Lee [1]가 최근에 연구 수행한 미교란 방법(small-disturbance approach)에 근거하여 이루어졌다. 고전적 핵 생성 모델과 작은 물방울 성장(droplet growth)모델을 이용한 이 방법에서는 비평형 균질 응축과정에서 일어나는 열 방출을 묘사한다. 응축에 의한 열전달, 압축성 유동의 운동에너지, 그리고 유동의 열적 상태량들 사이에서 일어나는 비선형 상호영향을 조사하고, 또한 주어진 문제를 지배가호 있는 상사 파라미터들을 제시하였다. 계산 결과들은 Euler 방정식을 사용하여 얻은 선행 수치계산들과 비교하여 잘 일치됨을 보였다. 상사법칙은 유동 동역학과 응축 상태량들이 상당히 비슷하게 거동하는 다양한 유동 형태들을 제안한다. 압축성 습공기 유동은 유체기계에 사용되는 익형들의 공력 성능을 증가시키는데 응용될 수 있다.

• 설비공학논문집
• /
• 제3권5호
• /
• pp.337-349
• /
• 1991

Heat and mass transfer rates to spray water droplets for spray transients in a high pressure vessel have been predicted by two different droplet models: the complete mixing model and the non-mixing model. In this process, the ambient fluid surrounding the droplets is a real-gas mixture composed of saturated steam and noncondensable hydrogen gas at high pressure. The physical properties of the mixture are estimated by applying the concept of compressibility factor and using appropriate correlations. A computer program, DROPHMT, to calculate the heat and mass transfer rates for two different droplet models has been developed. As an illustrative application of the computer program to engineering practices, heat and mass transfer rates to spray water droplets for spray transients in a Pressurized Water Reactor (PWR) pressurizer have been calculated, and the typical results have been provided.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.514-519
• /
• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.562-567
• /
• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• 대한기계학회논문집B
• /
• 제30권2호
• /
• pp.186-192
• /
• 2006

We applied a new charging system using the condensation and evaporation method to charge the submicron particles with a uniform charging performance. The monodispersed NaCl submicron particles were condensed by n-butanol vapor and grew up to micron droplets with a same size, regardless of their initial size. Those condensed droplets were charged in an indirect corona charger. The indirect corona charger consisted of the ion generation zone and the particle charging zone. In the ion generation zone, Ions were generated by corona discharge and some of them moved into the particle charging zone by a carrier gas and mixed with the condensed droplet. And finally, the charged and condensed droplets dried through an evaporator to shrink to their original size. The average charge and penetration rate of the particles before and after evaporation were measured by CPC and aerosol electrometer and compared with those of a conventional corona charger. The results showed that the average charge was $5\~7$ charges and the penetration rate was over $90\%$, regardless of the initial particle size.

• 한국분말재료학회지
• /
• 제11권1호
• /
• pp.50-54
• /
• 2004

Nanoparticles of iron oxides have been prepared by the levitational gas condensation (LGC) method, and their structural and magnetic properties were studied by XRD, TEM and Mossbauer spectroscopy. Fe clusters were evaporated from a surface of the levitated liquid Fe droplet and then condensed into nanoparticles of iron oxide with particle size of 14 to 30 nm in a chamber filled with mixtures of Ar and $O_2$ gases. It was found that the phase transition from both $\gamma$-$Fe_2O_3$ and $\alpha$-Fe to $Fe_3O_4$, which was evaluated from the results of Mossbauer spectra, strongly depended on the $O_2$ flow rate. As a result, $\gamma$-$Fe_2O_3$ was synthesized under the $O_2$ flow rate of 0.1$\leq$$Vo_2$(Vmin)$\leq$0.15, whereas $Fe_3O_4$ was synthesized under the $O_2$, flow rate of 0.15$\leq$$Vo_2$(Vmin)$\leq$0.2.

• 수산해양교육연구
• /
• 제4권1호
• /
• pp.47-61
• /
• 1992

An experimental study was carried out to investigate the condensation performance for the horizontal cylindrical heat transfer tube with various fin attached using R-11 vapor. The heat transfer tube used in this study was supplied by SUNG HYUNG METAL CO., LTD. Four different types of heat transfer tubes (plain tube, SH-CYR tube, thermocor tube and thermoexcel tube) were used. Each tube was surrounded by circular acrylate tube, and R-11 gas heated by boiler flows into the acrylate tube. Cooling water counter-flows in heat transfer tubes. Heat transfer coefficient of the plain tube from measured data was compared with those of three other tubes. The results are summarized as follows: 1. As the cooling water temperature decreased, the liquid film of R-11 turned to droplet drop on the top surface of the horizontal tube. 2. Heat transfer coefficient calculated theoretically was higher than that obtained from the experimental data. 3. As far as the condensation concerns the thermocor tube is the highest, the SH-CYR tube is the second, and the thermoexcel tube is the third excluding the plain tube.

• Journal of Korean Society for Atmospheric Environment
• /
• 제21권E1호
• /
• pp.23-35
• /
• 2005

Size distribution of particulate water-soluble ion components was measured at Gosan, Korea using a micro-orifice uniform deposit impactor (MOUDI). Sulfate, ammonium, and nitrate showed peaks in three size ranges; Sulfate and ammonium were of dominant species measured in the fine mode ($D_{p} < 1.8 {\mu}m$). One peak was observed in the condensation mode ($0.218\sim0.532{\mu}m$), and the other peak was obtained in the droplet mode ($0.532\sim1.8{\mu}m$). Considering the fact that the equivalent ratios of ammonium to sulfate ranged from 0.5 to 1.0 in these size ranges, it is inferred that they formed sufficiently neutralized compounds such as ($NH_{4})_{2}SO_{4} and (NH_{4})_{3}H(SO_{4})_{2}$ during the long-range transport of anthropogenic pollutants. On the other hand, nitrate was distributed mainly in the coarse mode ($3.1\sim6.2{\mu}m$) combined with soil and sea salt. Two sets of MOUDI samples were collected in each season. One sample was collected when the concentrations of criteria air pollutants were relatively high, but the other represented relatively clean air quality. The concentrations of sulfate and ammonium particles in droplet mode were the highest in winter and the lowest in summer. When the air quality was bad, the increase of nitrate was observed in the condensation mode ($0.218\sim0.282{\mu}m$). It thus suggests that the nitrate particles were produced through gas phase reaction of nitric acid with ammonia. Chloride depletion was remarkably high in summer due to the high temperature and relative humidity.