• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.218-222
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• 2009

A level-set (LS) method is presented for computation of boiling phenomena which involve liquid-vapor interfaces that evolve, merge and break up in time, the flow and temperature fields influenced by the interfacial motion, and the microlayer that forms between the solid and the vapor phase near the wall. The LS formulation for tracking the phase interfaces is modified to include the effects of phase change on the liquid-vapor interface and contact angle on the liquid-vapor-solid interline. The LS method can calculate an interface curvature accurately by using a smooth distance function. Also, it is straightforward to implement for two-phase flows in complex geometries. The numerical method is applied for analysis of nucleate boiling on a horizontal surface and film boiling on a horizontal cylinder.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.23-30
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• 2002

This present study experimentally investigates the behavior of liquid and vapor phase of fuel mixtures with changing the in-cylinder air motion in an optically accessible engine. The conventional MPI/DOHC engine was modified to gasoline direct injection engine with swirl motion. The images of liquid and vapor phases were captured in the motoring operation condition using exciplex fluorescence method. Two dimensional spray fluorescence images of liquid and vapor phases were acquired to analyze spray behaviors and fuel distribution inside of cylinder respectively, In early injection timings $(BTDC\;270^{\circ},\;180^{\circ})$, tumble flow transported most of vapor phase to the lower region and the both sides of cylinder, so vapor phase didn't become uniform distribution up to the half of the compression stroke. In the case of swirl flow, the fuel mixture was confined near the swirl origin in upper region of cylinder. In late injection timings $(BTDC\;90^{\circ})$, tumble flow transported vapor phase to the intake valve and swirl flow to the exhaust valve.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2001년도 정기총회 및 제3회 특별지포지움
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• pp.94-103
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• 2001

유기 석유화학 오염 물질인 휘발유가 지하 분포 시, 지하수면 위 토양 매질(vadose zone)내에 존재할 수 있는 기체 상태(vaporphase)와, 지하수면의 상승 또는 하강에 의해 분포 할 수 있는 residual phase의 유류 오염 물질이 GPR에 미치는 반응을 조사하기 위하여 모래와 자갈을 토양 매질로서 채운 탱크를 이용한 모델 실험이 수행되었다. 물만 사용하여 지하수면의 상승과 하강을 유도한 후, 석유 수송을 위하여 지하에 매장된 파이프 혹은 석유저장을 위한 지하 탱크로부터 지하수면으로의 유류 오염을 simulation하기 위하여 모델 탱크바닥을 통하여 휘발유가 주입되었다. 본 연구 결과, 수분 함량에 따른 GPR의 민감성과 지하수면의 변화 관측에의 GPR 효율성이 입증되었다. 또한, 휘발성 유류 오염 물질의 기체상태가 vadose zone에 분포 시 GPR를 이용하여 탐지할 수 있는 가능성과, 지하수면의 상승에 의해 지하수면 밑의 물로 포화된 토양(water saturated zone)에 분포할 수 있는 residual phase의 유류 오염 물질의 탐지 가능성이 모델 실험을 통하여 확립되었다 그리고, residual phase의 유류 오염 물질이 지하수면 아래에 분포하는 오염지역에서 GPR을 이용한 유류 오염물질을 탐지할 수 있는 새로운 탐사전략이 제시되었다.

• 대한기계학회논문집B
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• 제27권1호
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• pp.17-24
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• 2003

A mathematical model of the hydrodynamic and heat transfer performances of two-phase flow (gas-liquid) in thin film region of micro channel is proposed. For the formulation of modeling, the flow of the vapor phase and the shear stress at the liquid-vapor interface are considered. In this work, disjoining pressure and capillary force which drive the liquid flow at the liquid-vapor interface in thin film region are adopted also. Using the model, the effects of the variations of channel height and heat flux on the flow and heat transfer characteristics are investigated. Results show that the influence of variation of vapor pressure on the liquid film flow is not negligible. The heat flux in thin-film region is the most important operation factor of micro cooler system.

• Journal of Mechanical Science and Technology
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• 제14권10호
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• pp.1143-1150
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• 2000

The effects of ambient conditions on vaporizing sprays from a high-pressure swirl injector were investigated by an exciplex fluorescence method. Dopants used were 2% fluorobenzene and 9% DEMA (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to examine the behavior of liquid and vapor phases inside of vaporizing sprays, ambient temperatures and pressures similar to engine atmospheres were set. It was found that the ambient pressure had a significant effect on the axial growth of spray, while ambient temperature had a great influence on the radial growth. The spatial distribution of vapor phase at temperatures above 473K became wider than that of liquid phase after half of injection duration. From the analysis of the area ratio for each phase, the middle part (region II) in the divided region was the region which liquid and vapor phases intersect. For liquid phase, fluorescence-intensity ratio was greatly changed at lms after the start of injection. However, the ratio of vapor phase was nearly uniform in each divided region throughout the injection.

• Korean Membrane Journal
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• 제6권1호
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• pp.61-69
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• 2004

Small angle light scattering (SALS) and field emission scanning electron microscope (FE-SEM) have been used to investigate the effects of alcohol on phase separation of chlorinated poly(vinyl chloride) (CPVC)/tetrahydrofuran (THF)/alcohol (9/61/30 wt%) solution during water vapor induced phase separation. A typical scattering pattern of nucleation & growth (NG) was observed for all casting solutions of CPVC/THF/alcohol. In the case of the phase separation of CPVC dope solution containing 30 wt% ethanol or n-propanol, the demixing with NG was observed to be heterogeneous. Meanwhile, the phase separation of CPVC dope solution with 30 wt% n-butanol was found to be predominantly homogeneous NG. Although the different phase separation behavior of NG was observed with types of alcohol additives, the resultant surface morphology had no remarkable differences. That is, even though the NG process by water vapor is either homogeneous or heterogeneous, this difference does not play a main role on the final surface morphology. However, it was estimated from the result of hydraulic flux that the phase separation by homogeneous NG provided the membrane geometry with lower resistance in comparison with that by heterogeneous one.

• 대한기계학회논문집B
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• 제22권4호
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• pp.499-509
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• 1998

In the absorption process of water vapor in a liquid film, the composition of the gas phase, in which a non-absorbable gas is combined with the absorbate influences the transport characteristics remarkably. In the present study, the absorption processes of water vapor into aqueous solution of lithium bromide in the presence of non-absorbable gases were investigated analytically. The continuity, momentum, energy and diffusion equations for the solution film and gas phase were formulated in integral forms and solved numerically. It was found that the mass transfer resistance in gas phase increased with the concentration of non-absorbable gas. However the primary resistance to mass transfer was in the liquid phase. As the concentration of non-absorbable gas in the absorbate increased, the liquid-vapor interfacial temperature and concentration of absorbate in solution decreased, which resulted in the reduction of absorption rate. The reduction of mass transfer rate was found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of an absorber where non-absorbable gases accumulated. At higher non-absorbable gas concentration, the decrease of absorption flux was almost linear to the volumetric concentration of non-absorbable gas.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.141-146
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• 2007

In this study, the effects of change in ambient gas viscosity on spray structure have been investigated in the high temperature and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation process. Emissions of diesel engines can be reduced by the control of the mixture formation process. Therefore, this study examines the evaporating spray structure in the constant volume chamber. The viscosity of ambient gas was selected as the experimental parameter, is changed from 21.7 mPa s to 32.1 mPa s by changing in ambient gas temperature. In order to obtain images of the liquid and vapor-phase of injected spray, exciplex fluorescence method was used in this study. The liquid and vapor-phase images were taken with 35mm still camera and CCD camera, respectively. Consequentially, it could be confirmed that the distribution of vapor concentration is more uniform in the case of the ambient gas with high viscosity than in that of the ambient gas with low viscosity.

• 대한기계학회논문집B
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• 제21권3호
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• pp.371-379
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• 1997

A theoretical study for a forced uniform flow impinging on a rotating disk, typically involved in Chemical Vapor Deposition(CVD) and Vapor-phase Axial Deposition(VAD) processes, has been carried out. A set of exact solutions for flow and temperature fields are developed by employing a similarity variable obtained from force balance on a control volume near the disk. The solutions depend on the rotating speed of the disk, .omega., and the forced flow speed toward the disk, a. For constant forced flow speed, the overall boundary layer thickness decreases when the rotating speed increases. Approximately 5%, 15%, and 30% decreases of the thickness are obtained for .omega./a = 2, 5, and 10, respectively, compared to the case of .omega./a = 0 (axisymmetric stagnation point flow). For constant rotating disk speed the boundary layer thickness immediately decreases as the forced flow speed increases, compared to the case of .omega./a .rarw. .inf. (induced flow near a rotating disk). Effects of .omega. and a on heat transfer coefficient are studied and explained with the boundary layer characteristics.

• 한국세라믹학회지
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• 제29권7호
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• pp.525-532
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• 1992

TiO2 fine powder was synthesized in the gas phase by chemical vapor deposition using hydrolysis of TiCl4. Content of rutile phase in the powder was investigated. Powder characteristics such as size, crystallinity and morphology were also studied by means of TEM, SEM and XRD. Rutile phase in TiO2 powder started to be formed from 100$0^{\circ}C$ and the content increased with the reaction temperature and TiCl4 concentration. As the temperature increased from 80$0^{\circ}C$ to 140$0^{\circ}C$, the primary particle size increased while secondary particle size decreased. Spherical secondary particle with fine primary crystals agglomerated was produced at low temperature of 80$0^{\circ}C$ whereas the grown primary particle being final particle size was produced at higher temperature of 140$0^{\circ}C$. Other effects of TiCl4 and H2O partial pressures on particle size were also reported in this study.