• Bulletin of the Korean Chemical Society
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• 제25권5호
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• pp.687-693
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• 2004

Composite membranes with a titania layer were prepared by soaking-rolling method with the titania sol of nanoparticles formed in the sol-gel process and investigated regarding the vapor permeation of various organic mixtures. The support modification was conducted by pressing $SiO_2$ xerogel of 500 nm in particle size under 10 MPa on the surface of a porous stainless steel (SUS) substrate and designed the multi-layered structure by coating the intermediate layer of ${\gamma}-Al_2O_3$. Microstructure of titania membrane was affected by heat-treatment and synthesis conditions of precursor sol, and titania formed at calcination temperature of 300$^{\circ}C$ with sol of [$H^+$]/[TIP]=0.3 possessed surface area of 210 $m^2$/g, average pore size of 1.25 nm. The titania composite membrane showed high $H_2/N_2$ selectivity and water/ethanol selectivity as 25-30 and 50-100, respectively. As a result of vapor permeation for water-alcohol and alcohol-alcohol mixture, titania composite membrane showed water-permselective and molecular-sieve permeation behavior. However, water/methanol selectivity of the membrane was very low because of chemical affinity of permeants for the membrane by similar physicochemical properties of water and methanol.

• 한국가시화정보학회지
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• 제8권3호
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• pp.56-62
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• 2010

The interaction patterns between shock wave and boundary layer in a rocket nozzle are mainly classified into two categories, FSS(Free Shock Separation) and RSS(Restricted Shock Separation), both of which are associated with the thrust characteristics as well as side loads of the engine. According to the previous investigations, strong side loads of the engine are produced during the period of transition from FSS to RSS or vice versa. The present work aims at investigating the unsteady behavior of the separation shock waves in a two-dimensional supersonic nozzle, using experimental method and CFD. Schlieren optical method was employed to visualize the time-mean and time-dependent shock motions in the nozzle. The unsteady, compressible N-S equations with SST K-$\omega$ turbulence closure were solved using a fully implicit finite volume scheme. The results obtained show the separation shock motions during the transition of the interaction pattern.

• 멤브레인
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• 제19권3호
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• pp.212-221
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• 2009

본 연구는 PVDF/PDMS 복합막을 제조하여 부탄올을 농축을 위한 투과증발특성에 대해 알아보았다. 또한 복합막의 제조 방법에 따른 투과특성을 알아보기 위해 지지층의 PVDF 농도변화와 활성층의 경화조건에 따라 투과증발 최적막을 선정하였다. 이 막을 사용하여 공급액의 농도, 온도 및 순환 유속을 변화시켜 부탄올의 투과특성에 미치는 영향에 대해 알아보았다. 그 결과 공급액의 농도, 온도, 순환 유속이 증가할 경우 부탄올의 플럭스와 투과 농도가 증가함을 확인하였으며 상용막인 GKSS사의 PVDF/POMS 복합막과 비교한 결과 부탄올 투과 플럭스, 투과 농도, 선택도 등 모두 높은 값을 나타내었다.

• 한국수소및신에너지학회논문집
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• 제21권2호
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• pp.117-122
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• 2010

BCY($Ba(Ce_{0.9}Y_{0.1})O_{3-\delta}$) oxide, shows high protonic conductivity at high temperatures, and are referred to as hydrogen separation membrane. For high efficiency of hydrogen separation ($H_2$ flux and selectivity) and low fabrication cost, ultimate thin and dense BCY-Ni layer have to be coated on a porous substrate such as $ZrO_2$. Aerosol depostion (AD) process is a novel technique to grow ceramic film with high density and nano-crystal structure at room-temperature, and would be applied to the fabrication process of AD integration ceramic layer effectively. XRD and SEM measurements were conducted in order to analyze the characteristics of BCY-Ni membrane fabricated by AD process.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.661-667
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• 2001

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7. According to a wake-passing through the cascade, two velocity deficits appear near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit is caused by a periodic wake and the second one appears after some delayed time. The second velocity deficit may be interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreases the duration time of separation appearance and the lesser loss of aerofoil is resulted.

• 한국건축시공학회지
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• 제7권2호통권24호
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• pp.99-106
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• 2007

The purpose of this study presents in Relations between cracks in self-leveling material and quality of floor groundwork surface are experimentally examined. As the first stage, the experiment to observe cracks in self-leveling material constructed on floor groundwork made from various kinds of concrete was carried. As a result, following basic findings were obtained. First, observation of cracks should be continued until an increase in width of cracks stop, without constructing any finishing material. Second, degree of cracks may be indicated quantitatively by the product of length and width. Finally, Cracks and separation is not be influenced by specimen size. Based on these findings, the method of predicting cracks by evaluating surface layer quality of floor groundwork will be established.

• 한국대기환경학회지
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• 제13권1호
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• pp.65-77
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• 1997

A theoretical and numerical investigation on the boundary-layer flow over a two- or three-dimensional hill is presented. The numerical model is based on the finite volume method with boundary-fitted coordinates. The k-$\varepsilon$ turbulence model with modified wall function and the low-Reynolds-number model are employed. The hypothesis of Reynolds number independency for the atmospheric boundary-layer flow over aerodynamically rough terrain is confirmed by the numerical simulation. Comparisons of the mean velocity profiles and surface pressure distributions between the numerical predictions and the wind-tunnel experiments on the flow over a hill show good agreement. The linear theory provides generally good prediction of speed-up characteristics for the gentle-sloped hills. The flow separation occurs in the hill slope of 0.5 and the measured reattachment points are compared with the numerical prediction. It is found that the k- $\varepsilon$ turbulence model is reasonably accurate in predicting the attached flow, while the low- Reynolds-number model is more suitable to simulate the separated flows.ows.

• 한국막학회:학술대회논문집
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• 한국막학회 2002년도 춘계 총회 및 학술발표회
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• pp.35-41
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• 2002

Dense oxygen ionic conducting materials can be used for oxygen separation membranes at high temperatures. However, they show relatively low permeation flux because of their large resistances. To reduce resistances and improve the oxygen permeation flux, thin dense yttria-stabilized-zirconia (YSZ)/Pd composite dual-phase membranes were fabricated by a new approach that combines the reservoir method and chemical vapor deposition (CVD). A thin porous YSZ layer was coated on a porous alumina support by dip-coating the YSZ suspension. A continuous Pd phase was formed inside pores of the YSZ layer by the reservoir method. The residual pores of the YSZ/Pd layer were plugged with yttria/zirconia by CVD to ensure the gas tightness of the membranes. The oxygen permeation fluxes through these composite membrane were 2.0$\times$10$^{-8}$ mol/cm$^2$.s and 4.8$\times$10$^{-8}$ mol/cm$^2$.s at 105$0^{\circ}C$ when air and oxygen were used as the permeate gases, respectively. These oxygen permeation values are about 1 order of magnitude higher than those of pure YSZ membranes prepared under similar conditions.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.280-287
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• 2003

The unsteady flow characteristics and the related noise of separated incompressible laminar boundary layer flows (Re$\sub$$\delta$/* = 614, 868, and 1,063) are numerically investigated. The characteristic lines of the wall pressure are examined to identify the primary noise source, related with the unsteady motion of the vortex at the reattachment point of the separation bubble. The generation and propagation of the vortex-induced noise in the separated laminar boundary layer are computed by the method of Computational Aero-Acoustics (CAA), and the effects of Reynolds number, Mach number and adverse pressure gradient strength are examined.

• International Journal of Aeronautical and Space Sciences
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• 제6권2호
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• pp.33-45
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• 2005

The 1/9-scale model of a fighter-type configuration was tested in the Micro-Craft 8ft ${\times}$ 12ft wind tunnel facility. An abrupt lift dump was found at a certain range of angle of attack under the pre-scheduled approach configuration. To avoid a probable unsatisfactory flight behavior due to the lift dump, various aerodynamic devices were suggested. Extensive tests applying the cutoff leading edge flaps, boundary layer fences, saw tooth and vortex generators were performed with flow visualization as well as force and moment measurements. Test results showed that the origin of the lift dump was caused by the secondary boundary layer flow separation generated from the strong interaction between wing and flap. Various solutions for avoiding the unfavorable feature were suggested with the merits and demerits.