• Nuclear Engineering and Technology
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• 제40권2호
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• pp.117-126
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• 2008

In this paper, a new reactor core design is proposed on the basis of a mixed core concept consisting of a thermal zone and a fast zone. The geometric structure of the fuel assembly of the thermal zone is similar to that of a conventional thermal supercritical water-cooled reactor(SCWR) core with two fuel pin rows between the moderator channels. In spite of the counter-current flow mode, the co-current flow mode is used to simplify the design of the reactor core and the fuel assembly. The water temperature at the exit of the thermal zone is much lower than the water temperature at the outlet of the pressure vessel. This lower temperature reduces the maximum cladding temperature of the thermal zone. Furthermore, due to the high velocity of the fast zone, a wider lattice can be used in the fuel assembly and the nonuniformity of the local heat transfer can be minimized. This mixed core, which combines the merits of some existing thermal SCWR cores and fast SCWR cores, is proposed for further detailed analysis.

• 한국광학회지
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• 제4권3호
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• pp.266-275
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• 1993

Si 기판 위에 low pressure chemical vapor deposition 방법에 의해 TEOS (tetraethylorthosilicate)와 TMPite (trimethylphosphite)를 재료로하여 집적광학용 $P_2O_5-SiO_2$ 박막을 만들고 그 특성을 조사하였다. TEOS의 반응에 TMPite가 참여함으로서 반응활성화에너지는 54.6 kcal/mole에서 39.2 kcal/mole로 크게 낮아졌으며 박막의 증착속도와 P 농도는 TMPite의 유량에 비례하여 증가하였다. 또한 증착온도가 높을스록 박막의 증착속도는 증가하나 P 농도는 감소하였다. 제작된 박막의 굴절률은 P 농도 1wt% 당 0.0019로 P 농도에 비례하여 증가하였다. 측정된 박막 불균일도는 두께 ${\pm}$7% 및 P 농도 ${\pm}$0.5wt% 정도로서 이러한 불균일성은 주로 TMPite의 불균일한 수송에 기인함을 보였다. 또한 P 농도가 10wt% 이상인 박막을 대기중에 장시간 노출하면 표면에 인산이 석출됨을 확인하였다.

• 대한기계학회논문집B
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• 제24권6호
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• pp.870-879
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• 2000

An experimental investigation is conducted to improve a slot film cooling system which can be used for the cooling of gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal-, parallel-, and counter-flow paths to the mainstream direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot with various injection types and coolant feeding directions. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The secondary flow at the lip exit has uniform velocity distributions for the parallel and vertical injection types, which are similar to the results of a two-dimensional slot injection. In the results of local heat/mass transfer coefficient, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effect of jet impingement. The lateral distributions of Sh with the parallel- and counter-flow paths are more uniform than the normal flow path. The averaged Sh with the injection holes are $2{\sim}5$ times higher than that of a smooth two-dimensional slot path.

• 대한기계학회논문집B
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• 제34권10호
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• pp.885-891
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• 2010

고분자 전해질 연료전지(PEMFC)의 열관리는 성능 향상과 내구성 측면에서 중요한 문제이다. 일반적으로 냉각수 순환 유로를 가진 냉각판이 여러 개의 단전지 사이에 삽입되어 PEMFC 내부에서 발생하는 반응열을 외부로 배출한다. 본 연구에서는 개선된 병렬 사형유로(MPSFF)를 향상된 냉각성능을 가진 냉각판 유로형상으로 제안하고, 이를 전산유체역학(CFD) 해석을 통하여 평가하였다. 비교를 위하여 냉각수 유로로 일반적으로 사용되는 사형유로 및 병렬형유로의 냉각성능에 대한 계산도 수행하였다. CFD 결과는 개선된 병렬 사형유로가 냉각판 표면에서의 온도의 비균일도를 상당히 감소시키고, 따라서 PEMFC의 내구성과 성능을 향상시킬 수 있음을 보여주었다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.211-218
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• 2000

Off-design experimental performance was investigated for a small centrifugal compressor, whose impeller diameter is about 125mm, used in an industrial gas turbine. Test rig was designed and manufactured with a radial inflow turbine and a combustor to supply driving power to the compressor. Static pressure was measured on the casing of the impeller, vaneless diffuser, vaned diffuser and volute. Total pressure was obtained using specially fabricated rakes at the vaned diffuser throat and exit. Circumferential nonuniformity was found, near surge, in the Impeller, vaned diffuser and volute region. Spanwise nonuniform flow from the impeller affected the total pressure defects in the vaned diffuser region. Static pressure distortion in the circumferential direction in the volute was found near surge, where the minimum occurred near 140 degree position.

• 대한기계학회논문집
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• 제19권6호
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• pp.1518-1528
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• 1995

The deformation and departure processes of a bubble attached to the wall are studied experimentally and numerically to understand the phenomena of the nucleate boiling heat transfer enhancement under DC electric field. An air-bubble is injected in a dielectric liquid with different electric fields generated by changing three types of electrode system (Type 1,2 and 3) in the bubble generator. Experimental variables are the electric field strength and the distance and the shape of the electrodes under DC electric field. From experimental results, it is observed that the bubble under Dc electric field is elongated in the same direction as the electric field and the contact angle increases. For the parallel plate electrode which generates a uniform electric field, bubble departure volume doesn't seem to decrease within our experimental range. However, when a needle is raised a few millimeters from the lower electrode to make a nonuniform electric field around the needle, bubble departure volume decreases continuously with the increase of an applied voltage. The reduction effect of bubble departure volume is the most effective under a strong nonuniform electric field generated with Type 3. As the nonuniformity of the electric field due to the shape of a electrode increases, the terminal velocity and the acceleration of a bubble increase largely. For the comparison with visualization results, the deformation of a bubble attached to the electrode is carried out by a numerical method. Numerical results show good agreement qualitatively with experimental results.

• 대한기계학회논문집B
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• 제36권2호
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• pp.225-232
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• 2012

희박 예혼합 가스터빈 연소기에서 배출되는 NOx, CO 와 같은 오염물질을 예측하기 위해서 화학반응기 네트워크 모델을 개발했다. 본 연구에서는 CHEMKIN 코드와 4 가지 NO 생성 메커니즘을 포함한 GRI 3.0 메탄-공기 연소 메커니즘을 이용해서 가스터빈의 부하조건을 변화시키며 NOx 및 CO 배출의 예측을 수행하였다. 모델의 검증을 위해서 계산된 결과를 모사연소기의 실험 데이터와 비교하였다. 여러부하조건에 따른 4 가지 NO 경로의 기여도를 조사하였다. 또한 인젝터의 질량유동 및 당량비의 불균일성이 NOx 배출이 끼치는 영향을 고찰하고 10ppm 이하의 저 NOx 연소기 개발을 위한 저감 방법을 제안했다.

• 한국주조공학회지
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• 제12권3호
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• pp.220-229
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• 1992

The degree of purification and the macrostructure of high purity aluminium were studied through the alternate stirring method in order to improve the nonuniformity of solute concentration in the unidirectional stirring method. The $2^3$ factorial design was done to examine the effects of experimental factors more qualitatively. In the relatively low stirring speed of 1500 rpm with alternate stirring mode, the uniform solute profile and refined grain structure were obtained due to strong washing effect and turbulent fluid flow. It was induced by the transition of the momentum boundary layer by alternation of the stirrer. It was concluded from this study that the alternate stirring mode was more effective to obtain the uniformity of solute even in the stirring speed of 1500 rpm. But the degree of purification decreased below the critical alternating period. When 2N(99.8wt.%) aluminium was used as the starting material the morphology of solid-liquid showed the cellular shape and the columnar grains were inclined to the direction of rotation. This inclined grain growth resulted from the difference of relative velocities of solid and liquid. The inclined angle was increased as the stirring speed increased and solidification proceeded. In the case of 4N aluminium, there was no inclined grain growth and it was confirmed from the macrostructure and SEM work that the morphology of solid-liquid interface was planar. From the factorial design, it was found that the alternate stirring mode showed poorer purification effect than that of unidirectional stirring mode at low speed(500 rpm). In addition, the factor that had the most significant effect on the degree of purification was the stirring speed.

• 한국농림기상학회지
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• 제11권4호
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• pp.151-161
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• 2009

토양수리특성을 규명하는 것은 사면에서의 수문과정을 이해하는 과정에서 중요한 부분이다. 이 연구에서는 토양공극발달 및 수리학적 특성의 시간적인 변화특성에 대해서 조사하였다. 특히, 대공극 흐름이나 수리전도도와 관련된 특성들을 설마천 유역의 범륜사 사면과 광릉연구유역의 원두부 소사면에서 관측하였다. 연직 흐름의 측정을 위해 사용된 기기는 장력 침투계로 약 8개월동안 토양층 표면의 수리전도도를 측정하였다. 측정된 결과는 3월, 6월, 9월의 수리전도도가 상대적으로 크지만, 5월과 10월의 경우는 낮은 값을 보여준다. 이는 식생의 세근활동 등과 관련된 공극구조의 발달양상과 선행강우사상으로 인한 토양수분의 영향으로 설명될 수 있다. 침투과정에서 있어서 대공극은 산림 유역에서의 수리전도도에 미치는 영향은 대단히 크며, 수문학적 과정에 있어서도 매우 중요한 기작이다. 본 연구는 현장에서 측정된 토양 수리특성의 시간적 불균일성을 보여주는 사례로 사면에서의 침투과정이 동적인 과정임을 보여주고 있고, 관련된 다양한 토양 수리학적 특성들은 국내 산지사면에서 발생되는 수문기작을 이해하는데 중요한 기초 자료가 된다.