• 한국항공우주학회지
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• 제34권9호
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• pp.82-88
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• 2006

벽면 냉각을 위해 장착되는 최외곽 연료 분사 또는 막냉각 장치는 액체로켓 추력실 내에서 반경방향으로 비균일한 추진제의 혼합분포를 야기하게 된다. 본 연구에서는 설계단계에서 이러한 특성들이 벽면 근방의 온도분포 및 추진 성능에 미치는 영향을 예측할 수 있는 해석방법을 개발하였다. 설계코드로서의 효용성을 높이기 위해 분사/미립화 영역에서 나타나는 복잡한 물리현상을 미시적으로 해석하는 대신에 분사기 종류와 배열에 따른 거시적 혼합특성을 모사할 수 있는 모델을 사용하였으며, 연소시험데이터를 이용한 성능 파라미터의 보정방법을 제안하였다. 위와 같은 방법을 통해 현재 개발 중인 30톤급 실물형 연소기에 대한 설계점 및 탈설계 작동영역에서의 성능 파라미터를 정확히 예측할 수 있었으며, 향후 재생냉각 연소기 설계에 유용한 해석적 방법론을 제공할 것으로 기대된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.466-469
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• 2002

In the sintering of YIG, abnormal grain growth phenomena was observed. This abnormal grain growth is related to the sintering temperature in this experiment. In the sintering below 145$0^{\circ}C$., the sintered body showed narrow size distribution. However, in the sintering at 145$0^{\circ}C$, a few grains grew rapidly with respect to other grains, and bimodal size distribution was appeared. Liquid phase was not observed far from the abnormally grown large grains, but only near the large grains. This means that the abnormal grain growth was caused by the nonuniform distribution of liquid phase which promote the grains growth. This nonuniform distribution of liquid phase was thought to be due to the nonuniform mixing of the starting materials. This abnormal grain growth was suppressed by enhance the compositional uniformity by multiple calcination.

• Nuclear Engineering and Technology
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• 제29권3호
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• pp.186-195
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• 1997

When asymmetric thermal-hydraulic conditions occur between cold legs, the core inlet temperature will be nonuniform if the coolant is not mixed perfectly in the lower plenum. These uneven core inlet conditions may induce the change in core power distribution. Thus realistic prediction of thermal mixing is important in such abnormal conditions. In this study, reactor internals, which are scaled down as to conserve the flow area ratio, are set up in the model of KORI Unit 1 with the scaling factor of 1/710 by volume and coolant temperatures are measured beneath the lower core plate. Based on experimental results, the ability of COMMIX-1B code to simulate the coolant mixing phenomena in the lower plenum is estimated. The results show that complete mixing never occurs in any conditions and the mixing pattern is characterized according to the plant type.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.71-81
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• 2017

When an integral pressurized water reactor is operated under low power conditions, once-through steam generator group operation strategy is applied. However, group operation strategy will cause nonuniform coolant flow distribution at the core inlet and lower plenum. To help coolant flow mix more uniformly, a flow mixing chamber (FMC) has been designed. In this paper, computational fluid dynamics methods have been used to investigate the coolant distribution by the effect of FMC. Velocity and temperature characteristics under different low power conditions and optimized FMC configuration have been analyzed. The results illustrate that the FMC can help improve the nonuniform coolant temperature distribution at the core inlet effectively; at the same time, the FMC will induce more resistance in the downcomer and lower plenum.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1131-1135
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• 2003

In the sintering of YIG, abnormal grain growth phenomena were observed. This abnormal grain growth is related to the sintering temperature in this experiment. In the sintering below 1450$^{\circ}C$, the sintered body showed narrow size distribution. However, in the sintering at 1450$^{\circ}C$, a few grains grew rapidly with respect to other grains, and bimodal size distribution was appeared. From the observation of the microstructure, liquid phase was not observed far from the abnormally grown large grains, but only near the large grains. This means that the abnormal grain growth was caused by the nonuniform distribution of liquid phase which promote the grains growth. Because the growth rate of grains near the liquid phase is much higher than that of the other grains, a few grains grow rapidly. This nonuniform distribution of liquid phase was thought to be due to the nonuniform mixing of the calcined powders. This abnormal grain growth was suppressed by enhancement of the compositional uniformity by multiple calcination.

• 한국안광학회지
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• 제2권1호
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• pp.91-95
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• 1997

균일하지 않게 코팅된 적분구의 효율성에 대한 일반적인 방정식이 제시되었다. 제시한 가정은 적분구 내부는 완전한 구형이고 모든 구내벽은 입사된 광선에 대해 완전하게 확산적으로 반사한다는 것이다. 제시한 방정식을 절대반사율 측정과 반구 반사율 측정이 혼합된 적분구에 대해서 기본적인 응용성을 시험하였다.

• 상하수도학회지
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• 제22권6호
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• pp.689-696
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• 2008

In a water treatment process a complete and homogeneous dispersion of the coagulants in the raw water could be most important factor. This research was performed to evaluate coagulation performance of the in-line-orifice mixer which was recently introduced as a rapid mixing device. The test was to determine the actual coagulant dispersion distribution on the overall cross-section at a distance of 1.6~3D from the chemical injection point by measuring zeta potential. From the results of zeta potential test, it was shown that the coagulant dispersion within the in-line orifice mixer was occurred very unevenly. The results have confirmed that it is necessary to increase the velocity of coagulants injection or pressurized water rates, in order to reduce nonuniform distribution of chemicals.

• 대한기계학회논문집B
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• 제37권1호
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• pp.67-74
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• 2013

주류공기에 수직으로 분사되는 JICF 분사시스템은 연소실내에서 주류공기의 영향을 최소화하면서 미립화 및 연소성능을 향상시키기 위한 추진시스템의 연료분사 방식으로 넓은 적용범위를 가지고 있다. 하지만 JICF 분사시스템에서 산화제인 공기와 연료의 불충분한 혼합성능은 연소실 내에서의 불균일한 화염구조를 형성한다. 따라서 본 연구에서는 JICF 분사시스템의 램제트 연소기에서 연료와 공기의 부족한 혼합성능에 기인한 연소의 불균일한 화염구조를 실험적으로 확인하고, 연료 제트의 침투깊이, 분열점 등을 예측하기 위한 상관관계식을 유도함으로서 JICF 분사시스템에서 연소성능에 영향을 미치는 액체제트와 주류공기와의 분무 및 혼합특성을 파악하였다. 특히, 액체 제트의 침투깊이를 주류공기의 유동방향의 상류와 하류로 나누어 상관관계식을 유도하여 좀더 정확한 침투깊이의 예측이 가능하도록 하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1262-1263
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• 2011

Sulfur hexafluoride is the most commly used insulation gas in electrical systems. Gas insulated systems are widely used in the electric power industry for transmission and distribution of electrical energy. When $SF_6$ was first discovered, the potential application was only considered for insulation because of good dielectric properties. But the widespread use of $SF_6$ gas by electric power and other industries has led to increase concentrations of $SF_6$ gas in the atmosphere. This concern as to possible effects on global warming because $SF_6$ is a potent greenhouse gas. That's why firstly we studied uniform and nonuniform field property by mixing $SF_6$ and N2 gas. This paper presents the dielectric strength and insulating property for particle contamination under $SF_6/N_2$ mixtures. Two types of mixed gases(50% $SF_6$_50%$N_2$, 20% $SF_6$_80%$N_2$) were applied. We performed tests for the length and shape of particle. Test gas pressure is from 0.3 to 0.7 Mpa. The study was conducted to develop environment-friendly insulating material for GIS that can reduce $SF_6$ gas and make a design criteria for mixtures.

• 한국가시화정보학회지
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• 제19권3호
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• pp.69-76
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• 2021

Printed circuit heat exchanger (PCHE) is a compact heat exchanger with good heat transfer performance, high structure integrity, and reliability over a wide range of temperatures and pressures. Instead of the traditional zigzag and straight shape channel, the sinusoidal shape channel was adopted in this study to investigate the relation of thermal-hydraulic performance and waviness factors (period and amplitude). The local flow characteristics and the heat flux distribution were compared to verify the effects of period and amplitude on heat transfer performance. As the period of channel becomes shorter, the rapid change of the flow direction can produce high flow separation around the corner leading to the disturbance of the boundary layer opposite wall. The nonuniform distribution of flow velocity appeared around the corner positions can promote fluid mixing and lead to higher thermal performance. An evaluation index was used to compare the comprehensive performance of PCHE considering the Nusselt number and Fanning factor. Based on the simulation results, the optimal design parameters of PCHE channel shape were found that the channel with an equivalent bending angle of 15° offers the highest heat flux capacity.