• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.162-169
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• 2005

The performance of oxygen combustion with $CO_2$ feeding was investigated in a pyrex tube furnace. The inverse type multi-hole burner was used for improving mixing and wide operating range. It introduced oxygen, fuel, and oxygen, respectively, from center tube to outer tubes. Oxygen combustion characteristics with excess oxygen ratio, oxygen feeding ratio, and $CO_2$ feeding flow rate were studied to optimize the operating condition and to apply the oxygen combustion with recirculation of flue gas to a real furnace. This paper presents results on the effect of $CO_2$ feeding flow rate on the structure of the flames and concentrations of NO and CO emissions. The visible flame length was shortest due to well mixing between fuel and oxygen when the oxygen feeding ratio was 0.25. The NO emission was reduced drastically regardless of excess oxygen ratio when the $CO_2$ feeding flow rate was larger than 15 lpm. The CO emission is varied by changing the $CO_2$ feeding flow rate but the CO emission characteristics is highly affected by excess oxygen ratio. When the excess oxygen ratio is below ${\lamda}=1.1$, the CO emission increased as the $CO_2$ feeding flow rate increased.

• 한국환경과학회지
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• 제20권4호
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• pp.501-509
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• 2011

Unlike many laboratory-scale studies on absorption of organic compounds (VOCs), limited pilot-scale studies have been reported. Accordingly, the present study was carried out to examine operation parameters for the effective control of a hydrophilic VOC (methyl ethyl ketone, MEK) by applying a circular pilot-scale packed-absorption system (inside diameter 37 cm ${\times}$ height 167 cm). The absorption efficiencies of MEK were investigated for three major operation parameters: input concentration, water flow rate, and ratio of gas flow-rate to washing water amount (water-to-gas ratio). The experimental set-up comprised of the flow control system, generation system, recirculation system, packed-absorption system, and outlet system. For three MEK input concentrations (300, 350, and 750 ppm), absorption efficiencies approached near 95% and then, decreased gradually as the operation time increased, thereby suggesting a non-steady state condition. Under these conditions, higher absorption efficiencies were shown for lower input concentration conditions, which were consistent with those of laboratory-scale studies. However, a steady state condition occurred for two input concentration conditions (100 and 200 ppm), and the difference in absorption efficiencies between these two conditions were insignificant. As supported by an established gas-liquid absorption theory, a higher water flow rate exhibited a greater absorption efficiency. Moreover, as same with the laboratory-scale studies, the absorption efficiencies increased as water-to-gas ratios increased. Meanwhile, regardless of water flow rates or water-to-gas ratios, as the operation time of the absorption became longer, the pH of water increased, but the elevation extent was not substantial (maximum pH difference, 1.1).

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1532-1539
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• 2019

This paper analyzes a new method for reducing boiling water reactor fuel temperature during a Loss of Coolant Accident (LOCA). The method uses a device called Reverse Flow Restriction Device (RFRD) at the inlet of fuel bundles in the core to prevent coolant loss from the bundle inlet due to the reverse flow after a large break in the recirculation loop. The device allows for flow in the forward direction which occurs during normal operation, while after the break, the RFRD device changes its status to prevent reverse flow. In this paper, a detailed simulation of LOCA has been carried out using the U.S. NRC's TRACE code to investigate the effect of RFRD on the flow rate as well as peak clad temperature of BWR fuel bundles during three different LOCA scenarios: small break LOCA (25% LOCA), large break LOCA (100% LOCA), and double-ended guillotine break (200% LOCA). The results demonstrated that the device could substantially block flow reversal in fuel bundles during LOCA, allowing for coolant to remain in the core during the coolant blowdown phase. The device can retain additional cooling water after activating the emergency systems, which maintains the peak clad temperature at lower levels. Moreover, the RFRD achieved the reflood phase (when the saturation temperature of the clad is restored) earlier than without the RFRD.

• 한국수자원학회논문집
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• 제38권2호
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• pp.143-153
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• 2005

최근 들어 자연형 하천과 하천생태계 복원에 대한 관심이 점증하면서 수리학적 기능 외에, 다양한 생태환경을 제공하고 하안 부근의 경관을 개선하는 기능을 가는 수제에 대한 관심이 커지고 있다. 그러나 현재 국내에는 수제설치에 대한 설계지침이 충분치 않을 뿐 만 아니라 국내 수행된 연구 자료가 매우 부족한 실정이다. 이에 본 연구에서는 수제 설계인자 해석을 위한 수리모형실험을 수행하였다. 실험조건은 수제선단 흐름변화와 수제하류부 재순환영역에 대한 고정상실험으로 수제길이와 투과율을 조절하여 수행하였다. 주요 분석은 수제 선단에서는 중앙부 유속증가와 세굴의 영향인자인 유속과 편향각을 측정하여 수제 선단유속비와 면적비에 대한 실험식을 제안하였다. 또한 수제하류부 재순환 영역에서는 수제 설치의 주요요인인 수제간격의 기초 자료를 해석하기 위해 흐름분리 길이와 입사각의 변화를 분석하였으며 투과율과 수제 설치각에 대한 실험식을 제안하였다.

• 설비공학논문집
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• 제24권10호
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• pp.739-744
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• 2012

This paper describes the blower performance used for single-stage high pressure regenerative blower. The blower considered is widely applied to the field of a fuel cell system, a medical equipment and a sewage treatment plant. Flow rate and rotating frequency of a impeller of the blower are considered as design parameters for the proper operation of the blower. Three-dimensional Navier-Stokes equations are introduced to analyze the performance and internal flow of the blower. Relatively good agreement between experimental measurements and numerical simulation is obtained. Throughout a numerical simulation, it is found that small and stable vortical flow generated inside the blade passage is effective to increase pressure and efficiency of the blower. Large local recirculation flow having low velocity in the blade passage obstructs the generation of stable vortical flow, thus increases the pressure loss of the blower. Detailed flow field inside the blower is also analyzed and discussed.

• 한국가시화정보학회지
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• 제8권1호
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• pp.31-38
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• 2010

An experimental study to evaluate dynamic structures of flow and turbulence characteristics in bubble-driven liquid flow in a rectangular tank with a varying flow rate of compressed air is conducted. Liquid flow fields are measured by time-resolved particle image velocimetry (PIV) with fluorescent tracer particles to eliminate diffused reflections, and by an image intensifier to acquire enhanced clean particle images. Instantaneous vector fields are investigated by using the two frame cross-correlation function and bad vectors are eliminated by magnitude difference technique. By proper orthogonal decomposition (POD) analysis, the energy distributions of spatial and temporal modes are acquired. When Reynolds number increases, bubble-induced turbulent motion becomes dominant rather than the recirculating flow near the side wall. The total kinetic energy transferred to the liquid from the rising bubbles shows a nonlinear relation regarding the energy input because of the interaction between bubbles and free surface.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.367-370
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• 2006

This paper deals with the modeling and simulation of the internal flowfield in a valveless airbreathing pulse detonation engine (PDE) currently under experimental development at the U.S. Naval Postgraduate School. The system involves no valves in the airflow path, and the isolation between the inlet and combustor is achieved through the gasdynamics in an isolator. The analysis accommodates the full conservation equations in axisymmetric coordinates, and takes into account variable properties for ethylene/oxygen/air system. Chemical reaction schemes with a single progress variable are implemented to minimize the computational burden. Detailed flow evolution during a full cycle is explored and propulsive performance is calculated. Effect of initiator mass injection rate is examined and results indicate that the mass injection rate should be carefully selected to avoid the formation of recirculation zones in the initial cold flowfield. Flow evolution results demonstrate a successful detonation transmission from the initiator to the combustor. However, strong pressure disturbance may propagate upstream to the inlet nozzle, suggesting the current configuration could be further refined to provide more efficient isolation between the inlet and combustor.

• 한국자동차공학회논문집
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• 제6권6호
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• pp.142-154
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• 1998

The effects of recirculated exhaust gas on the characteristic of soot emissions have been investigated by using an eight-cylinder, four-stroke, direct injection and water-cooled diesel engine operating at several loads and speeds. The experiments in this study are carried out at the fixed fuel injection timing of $38^{\circ}$ BTDC regardless of experimental conditions. The intake oxygen concentration and the mean equivalence ratio calculated by the intake air flow and fuel consumption rate are used to analyze and discuss the influences of EGR rate on soot emissions. Results of this study indicate that soot emissions increase owing to the drop of intake oxygen concentration and the rise of equivalence ratio as the EGR rate increases at a given engine load and speed, especially the high load.

• Journal of Advanced Marine Engineering and Technology
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• 제38권4호
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• pp.418-423
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• 2014

최근 소수력 발전은 화석에너지의 고갈 및 환경 문제를 해결할 수 있는 대안으로 우리나라 뿐만 아니라 세계 각국이 심혈을 기울이고 있다. 본 연구에서는 소수력 발전의 최적화를 위해 입지 조건 및 특성을 고려하여 저 중낙차 및 유량 변동이 심한 지역에 적합하도록 2개의 가이드 베인을 갖는 횡류수차를 개발하여 실증시험을 실시하였다. 또한 CFD를 이용한 선행 연구 결과를 바탕으로 하여 수차 입구단의 낙차를 일정하게 유지한 상태에서 공기 유입 및 밸브 위치에 따른 성능 변화를 검증하였다. 그 결과 공기 유입이 재순환 유동과 러너를 통과한 유체가 주축에 충돌하면서 발생하는 수력학적 손실을 최소화시킬 수 있어 수차의 성능과 효율 개선에 효과적임을 검증할 수 있었다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1604-1615
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• 2023

In an open-pool type research reactor with a downward forced flow in the core, pipes can be under sub-atmospheric pressure because of the large pressure drop at the reactor core in the atmospheric pool. Sub-atmospheric pressure can result in air inflow into the pipe from the pressure difference between the atmosphere and the inside of the pipe, which in a postulated pipe break scenario can lead to the breakdown of the cooling pump. In this study, a plant-scale experiment was conducted to study air inflow in large piping systems by considering the actual operational conditions of an advanced research reactor. The air inflow rate was measured, and the entrained air was visualized to investigate the behavior of air inflow and flow regime depending on the pipe break size. In addition, the developed drift-flux model for a large vertical pipe with a diameter of 600 mm was compared with other correlations. The flow regime transition in a large vertical pipe under downward flow was also studied using the newly developed drift-flux model. Consequently, the characteristics of two-phase flow in a large vertical pipe were found to differ from those in small vertical pipes where liquid recirculation was not dominant.