• Nuclear Engineering and Technology
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• v.41 no.6
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• pp.797-806
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• 2009

The Multichannel Analyzer for Transient and steady-state in Rod Array - Liquid Metal Reactor for Flow Blockage analysis (MATRA-LMR-FB) code for the analysis of a subchannel blockage has been developed and evaluated through several experiments. The current version of the code is improved here by the implementation of a distributed resistance model which accurately considers the effect of flow resistance on wire spacers, by the addition of a turbulent mixing model, and by the application of a hybrid scheme for low flow regions. Validation calculations for the MATRA-LMR-FB code were performed for Oak Ridge National Laboratory (ORNL) 19-pin tests with wire spacers and Karlsruhe 169-pin tests with grid spacers. The analysis of the ORNL 19-pin tests conducted using the code reveals that the code has sufficient predictive accuracy, within a range of 5 $^{\circ}C$, for the experimental data with a blockage. As for the results of the analyses, the standard deviation for the Karlsruhe 169-pin tests, 0.316, was larger than the standard deviation for the ORNL 19-pin tests, 0.047.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.3
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• pp.215-222
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• 2010

Long and slender body, like a fuel rod, oscillating in axial flow can be unstabilized even by the small cross flow which can be activated by the flow mixer or turbulent generator. It is important to include these effects of flow disturbance in dynamic stability analysis of nuclear fuel rod. This work shows how eigen frequency of a multi-span fuel rod can be changed by the swirl flow, which is discretely generated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was calculated. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.386-386
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• 2015

담수가 해수에서 흘러드는 하구에서는 성층이 관측되며 이것은 난류의 미세구조를 변화시키는 주요 원인으로 작용한다. 이러한 성층화 현상은 하구 내 부유사의 군집인 하구 최대혼탁수(Estuarine Turbidity Maximum, ETM)의 형성에 영향을 주게 된다. 본 연구는 성층의 하구 최대 혼탁수 생성 메커니즘에 관심을 두고 수치모델링을 활용한 미세 난류의 부유사 거동 분석에 초점을 두었다. 성층과 전단응력 사이의 난류 혼합을 대표하는 유동인 켈빈-헬름홀츠 불안정성(Kelvin-Helmholtz Instability)을 도입하고 성층 경계면 근처에서 부유사의 이송을 높은 레이놀즈수(Reynolds number) 유동에서 RANS(Reynolds-averaged Navier-Stokes Simulation)보다 다양한 규모의 에너지 획득이 가능하여 미세 난류 구조 재현에 장점을 갖는 Large-eddy Simulation(LES)를 활용하여 모사하였다. 여기에서, 부유사는 주위 유동의 물리적 특성 변화에 영향을 미치지 않는 Passive scalar로 가정하였으며 $6^{th}$-order Lagrangian 다항식 보간법을 적용하여 입자의 이동 속도를 계산하고 이를 시간에 대해 적분함으로써 이동 궤적을 추적하였다. 수치 모델 결과 Lock-exchange 유동 내에서 켈빈-헬름홀츠 불안정성이 발생함에 따라 경계면 주위에 위치한 부유사가 billow 내에서 트랩핑(trapping)되는 것을 보여주어 KH-billow 혹은 braids 내의 미세 난류에 의한 영향이 확인되었다. 본 연구에서는 LES를 활용하여 성층류 및 성층류 내의 부유사 혼합을 모사하여 난류의 정도에 따른 이동 궤적의 차이에 대해서 분석함으로써 성층의 난류 강도 저하에 따른 부유사의 군집으로의 영향에 대해 서술한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.150-156
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• 2008

A program based on a 2-D CFD code has been developed to simulate a gas turbine engine. 2-D Navier-Stokes implicit code with $k-\omega$ turbulent model is used in compressor and turbine. Lumped method chemical equilibrium code with 10 species of molecular is applied to combustor with assuming perfect mixture and 100% combustion efficiency at constant pressure state. Fluid properties are shared on interfaces between engine components. Compressor supplies outlet temperature and pressure to combustor. At the same time, combustor also carries temperature and pressure to turbine. The back pressure of compressor outlet is transferred by inlet pressure of turbine. Unsteady phenomena in rotor-stator are covered by mixing-plane method. The running condition of engine can be determined only by given the inlet condition of compressor, the outlet condition of turbine, equivalence ratio and rotating speed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.430-432
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• 2011

An experimental study of the flame response in a turbulent premixed combustor has been conducted in order to investigate mechanisms for combustion instabilities in lean premixed gas turbine combustor. A lab-scale combustor and mixing section system were fabricated to measure the flame transfer function. Measurements are made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results are analyzed to determine the phase and gain of the flame transfer function as a function of the modulation frequency and operating conditions.

• Journal of the Korea Safety Management & Science
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• v.19 no.4
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• pp.149-155
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• 2017

This study is analyzed combustion phenomena based on the environmental energy facility incinerator. It is assumed that combustible components of waste are composed of carbon and hydrogen, and the combustion process of fuel is by setting as multi-component / multistage reaction. As the combustion chamber is burned, the high temperature environment is achieved, also the heat transfer accompanied by the turbulent flow and the generation of NOx, a pollutant, are interpreted to predict the thermal and fluid characteristics and pollution emissions of the grate incinerator. As the result of internal flow analysis, the slow flow around the ash chute and the mixing effect due to the complicated turbulence around the combustion chamber were predicted to show excellent performance. It is shown to the internal average temperature was about $1024^{\circ}C$, around the about $1000^{\circ}C$ homogeneous temperature distribution. Due to the sudden temperature decrease in the boiler, the flue gas temperature at the outlet was estimated to be about $220^{\circ}C$.

• Journal of Korea Water Resources Association
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• v.47 no.8
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• pp.703-715
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• 2014

This study aims to investigating the effect of Schmidt number (${\sigma}_c$) on sediment suspension and hydrodynamics calculation. The range of ${\sigma}_c$ is also studied based on the flux Richardson number ($Ri_f$) and gradient Richardson number ($Ri_g$). Numerical experiments are carried out by 1 dimensional vertical model. Both cohesive and non-cohesive sediments are tested under the conditions of pure current and oscillatory flow. The turbulence damping effect due to sediment suspension is examined considering ${\sigma}_c$ as a constant for the damping effect. The results of this study show the consistent effect of ${\sigma}_c$ on sediment suspension regardless of hydrodynamic condition. It is also found that the model overestimates the flow velocity and turbulent kinetic energy when the damping effect is not considered. Under the conditions of $Ri_f$ and $Ri_g$ causing density stratification, it is known that the vertical mixing of sediment is reasonably calculated in the range of ${\sigma}_c$ from 0.3 to 0.5.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.12
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• pp.706-713
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• 2017

This study compared and analyzed the water treatment efficiency and the applicability of water treatment plant using the existing Mechanical Rapid-Mixer by introducing the Non-powered Vortex Mixer to the domestic water treatment plant. For this study, fluid flow characteristics and head loss of a Non-powered Vortex Mixer are calculated by Computational Fluid Dynamics (CFD)respectively. The head loss rate inside the mixer was 11.30% when the inflow velocity was 0.5 m/sec, 16.27% at 0.6 m/sec and 21.44% at 0.7 m/sec, the head loss rapidly increased at the optimal velocity of 0.5 m/sec. For the inflow velocity of 0.5 m/sec, the turbulent intensity at the inlet was 2.37% and at the outlet was 7.83%, so there was sufficient mixing strength for the particulate matter and the coagulant. The result of the water quality of the treatment plants with the inflow velocity of 0.38 m/sec that was operated in three years after replacing all 12 units of the existing Rapid-Mixer with the Non-powered Mixer met the standards. Hence, it is possible to reduce the energy consumption of 64,143 ~ 65,306 kWh/year since the Rapid-Mixer is replaced by the Non-powered Vortex Mixer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.2
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• pp.142-151
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• 1991

In the present investigation, it has been proposed to utilize a direct contact heat exchanger as an evaporator to solve the difficulties such as scaling, corrosion and law thermal efficiencies, associated with the conventional evaporator. Liquified nitrozen was utilized as a working fluid to investigate basic natures of bubble dynamics in the evaporator, and spray nozzles were adopted to inject liquified nitrozen into the spray column with varying flow rates of dispersed phase fluids. Experimentations were carried out in the range of $6.54{\times}10^{-4}kg/s$ - 0.030 kg/s for dispersed phase flow rates with one, three and five nozzle holes. Observing the bubble dynamics for the evaporator the feasibility of utilizing a direct contact heat exchanger as a LNG evaporator has been evaluated. The results show that no eruption phenomena was observed in the present investigation with $LN_2$ and the interface between $N_2$ bubbles and water was fully turbulent. It is believed that the high injection velocity of $LN_2$ through the spray nozzles provide good mixing effects for both heat and mass transfers between water and $N_2$ bubbles. Ice was formed on the surface of the spray nozzle for higher $LN_2$ flow rates. However, even in this case, it is observed that the ice was detached as soon as it was formed. Under the present experimental conditions, the shapes of $LN_2$ bubbles were in the spherical-cap region according to the Clift, Grace and Weber Graphs. The height of foam region caused by the breakup of larger bubbles keeps increasing with high injection velocities until it reaches it's maximum height.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1134-1141
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• 2003

Performance of a gas turbine combustor installed in a test facility has been studied by measuring spatially- and temporally-resolved temperature distributions using multiplex CARS technique. 500 CARS temperatures were determined at each measuring point to obtain a histogram of temperature distribution. Experiments were carried out in the aero-engine combustor sector rig burning standard kerosene fuel. The histograms were obtained around a triple-sector double annular rig running in ground idle conditions, showing features of flow mixing within the rig. The temperature histograms that prove the existence of high temperatures above 1900 K provide us valuable information to improve the design of the combustor structure suppressing NOx generation in turbulent combustion processes. The effects of swirl direction and pre-filmer on gas turbine combustion were investigated. When we installed radial swirls, a large recirculation zone was formed by the fuel module regardless of swirl directions and the pre-filmer installation. It is found that the swirl direction affects the shape of the reverse flow zone, however. Also, an attempt to estimate the flow field and flame structure is made using the histogram of temperature determined with the CARS technique.