• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.72-83
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• 2018

In this study, a series of CFD analyses were carried out for a hydrogen rocket combustor with a single shear coaxial injector. A hybrid RANS/LES approach was used for the turbulent combustion analysis with a two-dimensional axisymmetric configuration. Three reaction mechanisms, three spatial discretization methods, and three levels of grid resolution were compared to determine an appropriate CFD approach. The performance of the CFD prediction were investigated by comparing the wall heat flux with experimental data. Investigation of the flow field results provides an insight into the characteristics of the turbulent reacting flow of a rocket combustor with a shear coaxial injector.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.555-565
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• 2021

The goal of this study is to improve flow and noise performances of existing backward-curved blade centrifugal fan system used for circulating cold air in a refrigerator freezer by optimally designing airfoil shape. The unique characteristics of the system is to drive cold airflow with two volute tongues in combination with duct system in a back side of a refrigerator without scroll housing generally used in a typical centrifugal fan system. First, flow and noise performances of existing fan system were evaluated experimentally. A P-Q curve was obtained using a fan performance tester in the flow experiment, and noise spectrum was measured in an anechoic chamber in the noise experiment. Then, flow characteristics were numerically analyzed by solving the three-dimensional unsteady Navier-Stokes equations and noise analysis was performed by solving the Ffowcs Williams and Hawkins equation with input from the flow simulation results. The validity of numerical results was confirmed by comparing them with the measured ones. Based on the verified numerical method, blade inlet and outlet angles were optimized for maximum flow rate using the two-factor central composite design of the response surface method. Finally, the flow and noise performances of a prototype manufactured with the optimum design were experimentally evaluated, which showed the improvement in flow and noise performance.

• Journal of computational fluids engineering
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• v.12 no.1
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• pp.60-67
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• 2007

In this paper, the dispersion controlled dissipative (DCD) scheme is reviewed and then extended to simulate chemically reacting gas flows in multicomponent mixtures in the presence of strong shock waves. Furthermore, the properties of the reactive DCD (DCD-R) scheme are discussed, followed by several applications. The DCD scheme has been shown to have the following features: high accuracy and robustness for reacting gas flows in the presence of strong shock waves and contact discontinuities, and algorithmic simplicity.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.05a
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• pp.127-132
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• 1999

우리나라의 도시폐기물 소각로는 화격자 위에 폐기물을 공급하고 화격자 밑에서 공기를 공급하는 스토커식 소각로를 대부분 채택하고 있다. 이러한 스토커 소각로 연소실내에서는 매우 복잡한 연소현상이 발생하는데, 연소실로 투입된 쓰레기는 먼저 건조부에서 수분의 건조가 일어나고, 화격자의 구동에 의해 쓰레기가 혼합 및 이송되면서 열분해, 가스화, 가연성분의 탈휘발화 및 연소, 일부 고정탄소의 표면연소 등의 반응이 일어난다. 그리고 1,2차 연소실에서는 휘발분 및 비산된 고체의 연소가 일어나는데, 이때 대류 및 복사열전달 등의 복잡한 현상을 수반하는 유동장이 형성된다. 더욱이 불균질한 특성을 갖는 쓰레기층 내에서의 복잡한 현상으로 인하여 발생하는 경계조건 설정의 불확실성으로 연소실내의 연소 현상을 전산해석하는 데에는 상당한 어려움이 있다.(중략)

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.05a
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• pp.213-218
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• 1999

용융탄산염 연료전지 (MCFC) 스택의 운전시에 가장 문제가 되는 사항들 중의 하나는 전지 반응에 의해 생성되는 많은 열량으로서, 이로 인해 내부 온도가 상승하고 심한 온도 분포가 존재하게 되며 이는 출력 전압 또는 전류의 불균일을 초래하는 동시에 전지 성능 열화(degradation)를 가속시켜 장기 운전에 큰 장애 요인이 된다. 현재 국내에서 개발중인 100kW급 MCFC 발전 시스템의 스택은 전극 면적이 6,000 $ extrm{cm}^2$ 혹은 그 이상에 이르며 25 kW 모듈당 적층되는 전지는 40장으로서 운전시의 발열량 조절이 매우 큰 문제로 등장한다.(중략)

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.4
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• pp.295-303
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• 2012

Based on the data observed and analyzed on a groundwater flow system in the KURT (KAERI Underground Research Tunnel) site, the transport of radionuclides, which were assumed to be released at the supposed position, was calculated on the time-domain. A groundwater pathway from the release position to the surface was identified by simulating the groundwater flow model with the hydrogeological characteristics measured from the field tests in the KURT site. The elapsed time when the radionuclides moved through the pathway is evaluated using TDRW (Time Domain Random Walk) method for simulating the transport on the time-domain. Some retention mechanisms, such as radioactive decay, equilibrium sorption, and matrix diffusion, as well as the advection-dispersion were selected as the factors to influence on the elapsed time. From the simulation results, the effects of the sorption and matrix diffusion, determined by the properties of the radionuclides and underground media, on the transport of the radionuclides were analyzed and a decay chain of the radionuclides was also examined. The radionuclide ratio of the mass discharge into the surface environment to the mass released from the supposed repository did not exceed $10^{-3}$, and it decreased when the matrix diffusion were considered. The method used in this study could be used in preparing the data on radionuclide transport for a safety assessment of a geological disposal facility because the method could evaluate the travel time of the radionuclides considering the transport retention mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.849-855
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• 2012

The effect of electric fields on the response of diffusion flames in a counterflow has been investigated experimentally by varying the AC voltage and frequency. The result showed that the flame was stationary with high AC frequency above the threshold frequency, and it increased with the applied voltage and then leveled off at 35 Hz. Below the threshold frequency, however, the flame oscillated with a frequency that was synchronized with the applied AC frequency. This oscillation can be attributed to the ionic wind effect due to the generation of bulk flow, which arises from the momentum transfer by molecular collisions between neutral molecules and ions, where the ions in the reaction zone were accelerated by the Lorentz force.

• Fire Science and Engineering
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• v.27 no.6
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• pp.50-56
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• 2013

The radiation effects on the auto-ignition and extinction characteristics of a non-premixed fuel-air counterflow field were numerically investigated. A detailed reaction mechanism of GRI-v3.0 was used for the calculation of chemical reactions and the optically-thin radiation model was adopted in the simulations. The flame-controlling continuation method was also used in the simulation to predict the auto-ignition point and extinction limits precisely. As a result, it was found that the maximum H radical concentration, $(Y_H)_{max}$, rather than the maximum temperature was suitable to understand the ignition and extinction behaviors. S-, C- and O-curves, which were well known from the previous theory, were identified by investigating the $(Y_H)_{max}$. The radiative heat loss fraction ($f_r$) and spatially-integrated heat release rate (IHRR) were introduced to grasp each extinction mechanism. It was also found that the $f_r$ was the highest at the radiative extinction limit. At the flame stretch extinction limit, the flame was extinguished due to the conductive heat loss which attributed to the high strain rate although the heat release rate was the highest. The radiation affected on the radiative extinction limit and auto-ignition point considerably, however the effect on the flame stretch extinction limit was negligible. A stable flame regime defined by the region between each extinction limit became wide with increasing the fuel temperature.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.12
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• pp.1111-1118
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• 2010

Combustion measurements based on optical techniques have recently become of major interest as tools not only for clarifying the combustion mechanism but also for validating the computational results for the combustion fields. In this study, the particle behavior in turbulent pulverized coal flame are investigated using advanced optical diagnostics. A laboratory-scale pulverized coal combustion burner is specially fabricated as open type in order to apply various optical measurement techniques. The detailed particle behavior is performed by LDV (laser Doppler velocimetry) and SDPA (shadow Doppler particle analyzer). It is observed that the particle mean diameter increase as the distance from burner increases, and this is found to be caused by the decrease of small particles' diameter and increase of large particles' diameter. This is because of result in the char reaction and the particle swelling due to devolatilization, respectively. The size-classified streamwise velocities of pulverized coal particles in the central region of the jet show the same magnitude, whereas those in the outer region are different depending on the particle size. The results show that the velocity and size-classified diameter of the pulverized coal particles in the flame can be measured well by SDPA.

• Journal of the Mineralogical Society of Korea
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• v.19 no.4 s.50
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• pp.301-310
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• 2006

Smectites were synthesized from Na-P type and Na-A type zeolites by the hydrothermal synthetic method, and their physicochemical properties were studied. The optimal synthetic conditions for producing smectite were $290^{\circ}C$, 72 hr and $75{\sim}100kgf/cm^2$ in autogenous pressure. pHs of initial reaction solutions for the synthesis of smectites from Na-P type and Na-A type zeolite s were pH 6 and pH 10, respectively. The synthetic smectite was confirmed as $12{\AA}$-beidellite by a series of analysis such as X-ray diffraction analysis with random and oriented mounts, ethylene glycol treatment, and Greene-Kelly test, and their several physicochemical properties were studied.