• 전기학회논문지
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• 제60권9호
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• pp.1727-1732
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• 2011

In order to realize a high performance(low loss, high isolation) microwave power divider/combiner, we have designed the power combiner/divider precisely in accordance with the different hight of central part. In the case of the high central part of the hight of $h_r$=10.2, a compensating part of the conical line is inserted in the conical conversion transmission line, and in the case of low central part of the hight of $h_r$=5.0, the conical conversion transmission line is remodeled into the 2-stage bend structure. In both case, the reflection characteristics are improved to 30dB over the operating frequency range of 5GHz bandwidth. A resistance is inserted between the peripheral ports so as to try to improve the isolation characteristics of the device. For the 16-divider/combiner, the isolation characteristics are improved to 10dB over the operating frequency range of 5GHz bandwidth.

• 한국안전학회지
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• 제19권4호
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• pp.80-85
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• 2004

Electromagnetic interference(EMI) shielding characteristics of composite filled with Cu flake and carbon brush powder as hybrid conductive filler and EAF slag have been studied. The coaxial transmission line method of ASTM D4935-99 was used to measure the EMI Shielding effectiveness of composites as formulation in frequency rage $100\~1,000MHz$ The SE also increases with the increase in flier loading. The hybrid filler filled composites show higher SE compared to that of only Cu flake. The correlation between SE and conductivity of the various composites is also discussed. The results indicate that the composites having higher filler loading$({\geq}40wt.\%)$ can be used for the purpose of safety materials to protect hazardous electromagnetic interference.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제22회 KOSCI SYMPOSIUM 논문집
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• pp.147-155
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• 2001

The NOx emission characteristics of jet flames fueled with $H_2$ and $CH_4$ were studied. Experimental and numerical investigations were carried out for various flames with varying equivalence ratio, fuel flow rate and nozzle diameter. The Emission indices of NOx(EINOx) were measured by chemiluminescent method and calculated by simulation using detailed chemistry. The results show that EINOx of $CH_4$ and $H_2$ flames have different trends in terms of equivalence ratio and fuel flow rate but have the same trends in terms of nozzle diameter. These differences can be explained by the following Thermal and Prompt trends in both flames. Thermal EINOx trends can be describe in function of residence time in the high-temperature region weighted by the maximum flame temperature and Prompt EINOx trends can be described in function of flame surface area of each combustion conditions.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.305-313
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• 2005

Measurements of flame length, width and NOx emissions have been conducted to investigate the effect of an acoustic excitation on flame structure in turbulent hydrogen diffusion flames with coaxial air. The resonance frequency of oscillations was varied between 259 ,514 and 728 Hz with power rate of 0.405 and 2.88w. When these frequencies imposed to hydrogen flames, dramatic reduction of flame length and NOx emission was achieved. And acetone planar laser-induced fluorescence technique was used to measure a concentration of the near field of driven axisymmetric jet. The air-fuel stoichiometric line was plotted to investigate the mixing layer and development of air entrainment to fuel jet. Consequently, acoustic excitation on flame could enhance the air-fuel mixing resulting in abatement of NOx emission quantitatively.

• 한국연소학회지
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• 제15권4호
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• pp.1-8
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• 2010

Mild combustion is considered as a promising combustion technology for energy saving and low emission of combustion product gases. In this paper, the controllability of reaction region in mild combustion is examined by using co-axial air nozzle. For this purpose, numerical approach is carried out. Propane is considered for fuel and air is considered for oxidizer and the temperature of air is assumed 900K slightly higher than auto ignition temperature of propane. But unlike main air, the atmospheric condition of co-axial air is considered. Various cases are conducted to verify the characteristics of Co-Axial air burner configuration. The use of coaxial air can affect reaction region. These modification help the mixing between fuel and oxidizer. Then, reaction region is reduced compare to normal burner configuration. The enhancement of main air momentum also affects on temperature uniformity and reaction region. The eddy dissipation concept turbulence/chemistry interaction model is used with two step of global chemical reaction model.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.114-117
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• 2007

In IRR(Integral Rocket-Ramjet), the booster is integrated into the ramjet combustor. Such combustors do not contain combustor liners or flame holders within the combustor due to the limited volume and flame stabilization depends on the recirculation zones formed by the sudden expansion region between the inlet duct and the combustor. A numerical study was conducted on the effect of flame holder which could be added to the inlet duct of IRR. Two different types of flame holder installations, flame holder without sudden expansion region and flame holder with small sudden expansion region, were compared and showed different flame shapes and pressure rise in the combustor.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.7-12
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• 2007

To reveal the newly found liftoff height behavior of hydrogen jet, we have experimentally studied the stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition. The objectives of the present research are to report the phenomenon of a liftoff height decreasing as increasing fuel velocity, to analyse the flame structure and behavior of the lifted jet, and to explain the mechanisms of flame stability in hydrogen turbulent non-premixed jet flames. The velocity of hydrogen was varied from 100 to 300m/s and a coaxial air velocity was fixed at 16m/s with a coflow air less than 0.1m/s. For the simultaneous measurement of velocity field and reaction zone. PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. As results, it has been found that the stabilization of lifted hydrogen diffusion flames is related with a turbulent intensity, which means that combustion occurs where the local flow velocity is valanced with the turbulent flame propagation velocity.

• 한국연소학회지
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• 제17권1호
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• pp.30-36
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• 2012

Dynamic characteristics of combustion occurring in various combustion devices have been extensively studied since most of high-performance combustion devices are susceptible to hazardous, unstable combustion that deteriorates combustor's lifetime. One of the most severe unstable combustion phenomena is high-frequency combustion instability in which heat release fluctuations from combustion are coupled to resonant modes of the combustor. Here in this study, characteristics of high-frequency combustion instabilities observed in three different combustion devices have been presented. Lean-premixed combustion instability occurs mainly due to equivalence ratio fluctuations which induce large heat release oscillations at lean conditions. Liquid-fueled combustion also shows high-frequency instability from energy coupling between pressure and heat release oscillations.

• 한국통신학회논문지
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• 제19권2호
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• pp.225-230
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• 1994

전자장 해석을 위한 많은 수식들이 전계형 적분방정식으로 수식화되어 여러 가지 수치적인 방법으로 해석되어진다. 일반적으로 이 식은 특이점을 갖는 Kernel로 표현되어지며, 주어진 문제에 따라 식이 간략화 되어지지 않으면 해석시 수직과 프로그램이 복잡하여진다. 본 논문에서는 BOR구조의 도체에 적용할 수 있는 새로운 적분방정식을유도하였으며, 이 식은 직선형 wire도체의 경우에 더욱 간략화 되어진다. 동축선로로 급전되어지는 monopole안테나와 임의의 각도로 입사하는 평면파에 의한 도체의 산란문제를 응용예로서 다루었다.

• KIEAE Journal
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• 제10권4호
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• pp.75-80
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• 2010

Generally, ground-source heat pump (GSHP) systems have a higher performance than conventional air-source systems. However, the major fault of GSHP systems is their expensive boring costs. Therefore, it is important issue that to reduce initial cost and ensure stability of system through accurate prediction of the heat extraction and injection rates of the ground heat exchanger. Conventional analysis methods employed by line source theory are used to predict heat transfer rate between ground heat exchanger and soil. Shape of ground heat exchanger was simplified by equivalent diameter model, but these methods do not accurately reflect the heat transfer characteristics according to the heat exchanger geometry. In this study, a numerical model that combines a user subroutine module that calculates circulation water conditions in the ground heat exchanger and FEFLOW program which can simulate heat/moisture transfer in the soil, is developed. Heat transfer performance was evaluated for 3 different types ground heat exchanger(U-tube, Double U-tube, Coaxial).