• 한국연소학회지
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• 제7권1호
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• pp.23-30
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• 2002

Instability of oblique detonation waves (ODW) at off-attaching condition was investigated through a series of numerical simulations. Two-dimensional wedge of finite length was considered in $H_2/O_2/N_2$ mixtures at superdetonative condition. Numerical simulation was carried out with a compressible fluid dynamics code and a detailed hydrogen-oxygen combustion mechanism. Present result reveals that there is a chemical kinetic limit of the ODW detachment, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. Result also presents that ODW still attaches at a wedge as an oblique shock-induced flame showing periodically unstable motion, if the Rankine-Hugoniot limit of detachment is satisfied but the chemical kinetic limit is not. Mechanism of the periodic instability is considered as interactions of shock and reaction waves coupled with chemical kinetic effects. From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of the Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2139-2144
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• 2003

In steel-making processes of iron and steel industry, the purity and quality of steel can be dependent on the amount of CO contained in the molten metal. Recently, the supersonic oxygen jet is being applied to the molten metal in the electric furnace and thus reduces the CO amount through the chemical reactions between the oxygen jet and molten metal, leading to a better quality of steel. In this application, the supersonic oxygen jet is limited in the distance over which the supersonic velocity is maintained. In order to get longer supersonic jet propagation into the molten metal, a supersonic coherent jet is suggested as one of the alternatives which are applicable to the electric furnace system. It has a flame around the conventional supersonic jet and thus the entrainment effect of the surrounding gas into the supersonic jet is reduced, leading to a longer propagation of the supersonic jet. The objective of the present study is to investigate the supersonic coherent jet flow. A computational study is carried out to solve the compressible, axisymmetric Navier-Stokes equations. The computational results of the supersonic coherent jet are compared with the conventional supersonic jet.

• 한국연소학회지
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• 제5권1호
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• pp.43-53
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• 2000

Experimental studies on determination of the supply leading time of propellants to combustion chamber have been made to stably and efficiently guarantee the ignition process with liquid rocket engine. The propellant used is a Jet A-1 as fuel and a liquid oxygen as oxidizer. Unlike impinging FOOF type of injectors are arranged radially and the designed O/F ratio is 2.34. The present experiment program also includes the stability on the quadlet type of ignitor using the triethylalumimum as an ignition source and injector life tests. Experimental results clarifies that the propellant supply through LOx leading to combustion chamber is proper for stable ignition and combustion processes based on the fuel and oxidizer manifold pressures, combustion chamber pressure, and the variation of flame length from the nozzle exit with lapse time, and shows that the leading supply time of propellants affects the engine performance little. The effect of positioning cooling holes is remarkable to protect the injector face.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.803-810
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• 2017

초임계 조건에서의 연소반응에서는 액체산소가 초임계 상태로 천이되며 스도보일링과 급격한 물성치변화를 발생시킨다. 이때 초임계 상태에서 작동하는 분사기의 연소반응은 급격한 밀도차로 인한 난류확산에 의해 지배되며, 따라서 스도보일링과 함께 발생하는 확산유동에 대한 연구가 필요하다. 많은 연구자들에 의해 초임계 연소해석에서 발생하는 이 현상들에 대한 연구가 진행되었지만 다양한 변수들에 의한 사례연구가 부족한 상태이다. 본 연구에서는 초임계 압력조건에서 산화제-연료비(O/F)와 연소기 직경, 리세스비를 통해 재순환유동 및 액체산소코어 길이에 변화를 주어 이로 인한 유동구조 및 화염구조의 변화를 수치적으로 연구하였다.

• 펄프종이기술
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• 제40권1호
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• pp.23-28
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• 2008

Functional hanji was manufactured using the bast fiber of Broussonetia kazinoki and various inorganic compounds such as kaolin, talc, elvan, and ocher, and the physical and optical properties were investigated. The residual percentages of kaolin, talc, elvan and ocher in the functional hanji were above 50%. The density of the hanji increased with the increase of the content of inorganic compounds. The hanji manufactured using ocher showed the highest density. The breaking length and burst factor decreased with the increase of inorganic materials, indicating that physical properties of hanji were not improved by adding inorganic materials. The emission rates of far-infrared radiation increased in the hanji manufactured using inorganic materials. The higher emission rates were observed in the hanji with elvan or ocher. Addition of inorganic compounds to hanji showed the flame retardative effect. The colorfastness to light of the hanji with elvan or ocher was the degree of 4, which explained by the characteristic color of the inorganics.

• 한국수산과학회지
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• 제14권4호
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• pp.217-220
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• 1981

1980년 9월부터 1981년 8월까지 충남 서천군 서면솔리 해역의 바지락에서 검은 1상의 안점과 염세포가 명백하여 꼬리가 긴 Cercaria tapidis의 기생률과 기생된 바지락의 크기와 충체의 형태를 관찰하였다. Sporocyst의 크기는 $75\sim1550\times210\sim320{\mu}m$ 이고. 그 내부에 60여 개의 배세포와 발육중인 cercaria가 충만되어 있었다. cercaria의 충체부는 $245\sim320\times105\sim130{\mu}m$으로 타원형이고 꼬리늘 $1225\sim1650\times40\sim50{\mu}m$로 가늘고길며 충체부의 5배나 되었다. Cercaria의 flame cell 식은 [(2+3+2)+(3+3)]=30 이다. 총 2086개체의 바지락을 조사한 결과 120개체($5.75\%$)에서 기생된 Cercaria tapidis 검출하었다. 가장 높은 기생률은 12월로서 $23.27\%$였고, 가장 낮은 계절은 5월로서 $0.85\%$였다. 바지락의 각장별기생률을 보면 $3.1\sim4.0cm$의 3년생에서 $3.78\%$로서 가장 많이 검출되었다. $2.1\sim3.0cm$ 크기에서 $1.34\%$, $4.1\sim5.0cm$에서 $0.52\%$로 낮은 기생률이었다.

• 감성과학
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• 제24권4호
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• pp.149-156
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• 2021

본 연구에서는 1500℃ 이상의 극한 열 환경에서 사용되는 소재인 SiC (silicon carbide) 섬유를 복합방적사로 제조한 후에 원단을 제직하고 제직된 원단의 역학적 특성을 KES-FB system으로 측정하고 측정된 역학적 특성 값으로부터 착용성능을 분석하여 방화복으로의 활용 가능성을 알아보았다. 그 결과 직물의 역학적 특성에서는 인장선형성(LT)과 인장레질리언스(RT), 전단강성(G)을 나타내는 값이 원사의 제조형태에 따라서 그 특성 값의 차이를 보였으며, 직물의 두께와 평량, 밀도 값이 전단히스테리시스(2HG)와 압축레질리언스(RC) 값에 영향을 준다는 것을 알 수 있었다. 의복착용 성능에서는 착용 시 부피감을 나타내는 두께에 대한 압축에너지의 비(WC/T) 값에서 SiC 복합방적사로 제조된 직물의 값이 가장 우수한 값을 타나내었으며, 방염성능에서는 SiC 복합방적사로 제조된 직물이 탄화길이와 잔염시간에서 KFI 성능기준을 만족하여 방화복으로서의 활용이 가능함을 확인할 수 있었다.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1457-1463
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• 2000

Experimental studies on determination of the supply leading time of propellants to combustion chamber have been made to stably and efficiently guarantee the ignitions process with liquid rocket engine. The propellant used is a Kerosene as fuel and a liquid oxygen as oxidizer. FOOF type of three injectors are set with an angle of 135。 and the combustion chamber pressure is 200psi. The present experiment program also includes the stability on the quadlet type of ignitor using the triehylaluminum (TEAL) as an ignition source. Experimental results clarifies that the propellant supply through LOx leading to combustion chamber is proper for stable ignition and combustion processes based on the fuel and oxidizer manifold pressures, combustion chamber pressure, and the variation of flame length from the nozzle exit with lapse time, and shows that the leading supply time pf propellants effects the engine performance little.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.135-135
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• 2003

The fast evolution in the fold of optical communication systems demands powerful optical information treatment. These functions can be performed by integrated optical systems. A key component of such systems is erbium doped waveguide amplifier(EDWA). The intra 4f radiative transition of Er at 1.5 $\mu\textrm{m}$ is particularly interesting because this wavelength is standard in optical telecommunications. The fabrication of waveguide amplifier for integrated optics using sol-gel process has received an increasing attention. Potential advantage of lower cost by less capital equipment and easy processing makes this process an attractive alternatives to conventional technologies like flame hydrolysis deposition, ion exchange and chemical vapor deposition, etc. In addition, sol-gel process has been found to be extremely suitable for the control of composition and refractive index related directly with optical properties. The main drawback of such an amplifier with respect to the EDWA is the need for a much higher Er3+ concentration to compensate for the smaller interaction length. However, the high doping of Er might be resulted in the non-radiative relaxation by clustering of Er ions End co-operative upconversion. In order to solve this problem, we investigate the possibility of avoiding short Er-Er distances by encapsulation of Er3+ ions in hosts such as organic-inorganic hybrid materials. For inorganic-organic hybrid sols, methacryloxypropyltrimethoxysilane (MPTS), zirconyl chloride octahydrate and erbium(III) chloride hexahydrate were used as starting materials, followed by conventional sol-gel process. It was observed by TEM that nano sols having core/shell toplology were formed, depending on the mole ratio of Zr/Er. The surface roughness for the coatings on Si substrate was investigated by AFM as a function of Zr/Er ratio. The local environment and vibrational Properties of Er3+ ions were studied using Near-IR, FT-IR, and UV/Vis spectroscopy. Nano hybrid coatings derived from polymer and Er doped encapsulation Eave the good luminescence at 1.55$\mu\textrm{m}$.

• 한국연소학회지
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• 제10권2호
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• pp.26-34
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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 $\lambda=1.1$, the CO emission increased as the $CO_2$ feeding flow rate increased.