• 한국연소학회지
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• 제11권3호
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• pp.8-17
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• 2006

When a flame is stabilized in a tube of a finite thickness, a conductive heat transfer through the tube significantly changes the wall temperature and affects the flame characteristics. Thus the tube length and thermal boundary conditions affect on the structure of the flame in a conductive tube. A one-dimensional analytical study was conducted by employing two energy equations for tubes and mixtures and a species equation for the mixture. Variation of the maximum temperatures and indicating displacements were observed. A parametric study on the effects of inner Peclet numbers, normalized wall conductivities, and heat transfer conditions of the tube was conducted. This study provides essential data for a more efficient computational simulation of the flame stabilized in conductive tubes.

• 한국수소및신에너지학회논문집
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• 제29권5호
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• pp.512-522
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• 2018

This study was conducted to investigate on the combustion characteristic with the effects of mat thickness and fuel kinds in a metal-fiber burner. The mode transition point is confirmed by the K value, which was defined as the rate of flow velocity and laminar burning velocity. The ($T^4_{sur}-T^4_{\infty}$) is highest at methane flame with 3 T thickness. Through the measurement of the unburned mixture temperature, the possibility of submerged flame in surface combustion burner was confirmed. The rapid emission of CO occurs nearby limit blow out (LBO) because of the increase of flow velocity. In case of NOx, the trend is similar with surface temperature. However, it also considered that the NOx emission is affected by residence time with flame position.

• Journal of Advanced Marine Engineering and Technology
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• 제23권4호
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• pp.593-600
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• 1999

The structure of premixed turbulent flames in constant volume vessel was investigated by using a laser tomography. The flame structure was visualized by passing a laser sheet with 0.2mm thick and 2 cm wide through the turbulent flames to obtain their 2-D images. From the obtained images islands of reactants as well as of products were found at least in the 2-D images when the turbu-lence intensity was above 0.4m/s. Moreover in order to obtain the characteristic flamelet thickness the light intensities of them were digitized and processed into three colors incorporating two appro-priate threshold values in the image analysis. As the result the averaged value of charactertistic flamelet thickness was found to be about two times compared to laminar one.

• 한국세라믹학회지
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• 제35권6호
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• pp.569-574
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• 1998

자체의 반응열에 의해 반응이 자발적으로 진행되는 SHS법을 이용하여 $Ti_3AI$ 금속간 화합물의 생성반응에서의 화염대 두계, 반응속도 그리고 겉보기 활성화에너지에 대하여 고찰하였다. 이 반응에서 화염대 두께는 1.4mm이었고, 반응속도는 $0.4g/\textrm{cm}^2{\cdot}sec$이었다. 또한, 반응물의 상대밀도를 조절하여 얻은 실험 data를 이용하여 구한 반응의 겉보기 활성화에너지는 40kJ/mol이었다.

• 한국기계가공학회지
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• 제17권6호
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• pp.38-45
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• 2018

Molybdenum flame spray coatings are widely used in industrial fields to enhance the performance of mechanical component parts such as pistons, shafts and clutches. This study investigates the surface characteristics of high tensile brass with molybdenum flame spray treatment using the clutch material for small ship. The surface characteristics after molybdenum flame spray treatment in high tensile brass were quantitatively analyzed for surface composition, coating layer thickness, friction coefficient, abrasion width and phenomenon, micro-hardness, and surface roughness.

• Korean Chemical Engineering Research
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• 제47권5호
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• pp.572-579
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• 2009

본 연구에서는 분진폭발에 있어서 기초적 현상을 규명하고 분진의 화염구조와 메커니즘에 대하여 실험적으로 조사하였다. 실험장치는 길이 1.8 m, 단면이 0.15 m의 정방형인 수직연소관을 사용하였으며, 덕트 내를 전파하는 상방 분진층류화염과 화염면에 대하여 고속카메라를 사용하여 가시화하였다. 또한 슐리렌, 이온프로브, 열전대 등을 사용하여 예열대 및 반응대의 두께를 측정하였다. 석송자 분진화염의 예열대 두께는 4~13 mm로 탄화수소가스의 예혼합기 화염보다도 수배 크다. 입자화상유속법(PIV)에 의한 해석 결과, 예열대에서의 미연소 입자의 체류 시간은 입자의 열분해가스 생성에 필요하며, 체류시간은 화염전파속도, 입자속도 및 예열대 두께에 의존하는 것을 알았다.

• 대한기계학회논문집B
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• 제21권1호
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• pp.125-131
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• 1997

The extinction of premixed flames under the influence of stretch is studied numerically. A wide range of fuel (hydrogen, ethylene, acetylene, methane, propane and methanol) and air mixtures are established in an opposed jet and their flame properties such as flame speed, flame thickness, thermal diffusivity, and stretch rate at extinction are computed. Computations are made using several chemical kinetic mechanism (Smooke, Kee et al. and Peters). The major result is that, in contrast to the various previous claims of extinction Karlovitz number varying over three orders of magnitude, it is found to be constant around two for all of the mixtures tested. That is, premixed flames are extinguished when the physical flow time decreases (due to increased stretch rate) to the point where it approximately equals the chemical reaction time. Here the relevant chemical reaction time is not the one computed using the one-dimensional flame properties as originally suggested in the formulation of Karlovitz number, but rather it is the one obtained using the stretched flame properties which fully reflect the effect of straining on the flame structure.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.77-82
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• 2000

Numerical simulations of freely propagating flames burning stoichiometric $CH_4$/$O_2$/$N_2$ mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$ enrichment level on $CH_4$/Air flame. A chemical kinetic mechanism is employed, the adopted scheme involving 54 gas-phase species and 632 forward reactions. The calculated flame. speeds are compared with the experiments for the flames established at several $O_2$ enrichment level, the results of which is in excellent agreement. As a result of the increased $O_2$ enrichment level from 0.21 to 1, the mole fraction of CO in the burned gas is increased. The flame speed and the temperature in the burned gas are also increased, but the thickness of the flame is severely shrunken in the preheat region.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.386-397
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• 2012

The stability and structure of bluff-body stabilized hydrogen flames were investigated numerically and experimentally. The velocity of coflowing air was varied from subsonic velocity to a supersonic velocity of Mach 1.8. OH PLIF images and Schlieren images were used for analysis. Flame regimes were used to classify the characteristic flame modes according to the variation of the fuel-air velocity ratio, into jet-like flame, central-jet-dominated flame, and recirculation zone flame. Stability curves were drawn to find the blowout regimes and to show the improvement in flame stability with increasing lip thickness of the fuel tube, which acts as a bluff-body. These curves collapse to a single line when the blowout curves are normalized by the size of the bluff-body. The variation of flame length with the increase in air flow rate was also investigated. In the subsonic coflow condition, the flame length decreased significantly, but in the supersonic coflow condition, the flame length increased slowly and finally reached a near-constant value. This phenomenon is attributed to the air-entrainment of subsonic flow and the compressibility effect of supersonic flow. The closed-tip recirculation zone flames in supersonic coflow had a reacting core in the partially premixed zone, where the fuel jet lost its momentum due to the high-pressure zone and followed the recirculation zone; this behavior resulted in the long characteristic time for the fuel-air mixing.

• 한국세라믹학회지
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• 제37권6호
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• pp.524-529
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• 2000

Silica slab wavegudie was fabricated on Si substrates by FHD for planar optical passive devices. The slab waveguide consists of lower clad and core layers, where core layer index is controlled by GeO2 addition. Doping of GeO2 in silica is difficult because of the low deposition density due to nonspherical particle generation in FHD process. Silica core particles deposited at various conditions such as flame temperature and substrate scanning were analyzed by SEM and TEM. As the flame temperature increased, the surface roughness of the core layer was decreased up to 3.6 nm after consolidation. Index difference and thickness of core of slab waveguide were 0.3%, 8$\mu\textrm{m}$ respectively. Measured optical loss at TE mode was <0.04 dB/cm at 1.3$\mu\textrm{m}$ and <0.06 dB/cm at 1.55$\mu\textrm{m}$.