• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.1039-1046
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• 2002

Co-flow axisymmetric laminar premixed flame of methane was used to study the influence of air temperature and $N_2$ addition on the flame structure, temperature field and emission characteristics. OH 2-D images and temperatures along the centerline were measured experimentally by PLIF and CARS techniques respectively to observe the influences of dilution and thermal effects of $N_2$ in the gas mixture. Also, the concentration of NOx was measured at each condition by gas analyser to see the suppression effect of N2 addition on NOx emissions. It was found that OH concentrations distribute widely as air temperature goes higher, while the effect of $N_2$ addition is not significant. But $N_2$ addition highly contributes to the flame front and NOx emissions which was argued to be due to the reduction of flame temperature. In accordance with experimental study, numerical simulation using CHEMKlN code was carried out to compare the temperature results with those acquired by CARS measurement, and we could find that there is good agreement between those results.

• Journal of the Korean Institute of Gas
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• v.15 no.2
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• pp.75-81
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• 2011

For the safe handling of cyclohexane, the explosion limit at $25^{\circ}C$ and the temperature dependence of the explosion limits were investigated. Flash point and AIT(autoignition temperature) for cyclohexane were experimented. By using the literatures data, the lower and upper explosion limits of cyclohexane recommended 1.0 Vol% and 9.0 Vol%, respectively. Moreover lower flash points of cyclohexane recommended $-20^{\circ}C$. It was measured relationship between the AITs and the ignition delay times by using ASTM E659-78 apparatus for cyclohexane, and the experimental AIT was $255^{\circ}C$. The new equations for predicting the temperature dependence of the explosion limits of cyclohexane is proposed. The values calculated by the proposed equations were a good agreement with the literature data.

• Nuclear Engineering and Technology
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• v.38 no.1
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• pp.99-108
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• 2006

SNU-RCCS is a water pool type RCCS (Reactor Cavity Cooling System) developed for VHTR (Very High Temperature Reactor) application by SNU (Seoul National University). Since radiation heat transfer is the major process of passive heat removal in a RCCS, it is important to determine the precise emissivity of the reactor vessel. Review studies have used a constant emissivity in the passive heat removal analysis, even though the emissivity depends on many factors such as temperature, surface roughness, oxidation level, wavelength, direction, atmosphere conditions, etc. Therefore, information on the emissivity of a given material in a real RCCS is essential in order to properly analyze the radiation heat transfer in a VHTR. The objectives of this study are to develop a method for compensation of the factors affecting the emissivity measurement using an infrared thermometer and to estimate the true emissivity from the measured emissivity via the developed method, especially in the SNU-RCCS environment. From this viewpoint, we investigated factors such as the attenuation effect of the window, filling gas, and the effect of background radiation on the emissivity measurements. The emissivity of the vessel surface of the SNU-RCCS facility was then measured using a sight tube. The background radiation was subsequently removed from the measured emissivity by solving a simultaneous equation. Finally, the calculated emissivity was compared with the measured emissivity in a separate emissivity measurement device, yielding good agreement with the emissivity increase with vessel temperature in a range of 0.82 to 0.88.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.73-79
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• 2010

Propellant tank pressurizing gas injector is used in the pressurization system of liquid propellant rocket to reduce incoming gas velocity and distribute the gas in the tank. Temperature distribution in the propellant tank ullage is varied according to the gas injector shape, and it has influence on the required pressurant gas and thermal phenomena in the tank. In this paper, diffuser type gas injector was studied to make the ullage have stratified temperature distribution. Injected gas flow at the outlet of prototype diffuser was visulized using particle image velocimetry method and it was compared with the results of calculation. Calculation was well agreed with measurement and was used as an inlet condition of propellant tank ullage calculation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.572-578
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• 2001

This study conducts a laboratory measurement on a cylindrical electrostatic precipitator(ESP) with a 30mm-diameter cylinder. Several kinds of test aerosols are generated with an atomizer and a diffusion dryer. The effects of applied voltage, flow state, gas velocity, and gas temperature on the electrical characteristics of the precipitator and onset of corona are experimentally investigated. The corona onset voltage is decreased, as diameter of discharge electrode wire becomes small or temperature of the precipitator increases. As the fluid velocity or particle load in the precipitator increases, the corona current is decreased.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1039-1040
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• 2006

Vacuum degassing is essential in the preparation of RS P/M aluminum alloys to remove adsorbates and for the decomposition of hydrated-$Al_{2}O_3$ on the powder surface. Changes in the surface characteristics during vacuum degassing were investigated by X-ray photoelectron spectroscopy and temperature-programmed desorption measurement. Hydrated-$Al_{2}O_3$ decomposition to crystalline-$Al_{2}O_3$ and hydrogen desorption on the surface of argon gas-atomized aluminum powder occurred at 623 K and 725 K, respectively. This temperature difference suggests that the reaction converting hydrated-$Al_{2}O_3$ to crystalline-$Al_{2}O_3$ during vacuum degassing should be divided into the two reactions $"2Al+Al_{2}O_3{\cdot}3H_2O\;2Al_{2}O_3+6H_{surf}"and"6H_{surf}3H_2"$.

• Journal of the Korean Ceramic Society
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• v.28 no.3
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• pp.179-188
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• 1991

The semiconducting BaTiO3 ceramics used in this study were sintered in the reducing atomosphere(hydrogen gas) and neutral atmosphere(nitrogen gas), then were heat-treated in air to vary defect concentrations. In this experiment, the correlations between the composition analysis and electrical characteristics of these samples were investigated. When the BaTiO3 ceramics were sintered in N2 atmosphere, it was observed that the Ba contents near the interface were lower than that of the grain center, and these samples showed superior PTCR effects. From analysis of the resistivities of grains and grain boundaries by CIRM(Complex Impedance Resonance Method), it was confirmed that the PTCR effects were caused by the resistivity of grain boundaries. And from measurement of the capacitance at each temperature, the samples sintered in N2 atmosphere show the increase of room temperature resistance and the decrease of capacitance as a result of the increase of the charge depletion layers. This phenomenon agrees well with the cation deficiencies in the analytical results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.319-320
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• 2007

We researched basic study about electrical characteristics of Zinc Selenide (Faraday Cell), which is known for various temperature of good-performance, that applied measuring current or protecting instrument by Optical Current Transducer, on Gas Insulated Switchgear. Measuring System consists of VCSEL produced 850nm IR Laser, Pin Photo Diode made of GaAs surveyed as Optical Power Meter, and Optical Fibers specified Multi-mode. We observed optical output changes during measurement of currents increasing by 100[A] in range from 0[A] to 1,000[A] and set temperature condition increasing by $5[^{\circ}C]$ in a range from $30[^{\circ}C]\;to\;60[^{\circ}C]$.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.11a
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• pp.69-71
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• 1993

Fluoride compound potentiometric cell oxygen sensors were fabricated for the measurement of oxygen pressure in the low temperature range (300。K-500。K). The disk type sensors consist of a reference Air(0$_2$):Ag, a solid electrolyte SrF$_2$, and a sensing metel Ag electrode. And the buried reference electrode type sensor have a NiO/Ni reference electrode. The open circuit emf of the cell showed high sensivity to oxygen gas (60mv) at the measuring temperature 20$0^{\circ}C$. Also, The buried reference electrode type sensor showed 30mv from 1% to 10% oxygen pressure range.

• Journal of Information Processing Systems
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• v.1 no.1 s.1
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• pp.36-40
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• 2005

TRISO (Tri-Isotropic)-coated fuel particle is widely applied due to its higher stability at high temperature and its efficient retention capability for fission products in the HTGR (high temperature gas-cooled reactor), one of the highly efficient Generation IV reactors. The typical ball-type TRISO-coated fuel particle with a diameter of about 1 mm is composed of a nuclear fuel particle as a kernel and of outer coating layers. The coating layers consist of a buffer PyC, inner PyC, SiC, and outer PyC layer. In this study, a digital image processing algorithm is proposed to automatically measure the thickness of the coating layers. An FBP (filtered backprojection) algorithm was applied to reconstruct the CT image using virtual X-ray radiographic images for a simulated TRISO-coated fuel particle. The automatic measurement algorithm was developed to measure the coating thickness for the reconstructed image with noises. The boundary lines were automatically detected, then the coating thickness was circularly by the algorithm. The simulation result showed that the measurement error rate was less than 1.4%.