• 센서학회지
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• 제20권1호
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• pp.1-7
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• 2011

Undoped and Sb-doped $SnO_2$ nanofibers were prepared by electrospinning and their responses to $H_2$, CO, $CH_4$, $C_3H_8$, and $C_2H_5OH$ were measured. In the undoped $SnO_2$ nanofibers, the gas response ($R_a/R_g$, $R_a$: resistance in air, $R_g$: resistance in gas) to 100 ppm $C_2H_5OH$ was very high(33.9), while that to the other gases ranged from 1.6 to 2.2. By doping with 2.65 wt% Sb, the response to 100 ppm $C_2H_5OH$ was decreased to 4.5, whereas the response to $H_2$ was increased to 3.0. This demonstrates the possibility of detecting a high $H_2$ concentration with minimum interference from $C_2H_5OH$ and the potential to control the gas selectivity by Sb doping.

• 한국결정성장학회지
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• 제10권2호
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• pp.105-110
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• 2000

APCVD(Atrmos phere Pressure Vapor Deposition)법으로 $\alpha$-$Fa_{2}O_{3}/SnO_{2}$계 박막 가스센서 소자를 제조하여 열처리(Heat treatment)하였으며, 가연성 가스($CH_4$, $H_2$, LPG)에 대하여 감지 특성(Sensitivity)을 측정하였다. 감지특성 향상을 위해 소자를 $400^{\circ}C$, $450^{\circ}C$, $500^{\circ}C$, $550^{\circ}C$, $600^{\circ}C$에서 각각 2시간동안 열처리하였으며 $500^{\circ}C$에서 2시간 동안 열처리하였을 때 가장 우수한 감응도를 조사하였다. 특히 $H_2$에 대하여 가장 민감한 반응을 보였다. 최적의 작동온도를 찾기 위해 $100^{\circ}C$~$300^{\circ}C$으로 변화하며 가스 감응도를 조사하였다. 제작된 소자는 작동온도 $175^{\circ}C$, 측정 범위 500ppm ~ 10,000ppm에서 $H_2$일 경우 감지도가 62%~76%를 가졌으며, $CH_2$의 경우 16%~58%, LPG의 경우 8%~37%이였다. 또한 열처리한 것과 안한 것의 감응도의 차이는 약 10%이었다. LPG 1,000ppm에서의 장기안정성은 감응도 30%의 값으로 수렴하였다.

• 천문학회보
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• 제42권2호
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• pp.72.1-72.1
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• 2017

Energetic ionized gas outflows driven by active galactic nuclei (AGN) have been studied as a key phenomenon related to AGN feedback. To probe the kinematics of the gas in the narrow line region, [O III] ${\lambda}5007$ has been utilized in a number of studies, showing non-virial kinematic properties due to AGN outflows. We statistically investigate whether the $H{\alpha}$ emission line is influenced by AGN driven outflows, by measuring the kinematic properties based on the $H{\alpha}$ line profile, and by comparing them with those of [O III]. Using the spatially integrated spectra of ~37,000 Type 2 AGNs at z < 0.3 selected from the SDSS DR7, we find a non-linear correlation between $H{\alpha}$ velocity dispersion and stellar velocity dispersion, which reveals the presence of the non-gravitational component, especially for AGNs with a wing component in $H{\alpha}$. The large $H{\alpha}$ velocity dispersion and velocity shift of luminous AGNs are clear evidence of AGN outflow impacts on $H{\alpha}$ emitting gas, while relatively smaller kinematic properties compared to those of [O III] imply that the observed outflow effect on the $H{\alpha}$ line is weaker than the case of [O III].

• 대한기계학회논문집B
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• 제27권7호
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• pp.893-900
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• 2003

Numerical simulations of freely propagating flames burning stoichiometric C $H_4$/CHC1$_3$/ $O_2$/$N_2$ mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$ enrichment level and the CHC1$_3$/C $H_4$ molar ratio. A chemical kinetic mechanism is developed, which involves 69 gas-phase species and 379 forward and 364 backward reactions. The calculated flame speeds are compared with the experiments for the flames established at several CHC1$_3$/C $H_4$ molar ratio (R<1), the results of which is in excellent agreement. As a results of the increased $O_2$ enrichment level from 0.21 to 1, the flame speed and the temperature in the burned gas are increased. At high CHC1$_3$/C $H_4$ molar ratio two peak values appear on the $O_2$ consumption rate, which are affected by CC1$_2$＋ $O_2$$_{-}$>C1O+CC1O and H＋ $O_2$$_{-}$>O＋OH.＋OH.

• 대한기계학회논문집B
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• 제30권2호
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• pp.101-109
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• 2006

The narrow band-averaged transmissivity of $CO_2-H_2O$ mixtures is expressed by multiplying the transmissivities of $CO_2\;and\;H_2O$. Applying the multiplication property of narrow band transmissivities for gas mixtures of $CO_2-H_2O$ of the narrow band based WSGGM (weighted sum of gray gases model), the number of gray gases, required for accurate representation of the absorption characteristics by using the narrow band based WSGGM, is significantly increased. To reduce the computational loads by reducing the number of gray gases, we propose a gray gas regrouping process where the gray gases used for .the WSGGM are regrouped into a specified number of groups according to the magnitudes of absorption coefficients. To evaluate the proposed WSGGM for gas mixtures, the radiative transfer problems through 3-dimensional gas media are considered. The radiative source terms and the radiative heat fluxes obtained by using the proposed method are fairly well compared to previous results obtained by using the SNB model and other models. The regrouping technique results in an excellent computational efficiency with minor loss of accuracy.

• 한국세라믹학회지
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• 제40권11호
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• pp.1073-1077
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• 2003

Sn $O_2$ 가스센서는 낮은 농도의 가연성 가스 및 유독 가스를 표면 저항의 변화로부터 탐지할 수 있으나, 가스 선택성이 부족하다는 단점을 가지고 있다. 이러한 단점을 보완하기 위해서는 가스반응기구의 규명과 같은 기초이론 연구와 함께 선택성이 우수한 센서재료의 개발 및 적절한 신호처리방법의 적용이 필요하다. 본 논문에서는 Sn $O_2$ 표면에서 일어나는 에탄올 (C$_2$ $H_{5}$OH)과 아세토니트릴($CH_3$CN)의 촉매산화반응을 가스크로마토그래피 분석을 통해 확인하였다. PdCl$_2$가 첨가된 Sn $O_2$ 센서는 에탄올과 아세토니트릴에 대하여 높은 감도를 보였고, 반면에 La$_2$ $O_3$가 첨가된 Sn $O_2$ 센서는 에탄올에 대해서는 높은 감도를, 그리고 아세토니트릴에 대해서는 낮은 감도를 보였다. 이들 두 센서재료 개발 및 패턴인식기법적용을 통하여 아세토니트릴에 대한 선택성을 크게 증가시킬 수 있었다. 아세토니트릴에 대한 최소 탐지농도는, 공기 중에서는 15 ppm이었고, 다른 방해가스와 함께 존재할 경우에는 20 ppm에서 100 ppm 정도로 나타났다.

• 한국표면공학회지
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• 제50권2호
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• pp.85-90
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• 2017

The carbon steel formed the thick, somewhat porous, loosely adherent iron oxide scale when oxidized at $500-800^{\circ}C$ for 15 h in air. It formed the thicker, more porous, nonadherent scale consisting of FeS plus iron oxides in $Ar/1%SO_2$-mixed gas. It formed the much thicker, more porous, nonadherent scale consisting of FeS plus iron oxides in Ar/0.1% $H_2S$-mixed gas. However, the aluminized carbon steel formed the thin, protective $Al_2O_3$ surface scale even in $Ar/1%SO_2$-, and $Ar/0.1%H_2S$-mixed gas. Aluminizing drastically improved the corrosion resistance in (O, S, H)-containing gas.

• 한국대기환경학회지
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• 제23권2호
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• pp.225-241
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• 2007

A closed flux chamber system was used for measuring major greenhouse gas (GHG) emission from tideland and/or wetland soils in estuarine area at Saemankum, Kunsan in southwestern Korea during from months of February to June 2006. Hourly averaged GHG soil emissions were measured two to three times a day during the ebb tide hours only. Site soils were analyzed for soil parameters (temperature, pH, total organic contents, N and C contents in soil) in the laboratory. Soil GHG fluxes were calculated based on the GHG concentration rate of change measured inside a closed chamber The analysis of GHG was conducted by using a Gas Chromatography (equipped with ECD/FID) at laboratory. Changes of daily, monthly GHGs' fluxes were examined. The relationships between the GHG emissions and soil chemical contents were also scrutinized with respect to gas production and consumption mechanism in the soil. Soil pH was pH $7.47{\pm}0.49$ in average over the experimental period. Organic matter contents in sample soil was $6.64{\pm}4.98\;g/kg$, and it shows relatively lower contents than those in agricultural soils in Kunsan area. Resulting from the soil chemistry data, soil nitrogen contents seem to affect GHG emission from the tidal land surface. The tidal soil was found to be either source or sink for the major GHG during the experimental periods. The annual average of $CH_{4}\;and\;CO_{2}$ fluxes were $0.13{\pm}0.86\;mg\;m^{-2}h^{-1}\;and\;5.83{\pm}138.73\;mg\;m^{-2}h^{-1}$, respectively, which will be as a source of these gases. However, $N_{2}O$ emission showed in negative flux, and the value was $-0.02{\pm}0.66\;mg\;m^{-2}h^{-1}$, and it implies tidal land surface act as a sink of $N_{2}O$. Over the experimental period, the absolute values of gas fluxes increased with soil temperature in general. Averages of the ambient gas concentration were $86.8{\pm}6.\;ppm$ in $CO_{2},\;1.63{\pm}0.34\;ppm\;in\;CH_{4},\;and\;0.59{\pm}0.15\;ppm\;in\;N_{2}O$, respectively. Generally, under the presence of gas emission from agricultural soils, decrease of gas emission will be observed as increase in ambient gas concentration. We, however, could not found significant correlation between the ambient concentrations and their emissions over the experimental period. There was no GHG compensation points existed in tide flat soil.

• 오토저널
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• 제5권4호
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• pp.47-61
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• 1983

In this paper the simulation of a thermodynamic power cycle for a 4-stroke, single-cylinder, spark-ignition engine was studied. In this simulation the cylinder volume was restricted to two zones, a burnt and an unburnt zone, and the convective heat transfer from cylinder contents to surroundings was considered. The chemical species in burnt gas considered was 12 species including H$_{2}$O, H$_{2}$, OH, H, N$_{2}$, NO, N, CO$_{2}$, CO, $O_{2}$, O and Ar. Using this model, computer program for compression, ignition and expansion processes was composed and pressure, temperature and composition of cylinder gas at each crank angle were computed. The composition of CO$_{2}$, CO, $O_{2}$ in the burnt gas when exhaust valve opens, the maximum temperature, the maximum flame speed and the combustion duration were also computed as a function of equivalence ratio. The relation between burnt mass fraction and burnt volume fraction was also computed.

• 한국재료학회지
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• 제25권5호
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• pp.238-246
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• 2015

$H_2S$ is a flammable toxic gas that can be produced in plants, mines, and industries and is especially fatal to human body. In this study, CuO nanowire structure with high porosity was fabricated by deposition of copper on highly porous singlewall carbon nanotube (SWCNT) template followed by oxidation. The SWCNT template was formed on alumina substrates by the arc-discharge method. The oxidation temperatures for Cu nanowires were varied from 400 to $800^{\circ}C$. The morphology and sensing properties of the CuO nanowire sensor were characterized by FESEM, Raman spectroscopy, XPS, XRD, and currentvoltage examination. The $H_2S$ gas sensing properties were carried out at different operating temperatures using dry air as the carrier gas. The CuO nanowire structure oxidized at $800^{\circ}C$ showed the highest response at the lowest operating temperature of $150^{\circ}C$. The optimum operating temperature was shifted to higher temperature to $300^{\circ}C$ as the oxidation temperature was lowered. The results were discussed based on the mechanisms of the reaction with ionosorbed oxygen and the CuS formation reaction on the surface.