• Analytical Science and Technology
• /
• v.19 no.6
• /
• pp.553-558
• /
• 2006

In this study, an attempt was made to measure uncertainties involved in the VOC analysis for the VOC working standards prepared by a dilution technique using Tedlar bags. For this purpose, VOC standard gases of benzene, toluene, xylene, and styrene were prepared at four different concentrations (4, 8, 20, and 40 ppb). These standard samples were then loaded on to the GC system equipped with air server/thermal desorption (AS/TD) system. Each of these four standard concentrations was analyzed individually to derive their respective calibration results. These calibration data sets were then compared across four different compounds. According to this comparison, differences in calibration patterns were moderately insignificant within the selected concentration range of 4~40 ppb. It was also observed that the loss of styrene standard was fairly high compared to other VOCs investigated simultaneously. The results of our study suggest that the analytical uncertainty associated with the preparation of VOC starndard gas using a dilution technique can be assessed in a fairly reasonable manner for samples with a narrow concentration range.

• Geomechanics and Engineering
• /
• v.37 no.3
• /
• pp.293-306
• /
• 2024

Influenced by the alternating effects of dynamic and static pressure during the mining process of close range coal seams, the surrounding rock support of cross mining roadway is difficult and the deformation mechanism is complex, which has become an important problem affecting the safe and efficient production of coal mines. The paper takes the inclined longwall mining of the 10304 working face of Zhongheng coal mine as the engineering background, analyzes the key strata fracture mechanism of the large inclined right-angle trapezoidal mining field, explores the stress distribution characteristics and transmission law of the surrounding rock of the roadway affected by the mining of the inclined coal seam, and proposes a segmented and hierarchical support method for the cross mining roadway affected by the mining of the close range coal seam group. The research results indicate that based on the derived expressions for shear and tensile fracture of key strata, the ultimate pushing distance and ultimate suspended area of a right angle trapezoidal mining area can be calculated and obtained. Within the cross mining section, along the horizontal direction of the coal wall of the working face, the peak shear stress is located near the middle of the boundary. The cracks on the floor of the cross mining roadway gradually develop in an elliptical funnel shape from the shallow to the deep. The dual coupling support system composed of active anchor rod support and passive U-shaped steel shed support proposed in this article achieves effective control of the stability of cross mining roadways, which achieves effective control of floor by coupling active support and preventive passive support to improve the strength of the surrounding rock itself. The research results are of great significance for guiding the layout, support control, and safe mining of cross mining roadways, and to some extent, can further enrich and improve the relevant theories of roof movement and control.

• Journal of the Korean Institute of Gas
• /
• v.16 no.6
• /
• pp.55-66
• /
• 2012

The practical way to minimize the greenhouse gas is to reduce the emission of carbon dioxide. For this reason, CCS(Carbon Capture and Storage) technology, which could reduce carbon dioxide emission, has risen as a realistic alternative in recent years. In addition, the researcher is recently working into ways of applying CCS technologies with deep saline aquifer. In this study, the evaluation model on the feasibility of $CO_2$ sequestration in the deep saline aquifer using ANN(Artificial Neural Network) was developed. In order to develop the efficiency-evaluation model, basic model was created in the deep saline aquifer and sensitivity analysis was performed for the aquifer characteristics by utilizing the commercial simulator of GEM. Based on the sensitivity analysis, the factors and ranges affecting $CO_2$ sequestration in the deep saline aquifer were chosen. The result from ANN training scenario were confirmed $CO_2$ sequestration by solubility trapping and residual trapping mechanism. The result from ANN model evaluation indicated there is the increase of correlation coefficient up to 0.99. It has been confirmed that the developed model can be utilized in feasibility of $CO_2$ sequestration at deep saline aquifer.

• 한국신재생에너지학회:학술대회논문집
• /
• 2005.11a
• /
• pp.561-566
• /
• 2005

Polycrystalline silicon films were deposited using hot wire CVD (HWCVD). The deposition of silicon thin films was approached by the theory of charged clusters (TCC). The TCC states that thin films grow by self-assembly of charged clusters or nanoparticles that have nucleated in the gas phase during the normal thin film process. Negatively charged clusters of a few nanometer in size were captured on a transmission electron microscopy (TEM) grid and observed by TEM. The negatively charged clusters are believed to have been generated by ion-induced nucleation on negative ions, which are produced by negative surface ionization on a tungsten hot wire. The electric current on the substrate carried by the negatively charged clusters during deposition was measured to be approximately $-2{\mu}A/cm^2$. Silicon thin films were deposited at different $SiH_4$ and $H_2$ gas mixtures and filament temperatures. The crystalline volume fraction, grain size and the growth rate of the films were measured by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The deposit ion behavior of the si1icon thin films was related to properties of the charged clusters, which were in turn controlled by the process conditions. In order to verify the effect of the charged clusters on the growth behavior, three different electric biases of -200 V, 0 V and +25 V were applied to the substrate during the process, The deposition rate at an applied bias of +25 V was greater than that at 0 V and -200 V, which means that the si1icon film deposition was the result of the deposit ion of charged clusters generated in the gas phase. The working pressures had a large effect on the growth rate dependency on the bias appled to the substrate, which indicates that pressure affects the charging ratio of neutral to negatively charged clusters. These results suggest that polycrystalline silicon thin films with high crystalline volume fraction and large grain size can be produced by control1ing the behavior of the charged clusters generated in the gas phase of a normal HWCVD reactor.

• Journal of the Korean Vacuum Society
• /
• v.6 no.3
• /
• pp.255-262
• /
• 1997

Titanium nitride (TiN) films were prepared by reactive sputter deposition in mixed gas of Ar+$N_2$. The volume percentage of $N_2$ in the working gas was chosen so as to grow stoichiometric TiN films and the substrate temperature during film growth was set from room temperature to $700^{\circ}C$. Stoichiometric $Ti_{0.5}N){0.5}$ films with (111) texture were grown at temperatures over $600^{\circ}C$, while films prepared at temperatures below $600^{\circ}C$ showed N-rich TiN. The composition X and y in the $Ti_xN_y$ films determined by XPS and RBS varied within 5% with the substrate temperature. The sheet resistance of the TiN films decreases as the substrate temperature increased. TiN film prepared at $600^{\circ}C$ showed 14.5$\Omega\Box$, and it decreased to 8.9$\Omega\Box$ after the sample was annealed at $700^{\circ}C$, 30 sec in Ar-gas ambient by RTA. By far, high quality stoichiometric TiN films by reactive sputtering in the mixed gas ambient could be prepared at substrate temperature over $600^{\circ}C$.

• Journal of Sensor Science and Technology
• /
• v.11 no.1
• /
• pp.18-27
• /
• 2002

$LaFeO_3$-based thick films with 2wt.%, 5wt.% and 10wt.% $Al_2O_3$ additives were fabricated by screen printing method on $Al_2O_3$ substrates. Structural, electrical and ammonia gas sensing characteristics of the thick films with different heat treatment temperatures were examined. From XRD results, the compound of $LaFeO_3$ and $Al_2O_3$ was not found until the heat treatment at $1200^{\circ}C$. SEM microphotograph showed similar grain growth despite the amount of $Al_2O_3$ additives with the heat treatment. Thick films with high activation energy and low resistance in the electrical properties showed high sensitivity for gases. Thick films with 2wt % $Al_2O_3$ additives heat-treated at $1200^{\circ}C$ showed the sensitivities of 210% for 100 ppm $NH_3$ gas at the working temperature of $350^{\circ}C$. The thick films showed food selectivity to $NH_3$ gas.

• Journal of Sensor Science and Technology
• /
• v.6 no.4
• /
• pp.265-273
• /
• 1997

The TMA gas sensors are fabricated with the ZnO-based thin films grown by a RF magnetron sputtering method. We investigate the surface carrier concentration, Hall electron mobility, electrical resistivity and sensitivity according to temperature variation and TMA gas concentration. The ZnO-based thin film sensors prepared by sputtering in oxygen showed higher surface carrier concentration, higher Hall mobility, higher sensitivity, and lower electrical resistivity than sensors prepared by sputtering in argon. The doping ZnO-based thin film sensors showed the same electrical properties in comparison with nondoping sensors. In case of sputtering on the oxygen gaseous atmosphere, the ZnO-based thin film sensors doped with 4.0 wt.% $Al_{2}O_{3}$, 1.0 wt.% $TiO_{2}$, and 0.2 wt.% $V_{2}O_{3}$ showed the highest surface carrier concentration of $5.95{\times}10^{20}cm^{-3}$, Hall electron mobility of $177\;cm^{2}/V{\cdot}s$, lowest electrical resistivity of $0.59{\times}10^{-4}{\Omega}{\cdot}cm$ and highest sensitivity of 12.1(working temperature, $300^{\circ}C$, TMA gas, 8 ppm).

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.8
• /
• pp.1007-1013
• /
• 2013

This study aims to analyze the aerodynamics when the geometry of the turbine rotor is modified. The turbine used in this study is a small engine used in the APU of a helicopter. It is difficult to improve the performance of small engines owing to the structural weakness of the blade tip. Therefore, the improvement of the hub geometry is investigated in many ways. The working fluid of a turbine is a high-temperature and high-pressure gas. The heat transfer rate of the turbine surface should be considered to avoid the destruction of blade owing to the heat load. The SST turbulence model gives an excellent prediction of the aerodynamic behavior and heat transfer characteristics when the numerical simulations are compared with the experimental results. In conclusion, the aerodynamic efficiency is improved when a bulbous design is applied to the leading edge near the hub. The endwall loss is reduced by 15%.

• Journal of the Korean Institute of Gas
• /
• v.16 no.6
• /
• pp.80-86
• /
• 2012

From 1982, the Korean Ministry of Employment and Labor has executed the risk assessment regulation for manufacturing industries. When a manufacturing company install, transfer, or modify the major facilities, the program inspects and verifies safety of the working place to ensure safety against risks. This study performed cost-benefit analysis of the program for the eight industrial categories that were free from the program. The cost-benefit analysis is the basic method to estimate the effect of the policy execution, and used to justify the policy effectiveness. As a result, there is the biggest benefit in the manufacture of basic metal products and then motor vehicles, trailers and semitrailers, other manufacturing, other machinery and equipment, wood products of wood and cork, rubber and plastic products, food products, furniture in order. Thus the hazard prevention program should be applied into the 8 industrial categories in order to strengthen national competitiveness, protect labors's safety, reduce the social cost and improve the welfare.

• Journal of Aerospace System Engineering
• /
• v.13 no.6
• /
• pp.9-16
• /
• 2019

The experiment on the liquid jet in crossflow in supersonic BFS (backward-facing step) flow was conducted to investigate the mixing characteristics. The working fluids are nitrogen and water. The shadow graph technique was used to visualize the flow field. Images captured by the high-speed camera were applied to analyze the flow phenomena. The liquid jet was injected at the re-circulation zone created by the supersonic jet flow. Experimental conditions are defined based on the pressure of the nitrogen gas chamber and pressurized liquid tank. In respective cases, the penetration depth of liquid jet and location of the Mach disc were observed to be proportional to the momentum ratio of gas and liquid jets.