• Korean Journal of Materials Research
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• v.20 no.9
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• pp.494-499
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• 2010

Tin oxide thin films were prepared on borosilicate glass by rf reactive sputtering at different deposition powers, process pressures and substrate temperatures. The ratio of oxygen/argon gas flow was fixed as 10 sccm / 60 sccm in this study. The structural, electrical and optical properties were examined by the design of experiment to evaluate the optimized processing conditions. The Taguchi method was used in this study. The films were characterized by X-ray diffraction, UV-Vis spectrometer, Hall effect measurements and atomic force microscope. Tin oxide thin films exhibited three types of crystal structures, namely, amorphous, SnO and $SnO_2$. In the case of amorphous thin films the optical band gap was widely spread from 2.30 to 3.36 eV and showed n-type conductivity. While the SnO thin films had an optical band gap of 2.24-2.49 eV and revealed p-type conductivity, the $SnO_2$ thin films showed an optical band gap of 3.33-3.63 eV and n-type conductivity. Among the three process parameters, the plasma power had the most impact on changing the structural, electrical and optical properties of the tin oxide thin films. It was also found that the grain size of the tin oxide thin films was dependent on the substrate temperature. However, the substrate temperature has very little effect on electrical and optical properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.787-790
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• 2003

A rf triode magnetron sputtering system is designed and installed its construction in vacuum chamber. In order to calibrate the rf triode magnetron sputtering for thin films deposition processes, the effects of different glow discharge conditions were investigated in terms of the deposition rate measurements. The basic parameters for calibrating experiment in this sputtering system are rf power input, gas pressure, plasma current, and target-to-substrate distance. Because a knowledge of the deposition rate is necessary to control film thickness and to evaluate optimal conditions which are an important consideration in preparing better thin films, the deposition rates of copper as a testing material under the various sputtering conditions are investigated. Furthermore, a triode sputtering system designed in our team is simulated by the SIMION program. As a result, it is sure that the simulation of electron trajectories in the sputtering system is confined directly above the target surface by the force of $E{\times}B$ field. Finally, some teats with the above 4 different sputtering conditions demonstrate that the deposition rate of rf triode magnetron sputtering is relatively higher than that of the conventional sputtering system. This means that the higher deposition rate is probably caused by a high ion density in the triode and magnetron system. The erosion area of target surface bombarded by Ar ion is sputtered widely on the whole target except on both magnet sides. Therefore, the designed rf triode magnetron sputtering is a powerful deposition system.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.104-108
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• 2014

The recent Fukushima nuclear power plant accidents shows that the core make up at high RCS pressure condition is very important to prevent core melting. The core make up flow at high pressure condition should be driven by gravity force or passive forces because the AC-powered safety features are not available during a Station Black Out (SBO) accident. The reactor Coolant System (RCS) mass inventory is continuously decreased by releasing steam through the pressurizer safety valves after reactor trip during a SBO accident. The core will be melted down within 2~3 hours without core make up action by active or passive mode. In the new design concept of a Hybrid Safety Injection Tank (Hybrid SIT) both for low and high RCS pressure conditions, the low pressure nitrogen gas serves as a charging pressure for a LBLOCA injection mode, while the PZR high pressure steam provides an equalizing pressure for a high pressure injection mode such as a SBO accident. After the pressure equalizing process by battery driven initiation valve at a high pressure SBO condition, the Hybrid SIT injection water will be passively injected into the reactor downcomer by gravity head. The SBO simulation by MARS code show that the core makeup injection flow through the Hybrid SIT continued up to the SIT empty condition, and the core heatup is delayed as much.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.477-485
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• 2012

Fluid flow and heat transfer in horizontal ducts are strongly coupled with large changes in thermodynamic and transport properties near the critical region as well as the gravity force. Numerical analysis has been carried out to investigate convective heat transfer in horizontal rectangular ducts for water near the thermodynamic critical point. Convective heat transfer characteristics, including velocity, temperature, and the properties as well as local heat transfer coefficients along the ducts are compared with the effect of proximity on the critical point. When there is flow acceleration because of a density decrease, convective heat transfer characteristics in the ducts show transition behavior between liquid-like and gas-like phases. There is a large variation in the local heat transfer coefficient distributions at the top, side, and bottom surfaces, and close to the pseudocritical temperature, a peak in the heat transfer coefficient distribution resulting from improved turbulent transport is observed. The Nusselt number distribution depends on pressure and duct aspect ratio, while the Nusselt number peak rapidly increases as the pressure approaches the critical pressure. The predicted Nusselt number is also compared with other heat transfer correlations.

• Journal of the Korean Chemical Society
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• v.59 no.6
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• pp.508-519
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• 2015

In this study, the pre-service chemistry teachers’ understanding of potential energy curve was investigated. The subjects were 24 junior students and 26 senior students studying chemistry education in a college of education. A concept questionnaire consisted of thought experiments with different initial conditions was developed to survey the pre-service teachers’ conceptions of potential energy curve. The survey results showed that the pre-service chemistry teachers had difficulties to accept the negative values for potential energy and total energy. And they knew the mechanical energy conservation but they could not apply it properly to the thought experiment situations given in the questionnaire. Also they had the knowledge about the direction of force exerted between the two balls, but many of them believed that the balls would stop moving at the bottom of potential energy curve well. In addition, it was discovered that few pre-service teachers could relate the thought experiments to the chemical bonding, the liquefaction of gas, and the molecular vibration.

• Clean Technology
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• v.7 no.2
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• pp.127-132
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• 2001

The effects of activated-carbon (AC) packing length on the Pressure Swing Adsorption (PSA) performance was investigated for the hydrogen separation from the multicomponent mixture gas. Linear driving force model was used to describe mass transfer between two phase and coupled Langmuir isotherm was used for each component as a nonlinear adsorption isotherm. When two adsorbents with a different adsorption capacity were packed consecutively in one bed, it is very important to determine the packing ratio of zeolite to activated carbon affecting the purity and recovery of the product. The activated carbon packing length in adsorption tower of 120 cm was determinated by the ending point of $CO_2$ contration. The optimum length of an activated carbon layer was 65 cm for production of high-purity hydrogen.

• Journal of Welding and Joining
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• v.27 no.1
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• pp.65-70
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• 2009

Ir-192 radiation sealed sources are widely employed to the therapeutic applications as well as the non-destructive testing. Production of Ir-192 sources requires a delicate but robust welding technique because it is employed in a high radioactive working environment. A GTA(Gas Tungsten Arc) welding technique is currently well established for this purpose. However, this welding method requires a frequent replacement of the electrode, which results in the delay of the production to take a preparatory action such as to isolate the radiation sources from the working place before getting access to the welding machine. Hence, a resistance welding technique is considered as an alternative method of the GTA welding technique. The advantages of resistance welding are high welding speed and high-rate production. Also it has very long life of electrode comparing to GTA welding. In this study, the resistance welding system and proper welding conditions were established for sealing Ir-192 source capsule. As a results of various experiments, it showed that electrode displacement can be employed as a indicator to predict welding quality. We proposed two mathematical models(linear and curvilinear) to estimate electrode displacement with process parameters such as applied force, welding current and welding time by using regression analysis method. Predicting results of both linear and curvilinear model were relatively good agreement with experiment.

• Journal of the Korean Geotechnical Society
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• v.27 no.3
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• pp.75-83
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• 2011

Emerging issues related with fully coupled Thermo-Hydro-Mechanical (THM) behavior of unsaturated soil demand the development of a numerical tool in diverse geo-mechanical and geo-environmental areas. This paper presents general governing equations for coupled THM processes in unsaturated porous media. Coupled partial differential equations are derived from three mass balances equations (solid, water, and air), energy balance equation, and force equilibrium equation. With Galerkin formulation and time integration of these governing equations, finite element code is developed to find nonlinear solution of four main variables (displacement-u, gas pressure-$P_g$), liquid pressure-$P_1$), and temperature-T) using Newton's iterative scheme. Three cases of numerical simulations are conducted and discussed: one-dimensional drainage experiments (u-$P_g-P_1$), thermal consolidation (u-$P_1$-T), and effect of pile on surrounding soil due to surface temperature variation (u-$P_1$-T).

• Particle and aerosol research
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• v.15 no.4
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• pp.139-148
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• 2019

This study was performed for the application of a high-speed centrifugal cyclone to shale gas mining process. This device uses the centrifugal force to control particles similar to typical cyclones, and the disk located inside the cyclone is forced to rotate using a motor. The pressure difference occurred during the rotating of disk. Hence, inflow rate was generated without a blower fan. In addition, flow rate increased with elevating rpm of motor. The installing the disk in multiple stages on the inner rotor increased the instantaneous disk outlet flow. Hence, the control efficiency of oil particle increased from 1.05% to 31.2%. By modifying the structure of the disk so that the air flow to the opposite direction of the cyclone, the control efficiency of oil particles increased to 81.5%. By increasing the capacity of the motor and the size of the disk, the flow rate was increased to 2.5 ㎥/min because the rpm of motor and pressure difference increased. As rpm of motor increased, the cut-off diameter (d_pc) became smaller. Unlike the Lapple's equation, d_pc was inversely proportional to the effective number of rotations (N_e). The control efficiency was maintained even if the concentration of oil particles increased, for this reason, the higher the oil concentration, the more particles were accumulated and controlled.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.10
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• pp.1044-1048
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• 2015

Recently, the viability of the Northern Sea Route has been receiving a remarkable amount of attention. Owing to global warming, glaciers in the Arctic Ocean have been melting rapidly, which has opened up navigation routes for ships with commercial as well as research purposes. At present, vessels can be economically operated along the Northern Sea Route four months of the year. However, studies have shown that the economical operating time may increase to six months by 2020 and year-round by 2030. Even though the conditions of the Northern Sea Route are extreme, the main reason for its use is that the route is shorter than the existing route using the Suez Canal, which provides an economic benefit. In addition, 25% of the world's oil reserves and 30% of its natural gas are stored in the coastal areas of the East Siberian Arctic region. Many factors are leading to the expectation of commercial navigation using the Northern Sea Route in the near future. To satisfy future demand, the International Maritime Organization established the Polar Code in order to ensure navigation safety in polar waters; this is expected to enter into force on January 1, 2017. According to the code, a ship needs to reduce its speed and analyze the ice for safe operation before entering into it. It is necessary to enter an ice field at a right angle to break the ice safely and efficiently. This study examined the operation along the course for safe navigation of the passage under several conditions. The results will provide guidelines for traffic officers who will operate ships in the Arctic Ocean.