• Electrical & Electronic Materials
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• v.8 no.2
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• pp.217-223
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• 1995

In this paper, we investigated physical properties and electrical characteristics of the fluorocarbon that used as coolants for large power gas-insulated transformer. Volume resistivity of the fluorocarbon was .rho.=1.87*10$^{15}$ [.ohm.cm] at 1 atm, 27.deg. C. Dielectric constant was 1.86 and decreases as temperature increase. The breakdown voltage at 1 atm was higher than that of transformer oil. The breakdown voltage of fluorocarbon vapor was about 18kV when pressure in a test chamber increases over lkg/cm$^{2}$. When fluorocarbon was mixed with SF$_{6}$ gas, breakdown voltage of the mixed was higher than that of fluorocarbon. Then fluorocarbon leads to increase over 4kg/cm$^{2}$ in pressure as temperature increase. Therefore, when a gas-insulated transformer is manufactured, the design must be taken into consideration a high-pressure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1202-1208
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• 2006

This paper presents an experimental characteristics of electro-hydraulic proportional pressure control valve. In this study, poppet and valve body which are assembled into the proportional solenoid were designed and manufactured. The constant force characteristics of proportional solenoid actuator in the control region should be independent of the plunger position in order to be used to control the valve position in the fluid flow control system. The stroke-force characteristics of the proportional solenoid actuator is determined by the shape (or parameters) of the control cone. In this paper, steady state and transient characteristics of the solenoid actuator for electro-hydraulic proportional valve are analyzed using finite element method and it is confirmed that the proportional solenoid actuator has a constant attraction force in the control region independently on the stroke position. The effects of the parameters such as control cone length, thickness and taper length are also discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.130-134
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• 2010

The effects of design parameters of supersonic ejector system under the assumption of constant pressure mixing were performed. Design parameters were mass flow rate ratio, area ratio between primary and secondary flow, and primary Mach number. 1-D theoretical performance of ejector in terms of pressure ratio and contraction ratio with and without loss mechanism such as diffuser efficiency and friction were considered.

• Journal of Hydrospace Technology
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• v.1 no.1
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• pp.14-28
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• 1995

The hydrodynamic problem when the pressurized bag submerges partially into water and oscillates was formulated by Lee(1992), and the solution method was given, In his formulation, however, the compressilbility of air was neglected and the pressure inside the bag was assumed to be constant. In this paper, the formulation was done including the air compressibility and the wall to block fling around phenomenon. The compression process was assumed to be a isothermal process for a static problem, isentropic process for a dynamic problem. And the stability was analyzed for the static problem. Through the various numerical calculations, the forces and the shape of the bag were compared with those of a rigid body case, constant pressure case, and variable pressure case.

• Bulletin of the Korean Chemical Society
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• v.11 no.4
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• pp.343-347
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• 1990

A thermal decomposition of the tert-butoxy radical has been studied in the gas phase over the pressure range of 1-200 torr at $413_{\circ}K$ using di-tert-butyl peroxide + trimethylsilane mixtures. The relative rate constants were obtained by studying the competitive reactions between tert-butoxy radical decomposition 4(t-BuO·→ CH_3COCH_3 + CH_3·)$ and hydrogen abstraction reaction from trimethylsilane $(t-BuO·+ HSi(CH_3)_3 → t-BuOH + Si(CH_3)_3)·).$ The conventional RRKM calculations were carried out to compare the observed fall-off behavior of the decomposition rate constant $({\kappa}_d)$ with the theoretical predictions using reasonable values of input parameters. In all cases the calculated half-rate pressure $(P_{1/2})$ were significantly higher than those observed. The failure of RRKM to reproduce the fall-off behavior led us to suggest that not all of vibrational modes contribute to excitation (leading to decomposition) on the same time scale.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.17-23
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• 2004

A cylindrical constant volume combustion bomb is used to investigate the combustion characteristics and to analyze the heat quantity of homogeneous charge methane-air mixture under various initial pressures, excess air ratios and ignition times. As the overall pressure increase, the values of maximum combustion pressure, maximum heat release rate and cumulative heat release have been increased. But it is not very meaningful to compare with some values such as maximum combustion pressure, maximum heat release rate and cumulative heat release for different overall pressure due to the different heat energy of supplied fuel. So the each value is needed to be compared with normalized value, which is divided by the entered fuel energy. To analyze the heat quantity, some definitions including the CHR ratio, the UHC ratio and the HL ratio are needed and are calculated. As the overall pressure increase, the CHR ratios and the UHC ratios have been decreased, while the HL ratios have been increased. The CHR ratio of 300 ms has the higher value than that of 10000ms, and the HL ratios of 300 ms have a lower value.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.3
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• pp.129-139
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• 1995

This study investigates the combustion characteristics of methane-hydrogen-air premixture in a constant volume combustion chamber. Primary factors of the combustion characteristics of methane- hydrogen-air premixture are the equivalence ratio and hydrogen supplement rate. In the case of $\phi$= 1.1, maximum combustion pressure and heat release rate have peaks, and they increase as the initial pressure and hydrogen supplement rate increase. The total burning time is also the shortest at the $\phi$= 1.1, it shorten by lowering the initial pressure and by increasing the hydrogen supplement rate. The maximum flame temperature is shown at the $\phi$= 1.0, and increasing the initial pressure and hydrogen supplement rate, it increases. The concentration of NO reveals the highest value at the $\phi$= 0.9, and it increases by increasing the initial pressure and hydrogen supplement rate. It is also found that the limit of lean inflammability of methane-hydrogen-air premixture is greatly widened by increasing the hydrogen supplement rate.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.2
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• pp.1-9
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• 2010

This study was carried out to comparison of coefficient of consolidation and the prediction of excess pore water pressure in agricultural reservoir on soft clay ground. For the purpose of verification of the proposed equation, laboratory model tests and field tests were performed and excess pore water pressure was compared to those predicted with the Terzaghi's method. The predicted excess pore water pressure according to ponding was very applicable to practice because it was close to the observed data. Also, for the comparison of coefficient of consolidation, the oedometer, constant rate of strain (CRS), and Rowe cell tests were performed. The coefficient of consolidation at the Rowe cell and CRS tests showed a greate increase than in the oedometer test. The ratio of the vertical and horizontal coefficient of consolidation showed a large difference according to various tests method and mixing ratio. Therefore, it is recommended that careful attention should be paid to predicting the required consolidation period in agricultural reservoir.

• Journal of ILASS-Korea
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• v.11 no.4
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• pp.212-219
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• 2006

The initial film flow development of the high-pressure swirl spray was investigated at different injector operating conditions to analyze film flow development and to provide the input data for the modeling works. This result can be also useful to verify the previously simulated results. The initial flow conditions such as liquid film thickness, flow angle and flow divergence are obtained by visualizing the inside and near the nozzle flow with a microscopic imaging system. The visualized images are quantified using an image processing tool. From the information of liquid film thickness and flow angle, the initial axial and tangential velocity and the swirl number of the swirl spray are successfully determined at various operating conditions. The experimental results showed that the initial liquid film thickness, flow angle and flow divergence are remained constant when the injection pressure is increased. However, initial film conditions are severely changed when the fuel temperature is increased. The swirl number remained constant when the injection pressure is increased while it showed increased value at high fuel temperature condition.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.387-394
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• 2000

Theoretical and experimental study is conducted on the contact pressure distribution of a radial tire in motion under various camber angles. Tire construction is modelled by a spring bedded elastic ring, consisted of sidewall springs and a composite belt ring. The contact area is assumed to be a trapezoidal shape varying with camber angles and weighted load. The basic equation in a quasi-static form is derived for the deformation of a running belt with a constant velocity by the aid of Lagrange-Euler transformation. Galerkin's method and stepwise calculation are applied for solving the basic equation and the mechanical boundary condition along both sides of the contact belt part subjected to shearing forces transmitted from the sidewall spring. Experimental results on the contact pressure, measured by pressure sensors embedded in the surface of the drum tester, correspond well with the calculated ones for the test tire under various camber angles, running velocities and weighted loads. These results indicate that a buckling phenomenon of the contact belt in the widthwise direction occurs due to the effect of camber angle.