• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.9
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• pp.491-496
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• 2015

Generally, the phase of the refrigerants that circulate in air-conditioning systems is repeatedly changed from liquid to gas and from gas to liquid. In vapor-compression refrigeration, the refrigerant at the inlet of the evaporator is in a gas-liquid two-phase state; therefore, to enhance the heat-transfer performance of the evaporator, the even distribution of the refrigerant across multiple passages of the evaporator is essential. Unlike the distribution of a single-phase refrigerant, multi-phase distribution requires further considerations. It is known that the multi-phase distribution at the outlet of the distributor is affected by factors such as the operating condition, the distributor's shape, and the insertion depth of the outlet pipes; here, the insertion depth of the outlet pipes is especially significant. In this study, for a cylindrical distributor with a 90-degree bend entrance and three outlet pipes, the flow uniformity at the outlet pipes was numerically tested in relation to variations of the insertion depth of the outlet pipes.

• Proceedings of the KIEE Conference
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• 2000.07e
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• pp.17-21
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• 2000

A Study on the electron energy distribution function in $SF_6+Ar$ mixtures gas used by MCS-BE algorithm, the electron swam parameters in the 0.5% and 0.2% $SF_6+Ar$ mixtures are measured by time of flight method over the E/N(Td) range from 30 to 300(Td). A two-term approximation of the Boltzmann equation analysis and Monte Carlo simulation have been also used to study electron transport coefficients. The electron energy distribution function has been analysed in $SF_6$ gas and $SF_6+Ar$ mixtures at E/N : 200(Td) for a case of the equilibrium region in the mean electron energy. The measured results and the calculated results have been compared each other.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2418-2425
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• 1993

A two-dimensional transient heat transfer model for reactive gas assisted laser cutting process with a moving Gaussian heat source is developed using a numerical finite difference technique. The kerf width, melting front shape and temperature distribution were calculated by using the boundary-fitted coordinate system to handle the ejection of workpiece material and heat input from reaction and evaporation. An analytical solution for cutting front movement was adopted and numerical simulation was performed to calculate the temperature distribution and melting front thickness. To calculate the moving velocity of cutting front, the normal distribution of the cutting gas velocity was used. The kerf width was revealed to be dependent on the cutting velocity, laser power and cutting gas velocity.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.12
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• pp.33-39
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• 2015

This paper examines the insulation performance of synthetic air and dry air. This examination was conducted based on dielectric strength in uniform and non-uniform field, electric field distribution by interior structure and defects in gas insulation switchgear (GIS) and insulation performance in different temperatures. From this review, it was found that eco-insulation gas required to possess low moisture content for power equipment in the distribution class. The results of this paper are valuable to ensure the insulation design and insulation reliability of GIS using air.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.61-67
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• 2013

This study introduces the design methods for air flow distribution at the level of preliminary design, and reviews the typical combustion process and main functions of sub-components of aircraft gas turbine combustors. There are lots of design approaches and empirical equations introduced for air flow distributions at the combustors. It is shown that a decision on which design approaches work for the combustor development is totally dependent upon the objective of engine design, target performance, and so on. The current results suggested for preliminary air flow distributions need to be validated by combustor geometry checkups and performance evaluations for future works.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.7
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• pp.647-656
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• 2014

To supplement the ISO-GUM method for the evaluation of measurement uncertainty, a simulation program using the Monte Carlo method (MCM) was developed, and the MCM and GUM methods were compared. The results are as follows: (1) Even under a non-normal probability distribution of the measurand, MCM provides an accurate coverage interval; (2) Even if a probability distribution that emerged from combining a few non-normal distributions looks as normal, there are cases in which the actual distribution is not normal and the non-normality can be determined by the probability distribution of the combined variance; and (3) If type-A standard uncertainties are involved in the evaluation of measurement uncertainty, GUM generally offers an under-valued coverage interval. However, this problem can be solved by the Bayesian evaluation of type-A standard uncertainty. In this case, the effective degree of freedom for the combined variance is not required in the evaluation of expanded uncertainty, and the appropriate coverage factor for 95% level of confidence was determined to be 1.96.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.137-142
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• 2002

The fluid mechanics and operating conditions of gas-lubricated proceeding bearings in micro rotating machinery such as micro polarization modulator and micro gas turbine are different from their larger size ones. Due to non-continuum effects, there is a slip of gas at the walls. Thus in this paper, the slip flow effect is considered to estimate the pressure distribution and load-carrying capacity of micro gas-lubricated proceeding bearings as the local Knudsen number at the minimum film thickness is greater than 0.01. Based on the compressible Reynolds equation with slip flow, the static characteristics of micro gas-lubricated proceeding bearings are obtained. Numerical predictions compare the pressure distribution and load capacity considering slip flow with the performance of micro proceeding bearings without slip f]ow for a range of bearing numbers and eccentricities. The results clearly show that the slip flow effect on the static characteristics is considerable and becomes more significant as temperature increases.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.129-132
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• 2008

Combustion characteristics of a gas generator for a 30 ton-class liquid rocket engine were studied. At the early stage of development, the combustion tests of the gas generator were performed by only using the nozzle which substitute for a turbine manifold exit. Then, the extension tube was applied between the gas generator and the nozzle for imitating the resonant mode of gas generator and turbine manifold. Finally, the hot-firing tests were performed on the condition of connecting the gas generator with the turbine manifold. In the paper, the step-by-step results such as temperature distribution and pressure fluctuations were analyzed.

• Journal of The Korean Astronomical Society
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• v.53 no.6
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• pp.117-123
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• 2020

We investigate the plausibility of mass return, from stellar mass loss processes within the central ~100 pc region of the Milky Way (the inner nuclear bulge), as a mass supply mechanism for the Circumnuclear Disk (CND). Gas in the Galactic disk migrates inward to the Galactic centre due to the asymmetric potential caused by the Galactic bar. The inward migration of gas stops and accumulates to form the central molecular zone (CMZ), at 100-200 pc from the Galactic center. It is commonly assumed that stars have formed in the CMZ throughout the lifetime of the Galaxy and have diffused inward to form a 'r-2 stellar cusp' within the inner nuclear bulge. We propose that the stars migrating inward from the CMZ supply gas to the inner nuclear bulge via stellar mass loss, resulting in the formation of a gas disk along the Galactic plane and subsequent inward migration down to the central 10 pc region (CND). We simulate the evolution of a gas distribution that initially follows the stellar distribution of the aforementioned stellar cusp, and illustrate the potential gas supply toward the CND.

• Journal of the Korean Institute of Gas
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• v.21 no.4
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• pp.1-5
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• 2017

Leaking of natural gas, which is mostly methane, in a confined living space creates flammable atmosphere and gives rise to explosion accident. The minimum amount of leaked methane for explosion is highly dependent on the degree of mixing in the confined space. This paper proposes a method for estimating minimum amount of flammable gas for explosion by using Gaussian distribution explosion model(GDEM) and experimental explosion data. The explosion pressure in the confined space can be estimated by assuming the Gaussian distribution of flammable gas along the height of an enclosure and estimating the maximum amount of gas within flammable limits, combustion of the estimated gas with constant volume and adiabatic or isothermal mixing in the confined space. The predicted minimum gas amount for an explosion is tied to explosion pressure that results in a given building damage level. The result shows that very small amount of methane leaking in the confined space may results in a serious gas explosion accident. This result could be applied not only to setting the leak criteria for developing a gas safety appliance but also to accident investigating of explosion.