• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.238-243
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• 2003

As there are many advantages on underground caverns, such as safety and operation, they can also be used for gas storage purpose. When liquefied gas is stored underground, the cryogenic temperature of the gas will affect the stability of the storage cavern. In order to store the liquefied gas successfully, it is essential to estimate the exact temperature distribution of the rock mass around the cavern. In this study, an analytic solution and a conceptual model that can estimate three-dimensional temperature distribution around the storage cavern are suggested. When calculating the heat transfer within a solid, it is likely to consider the solid as the intersection of two or more infinite or semi-infinite geometries. Therefore heat transfer solution for the solid is expressed by the product of the dimensionless temperatures of the geometries, which are used to form the combined solid. Based on the multi-dimensional transient heat transfer theory, the analytic solution is successfully derived by assuming the cavern shape to be of simplified geometry. Also, a conceptual model is developed by using the analytic solution of this study. By performing numerical experiments of this multi-dimensional model, the temperature distribution of the analytic solution is compared with that of numerical analysis and theoretical solutions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.150-155
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• 2010

Liquid rocket injectors play crucial roles on propulsive performance, combustion stability, and heat transfer characteristics. Nevertheless, their developments have mainly relied on empirical methods and expensive hot-firing tests due to lack of fundamental understanding of high pressure combustion phenomena in the near-injector regions. The present study was motivated by recent efforts to develop reliable modeling of liquid rocket combustion. The turbulent combustion model based on the flamelet concept has been extended to take into account real-fluid behaviors occurred at supercritical pressures, and validated against measurements for a cryogenic nitrogen injection, a non-premixed turbulent jet flame at atmospheric pressure, and a LOx/$GH_2$ coaxial shear injector at a supercritical pressure.

• Membrane Journal
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• v.31 no.1
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• pp.61-66
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• 2021

This study was a study on an facilitated transport membrane to replace the cryogenic separation method currently used in olefin/paraffin separation. Cost reduction is also a very important factor to commercialize facilitated transport membranes. However, AgBF4, which has been studied a lot, is a relatively expensive silver salt. To replace this, a PEBAX-2533/ AgCF3SO3/Al(NO3)3 composite film was prepared using relatively inexpensive AgCF3SO3. It was analyzed through SEM, FT-IR, and RAMAN. Through this study, it was confirmed that the polymer matrix affects the long-term stability.

• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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• pp.27-30
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• 2007

The electrical insulation design and withstanding test of mini-model coils for 600 kJ class conduction cooled high temperature superconducting magnetic energy storage (HTS SMES) have been studied in this paper. The high voltage is generated to both ends of magnet of HTS SMES by quench or energy discharge. Therefore, the insulation design of the high voltage needs for commercialization, stability, reliability and so on. In this study, we analyzed the insulation composition of a HTS SMES, and investigated about the insulation characteristics of the materials such as Kapton, AIN and vacuum in cryogenic temperature. Base on these results, the insulation design for 600 kJ conduction cooled HTS SMES was performed. The mini-model was manufactured by the insulation design, and the insulation test was carried out using the mini-model.

• Publications of The Korean Astronomical Society
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• v.24 no.1
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• pp.53-64
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• 2009

MIRIS is the main payload of the STSAT-3 (Science and Technology Satellite 3) and the first infrared space telescope for astronomical observation in Korea. MIRIS space observation camera (SOC) covers the observation wavelength from $0.9{\mu}m$ to $2.0{\mu}m$ with a wide field of view $3.67^{\circ}\times3.67^{\circ}$. The PICNIC HgCdTe detector in a cold box is cooled down below 100K by a micro Stirling cooler of which cooling capacity is 220mW at 77K. MIRIS SOC adopts passive cooling technique to chill the telescope below 200 K by pointing to the deep space (3K). The cooling mechanism employs a radiator, a Winston cone baffle, a thermal shield, MLI (Multi Layer Insulation) of 30 layers, and GFRP (Glass Fiber Reinforced Plastic) pipe support in the system. Optomechanical analysis was made in order to estimate and compensate possible stresses from the thermal contraction of mounting parts at cryogenic temperatures. Finite Element Analysis (FEA) of mechanical structure was also conducted to ensure safety and stability in launching environments and in orbit. MIRIS SOC will mainly perform Galactic plane survey with narrow band filters (Pa $\alpha$ and Pa $\alpha$ continuum) and CIB (Cosmic Infrared Background) observation with wide band filters (I and H) driven by a cryogenic stepping motor.

• Journal of the Korean Institute of Gas
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• v.18 no.1
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• pp.17-24
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• 2014

LNG storage tank is a facility to store liquefied natural gas (LNG) and its safety and stability to be greatly needed. When there is a LNG leakage in case of primary container problem, a special facility such as a bund wall should be constructed to store the leaked LNG. But this method makes the land usage inefficient and construction price high. So nowadays the full containment type LNG storage tank is selected instead of constructing a bund wall. In the full containment type tank, the concrete sidewall has the ability to store LNG temporarily. There are largely two methods to give the concrete sidewall the ability. In a method, rebar should be used when constructing the side wall of the LNG storage tank. In the other method, the protecting material such as sprayed polyurethane foam should be applied on the inner surface of the concrete sidewall. Sprayed PUF keeps the temperature of the sidewall above the specified temperature during the specified periods. Recently the thermal stability reinforcing method using sprayed polyurethane foam has been applied to all LNG storage tank built in Korea.

• Journal of Electrical Engineering and Technology
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• v.7 no.5
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• pp.765-771
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• 2012

$SF_6$ gas has been used as arc quenching and insulating medium for high and extra high voltage switching devices due to its high dielectric strength, its excellent arc-quenching capabilities, its high chemical stability and non toxicity. Despite of its significant contributions, the gas was classified as one of the greenhouse gas in the Kyoto Protocol. Thus, many researches are conducted to find out the replacement materials and to develop the $SF_6$ gas useless electrical equipment. This paper describes experiments on the temperature change-related breakdown characteristics of $SF_6$ gas ($SF_6$) and $SF_6$ liquid ($LSF_6$) in a model GIS(Gas-Insulated Switchgear) chamber in order to show the possibility of more stable and safe usages of $SF_6$ gas. The breakdown characteristics are classified into three stages, namely the gas stage of $SF_6$ according to Paschen's law, the coexisting stage of $SF_6$ gas with liquid in considerable deviation at lower temperature, and the stage of $LSF_6$ and remaining air. The result shows that the ability of the $LSF_6$ insulation is higher than the high-pressurized $SF_6$. Moreover, it reveals that the breakdown characteristics of $LSF_6$ are produced by bubble-formed $LSF_6$ evaporation and bubbles caused by high electric emission and the corona. In addition, the property of dielectric breakdown of $LSF_6$ is determined by electrode form, electrode arrangement, bubble formation and movement, arc extinguishing capacity of the media, difficulty in corona formation, and the distance between electrodes. The bubble formation and flow separation phenomena were identified for $LSF_6$. It provides fundamental data not only for $SF_6$ gas useless equipment but also for electric insulation design of high-temperature superconductor and cryogenic equipment machinery, which will be developed in future studies.

• Progress in Superconductivity and Cryogenics
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• v.19 no.2
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• pp.38-43
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• 2017

The role of current lead in high-temperature superconducting synchronous machine (HTSSM) is to function as a power supply by connecting the power supply unit at room temperature with the HTS field coils at cryogenic temperature. Such physical and electrical connection causes conduction and Joule-heating losses, which are major thermal losses of HTSSM rotors. To ensure definite stability and economic feasibility of HTS field coils, quickly and smoothly cooling down the current lead is a key design technology. Therefore, in this paper, we introduce a novel concept of a cooling anchor to enhance the cooling performance of a metal current lead. The technical concept of this technology is the simultaneously chilling and supporting the current lead. First, the structure of the current lead and cooling anchor were conceptually designed for field coils for a 1.5 MW-class HTSSM. Then, the effect of this installation on the thermal characteristics of HTS coils was investigated by 3D finite element analysis.

• Journal of the Korean Magnetics Society
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• v.8 no.1
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• pp.21-26
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• 1998

The temperature dependence of the magnetoimpedance (MI) effect is important both for scientific study and for thermal stability of MI sensor. We have performed the measurement of MI effect in amorphous $Co_{66}Fe_1Ni_1B_{14}Si_{15}$ (Metglas 2714 A) ribbon from a cryogenic chamber where the temperature of the sample can vary from 10 K to 300 K. The ac current was fixed at 10 mA for all measured frequencies ranging from 100 KHz to 10 MHz. The magnetoimpedance ratio (MIR) was revealed the drastic increment as a function of MIR (T) = MIR (0) exp(cT$^2$) where c is a constant. The measured MIR values at room temperature are usually 2-3 times larger than the data measured at 10 K for all measured frequencies. However, the shapes of the MIR curves are remained. This result shows the potential application of the MI effect for a temperature sensor. The frequency dependence of MIR has shown the typical tendency where the maximum values of MIR are increasing ans also the shapes of MIR curves are getting broader as the measured frequency increases.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.155.1-155.1
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• 2011

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS (Immersion Grating Infrared Spectrograph). The white-pupil design of the instrument optics uses 7 cryogenic mirrors including 3 aspherical off-axis collimators and 4 flat fold mirrors. Two of the 3 collimators are H- and K-band pupil transfer mirrors and they are designed as compensators for the system alignment in each channel. Therefore, their mount design will be one of the most sensitive parts in the IGRINS optomechanical system. The other flat fold mirrors are designed within the limited area. Each of those includes the features of 3 axial hard points and 2 radial hard points with one spring plunger in order for the proper deflection of the mirror. The design work will include the computer-aided 3D modeling and finite element analysis (FEA) to optimize the structural stability and the thermal behavior of the mount models. The mount body will also include a tip-tilt and translation adjustment mechanism to be used as the alignment compensators.