• Transactions of the Korean hydrogen and new energy society
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• v.35 no.2
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• pp.146-151
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• 2024

The demand for research on materials with excellent cryogenic strength and ductility has been increasing, particularly for applications such as liquid hydrogen (20 K) storage tanks. To effectively utilize liquid hydrogen, a system capable of maintaining and operating at 20 K is essential. Therefore, preliminary research and verification of the cooling system are crucial. In this study, a heat transfer analysis was conducted on a cooling system to meet the cryogenic environment requirements for cryogenic hydrogen chamber, which are conducted at liquid helium temperatures (4 K). The cooling mechanism in a helium cooling system was examined using numerical analysis. The numerical cooling trends were compared with experimentally obtained cooling results. The good agreement between numerical and experimental results suggests that the numerical approach developed in this study is applicable over a wide range of cryogenic systems.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.1
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• pp.93-100
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• 2011

The thermal property of insulation material is essential in developing a high-temperature superconductor (HTS) power cable to be operated at around liquid-nitrogen temperature. Unlike metallic materials, nonmetallic materials have a high thermal resistance; therefore, accurate estimate of the heat flow is difficult in the case of nonmetallic materials. The aim of this study is to develop an instrument for precisely measuring the thermal conductivity of insulating materials over a temperature range of 30 K to approximately the room temperature by using a cryocooler. The details of the thermal-conductivity measurement system, including the design and fabrication processes, are described in this paper. In addition, the design optimization to minimize unavoidable heat leakage from room temperature is discussed.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.1
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• pp.28-38
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• 2014

The organic-inorganic composite membrane in polymer exchange membrane fuel cells (PEMFCs) have several fascinating technological advantages such as a proton conductivity, thermal stability and mechanical properties. As the inorganic filler, silicon carbide (SiC) fiber have been used in various fields due to its unique properties such as thermal stability, conductivity, and tensile strength. In this study, composite membrane was successfully fabricated by modified-silicon carbide fiber. Modified process, as a novel process in SiC, takes reaction by phosphoric acid after oxidation process (generated homogeniusly $SiO_2$ layer on SiC fiber). The mechanical property which was conducted by tensile test of the 5wt% modified-$SiO_2@SiCf$ composite membrane was better than that of Aquivion casting membrane as well as ion cxchange capacity(IEC) and proton conductivity. In addition, the single cell performance was observed that the 5wt% modified-$SiO_2@SiCf$ composite membrane was approximately $0.2A/cm^2$ higher than that of a Aquivion casting electrolyte membrane and electrochemical impedance was improved with the charge transfer resistance and membrane resistance.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1703-1706
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• 1996

The purpose of this study is to research and develop polypyrrole(PPy) positive for thin film rechargeable lithium battery. We investigated cyclic voltammetry, AC impedance response and charge/discharge cycling of PPy/SPE/Li cells as a function of temperature. The redox capacity of $PPy/CF_{3}SO_{3}$ film was the most large. The discharge capacity of PPy/SPE/Li cell with $PPy/CF_{3}SO_{3}$ film was higher than those of $PPy/ClO_{4}$ and $PPy/AsF_6$ films at all cycles. The energy density of PPy/SPE/Li cells during 1st cycle was 73, 90 and 101Wh/kg at $25^{\circ}C$, $45^{\circ}C$ and $60^{\circ}C$, respectively. The improvement of energy density is due to reduction of charge-transfer resistance associated doping-undoping process in PPy film with Increasing temperature. $PPy/CF_{3}SO_{3}$ film shows a good property on charge/discharge cycling in PEO-$LiClO_4$-PC-EC electrolyte.

• Journal of the Society of Disaster Information
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• v.9 no.2
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• pp.178-187
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• 2013

This paper studied the potential risk of high-rise apartment by analysis of the loss ratio of housing fire insurance, statistics related high-rise apartment fire, and the insured amount of housing fire insurance, and, found that it is so high and need the improvement of risk management measures for high-rise apartment. Accordingly, the study recommend the composit risk management measures including preventing of fire expanding for higher stories, a shelter for people of hire-rise apartment, and sprinkler protection, etc. Also as risk transfer measures, the composit risk measures for high-rise apartment includes the full insurance of housing fire insurance, third party property liability insurance, and development of endorsement for special risk such as a typhoon, liability etc.

• Resources Recycling
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• v.23 no.1
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• pp.48-57
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• 2014

In this study, we have investigated the influence of the nature of solvent on the grafting reaction of maleic anhydride onto polyethylene wax obtained as a by-product in a high density polyethylene plant. The results show that the grafting ratio in xylene as a solvent was higher than toluene. This is because xylene has excellent monomer solubility, swelling property and miscibility. It has been also observed that grafting degree shows an initial jump in percentage of grafting with increasing amount of solvent, from 0% v/w to 200% v/w giving maximum grafting in 200% v/w and then slightly decreases on further increase in the amount of solvent and becomes almost constant. It can be also seen that gel content was not formed under the use of solvent. It means that solvent prevented cross-linking reaction due to chain transfer reactions to solvent molecules. Studies of melt viscosity at $140^{\circ}C$ showed that viscosity increased after grafting of maleic anhydride onto polyethylene wax.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1115-1128
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• 1994

The condition of temperature gradients in asphaltic concrete (Ascon) pavement have been analyzed based on the data collected from 5 major sites in Korea. From this. considering heat transfer by insolation flux and air temperature within pavement slab. temperature variation on the surface of pavement was computed and numerical model using the theory of thermal conductivity was applied to estimate the temperature gradients in depth. To investigate the present condition of asphalt generally used in Korea. the asphalt property tests were applicated on 5 different AP-3 (AC 85~100), and AP-5 (AC 60~70) asphalts classified by penetration index. Uniaxial compression test and indirect tensile test were also carried out for varying temperature conditions to analyze the effect of temperature on the deformation characteristics of Ascon pavement by calculating the variation of static elastic modulus and layer coefficients.

• Korean Chemical Engineering Research
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• v.55 no.1
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• pp.115-120
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• 2017

In recent, it is worldwide issued that nanoscale science and technology as a solution have supported to increase the sensing performance in carbon nanotube based biosensor system. Containing material chemistry in various nanostructures has formed their high potentials for stabilizing and activating biocatalyst as a bioreceptor for medical, food contaminants, and environmental detections using electrode modification technologies. Especially, the large surface area provides the attachment of biocatalysts increasing the biocatalyst loading. Therefore, nano-scale engineering of the biocatalysts have been suggested to be the next stage advancement of biosensors. Here, we would like to study the electrical mechanism depending on the exposure methods (soaking or dropping) to the sample solution to the assembled carbon nanotubes (CNTs) on the gold electrodes of biosensor for a simple and highly sensitive detection. We performed various experiments using polar and non-polar solutions as sampling tests and identified electrical response of assembled CNTs in those solutions.

• Journal of Satellite, Information and Communications
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• v.10 no.1
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• pp.17-21
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• 2015

In this paper, we introduce satellite communication for new wireless disaster network to be built on the basis of amateur radio HR (HAM Radio) as a wireless package system, and channel environments of a D2D terminal that tries to connect and communicate with the wireless disaster network. In this disaster network, we propose a LOS component ratio based adaptive channel modeling approach to accurately estimate a variety of channels whose the D2D terminal could have and smoothly transfer to the level of multimedia data based on the Okumura-Hata channel model. As a result of computer simulation, performance of the proposed method was compared with the that of Okumura-Hata model of open area and urban area model and we were confirmed that there is a gain of BER performance from the results of the computer simulation.

• Journal of the Korean Institute of Intelligent Systems
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• v.13 no.2
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• pp.175-179
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• 2003

Convergence condition determines performance of iterative learning control (ILC), for example, convergence speed, remaining error, etc. Hence, the performance can be elevated and a feasible set of learning controllers grows if a less conservative condition is obtained. In the frequency domain, the $H_{\infty}$ norm of the transfer function between consecutive errors has been currently used to test convergence of a learning system. However, even if the convergence condition based on the $H_{\infty}$ norm has a clear property about monotonic convergence, it has a few drawbacks, especially in MIMO plants. In this paper, the relation between the condition and the monotonicity of convergence is clarified and a modified convergence condition is found out using a frequency domain Lyapunov equation, which supersedes the conventional one in the frequency domain.