• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.720-729
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• 1996

An analysis of convective boiling heat transfer for refrigerant mixtures is performed for an annular flow to investigate the degradation of the heat transfer rate. Annular flow is selected in this study because a great portion of the evaporator in the refrigeration and air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor is included in this analysis, which is considered to be one of driving forces for the mass transfer at the interface. Due to the concentration gradient at the interface the mass transfer is interfered, so is the evaporative heat transfer at the interface. The mass transfer resistance makes the interface temperature slightly higher and, as a result, the heat transfer coefficients decrease compared with those without mass transfer effects. The degradatioin of the heat transfer rate reaches its maximum at a certain composition. The composition difference between vapor core and vapor at the interface has a direct effect on the temperature difference between the vapor core and the interface and the degradation of the heat transfer rate. Correction factor $C_{F}$ for the mixture effects is added to the correlation for pure substances and the flow boiling heat transfer coefficients can be calculated using the modified equation.n.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.255-262
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• 2016

There has been intense research on self-diagnosis systems in railway applications, since stability and reliability have become more and more significant issues. Wired sensors have been widely used in the railway vehicles, but because of the difficulty in their maintenance and accessibility, they ar not considered for self-diagnosis systems. To have a self-monitoring system, wireless data transmission and self-powered sensors are required. For this purpose, a thermoelectric energy harvesting module that can generate electricity from temperature gradient between the bogie axle box and ambient environment was introduced in this work. The temperature gradient was measured under actual operation conditions, and the behavior of the thermoelectric module with an external load resistance and booster circuits was studied. The proposed energy harvesting system can be applied for wireless sensor nodes in railroad vehicles with optimization of thermal management.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.382-384
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• 2013

LED is much brighter than the traditional incandescent, and low power consumption. Development and commercialization of LED fluorescent lamp is made in order to improve efficient fluorescent lamps with this existing and environmental problems. Because, unlike fluorescent lamps, it is not possible to directly use AC power to the unidirectional element having a polarity, LED requires a power supply. The power supply function is lowered as compared with the fluorescent lamp common in terms of maintenance costs because of the high price large. In this study, we constructed a circuit that can be controlled with a constant current in order to eliminate a phenomenon that brightness of the light which rectifies the AC power supply easy to place in the power supply due to the current change due to the voltage fluctuation is changed, in maintenance, I would like to propose how to develop a device which can be easily replaced less expensive composed of interchangeable modules of Plug in / out method to distinguish the LED module this.

• Journal of the Korea Institute of Building Construction
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• v.17 no.5
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• pp.419-427
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• 2017

In order to examine the possibility of practical use of aluminate cement concrete at low-temperature environment with insulation method, an experimental studies on flowability, setting time, freezing temperature, size variation and compressive strength of the mortar at low-temperature were conducted. Compressive strength was increased in use of CSA, aluminate cement with gypsum. Workability and physical properties were improved by using aluminate cement and gypsum. In addition, freezing resistance and physical properties were improved by applying the insulation curing method. Especially, when alumina cement and gypsum were used together, the insulation curing method was more effective in improving the compressive strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.93-101
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• 2012

Bridge deck has a role in a comfortable and safe passage of vehicles. At the same time, it preserves upper structure against the abrasion and shearing due to impact of traffic loads in bridges or has a role to protect the plate from off adverse effect of climatic process as rain, chemicals. Currently, the total number of inspected bridges is 6,248 in the general national road and to maintain effectively, Introduction of GPR system mounted in the vehicle has been considered. In this research, the comparison and analysis of bridge deck condition on general national road has been performed with major variations of superstructure type, span lengths, located region and ages by using 'the current status of road bridge and tunnel' that is provided by MLTM(Ministry of Land, Transport and Maritime Affairs). As a result, Condition assessment grade, superstructure type, age and length were derived as a major factor to determine priority for the condition assessment.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.331-339
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• 2003

The study discussed in this paper investigated the material characteristics for the Thermo-Mechanical Control Process(TMCP) plates, which are controlled by several factors such as rolling, cold-stripping, cooling rate, and fixed carbon quantity. The suitability of thick TMCP steel plates as structural steel was also estimated through several experiments and with the us of a statistical method to analyze mill certificate sheets provided by the manufacturer. The results of this study are as follows: the TMCP steel plates showed stable values of the composition parameter ($P_cm$) and the carbon equivalents ($C_eq$ ) with satisfied yield strength, ultimate strength, and low-yield ratio.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.217-217
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• 2010

유기물/무기물 나노 복합재료는 고온과 저전력에서 동작해야하는 차세대 전자 소자와 광소자 제작에 대단히 유용한 소재이다. 간단하고 저렴한 제조 방법과 휘어짐이 가능한 특성을 이용하여 유기물/무기물 나노 복합재료를 사용한 비휘발성 메모리 소자의 제작과 메모리 특성에 대한 연구가 수행되었으나, SnO2 나노 입자가 삽입된 고분자 박막을 기반으로 제작한 저항 구조의 비휘발성 메모리 소자인 유기 쌍안정성 소자에 대한 연구는 상대적으로 미흡하다. 본 연구에서는 poly(methyl methacrylate) (PMMA) 박막 안에 분산된 SnO2 나노 입자를 사용하여 제작한 유기 쌍안정성 소자의 메모리 특성을 관찰하였다. 소자를 제작하기 위해 나노 입자의 전구체인 Tin 2-ethylhexanoate을 dibutyl ether에 용해시킨 후, 화학적 방법을 사용하여 용매 안에서 SnO2 나노 입자를 합성하였다. 합성한 SnO2 나노 입자와 PMMA를 클로로벤젠에 용해하여 고분자 용액을 제작하였다. 전극인 indium-tin-oxide가 증착된 유리 기판 위에 제작한 고분자 용액을 스핀 코팅하고, 열을 가해 용매를 제거하여 SnO2 나노 입자가 분산되어 있는 PMMA 나노복합체를 형성하였다. 그 위에 Al 전극을 증착하여 유기 쌍안정성 소자를 완성하였다. 제작된 소자에 전압을 인가하여 전류를 측정한 결과 유기 쌍안정성 소자에서는 동일 전압에서 높은 전류 (ON 상태)와 낮은 전류 (OFF 상태)가 흐르는 쌍안정성 특성을 나타냈다. 그러나 SnO2 나노 입자가 없는 PMMA 박막으로 형성된 소자에서는 전류-전압 측정에서 쌍안정성 특성이 나타나지 않았다. 따라서 PMMA 박막 안에 삽입된 SnO2 나노 입자가 유기 쌍안정성 소자의 메모리 효과를 나타내는 원인임을 알 수 있었다. 전류-시간 측정 결과는 소자의 ON 상태 및 OFF 상태 전류가 시간에 따른 큰 변화 없이 1000 사이클 이상 지속적으로 유지 하고 있음을 보여 줌으로써 유기 쌍안정성 소자를 장시간 사용할 수 있음을 확인시켜 주었다.

• Korean Journal of Food Science and Technology
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• v.45 no.3
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• pp.370-375
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• 2013

Propolis is a resinous mixture found in the tree buds, sap flows, and other botanical sources, which is used by honey bees in the construction of their hives. Antimicrobial effects of propolis were evaluated against Streptococcus mutans KCTC 3065, S. sobrinus KCTC 3308, S. sobrinus KCTC 5134, and Porphyromonas gingivalis KCTC 5352 by an agar diffusion assay. Sensitivity of these microorganisms to propolis was evaluated in broth containing different concentrations of propolis at $37^{\circ}C$, followed by observation using transmission electron microscopy (TEM). Propolis inhibited all oral microorganisms tested at the minimum inhibitory concentration (MIC) of $0.14mg/{\mu}L$ in the agar diffusion assay. Treatment with 0.06 and $0.22mg/{\mu}L$ of propolis had a bactericidal effect in a concentration- and treatment time-dependent manner against the tested microorganisms. TEM of propolis-treated S. mutans KCTC 3065 and P. gingivalis KCTC 5352 revealed structural damage of the cell membrane. The activity of propolis was affected by heat and pH treatment. The results indicate that propolis shows antibacterial activity against oral microorganisms and that it has potential for future applications in the food industry.

• Fire Science and Engineering
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• v.19 no.1 s.57
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• pp.93-98
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• 2005

The purpose of this paper is to judge the damage cause of instrument transformer(MOF; Metering Out Fit) installed in 22.9kV power receiving system. In the three-dimensional analysis of the restored MOF, the damage pattern progressed from inside to outside, there was no damaged part in the upside. The resistance of the carbonized middle part is roughly $100\kappa\Omega$ and the exothermic temperature at inside is presumed as about $300\~800^{\circ}C$ in the result of metallurgical structure analysis. The structure and the composition rate on metal surface by SEM is similar. In the result of FT-IR analysis, we can observe the absorbtion peak at $1500cm^{-1}\;and\;1730 cm^{-1}$ is small. The high exothermic peak showed at the center part of the coil in the result of DTA.

• Fire Science and Engineering
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• v.28 no.1
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• pp.26-30
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• 2014

A Compensation-type fire detector (CFD) is operated with two functions of a differential-temperature detector and as a fixed-temperature detector. The differential-temperature detector observes a rate of temperature increase, and the fixed-temperature detector measures a given fixed temperature. The differential-temperature detector does not observe the outbreak of fire in slowly increasing temperature conditions, whereas the fixed-temperature detector is not able to observe the outbreak of fire in conditions under predetermined temperature level. We developed a CFD to compensate for weaknesses of both detectors. To compensate for the disadvantages, a sensor of the sensor metal-insulator-transition critical-temperature sensor was used. Temperature coefficient of resistance is the sensitivity for sensor. At $55^{\circ}C$, temperature coefficient of resistance of metal-insulator-transition critical-temperature sensor was 14.15%. Temperature coefficient of resistance of thermistor was about 0.5%. This CFD was operated as two ways that fixed-temperature detector and differential-temperature detector in one sensor.