• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.211-214
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• 1999

염화물 및 방청제가 함유된 철근 콘크리트의 부식특성을 마크로 셀 부식측정 방법인 갈바닉 전류 측정과 마이크로 셀 부식측정 방법인 선형분극 측정법 및 교류 임피던스법을 이용하여 염화물 및 방청제의 영향을 평가하였다. 마크로/마이크로 셀 부식측정기 Calcium Nitrite 방청제가 첨가된 시험체의 경우 갈바닉 전류 측정결과 낮은 전류값을 유지하였고, 교류 임피던스 측정결과 분극저항의 감소가 나타나지 않았으므로, 방청제의 첨가가 콘크리트내 철근의 부동태 피막을 보호하여 부식저항성을 향상시킴을 알 수 있었다.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.114.1-114.1
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• 2005

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1999.06a
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• pp.249-252
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• 1999

전도성 충진제가 포함된 결정성 고분자내에 대전류가 흐르게 될 경우 Joule 효과로 소재자체의 발열현상이 발생하며 온도가 증가함에 따라 고분자의 용융점 부근에서 급격한 열팽창으로 인하여 고분자 내에 분포되어 있던 전도성 충진재 입자사이의 간격이 증가하게 되며 전자들의 흐름이 방해를 받게 된다. 이에 따라 전기저항이 커져 전류의 흐름이 감소되는 철상이 발생하며 이를 PTC(Positive Temperature Coefficient)라 하고 온도 증감에 따른 전도성 충진제 간의 electron tunnelling과 고분자의 결정변화에 의해 민감한 전기저항변화 특성을 나타낸다. (중략)

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.9
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• pp.22-26
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• 1994

In this paper a method of designing FIR filters without digital arithmetic operationsi is persented. The filter coefficients are represented by resistors combined with a differential amplifier. With this method an FIR filter can be simply impemented without refering to complex digital arithmetic operations. Furthermore, in this scheme, no additional D/A converter is needed for D/A conversion. Spectral response response of a pulse shaping filter of 17 coefficients is shown as an illustration.

• Journal of Bio-Environment Control
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• v.11 no.3
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• pp.101-107
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• 2002

This study was carried out to improve the performance of heat recovery device attached to exhaust gas flue connected to combustion chamber of greenhouse heating system. Three different units were prepared far the comparison of heat recovery performance; A-type is exactly the same with the typical one fabricated for previous study of analyzing heat recovery performance in greenhouse heating system, other two types (B-type and C-type) modified from the control unit are different in the aspects of airflow direction (U-turn airflow) and pipe arrangement. The results are summarized as follows ; 1. In the case of Type-A, when considering the initial cost and current electricity fee required for system operation, it was expected that one or two years at most would be enough to return the whole cost invested. 2. Type-B and Type-C, basically different with Type-A in the aspect of airflow pattern, are not sensitive to the change of blower capacity with higher than 25m$^3$.min$^{-1}$ . Therefore, heat recovery performance was not improved so significantly with the increment of blower capacity. This was assumed to be that air flow resistance in high air capacity reduced the heat exchange rate as well. Never the less, compared with control unit, resultant heat recovery rate of Type-B and Type-C was improved by about 5％ and 13％, respectively 3. Desirable blower capacity of these heat recovery units experimented were expected to be about 25m$^3$.min$^{-1}$ , and at the proper blower capacity, U-turn airflow units showed better heat recovery performance than control unit. But, without regard to the type of heat recovery unit, it was recommended that comprehensive consideration of system's physical factors such as pipe arrangement density, unit pipe length and pipe thickness, etc., was required for the optimization of heat recovery system in the aspects of not only energy conservation but economic system design.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.179-184
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• 2010

This experimental study investigated the effect of tip clearance and bypass flow on the cooling performance of a straight fin heat sink. Both the horizontal and vertical directions of the bypass flow were studied by using a mass flow controller and test sections. The thermal resistance of a heat sink was obtained to elucidate the response of the cooling performance to tip clearance and bypass flow. The thermal resistance of a straight fin heat sink gradually increases with increasing tip clearance. A flow guide unit was employed to reduce the bypass flow. An optimal distance from the leading edge of the heat sink to the flow guide unit was found for the fixed volume flow rate. The contribution of the flow guide unit to the thermal performance of a heat sink increases with increasing volume flow rate.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.67-74
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• 2013

A low-power 12-bit resistor string DAC for wireless sensor applications is presented. Two-step approach reduces complexity, minimizes power consumption and area, and increases speed. This chip is fabricated in 0.18-${\mu}m$ CMOS and the die area is $0.76mm{\times}0.56mm$. The measured power consumption is 1.8mW from the supply voltage of 1.8V. Measured SFDR(Spurious-Free Dynamic Range) is 70dB when the sampling frequency is less than 1 MHz.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.10
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• pp.881-887
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• 2014

Micro-sized Peltier coolers are generally employed for uniformly distributing heat generated in the multi-chip packages. These coolers are commonly classified into vertical and planar devices, depending on the heat flow direction and the arrangement of thermoelectric materials on the used substrate. Owing to the strong need for evaluation of performance of thermoelectric modules, at present an establishment of proper theoretical model has been highly required. The design theory for micro-sized thermoelectric cooler should be considered with contact resistance. Cooling performance of these modules was significantly affected by their contact resistance such as electrical and thermal junction. In this paper, we introduce the useful and optimal design model of small dimension thermoelectric module.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.786-790
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• 2016

This paper discusses numerically explored orientation effects on the thermal performance of hollow hybrid fin heat sinks (HHFHSs) under natural convection. A HHFHS consists of an array of hollow pin fins concatenated with plate fins and having perforations near the fin bases. Orientation effects on the footprint-based and mass-based thermal performance of the HHFHS were numerically studied for orientation angles ranging from $0^{\circ}$ to $180^{\circ}$. The performance of the HHFHS was compared with that of a pin fin heat sink (PFHS) having similar physical parameters. The results show that the thermal resistance of the HHFHS did not vary considerably from $0^{\circ}$ to $45^{\circ}$. The thermal resistance increased from $45^{\circ}$ to $90^{\circ}$, reached its maximum at $90^{\circ}$, and decreased consistently from $90^{\circ}$ to $180^{\circ}$. Dissimilar behaviors of the thermal resistance of the HHFHS vs. the PFHS resulted mainly from the effect of heat pumping induced by the internal flows of the hollow fins. Despite various orientations, the mass-based thermal resistance of the HHFHS was found to be nearly 30% smaller than that of the PFHS. This result shows the feasibility of the HHFHS for the lightweight thermal management of electronics under natural convection.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1996.10b
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• pp.181-189
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• 1996

회전열파이크는 전기모터, 고온가스터빈 등의 냉각에 이용함으로써 성능개선을 얻을 수 있다는 점에서 지난 20년 동안 많은 연구가 이루어져왔다. 그동안 내부벽면형상개발은 Taper를 설치하거나, 계단식 단면변화 또는 Impeller설치와 같은 기술들이 연구되었다. 본 연구는 회전 열파이프 용기내벽에 Coil Insert를 설치하여 응축액막 유동효과에 대한 가시화실험 및 열전달 성능실험을 통하여 그 특성을 검토하였고 아래와 같은 결과를 얻을 수 있었다. 1) Pool 영역에서는 Coil Insert에 의한 축방향 펌프효과가 매우 크며, 그 효과는 나선각이 클수록 크게 나타난다. 2) Coil Insert는 Pool에서 환상류로 천이를 촉진시키며, 나선각이 클수록 그 효과가 크게 나타난다. 3) Coil insert 열파이프의 열저항에 미치는 효과는 크지 않은 것으로 보인다. 4) Coil Insert에 의해 Dry-out한계의 증가가 예상되지만, 실험장치의 열부하한계에 의해 확인할 수 없었다.