• Bulletin of the Korean Chemical Society
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• 제31권8호
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• pp.2207-2210
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• 2010

This paper describes the preparation and study of thermally stimulated discharge conductivity (TSDC) study of cellulose triacetate (CTA) - multiwalled carbon nanotubes (MWNTs) film thermoelectrets. TSDC has been carried out in the temperature range 308 - 503 K and at four different polarizing fields. The conductivity of the polymer blends increased with increase in temperature showing a semi-conducting behavior. The apparent activation energy also showed a pronounced effect with the increase in the content of MWNTs.

• 한국지열·수열에너지학회논문집
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• 제8권1호
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• pp.21-31
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• 2012

This paper reviewed and evaluated some of the commonly used prediction models for thermal conductivity of soils with the experimental data. Semi-theoretical models for two-component materials were found inappropriate to estimate the thermal conductivity of dry state soils. It came out that the model developed by Cote and Konrad gave the best overall prediction results for unsaturated soils available in the literature. However, it still needs to be improved to cover a wider range of soil types and degrees of saturation. In the present study, parametric analysis is also conducted to investigate the effect of soil type and moisture content on the horizontal ground heat exchanger design. The analysis shows that horizontal ground heat exchanger pipe length is reduced with the increase of soil thermal conductivity and water content. The calculation results also show that horizontal ground heat exchanger size can be reduced to a certain extent by using backfilling material with a higher thermal conductivity of solid particles.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.813-824
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• 2010

Thermal conductivity of soils is one of the most important parameters to design horizontal ground heat exchangers. It is well known that the thermal conductivity of soil is strongly influenced by its density and water content because of soil's particulate structure. This paper reviewed and evaluated some of the commonly used prediction models for thermal conductivity of soils with the experimental data available in the literature. Semi-theoretical models for two-component materials were found inappropriate to estimate the thermal conductivity of dry state sands. It came out that the model developed by Cote and Konrad gave the best overall prediction for unsaturated sands available in the literature. Also, a parametric analysis is conducted to investigate the effect of thermal conductivity and water content, soil type on the horizontal ground heat exchanger design. The analysis shows that a required pipe length for the horizontal ground heat exchanger is reduced with the increase of soil thermal conductivity and water content. The calculation results also show that the dimension of the horizontal ground heat exchanger can be reduced to a certain extent by using backfilling material with a higher thermal conductivity of solid particles.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.2039-2044
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• 2011

A semi-continuous and automated method for quantifying atmospheric ammonia at the parts per billion level has been developed. The instrument consists of a high efficiency diffusion scrubber, an electrolytic on-line anion exchange device, and a conductivity detector. Water soluble gases in sampled air diffuse through the porous membrane and are absorbed in an absorbing solution. Interferences are eliminated by using an anion exchange devises. The electrical conductivity of the solution is measured without chromatographic separation. The collection efficiency was over 99%. Over the 0-200 ppbv concentration range, the calibration was linear with $r^2$ = 0.99. The lower limit of detection was 0.09 ppbv. A parallel analysis of Seoul air over several days using this method and a diffusion scrubber coupled to an ion chromatography system showed acceptable agreement, $r^2$ = 0.940 (n = 686). This method can be applied for ambient air monitoring of ammonia.

• 열처리공학회지
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• 제16권5호
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• pp.267-274
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• 2003

The effect of the thermo-mechanical treatment on the microstructural development and the electric conductivity of Cu-Ca alloys are studied for the thixoforming processed rotor of the induction motor The Cu-Ca alloys containing Ca less than 1.0wt% show the electrical conductivity higher than 80% IACS They also show broad melting range over $150^{\circ}C$ which is desirable for the thixoforming process The semi-solid microstructure of cast alloy changes from the dendrite structure to globular structure by prior deformation before reheating. The details of microstructural changes by the thermo-mechanical treatment are discussed.

• 소성∙가공
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• 제14권2호
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• pp.147-152
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• 2005

The objective of this study is to develop an optimal drawing die for the clad wire drawing process. Cu-clad wire, which has the advantages of the high strength of a steel core and the electro-conductivity, corrosion resistance of a copper layer, is widely being used in the field of the telecommunications, electric-electronic and military technology industries. It is important to obtain uniformly coated rate when producing clad wires. Drawing process of clad wire will be influenced on damage and coated rate of core and sleeve for process variables such as semi-die angle and reduction in area. Therefore, in this study, the finite-element result obtained in this study was analyzed to the effect of the various forming parameters, which included the semi-die angle and reduction in area. The coated rate will be predicted with observation of copper coated rate variation according to total reduction in area and the optimal pass schedule will be set up through proper reduction in area and semi-die angle variation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.310-315
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• 2008

Authors design a rotary-type small-scaled linear induction motor(LIM) and a performance test machine before manufacturing a real-scaled LIM for a railway transit. The designed LIM is a single-sided, short primary type and its primary has 4 poles. The rated power is 10(kW). In order to analyze characteristics of the LIM, authors use a mixed 2D-3D FEM analysis. 3-D FEM analysis is used for calculating a distribution of eddy-current on the semi-caped AL-sheet of the secondary reaction. Authors calculate a correction factor of conductivity and an equivalent conductivity on the secondary AL-sheet using a normalized eddy-current. The equivalent conductivity which is calculated in this way includes a transverse edge-effect of the LIM. Authors apply the equivalent conductivity on the secondary AL-sheet of 2D-FEM model and get performance characteristics of the LIM. Basic characteristics such as thrust and normal force, input current, efficiency and power factor of the LIM have been analyzed with the variation of frequency and speed. In order to apply an air-gap control system, the variation of the basic characteristics have been analyzed with the air-gap length variation of the LIM. Finally, authors introduce an operation mode using the air-gap control system and conduct a research on feasibility of the system.

• 지질공학
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• 제9권3호
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• pp.227-241
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• 1999

단열암반 내의 지하수 흐름은 단열의 분포특성과 밀접한 관계를 갖고 있으며, 수리전도도와 직접적인 관계를 갖는 인자로서 단열 틈의 크기와 단열 교차빈도가 고려된다. 본 연구는 여수반도 북부지역의 화산암에 분포하는 단열의 간격과 틈의 크기에 대한 확률밀도함수의 유형과 단열의 분포특성이 수리전도도 값에 미치는 영향 및 상관관계를 분석하였다. 단열의 분포특성은 core logging과 초음파주사 검층을 통하여 조사되었으며, 일정구간별 수리전도도는 이중패커를 이용한 정압/압력강하 시험으로서 산출되었다. 연구지역에 분포하는 단열간격과 단열조별 틈의 크기는 대수정규분포를 나타내지만, 개구성 단열 틈의 크기는 정규분포에 가깝다. Core logging에 의한 투수성 단열, 텔레뷰어 검층에 의한 개구성 단열군, 그리고 Set 1에 속하는 단열들이 교차되는 수리시험 구간에서는 수리전도도 값과 양의 상관관계를 보였다. 단열암반의 수리전도도는 투수성 단열 틈의 크기에 1차적인 영향을 받으며 단열의 교차정도 및 크기에 2차적인 영향을 받는 것으로 해석된다.

• 한국전기전자재료학회논문지
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• 제36권6호
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• pp.603-608
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• 2023

Carbon black with high purity and excellent conductivity is used as a conductive filler in the semiconductive compound for EHV (Extra High Voltage) power cables of 345 kV or higher. When carbon black and CNT (carbon nanotube) are applied together as a conductive filler of a semiconductive compound, stable electrical properties of the semiconductive compound can be maintained even though the amount of conductive filler is significantly reduced. In EHV power cables, since the semi-conductive layer is close to the conductor, stable electrical characteristics are required even under high-temperature conditions caused by heat generated from the conductor. In this study, the theoretical principle that a semiconductive compound applied with carbon black and CNT can maintain excellent electrical properties even under high-temperature conditions was studied. Basically, the conductive fillers dispersed in the matrix form an electrical network. The base polymer and the matrix of the composite, expands by heat under high temperature conditions. Because of this, the electrical network connected by the conductive fillers is weakened. In particular, since the conductive filler has high thermal conductivity, the semiconductive compound causes more thermal expansion. Therefore, the effect of CNT as a conductive filler on the thermal conductivity, thermal expansion coefficient, and volume resistivity of the semiconductive compound was studied. From this result, thermal expansion and composition of the electrical network under high temperature conditions are explained.

• 한국환경과학회지
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• 제24권1호
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• pp.17-23
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• 2015

This study was aimed to determine the effect of basal application of Effective Microorganisms (EM) on the grow and yield of cucumber. For treatments, the EM was applied to soil with fertilizer composed with $N-P_2O_5-K_2O$-manure (24.0-16.4-23.8-2,000kg) in the 1.0 strength (defined as EM+1S), 2/3 strength (defined as EM+2/3S), 1/2 strength (defined as EM+1/2S), without fertilizer (defined as EM), or only fertilizer in the 1.0 strength (defined as 1S). In result, there was no significant differences of organic substance content and pH with the EM treatment. While the EC (Electric conductivity) concentration was decreased, plant-available P (phosphorus) was markedly increased. Chlorophyll content was highest in the treatment of EM+standard application rate for both semi-forcing and retarding culture. In contrast, no significant difference was found in plant height and internode length under the fertilizer treatment. Weekly harvested number of cucumber was highest at the treatment of EM+standard application for the semi-forcing culture, while it was 3.6 at the EM+1/2 application for the retarding culture. Weekly yield was greatest at the EM+standard application treatment and decreased with the decrease of fertilizer application rate. In addition, weekly yield was significantly reduced in the treatment of EM. There was no significant difference in yields by production time with the fertilizer applications?. Yield was increased with temperature for the semi-forcing culture, while consistent pattern was maintained for the retarding culture.