• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.26-26
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• 2003

Lithium storage electrodes for rechargeable batteries require mixed electronic-ionic conduction at the particle scale in order to deliver desired energy density and power density characteristics at the device level. Recently, lithium transition metal phosphates of olivine and Nasicon structure type have become of great interest as storage cathodes for rechargeable lithium batteries due to their high energy density, low raw materials cost, environmental friendliness, and safety. However, the transport properties of this family of compounds, and especially the electronic conductivity, have not generally been adequate for practical applications. Recent work in the model olivine LiFePO$_4$, showed that control of cation stoichiometry and aliovalent doping results in electronic conductivity exceeding 10$^{-2}$ S/cm, in contrast to ~10$^{-9}$ S/cm for high purity undoped LiFePO$_4$. The increase in conductivity combined with particle size refinement upon doping allows current rates of >6 A/g to be utilized while retaining a majority of the ion storage capacity. These properties are of much practical interest for high power applications such as hybrid electric vehicles. The defect mechanism controlling electronic conductivity, and understanding of the microscopic mechanism of lithiation and delithiation obtained from combined electrochemical and microanalytical techniques, will be discussed

• Nuclear Engineering and Technology
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• 제29권4호
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• pp.336-347
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• 1997

During postulated severe accidents in Light water Reactors, molten corium which was ejected from the reactor vessel bottom, may erode the concrete basemat of the containment and there by threaten the containment integrity. This study experimentally examines the molten core-concrete interaction (MCC) using 20kg of thermite melt (Fe + $Al_2$O$_3$) and the concrete, used in Yonggwang Nuclear Power Plant Units 3 and 4 (YGN 3 & 4) in Korea. The measured data are the downward heat fluxes, concrete erosion rate, gases and particle generation rates during MCCI. Transient results ore compared with those of TURCIT experiment conducted by SNL in USA. The peak downward heat flux to the concrete was measured to be about 2.1㎿/$m^2$. The initial concrete erosion rate was 175cm per hour, decreasing to 30cm per hour. It was shown from the post-test that the erosion was progressed downward up to 18mm in the concrete slug.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1523-1525
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• 1996

Partial discharges(PD) in air insulated electric power systems cause power loss, produce interfering electromagnetic radiation, and can indicate incipient failure. An understanding of PD in air gap is clearly important. The Wavelet transformation is an extended method of fourier transformation. The fourier method is a powerful tool for signal analysis, but it can't include informations for time. However tile wavelet transformation analysis can include on the informations of time and frequency at the same time. In this paper we apply the wavelet transformation to the PD signals in needle-plane air gap for tile purpose of analysis of developing aspects of PD. We can analyze the developing aspects of PD, namely, PD current, repetition rates, width of pulse distribution region, pulseless region and frequencies distribution of PD pulses.

• 대한안전경영과학회지
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• 제1권1호
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• pp.241-258
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• 1999

For hazardous air pollutants(HAP) such as NO and $NO_{2}$ decomposition efficiency, power consumption, and applied voltage were investigated by SPCP(surface induced discharge plasma chemical processing) reactor to obtain optimum process variables and maximum decomposition efficiencies. Decomposition efficiency of HAP with various electric frequencies(5~50 kHz), flow rates(100~1,000 mL/min), initial concentrations(100~1,000 ppm), electrode materials(W, Cu, Al), electrode thickness(1, 2, 3 mm) and number of electrode windings(7, 9, 11) were measured. Experimental results showed that for the frequency of 10 kHz, the highest decomposition efficiency of 94.3 % for NO and 84.7 % for $NO_{2}$ were observed at the power consumptions of 19.8 and 20W respectively and that decomposition efficiency decreased with increasing frequency above 20 kHz. Decomposition efficiency was increased with increasing residence times and with decreasing initial concentration of pollutants. Decomposition efficiency was increased with increasing thickness of discharge electrode and the highest decomposition efficiency was obtained for the electrode diameter of 3 mm in this experiment. As the electrode material, decomposition efficiency was in order : tungsten(W), copper(Cu), aluminum(Al).

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1759-1768
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• 2018

The energy density, power density and ohm resistance of battery change significantly as results of battery aging, which lead to decrease in the accuracy of the equivalent model. A parameter identification method of the equivale6nt circuit model with 3 R-C branches based on the test database of battery life cycle is proposed in this paper. This database is built on the basis of experiments such as updating of available capacity, charging and discharging tests at different rates and relaxation characteristics tests. It can realize regular update and calibration of key parameters like SOH, so as to ensure the reliability of parameters identified. Taking SOH, SOC and T as independent variables, lookup table method is adopted to set initial value for the parameter matrix. Meanwhile, in order to ensure the validity of the model, the least square method based on variable forgetting factor is adopted for optimizing to complete the identification of equivalent model parameters. By comparing the simulation data with measured data for charging and discharging experiments of Li-ion battery, the effectiveness of the full life cycle database and the model are verified.

• 비파괴검사학회지
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• 제28권4호
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• pp.339-345
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• 2008

원자력발전소 열교환기 튜브의 대부분은 구리, 티타늄, 인코넬합금 등의 비자성체로 제작되어 있으나 2차 터빈계통의 습분분리재열기(moisture separator & reheater), 급수가열기 등의 튜브는 고압, 고온 등의 열악한 운전조건에서 상대적으로 고온 강도가 우수한 탄소강 또는 페라이트계열 스테인레스강 등의 자성체로 제작되어 있다. 특히 습분분리재열기 튜브와 같은 열교환 매체가 증기인 경우 열전달 능력을 증가시키기 위해서 핀 튜브를 사용한다. 탄소강 또는 페라이트계열 스테인레스강 등의 자성체 튜브는 고온, 고압에서 강도가 우수하지만 운전 중에 증기 커팅, 침식, 기계적 진동 마모, 응력부식균열 등의 사용 중 결함이 발생하여 발전소 정상운전에 지장을 초래할 수 있기 때문에 전열관의 건전성 평가를 위한 주기적인 비파괴검사의 수행이 필요하다. 하지만 자성체 열교환기 튜브는 투자율이 높은 전기적 특성으로 인하여 기존의 와전류검사기술로는 비파괴검사가 어렵기 때문에 원격장검사기술을 적용해야 한다. 따라서 본 연구에서는 원자력발전소 습분분리재열기세관의 현장적용에 필요한 검사기술을 개발하기 위해서 원격장탐촉자, 인공결함 시험편 및 탐촉자 구동장치를 설계하였으며, 이를 활용하여 발전소 현장 검사에 적용하였다.

• KIEAE Journal
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• 제14권2호
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• pp.37-46
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• 2014

University buildings are energy-guzzling facility that consume more than 10,000TOE within a campus annually. Even the consumption is on an upswing trend. Behind such high consumption are there cheap power rates for education facility, lack of high-efficiency equipment and ever-increasing use of various information equipment. Being keenly aware that greenhouse gas emission increases due to such rise of energy consumption, the present study carried out a case study. In the case study, the study chose the buildings of E university from top 10 universities that consume energy most in Seoul and examined the current status of their energy consumption and greenhouse gas emission. And then it set the reduction target of greenhouse gas by year. Putting aside a middle and long-termed strategy for later endeavor, it first established the 1st year's implementation plan (2014) for energy saving and greenhouse gas reduction with limited budget and according to greenhouse gas reduction target. The plan is specified as follows. Targets for energy saving are mainly divided into two sectors: machine equipment and electric equipment. 7 ideas were proposed. Three ideas to improve machine equipment are to replace with high-efficiency boilers and chillers and to adjust the position of the cooling tower. By doing so, it was estimated that energy could be saved by 176.34TOE in total and greenhouse gas could be reduced by 370.771t$CO_2$-eq. Four ideas to improve electric equipment include the replacement with LED lights, LED emergency lights and high-efficiency motors and the installation of motion sensors. It was calculated that such replacement could conserve 1,076.08TOE (electric energy) and reduce 2,181.420t$CO_2$-eq (greenhouse gas).

• Carbon letters
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• 제16권2호
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• pp.78-85
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• 2015

Activated carbons (ACs) were prepared by activation of coal tar pitch (CTP) in the range of $700^{\circ}C-1000^{\circ}C$ for 1-4 h using potassium hydroxide (KOH) powder as the activation agent. The optimal activation conditions were determined to be a CTP/KOH ratio of 1:4, activation temperature of $900^{\circ}C$, and activation time of 3 h. The obtained ACs showed increased pore size distribution in the range of 1 to 2 nm and the highest specific capacitance of 122 F/g in a two-electrode system with an organic electrolyte, as measured by a charge-discharge method in the voltage range of 0-2.7 V. In order to improve the performance of the electric double-layer capacitor electrode, various mixtures of CTP and petroleum pitch (PP) were activated at the optimal activation conditions previously determined for CTP. Although the specific capacitance of AC electrodes prepared from CTP only and the mixtures of CTP and PP was not significantly different at a current density of 1 A/g, the AC electrodes from CTP and PP mixtures showed outstanding specific capacitance at higher current rates. In particular, CTP-PP61 (6:1 mixture) had the highest specific capacitance of 132 F/g, and the specific capacitance remained above 90% at a high current density of 3 A/g. It was found that the high specific capacitance could be attributed to the increased micro-pore volume of ACs with pore sizes from 1 to 2 nm, and the high power density could be attributed to the increased meso-pore volume.

• 대한환경공학회지
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• 제22권2호
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• pp.217-229
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• 2000

입상 및 분말 활성탄에 대한 페놀의 흡착평형실험을 $25{\pm}1^{\circ}C$에서 행하였으며 그 결과를 Freundlich isotherm으로 나타내었다. 흡착속도 실험은 회분식 흡착법으로 입자외부 물질이동저항이 무시되는 조건하에서 행하였으며, 실험결과는 LDF 흡착속도상수를 구하기 위하여 Miller의 방법으로 해석하였다. 고정층 흡착칼럼에서 페놀-활성탄계의 흡착실험을 행하였다. 흡착칼럼실험은 온도를 $25{\pm}1^{\circ}C$로 일정하게 유지하면서, 흡착대의 길이는 추산한 흡착대 길이보다 크게 하여 정형농도분포가 이루어지도록 하였다. 그리고 각기 다른 두 가지 공탑유속의 경우에 대해 실험하였다. LDF 모델식의 흡착속도계수는 흡착율에 따라 변화되며, 이 가변성 흡착속도계수를 사용하여 정형 농도변화곡선을 추정한 결과 일정 평균치를 사용한 경우보다 실험결과와 더 일치하였다.

• 공업화학
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• 제28권6호
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• pp.638-644
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• 2017

전기이중층 커패시터(electric double layer capacitor, EDLC) 전극용 핏치계 활성탄소섬유의 고출력 특성을 향상시키기 위하여 불소와 산소 혼합가스의 다양한 불소분압에 따라 함산소불소화 표면처리를 수행하였다. 함산소불소화 처리된 핏치계 활성탄소섬유는 불소 부분압이 증가함에 따라 선형적인 불소관능기의 증가를 보였고, 산소관능기는 증가하였으나 부분압에 따라 차이가 없었다. 또한 함산소불소화를 통하여 활성탄소섬유 표면의 식각 반응으로 인하여 비표면적 및 기공부피는 감소하였으나 중간기공 부피는 약 4.5배 증가하였다. 50%의 불소가스 분압으로 처리한 활성탄소섬유의 경우 5와 50 mV/s의 전압주입속도에서 비정전용량이 약 29%와 61%로 증가함을 확인하였다. 이러한 비정전용량의 향상은 함산소불소화 처리를 통한 활성탄소섬유 표면의 산소 및 불소 관능기의 도입과 중간기공의 증가에 의한 효과로 사료된다.