• 한국항행학회논문지
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• 제14권5호
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• pp.655-660
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• 2010

본 논문에서는 무선전력전송을 위한 정류회로의 RF-to-DC 변환효율 개선에 대해 연구하였다. 정류회로는 지역통과 필터, 다이오드 회로, 직류 통과필터로 구성되어 있는데, 이것들 모두가 변환 효율에 영향을 미친다. 시뮬레이션을 통해 이러한 부분들이 어떻게 변환효율에 영향을 주는지 조사를 하였고, 이러한 내용을 바탕으로 10dBm의 저전력에서 약 50%의 변환효율을 갖는 912MHz의 정류회로를 제작하여 특성을 측정하였다.

• 한국전기전자재료학회논문지
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• 제30권11호
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• pp.699-704
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• 2017

The amount of electric power for photovoltaic power generation depends on the location of the power plant and the direction of solar cell. The solar cell controls the generation of solar power plants. Therefore, the structure of solar cell, manufacturing method, and optic technology were factors contributing to increased solar cell efficiency; however, the technical limit has been reached. Herein, we propose a new method to increase the solar cell efficiency using a wavelength conversion technology that converts ultraviolet and infrared rays, which are not effectively used in solar cells, into effective wavelength of solar cell. We used fluoride $Na(Ca)YF_4$ phosphor for wavelength conversion. Then, a wavelength-conversion fluorescent paste, prepared using an organic-silicon binder, was used to prepare a film that was applied to Si solar cells. It was confirmed that conversion efficiency improved by 5% or more.

• 산업기술연구
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• 제30권A호
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• pp.69-73
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• 2010

In this paper, we designed the RF-DC converter used in wireless power transmission system and studied how to design the RF-DC converter of high conversion efficiency. The RF-DC converter operate at 2.45GHz and the diode is connected with series. The RF-DC converter uses shorted stub for DC loop and matching. We can divide the RF-DC converter circuit into four blocks. The reflection coefficients between the blocks were optimized for the maximum conversion efficiency at 0 dBm input power and $1300{\Omega}$ load impedance. The final design of the RF-DC converter has a 52 percent conversion efficiency.

• 한국자동차공학회논문집
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• 제13권3호
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• pp.123-130
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• 2005

In this study, we evaluated the CH4 and CO conversion efficiencies over the oxidation catalysts for natural gas vehicle with lean-burn system. On the fresh catalyst, the conversion efficiency was increased when the loading of precious metal was increased. On the aged catalyst, the conversion efficiency was decreased as increasing the excess air ratio. We could confirm the measuring conversion efficiency of the unsteady state with the FTIR and that of steady state with the GC The temperature increasing ratio of unsteady state is acceptable from 3$^{\circ}C$/min. to 15$^{\circ}C$/min. for the evaluation of catalyst conversion performance , which has within the 4$\%$ of the difference of conversion efficiency. We observed a physical behavior of the thermal aged catalyst's surface using TEM and BET device. It was found that the precious metal was grown to the micro-scopic size by thermal aging process.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.97.1-97.1
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• 2011

Dimethyl ether (DME) is an attractive fuel as a hydrogen carrier for mobile PEMFC applications. However, its reforming technologies are rarely studied especially by using autothermal reforming (ATR) method. This work explored the impact of operating conditions to the performance of DME ATR. Temperature, Steam to carbon ratio(SCR), Oxygen to carbon ratio(OCR) and Gas hourly space velocity(GHSV) were considered as the operating conditions. As results, conversion efficiency was increased as the temperature increased, but saturated around $700^{\circ}C$. There was no significant effect of SCR on conversion efficiency, but high SCR led reactions in endothermic manner. High OCR substantially suppressed conversion efficiency, but it helped to sustain the temperature by stimulating exothermic reactions. Conversion efficiency was decreased as GHSV increased. The optimized operating conditions was suggested: $700^{\circ}C$, SCR of 1.5, OCR of 0.45 and GHSV below 15000/h and conversion efficiency was ~85% at the conditions.

• Journal of the Optical Society of Korea
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• 제17권1호
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• pp.22-26
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• 2013

The author analyzes the luminous efficiency of the phosphor-conversion white light-emitting diode (LED) that consists of a blue LED chip and a yellow phosphor. A theoretical model is derived to find the relation between luminous efficiency (LE) of a white LED, wall-plug efficiency (WPE) of a blue LED chip, and the phosphor absorption ratio of blue light. The presented model enables to obtain the theoretical limit of LE and the lower bound of WPE. When the efficiency model is applied to the measured results of a phosphor-conversion white LED, the limit theoretical value of LE is obtained to be 261 lm/W. In addition, for LE of 88 lm/W at 350 mA, the lower bound of WPE in the blue LED chip is found to be ~34%. The phosphor absorption ratio of blue light was found to have an important role in optimizing the luminous efficiency and colorimetric properties of phosphor-conversion white LEDs.

• 한국산학기술학회논문지
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• 제10권6호
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• pp.1304-1316
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• 2009

본 연구는 효율성에 기초한 환산지수의 도입 가능성을 알아보기 위한 기초 연구로 시도되었다. DEA 효율성지표와 환산지수가 전공의 수련교육을 실시하고 있는 60 개 병원을 그룹화하는데 얼마나 유용하게 사용될 수 있는가를 고찰하였다. 이러한 목적을 달성하기 위해 자료수집이 가능한 표본병원의 환산지수와 AHP 개념을 도입해 DEA 모형의 투입변수와 산출변수를 선정하였다. 그 결과 병상규모가 클수록 규모적 비효율성이 큰 것으로 나타났으며 기술적으로 또는 규모적으로 비효율적인 병원일수록 환산지수가 더 큰 것으로 나타났다. 환산지수와 효율성지표는 수련병원을 병원의 종별에 따라 종합전문병원과 종합병원으로 구분하는데 유용하게 사용될 수 있었다. 또한 DEA 효율성을 구하는 과정에서 독립변수로 사용된 투입 산출변수를 판별함수에 도입하였음에도 불구하고 환산지수와 효율성지표는 판별함수를 구성하는 주요 변수로 작용함을 확인하였다. 따라서 만약 모집단을 대표할 수 있는 많은 표본을 기초로 보다 명확한 결과를 얻을 수 있다면 건강보험의 수가계약제 하에서 효율성 개념을 바탕으로 한 환산지수계약의 도입을 신중하게 고려해 볼 수 있다.

• 한국가스학회지
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• 제19권6호
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• pp.40-46
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• 2015

이론공연비방식 엔진은 삼원촉매를 이용하여 유해배기가스를 매우 효과적으로 저감시킬 수 있는 장점을 가지고 있다. 삼원촉매는 높은 정화효율을 보이는 공연비범위가 좁기 때문에 엔진에서의 공연비 제어가 매우 중요하다. 본 연구에서는 삼원촉매 성능을 평가하기 위하여 다양한 운전영역에서 삼원촉매의 전환효율을 비교 분석하였다. 최적의 전환효율을 보이는 당량비를 확인하기 위하여 당량비 제어값 변화에 의한 전환효율을 살펴보았다. 실험결과 당량비 제어를 통하여 각 운전조건에서 NMHC, CH4, CO 및 NOx의 전환효율이 95%이상 나타내는 최적 운전조건을 찾을 수 있었다. 동등한 배기가스 온도 조건에서는 출력이 증가할수록 최적당량비가 선형적으로 증가하는 경향을 보였다.

• 한국분무공학회지
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• 제25권4호
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• pp.196-203
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• 2020

Nowadays, urea SCR technology is considered as the most effective NOx reduction technology of diesel engine. However, low NOx conversion efficiency under low temperature conditions is one of its problems to be solved. This is because injection of UWS (Urea Water Solution) is impossible under such a low temperature condition due to the problem of insufficient of urea decomposition and urea deposits. In several previous studies, it has been reported that appropriate control of the amount of ammonia adsorbed on SCR catalyst can improve the NOx conversion efficiency under low temperature conditions. In this study, we tried to find out how much the NOx conversion efficiency increases with respect to the amount of ammonia adsorbed on the catalyst, and what the temperature conditions that the ammonia slip occurs. This study shows the results of 8 times repeated WHTC test with a diesel engine, in which UWS was injected with NH3/NOx mole ratio of '1'. Through this study, it was found that 13% of the NOx conversion efficiency of WHTC increased while the θ (ammonia adsorption rate) increased from "0%" to "22%". In addition, it is found that in cases of high θ value, the significant improvement of NOx conversion efficiency at low temperatures presented during the beginning period of WHTC and at high temperature and transient conditions presented during last part of WHTC test. The NH3 slip occurring condition was 250℃ of catalyst temperature and 10% of θ, and the amount of NH3 slip increased as the temperature and θ are increased.

• 한국자동차공학회논문집
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• 제13권3호
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• pp.80-86
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• 2005

In this study, we investigated the characteristics of the conversion efficiency and the effect of ageing Diesel Oxidation Catalyst (DOC). The DOC was composed of Warm-up Catalytic Converter (WCC) and Underbody Catalytic Converter (UCC). As the result, the conversion efficiency of THC was 10$\~$50$\%$ on WCC and 30$\~$40$\%$ on UCC .The conversion efficiency of CO was 80$\~$90$\%$ on WCC and remained 10$\~$20$\%$ of CO was purified on UCC. The WCC shows high conversion efficiency on CO. After 20 hours aging process of engine bench, conversion efficiencies of THC and CO were improved a little, because it was activated catalyst surface by 20 hours aging. In case of 80 hours aging, the conversion efficiencies of THC and CO were decreased on WCC. However, the UCC was not affected by aging process .