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윤현기,탁혜영,이창문,변헌수,윤순도 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1
In this work, biodegradable films were prepared by using jerusalem artichoke-JA, mungbean starch-MBS, polyvinyl alcohol-PVA, and plasticizers( glycerol-GL, citric Acid-CA, and ascorbic Acid-AsA). The prepared films were synthesized by using UV curing process. The films were characterized by scanning electron microscope-SEM and fourier transform infrared(FT-IR). The physical/optical properties of the films was investigated including their tensile strength-TS, elongation at break-%E, swelling behavior-SB, solubility-S, and water vapor absorption. The results, it could be verified that TS and water resistance were improved by the addition of JA. In addition, the biodegradability in soil and applicability of the coating on a fruit were evaluated. The degree of biodegradability revealed that the films are degraded by about 40-80% after 170days. When compared with the decomposition of an uncoated apple and a coated apple revealed that even after 70 days, the coated apple did not decompose.
전압 리플을 이용해 영전류 스위칭하는 두 개의 트랜스포머를 가지는 위상천이 풀-브릿지 컨버터
윤현기,한상규,문건우,윤명중 전력전자학회 2006 전력전자학회 논문지 Vol.11 No.1
This paper presents a Zero-Current Switching(ZCS) two-transformer phase-shifted full-bridge(TTFB) converter using voltage ripple. The proposed converter provides Zero-Voltage Switching(ZVS) of leading leg switches and ZCS of lagging leg switches using voltage ripple. Especially, circulating current is reduced by ZCS operation and there are no additional components required for the soft switching of power switches. Furthermore, in case of light load, ZVS operation of lagging leg can be achieved. The operations, analysis and design consideration of proposed converter are presented. To verify the validity of the proposed converter, experimental results for a 410W (205[V], 2[A]) prototype are presented. 본 논문에서는 출력 전압의 리플을 이용하여 지상 레그(lagging leg)의 스위치들의 영전류 스위칭(ZCS)을 수행하는 두 개의 트랜스프머를 가지는 위상천이 풀-브릿지 컨버터를 제안하다. 제안된 컨버터는 진상 레그(leading leg)의 스위치들은 영전압 스위칭(ZVS)을 수행하고, 지상 레그의 스위치들은 출력 전압-더블러(Voltage-Doubler)의 전압 리플차를 이용해 출력 다이오드의 전류 전환(commutation)이 빠르게 이루어지도록 하여서 중부하에는 영전류 스위칭을, 경부하에서는 영전압 스위칭을 가능하게 한다. 또한 출력측의 전압 리플차를 이용하기 때문의 기존의 1차측 부스트 캐패시터를 이용하는 컨버터에 비해 턴비를 이용하여 보다 빠른 전류 전환을 수행할 수 있는 장점을 가진다. 따라서 별도의 추가적인 소자없이 모든 스위치의 소프트스위칭이 가능하도록 하고, 지상 레그의 영전류 스위칭을 통해서 환류구간의 순환전류도 없애줌으로써 높은 효율을 얻을 수 있다. 모드 해석과 실험을 통하여 제안 컨버터의 성능을 검증한다.
Discharge header design inside a reactor pool for flow stability in a research reactor
윤현기,최용석,서경우,김성훈 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.10
An open-pool type research reactor is designed and operated considering the accessibility around the pool top area to enhance the reactor utilization. The reactor structure assembly is placed at the bottom of the pool and filled with water as a primary coolant for the core cooling and radiation shielding. Most radioactive materials are generated from the fuel assemblies in the reactor core and circulated with the primary coolant. If the primary coolant goes up to the pool surface, the radiation level increases around the working area near the top of the pool. Hence, the hot water layer is designed and formed at the upper part of the pool to suppress the rising of the primary coolant to the pool surface. The temperature gradient is established from the hot water layer to the primary coolant. As this temperature gradient suppresses the circulation of the primary coolant at the upper region of the pool, the radioactive primary coolant rising up directly to the pool surface is minimized.Water mixing between these layers is reduced because the hot water layer is formed above the primary coolant with a higher temperature. The radiation level above the pool surface area is maintained as low as reasonably achievable since the radioactive materials in the primary coolant are trapped under the hot water layer. The key to maintaining the stable hot water layer and keeping the radiation level low on the pool surface is to have a stable flow of the primary coolant. In the research reactor with a downward core flow, the primary coolant is dumped into the reactor pool and goes to the reactor core through the flow guide structure. Flow fields of the primary coolant at the lower region of the reactor pool are largely affected by the dumped primary coolant. Simple, circular, and duct type discharge headers are designed to control the flow fields and make the primary coolant flow stable in the reactor pool. In this research, flow fields of the primary coolant and hot water layer are numerically simulated in the reactor pool. The heat transfer rate, temperature, and velocity fields are taken into consideration to determine the formation of the stable hot water layer and primary coolant flow. The bulk Richardson number is used to evaluate the stability of the flow field. A duct type discharge header is finally chosen to dump the primary coolant into the reactor pool. The bulk Richardson number should be higher than 2.7 and the temperature of the hot water layer should be 1 C higher than the temperature of the primary coolant to maintain the stability of the stratified thermal layer.