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마이크로 소결 구조 채널에서의 흐름 비등 열전달 특성 연구
김영환,신동환,김진섭,문우용,허재훈,이정호,KIM, YEONGHWAN,SHIN, DONG HWAN,KIM, JIN SUB,MOON, YOOYONG,HEO, JAEHUN,LEE, JUNGHO 한국수소및신에너지학회 2018 한국수소 및 신에너지학회논문집 Vol.29 No.1
The flow boiling heat transfer of water was experimentally investigated on plain and sintered microporous surfaces in a mini-channel. The effects of microporous coating on flow boiling heat transfer of subcooled water were investigated in a 300 mm long mini-channel with a cross section of $20{\times}10mm^2$. The test section has sufficiently long entrance length of 300 mm which provides a fully-developed flow before the channel inlet. The bottom side of the channel was heated by a copper block assembled with a high-density cartridge heater and other sides of the channel were insulated. The microporous surface was fabricated by sintering copper particles with the average particle size of $50{\mu}m$ on the top side of the copper block. Heat transfer measurement was conducted at the mass flux of $208kg/m^2s$ and the heat flux up to $500kW/m^2$. Microporous coated surface showed an earlier boiling incipience compared with plain surface regardless of the mass flux. Microporous coating were significantly attributed to local wall temperature and local heat transfer coefficient for flow boiling.
김영환(Yeonghwan Kim),권구형(Kuhyung Kwon),이충용(Chungyong Lee) 대한전자공학회 2017 전자공학회논문지 Vol.54 No.2
본 논문은 차량 내부에서 무선 에너지 전송 기술을 지원하기 위해 분산 안테나 시스템의 사용을 제안한다. 차량 내 무선 에너지 전송 시스템은 에너지 수신 단말기의 이동이 제한적이고, 채널 환경이 정적이며, 인체가 송신기와 가까운 특징을 갖는다. 이러한 상황에서 송신기의 배치는 인체에서의 수신 에너지와 에너지 수신 단말기에서의 수신 에너지의 양에 큰 영향을 미친다. 이에 본 논문은 기존 무선 통신 시스템에서 사용되는 중앙 집중형 안테나 시스템과 분산 안테나 시스템을 적용하였을 때의 차량 내 무선 에너지 전송 성능을 모의실험을 통해 비교하고, 분산 안테나 시스템이 더 좋은 성능을 가짐을 보인다. This paper considers an application of distributed antenna system (DAS) to a system of intra-vehicle wireless energy transfer (WET). The intra-vehicle WET system has features such as limited mobility of energy receiver, static channel environment and short distance between transmitter and human body. Under these conditions, location of transmitter highly affects the amount of energy received by human body and the energy received by energy receiving devices. We compare centralized antenna system (CAS) and the DAS in intra-vehicle WET system by simulation. The results show the DAS has superior performance to the CAS.
MDT 데이터를 활용한 심층 신경망 기반의 실내외 구분 기법
김영환(Yeonghwan Kim),김진만(Jinman Kim),이충용(Chungyong Lee) 대한전자공학회 2018 전자공학회논문지 Vol.55 No.10
본 논문은 LTE (long term evolution) 시스템에서 사용하는 minimization of drive test (MDT) 데이터를 이용한 심층 신경망(deep neural network, DNN) 기반의 실내외 구분 기법을 제안한다. 제안하는 기법은 MDT 데이터 중 실내외 구분에 가장 적합한 기준 신호 수신 전력(reference signal received power, RSRP)을 네트워크의 입력으로 사용한다. 이때 채널 페이딩의 효과를 줄이기 위해 RSRP는 이동 평균 필터에 통과시켜 전처리한 뒤 사용한다. 측정 조건에 따른 RSRP 값의 변동성에 강인한 네트워크를 구성하기 위하여 제안하는 기법은 실내외 상태 변화에 초점을 맞춰 동작하며 현재의 RSRP 값과 함께 과거의 RSRP값을 입력으로 사용한다. 또한 출력은 실내, 실외, 실내에서 실외로 이동, 실외에서 실내로 이동의 네 가지 상태로 구성된다. 실측 데이터를 이용한 실험 결과 제안하는 기법은 96.1%의 추정 정확도를 얻음을 확인하였다. In this paper, we propose a DNN-based indoor-outdoor (I/O) detection scheme using MDT data of LTE system. The proposed scheme utilize RSRP which is the most appropriate for I/O detection among MDT data as an input of the network. To minimize effect of channel fading, we pre-process RSRP with moving average filter. In order to construct a network robust to varying RSRP level, which changes according to its measured condition, the proposed scheme focuses on a I/O state transition and utilize present RSRP and past RSRP as an input. An output of the proposed scheme consists of 4 I/O states; indoor, outdoor, indoor-to-outdoor, outdoor-to-indoor. The proposed scheme achieves 96.1% accuracy according to simulation with field-measured data.
충전 조건에 따른 2상 밀폐 열사이펀의 열전달 특성 연구
김영환(Yeonghwan Kim),신동환(Dong Hwan Shin),김진섭(Jin Sub Kim),이정호(Jung Ho Lee) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
This research investigates the heat transfer characteristics of two-phase closed thermosyphon on various filling conditions. The thermosyphon consists of three sections such as evaporator, adiabatic and condenser, which are 300, 300 and 325 mm long, respectively, and the inner diameter is 25 mm. Deionized water is used as a working fluid. Local wall temperatures at both top and bottom surfaces of each section are measured at six different points of the thermosyphon using T-type thermocouples. The internal temperatures at the same points are also measured by inserting the thermocouples into the thermosyphon. Three filling conditions are considered as following degassed, degassed & vacuum and non-degassed. The thermal performance of the thermosyphon is measured at the heat flux ranging from 10 to 300 kW/m² and inclination angles of 15°, 45° and 90°. The results show that the evaporation heat transfer coefficients of three cases are similar at the lower heat flux than 100 kW/m². However, at the higher heat flux over 100 kW/m², the heat transfer coefficients of the top surface at inclination angle of 15° decrease due to the local dry out. In contrast, the heat transfer coefficients of the condenser section have totally different tendency between degassed and non-degassed cases at the low heat flux up to 150 kW/m². In is concluded that the non-condensable gas in the working fluid mainly affects the condensation heat transfer.