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정지환,Jeong, Ji-Hwan 한국과학기술단체총연합회 1996 과학과 기술 Vol.29 No.7
1249년부터 최근까지 설립된 44개의 컬리지로 구성된 영국의 옥스포드대학교는 역대 영국 수상의 절반을 배출한 명문교로 모든 영국인들이 마음의 고향처럼 동경하는 대학교이다. 대학이 가장 자랑하는 1602년에 설립된 보들레이안 도서관은 7백여만권의 장서를 소장하고 있으며 현재 50여명의 한국 유학생과 20여명의 교환교수 및 박사후연구과정생들이 있다.
RFID 시스템에서 파워 컨트롤을 적용한 각 다중 태그 충돌 방지 알고리즘의 성능분석
정지환(Ji-Hwan Jeong),엄준봉(Jun-Bong Eom),이태진(Tae-Jin Lee) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.11
As the mobile RFID reader has been widely used, reducing power consumption of RFID reader needs to be considered. Tag Anti-collision Algorithms - DFSA Algorithm and Binary Tree Algorithm using Power-control has been proposed to reduce power consumption of RFID reader effectively in this paper. Also the proposition has been simulated for the performance comparison with Tag Anti-collision Algorithms not using Power-Control.
정지환(Ji Hwan Jeong),장근선(Keun Sun Chang),이현우(Hyun Woo Lee) 한국유체기계학회 2003 유체기계 연구개발 발표회 논문집 Vol.- No.-
An experimental study was performed to examine the heat transfer performance of individual rows of fin-tube heat exchangers. The heat transfer performance was measured using air-enthalpy type calorimeter. The examined heat exchangers consists of 7φ tube and fin patterns of them are slit and louver types. Equivalent fin spacing are 18 FPI for all samples, and the number of tube rows were 2. In order to confirm that thermal boundary condition on fins of each row are the same, physically separated between two rows as well as connected heat exchangers were used. The frontal air velocity varied from 0.7 to 2.5 m/s. Heat transfer performance for each row are measured. It was observed that the heat transfer coefficient of the 2nd row were smaller than that of the 1st row at low Reynolds number while larger at high Reynolds number.
CFD를 이용한 OPR1000 발전소 파단방출 이물질이동 해석
정지환(Ji Hwan Jeong),박종필(Jong Pil Park),김원태(Won Tae Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
In response to GSI-191, Potential of PWR Sump Blockage Post-LOCA, NEI and the industry formed the PWR Sump Performance Task Force. Its main purpose was to create a methodology document that could be used as a guideline for PWR operators to be addressed the issue. The NEI methodology document provides basic guidance on approach and various methods available. But some additional information will be required in order to apply to specific plants, such as OPR1000. The present work aims to evaluate debris transport during LOCA blow-down, the first transport mode, based on CFD analysis. The target plant is U1chin 3&4 which is OPR-1000 plant. The results indicate that flow patterns are strongly affected by structural features of containment, and location of components such as steam generator, RCP and pipes. The present work takes advantage of 3D CAD model so that real geometry of OPR1000 plant was used. The analysis results give a clear figure about flow pattern in containment during LOCA blow-down, and fraction of debris transport to upper containment, which is one of major safety issues.
Ji Hwan Jeong(정지환),Young Chel Kweon(권영철),Hyun Jung Kim(김현정) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
The experimental measurements show that the heat transfer performance of heaters submerged in a water pool was enhanced when ultrasonic vibration is applied to the water pool. The increase rate in CHF values varied depending on inclination angle of heated surface with the maximum when horizontal downward facing. The experimental conditions inside the water pool with and without ultrasonic vibration were analysed using FLUENT. Steam bubbles are not simulated using FLUENT due to its limitation. Based on the examination results, it can be concluded that an ultrasonic vibration enhances fluid mixing around heater itself and thus provides heated surface with fresh water. This has an effect of lowering liquid temperature adjacent to heater surface, and in turn, leads to a heat transfer augmentation.