한국해양대학교

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하향 가열면을 갖는 경사채널에서의 유동비등

DC Field Value Language
dc.contributor.author 김형탁 -
dc.date.accessioned 2017-02-22T07:15:08Z -
dc.date.available 2017-02-22T07:15:08Z -
dc.date.issued 2016 -
dc.date.submitted 57097-01-20 -
dc.identifier.uri http://kmou.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000002231425 ko_KR
dc.identifier.uri http://repository.kmou.ac.kr/handle/2014.oak/10518 -
dc.description.abstract The recent accidents of the Fukushima nuclear power plants were of great concern worldwide. In a nuclear reactor severe accident involving core melt and reactor pressure vessel failure, it is important to provide an accident management strategy that would allow the molten core material to cool down, stabilize thermally and bring the core debris to a coolable state. One countermeasure for the molten corium ejected from the reactor vessel is to retain the core melt on a so-called core catcher as a newly engineered passive corium cooling system residing on the reactor cavity floor. The retained core melt is cooled by natural circulation flow of water coolant through the inclined cooling channel underneath the core catcher as well as the water pool overlaid on the melt layer. Two-phase flow boiling with downward-facing heated wall in the inclined cooling channel of the core catcher has drawn a special attention because this orientation of heated wall may cause boiling crisis at lower heat flux than that of a vertical or upward-facing heated wall. Although numerous studies have been carried out in experiments and modeling, flow boiling with downward facing heated surface has not been clearly understood due to its complex nature of the problem. Heat flux partitioning model such as ANSYS-CFX's wall boiling model calculates the individual heat flux components independently and can be used to predict the overall wall heat flux. However, these models require sub-models for the parameters on the physical heat transfer processes involved. In order to investigate boiling behavior in this inclined cooling channel with downward-facing heated wall and in particular to get some insight for developing a wall boiling model in thermal analysis of the core catcher, a lab-scale experiment was carried out with 1.2 m long rectangular channel, inclined by 10°~ 30°from the horizontal plane, 0.1 m x 0.1 m of channel cross section. The size of the heated wall was 0.06 m wide, 0.75 m long and the heat flux was provided by the Joule heating of the wall using DC electric current. The tests were conducted with near-saturated water at atmospheric pressure. The heat flux was varied in the ranges of 60 ~ 200 ㎾/㎡ for the mass flux of 100 ~ 300 ㎏/㎡s. Ten thin thermocouples of K-type were attached on the back of the heated steel plate at 5 points with a proper electrical insulation for the wall temperature measurement. These wall temperatures were measured to obtain the local heat transfer coefficients. High-speed video images showed that bubbles were sliding, continuing to grow, and combining with small bubbles growing at their nucleation sites in the downstream. Then the large bubbles coalesced when the bubbles grew too large to have a space between them. Finally, an elongated slug bubble formed nearly covering the heated wall and liquid film under the elongated slug bubble began to evaporate on the heated wall. The wall superheats were 5 ~ 18℃ for 60 ~ 200 ㎾/㎡ heat flux, 200 ㎏/㎡s mass flux, and 10°inclined angle. The f1ow boiling heat transfer coefficients were obtained by dividing the heat flux by the difference between the wall temperature and the bulk temperature of water. The measured flow boiling heat transfer coefficients for the range of test parameters were 5,000 ~ 12,000 W/㎡K. To account for the liquid film evaporation in the RPI wall boiling model in ANSYS CFX, the amount of liquid film evaporation was converted to an equivalent nucleate site density. The total nucleate site density consisted of two contributions: typical nucleate sites in liquid region and converted nucleate sites from liquid film evaporation in vapor slug region. With this improved model, numerical analysis using ANSYS CFX code was performed and the predicted wall superheat agreed well with the experimental data, while the original RPI model largely overpredicted the wall superheat. To validate the model predictions, another numerical analysis was conducted for the KAERI flow boiling experimental data. The model slightly underpredicted the wall superheat of the experimental data. Despite of the limited information of the KAERI experiment, the prediction of wall superheat by the improved model agreed somewhat well with the experimental data. -
dc.description.tableofcontents 목 차 Abstract i List of Tables vi List of Figures vii NOMENCLATURE xv 제 1 장 서론 1.1 연구배경 1 1.2 연구목적 3 제 2 장 문헌 조사 2.1 Flow Boiling의 정의 6 2.1.1 비등열전달 6 2.1.2 풀비등 7 2.1.3 유동비등 9 2.1.4 수직 가열 벽면에서 이탈하는 기포에 작용하는 힘 10 2.2 하향 가열면 (Downward-Facing Surface) 선행연구 11 2.2.1 풀비등에서의 경사각 실험 11 2.2.2 풀비등에서의 단일 기포 실험 11 2.2.3 풀비등에서의 경사각 실험 및 모델링 12 2.2.4 유동 비등 실험 13 2.3 Wall Boiling Model 14 2.3.1 Wall boiling model in ANSYS-CFX 17 2.3.2 Submodels for wall boiling model 18 제 3 장 경사채널 비등실험 3.1 실험 장치 41 3.1.1 실험 장치 구성 및 설계 조건 41 3.1.2 장치 세부 구성 및 계측 42 3.1.3 실험 변수 및 절차 46 3.2 실험 결과 및 고찰 48 3.2.1 실험 가시화 48 3.2.2 실험 열전달계수 측정 50 3.2.3 기포 slug 영상 분석 53 제 4 장 해석모델 개발 및 검증 해석 4.1 경사벽면에서의 Wall Boiling Model 90 4.1.1 액막 증발 모델 (Liquid Film Evaporation Model) 91 4.1.2 개선된 벽면비등모델 개요 94 4.2 해석모델 검증 95 4.2.1 경사채널 비등실험 해석 95 4.2.2 KAERI 실험 해석 100 제 5 장 결론 128 참고문헌 131 -
dc.language kor -
dc.publisher 한국해양대학교 대학원 -
dc.title 하향 가열면을 갖는 경사채널에서의 유동비등 -
dc.title.alternative A Study on the Flow Boiling in Inclined Channels With Downward-Facing Heated Wall -
dc.type Thesis -
dc.date.awarded 2016-02 -
dc.contributor.alternativeName Hyoung-Tak Kim -
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