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ANSYS-CFX 코드를 이용한 저압 미포화비등 조건에서의 기포율 분포 해석

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Abstract
The boiling phenomena may occur near the heater surface, which has higher temperature than the liquid saturation temperature, although the liquid temperature doesn't reach the saturation temperature. This is called the subcooled boiling flows. These phenomena could occur in transient state such as LBLOCA(Large Break Loss Of Coolant Accident), and lead the precipitation of boron at the surface of fuel. Therefore, it is important phenomena on operation and safety of nuclear reactors.
Many studies have focused on flow boiling at high-pressure conditions. However, the low-pressure subcooled boiling could take place in the passive heat exchanger and severe accident mitigation features. There is the difference of thermal-hydrodynamic characteristics at low-pressure from those at high-pressures, such as the behavior of vapor bubbles, density of liquid and vapor. Because the flow becomes consequently complicated, assessment and verification of related models are required.
Existing CFD(Computational Fluid Dynamic) codes have been mostly adopting the heat partition model as the wall boiling model. The results of simulation may sensitively vary with sub-models of major parameters on this model. For the above reasons, it is not appropriated to directly apply the same models on major parameters both to high-pressure and low-pressure conditions. Therefore, it is required to sensitivity analyses of sub-models for accurate simulations.
In this study, subcooled boiling experiments were analyzed using a commercial CFD code, ANSYS-CFX, 17.2, that adopts the heat partition model. The experiments for simulation includes those conducted at high- and low-pressure conditions. The predicted distribution of the void fraction are compared with the experiment results. The ANSYS-CFX code was applied to the experiments of Bartolomey and Christensen at high-pressure conditions, and showed good agreement with measured data for the void fraction. On the other hand, at low-pressure conditions, the distribution of void fraction did not match for SUBO and JNU experiments. In simulation of both experiments, the concentration of bubbles is near the heated surface with default models. Therefore, the sensitivity analysis of bubble departure diameter, D_d, in the heat partition model was performed to evaluated the parametric effect on void fraction distribution and to improve the prediction capability. As a result, it was improved to predict the area-averaged void fraction along the axial direction for the experimental data.
Furthermore, the simulation of IVR-ERVC(In-Vessel corium Retention through External Reactor Vessel Cooling) was performed for innovative safety plant, iPOWER. The iPOWER adopts the PMCCS(Passive Molten Core Cooling System) for the severe accident mitigation features. The PMCCS considers not only IVR-ERVC but Core Catcher. Both of them, there may be the subcooled boiling flow under the low-pressure conditions during mitigation of accidents as the indirect cooling method. Therefore, in this study, two-phase flow was investigated through the multidimensional numerical analysis of iPOWER IVR-ERVC under the low-pressure subcooled boiling flow using ANSYS-CFX code.
Author(s)
현수연
Issued Date
2018
Awarded Date
2018. 2
Type
Dissertation
URI
http://dcoll.jejunu.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000008400
Alternative Author(s)
Hyeon, Su Yeon
Affiliation
제주대학교 일반대학원
Department
대학원 에너지공학과
Advisor
이연건
Table Of Contents
LIST OF FIGURES ⅲ
LIST OF TABLES ⅴ
SUMMARY ⅵ
Ⅰ. 서론 1
Ⅱ. ANSYS-CFX 모델 3
1. Two-fluid 모델 3
2. 열분배 모델 5
3. 열분배 모델 내 부모델 8
1) 핵비등생성밀도 8
2) 기포이탈빈도수 9
3) 기포이탈직경 9
Ⅲ. 고압 미포화비등 실험 해석 11
1. Bartolomey 실험 해석 12
2. Christensen 실험 해석 15
Ⅳ. 저압 미포화비등 실험 해석 18
1. SUBO 실험 해석 18
2. JNU 실험 해석 26
3. 계면 운동량 전달 및 기포율 분포 30
4. 기포이탈직경 모델 수정 및 민감도 분석 35
Ⅴ. IVR-ERVC 조건에서의 미포화비등 해석 39
1. iPOWER IVR-ERVC 39
2. IVR-ERVC 조건에서의 미포화비등 해석 41
Ⅵ. 결론 49
REFERENCE 51
감사의 글
Degree
Master
Publisher
제주대학교 일반대학원
Citation
현수연. (2018). ANSYS-CFX 코드를 이용한 저압 미포화비등 조건에서의 기포율 분포 해석
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Faculty of Applied Energy System > Energy and Chemical Engineering
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