Effect of Nucleation Density Model on CHF of Curved Surface
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摘要: 反应堆发生严重事故时，必须及时对反应堆压力容器（RPV）下封头进行外部冷却以降低下封头损毁可能性，事故期间下封头具有很高的热流分布，在实施外部冷却时可能出现由于过冷沸腾导致的气泡聚集而产生换热恶化从而烧毁。本研究利用ANSYS Fluent软件进行RPV外部冷却的临界热流密度（CHF）数值计算，并通过实验对比发现Basu Warrier和Dhir研究的成核密度模型可以很好地应用于球形表面CHF计算。通过对比球形和椭球形下封头CHF，认为椭球形下封头的CHF特性与球形结构完全不同，并不能用球形结构的实验和计算结果去推测椭球形结构的数值和变化规律。
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关键词:
- 临界热流密度（CHF） /
- 气泡成核密度 /
- 球形表面 /
- 椭球形表面
Abstract: In the event of a serious accident, external cooling can be applied to the lower head of the reactor pressure vessel (RPV) in order to reduce the possibility of damage to the lower head. However, there will be great heat flow surrounding the lower head of the RPV, so external cooling may cause subcooled boiling, which gathers bubbles and deteriorates heat exchange, even burns out. This research uses ANSYS Fluent to calculate the critical heat flux (CHF) for external cooling of the RPV, and it is found that the nucleation density model studied by Basu Warrier and Dhir can be well applied to the calculation of CHF on the spherical surface. By comparing the CHF of the spherical and ellipsoidal lower head, it is believed that the CHF characteristics of the ellipsoidal lower head are completely different from the spherical structure. The experimental and calculation results of the spherical structure cannot be used to infer the numerical value and variation of the ellipsoidal structure. -
图 5 上海交通大学实验几何模型
铜块(15°)—固体域为15°可移动铜块
Figure 5. Geometry of Test in Shanghai Jiao Tong University
图 8 球形和椭球形下封头CHF随角度的分布
Figure 8. CHF Distribution with Angle of Ellipsoidal and Spherical Geometry
表 1 弧形流道二维几何模型尺寸 单位：m
Table 1. Specific Size of a Two-Dimensional Geometry
弧形流道
内半径流道
宽度进口
宽度出口附加
段高度入口腔
室高度入口腔
室宽度1.485 0.076 0.076 0.3 0.305 0.686 
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表 2 3种稀疏不同的网格数
Table 2. Three Different Grids
网格类型 单元格 表面 节点 粗糙网格 49284 99973 50690 基础网格 139385 281116 141732 精细网格 202908 408632 205725
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θ 20° 30° 60° 80° 消除θ影响 CHF/（MW·m−2） 0.884 0.8385 0.7410 0.6955 0.767
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表 4 ULPU-V实验几何尺寸 单位：m
Table 4. Geometric Size of ULPU-V
流体域 固体域 几何 弧形流道
内半径进口
宽度流道宽度 入口腔室 出口延
长高度厚度 开始 结束 高度 宽度 几何1 1.485 0.076 0.076 0.076 0.305 0.686 0.3 0.076 几何2 1.485 0.076 0.152 0.152 0.305 0.686 0.3 0.076 几何3 1.485 0.076 0.076 0.152 0.305 0.686 0.3 0.076
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表 5 上海交通大学实验几何模型具体尺寸 单位：m
Table 5. Specific size of Shanghai Jiao Tong University
流体域内
半径流道
宽度出口附加段
高度进口附加段
高度固体域
厚度2 0.15 0.3 1 0.08
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表 6 实验值与数值计算值比较
Table 6. Comparison of Experiment and Numerical Calculation
实验 几何结构 热流分布 进口温度/
℃流量/
(m3·min−1)CHF计算值/
(MW·m−2)气相换热位置 CHF实验值/
(MW·m−2)CHF实验位置 误差/
%ULPU-V实验 几何1 图7 90 0.644 1.502 70.6°~78.3° 1.782 71° 15.7 几何2 图7 90 0.690 1.451 65.4°~79.1° 1.672 71° 13.2 几何3 图7 90 0.689 1.552 64.2°~78.1° 1.919 71° 19.1 上海交通大学实验 7.5° 均匀 70 0.125 0.95 5.4°~7.3° 0.953 — 0.30 37.5° 均匀 98 0.127 1.1 34.8°~35.8° 1.030 — −6.8 67.5° 均匀 98 0.144 1.2 53°~55.5° 1.158 — −3.63 82.5° 均匀 98 0.142 1.6 80°~83.4° 1.534 — −4.30 “—”表示实验中无明确数值
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表 7 弧形流道几何尺寸 单位：m
Table 7. Specific Size of Curved Geometry
流体域 固体域 弧形流道长轴 弧形流道短轴 流道宽度 厚度 1.871 0.935 0.076 0.076 1.485 1.485 0.076 0.076
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