Numerical Study of Spacer Effects on Convective Heat Transfer at Low Flow Rates
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摘要: 针对带格架圆管在低流量高热流密度下的热工水力特性开展了数值研究。通过经验关联式与实验数据分别对光滑圆管内单相水低流量对流传热与格架效应进行标定，确立了基于SST k-ω模型的计算流体动力学（CFD）方法。模拟结果表明，格架下游传热特性取决于浮升力参数大小。强迫对流区与混合对流传热下降区，格架下游传热始终增强，努塞尔数呈指数衰减；混合对流传热恢复区与自然对流区，由于流场与传热的耦合作用，格架下游传热存在恶化现象，努塞尔数呈阻尼振荡。格架下游传热影响范围随着浮升力参数的增加先增大后减小。格架阻塞比越大，传热振荡越剧烈，格架致传热恶化的程度提高。该研究可为低流量堆芯内格架设计提供参考。Abstract: A numerical study is carried out for the thermal-hydraulic characteristics of a circular tube with spacer at low flow rates and high heat flux. The convective heat transfer of single-phase water in a smooth circular tube at low flow rates and the spacer effects are calibrated by the empirical correlation and experimental data. A CFD method based on the SST k-ω model is established. The simulation results show that the heat transfer characteristics downstream of the spacer depend on the buoyancy lift parameter. For the forced convection zone and mixed convection heat transfer decreasing zone, the heat transfer downstream of the spacer is always enhanced and the Nussel number decays exponentially. For the mixed convection heat transfer recovery zone and natural convection zone, due to the coupling effect of flow field and heat transfer, the heat transfer downstream of the spacer deteriorates and the Nussel number oscillates with damping. The influence range of heat transfer at the downstream of the spacer first increases and then decreases with the increase of buoyancy lift parameters. The larger the spacer blocking ratio is, the more severe the heat transfer oscillation is, and the worse the heat transfer caused by the spacer is. This study can provide a reference for the design of core in a low-flow core.
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图 1 光滑圆管内数值模拟值与Jackson关系式[2]对比
Figure 1. Comparison of Numerical Simulation with Jackson’s Correlation in a Smooth Circular Tube
图 2 格架下游数值模拟结果与实验数据对比
Figure 2. Comparison of Numerical Simulation with Experimental Data Downstream of the Spacer
图 3 不同浮升力参数下光滑圆管内归一化速度与湍动能分布
u—径向速度；uτ—摩擦速度；τw—壁面切应力；y—远离壁面距离；R—管内半径
Figure 3. Distribution of Normalized Velocity and TKE in a Smooth Circular Tube with Different Buoyancy Lift Parameters
图 5 不同工况下格架下游传热特性
Figure 5. Heat Transfer Characteristics Downstream of the Spacer with Different Working Conditions
图 6 工况2沿轴向速度与涡粘度分布
μt—涡粘度
Figure 6. Distribution of Velocity and Eddy Viscosity along the Axial Direction in Case 2
图 7 工况4沿轴向速度与涡粘度分布
Figure 7. Distribution of Velocity and Eddy Viscosity along the Axial Direction in Case 4
图 8 格架影响下圆管内流场云图
r—远离圆管中心距离
Figure 8. Cloud Chart of Flow Field in a Circular Tube with the Influence of the Spacer
图 9 不同BR下格架下游传热特性
Figure 9. Heat Transfer Characteristics Downstream of the Spacer with Different BRs
表 1 几何参数与边界条件设置
Table 1. Setting of Geometric Parameters and Boundary Conditions
参数名 参数值 圆形通道内径（D）/mm 11.9 圆形通道长度（L）/m 3（约252D） 采样点位置（X）/m 1.5（约126D，充分发展段） 工作介质与物性参数 单相水和美国国家标准与技术研究院（NIST） Real Gas模型 运行压力（P）/MPa 15.5 质量流速（G）/(kg·m−2·s−1) 70~200 热流密度（q）/(kW·m−2) 10~50 入口温度（Tin）/℃ 150~200 
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表 2 计算工况参数
Table 2. Parameters of Calculation Conditions
工况 区域 G/
(kg·m−2·s−1)q/
(kW·m−2)Tin/℃ Bo 1 强迫对流区 200 10 200 5.02×10−7 2 混合对流传热下降区 150 20 200 2.67×10−6 3 混合对流传热恢复区 100 25 200 1.33×10−5 4 自然对流区 70 50 150 9.04×10−5 表中G、q、Tin为本文推荐值，工况仅依据Bo进行划分
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