Numerical Simulation and Analysis of Flow and Heat Transfer Characteristics in Annular Helical Cruciform Fuel Elements
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摘要: 螺旋十字燃料作为一种较为新型的燃料元件，由于其独特的强搅混作用和自支撑等优点而受到广泛关注，但是仍存在中心温度偏高等问题。为解决相关问题，本文提出一种环形螺旋十字燃料，并采用数值模拟的方法研究其内部的流动与换热特性。结果表明，功率计算采用余弦分布的方法会存在轴向功率梯度太大等问题，也会导致计算得到的燃料元件最高温度比实际情况下偏高。此外，相比于螺旋十字燃料，环形螺旋十字燃料具有更强的搅混作用和更低的燃料元件最高温度；并且，入口速度的增加可以进一步加强冷却剂之间的搅混作用从而增强换热能力，但入口温度以及功率密度对搅混作用的影响较小。在燃料元件温度分布方面，环形螺旋十字燃料元件在不同高度处的最高温度位置会受到冷却剂横向速度大小的影响，在冷却剂横向速度大的位置，对燃料元件的换热更强，因此此处的燃料元件温度更低。Abstract: Helical cruciform fuel, as a relatively new type of fuel element, has attracted widespread attention due to its unique advantages such as strong mixing effects and self-supporting. However, helical cruciform fuel still faces issues such as high central temperature. To address these problems, this paper proposes an annular helical cruciform fuel and investigates its internal flow and heat transfer characteristics using numerical simulation methods. The results indicate that using a cosine distribution for power calculation leads to issues such as excessive axial power gradient and overestimation of fuel peak temperature compared to the actual situation. Furthermore, compared to helical cruciform fuel, annular helical cruciform fuel exhibits stronger mixing effects and lower maximum fuel temperature. Additionally, increasing inlet velocity can further enhance the mixing between coolant channels, thereby improving heat transfer capability, but the effects of inlet temperature and power density on mixing are minor. Regarding fuel temperature distribution, the location of maximum temperature at different heights of the annular helical cruciform fuel element is influenced by the magnitude of coolant transverse velocity. Higher transverse velocity results in stronger heat transfer to the fuel element, leading to lower fuel element temperatures in these regions.
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图 7 燃料元件不同轴向位置功率分布
Figure 7. Power Distribution of Different Axial Positions of Fuel Elements
图 8 不同功率分布下燃料元件最高温度
Figure 8. Maximum Temperature of Fuel Element Under Different Power Distributions
图 10 有效增殖因数与水铀比的关系
keff—有效增殖因数；$V_{{\mathrm{H}}_2{\mathrm{O}}} $/VU—水铀比，表示慢化剂和燃料的体积比
Figure 10. Relationship Between the keff and the Water-to-Uranium Ratio
图 11 环形螺旋十字燃料冷却剂与燃料表面温度
Figure 11. Coolant and Fuel Surface Temperature of Annular Helical Cruciform Fuel Element
图 14 不同入口速度和功率密度对平均二次流的影响
Figure 14. Impact of Different Inlet Velocities and Power Densities on Secondary Flow
图 15 不同入口温度对平均二次流的影响
Figure 15. Impact of Different Inlet Temperatures on Secondary Flow
图 16 不同条件下的燃料沿程平均对流换热系数
h—平均对流换热系数
Figure 16. Average Convective Heat Transfer Coefficient Under Different Conditions
图 17 不同入口速度下轴向冷却剂温度
Figure 17. Axial Coolant Temperature at Different Inlet Velocities
图 18 不同条件下冷却剂温度分布
Figure 18. Coolant Temperature Distribution under Different Conditions
图 19 不同位置处燃料元件冷却剂横向速度分布和燃料截面温度分布
Figure 19. Transverse Velocity Distribution of Coolant and Temperature Distribution of Fuel Cross-section at Different Locations
表 1 环形螺旋十字燃料元件结构参数
Table 1. Structural Parameters of Annular Helical Cruciform Fuel Element
参数 螺旋十字燃料元件 环形螺旋十字燃料元件 轴向长度/m 0.5 0.5 RE/mm 3 1.51（外），3.74（内） r/mm 2.157 3.65（外），1.42（内） L/mm 0.044 0.044 螺距/cm 100 100 
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表 2 冷却剂和燃料元件热物性参数
Table 2. Thermal Properties of Coolant and Fuel Element
物理量 冷却剂 燃料元件 密度
ρ/(kg∙m−3)ρ=−3694+17.547T−0.01716T2 5212 定压比热容
cp/(J∙kg−1∙K−1)cp=−3.58×106+18905.8T−33.3T2+0.01955T3 871 导热系数
λ/(W∙m−1∙K−1)λ=−1.66482+0.00939T−9.6×10−6T2 60
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