Abstract In this paper, the thermal-hydraulic performance in the downstream of the spacer grid in a 7 × 7 rod bundle is numerically studied. The guide tubes effects are revealed by the comparisons of the flow and heat transfer behavior in two types of rod bundles, one without guide tubes and the other with guide tubes. It is found that the cross flow diagonals are fully developed at Z = 2 Dh and unable to sustain at Z = 8 Dh downstream of the spacer grid. The guide tubes discontinue the cross flow diagonals and would decrease the secondary flow intensity. The downstream temperature distribution is influenced by the evolution of the secondary flow as well as the guide tubes. The non-uniformity of the temperature distribution has the lowest value at Z = 2 Dh and the guide tubes would make the temperature distribution more uneven. Furthermore, the normalized Nusselt number in both fuel rod bundles reaches the peak at Z = 2 Dh and then decreases consistently. However, the heat transfer can be enhanced by 15% at least because the secondary flow still exists. The normalized Nusselt numbers downstream of the spacer grid in the rod bundle with guide tubes are smaller than those without guide tubes. Overall, the guide tubes would inhibit the secondary flow and weaken the heat transfer capability downstream of the spacer grid.

中文翻译：

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带隔栅和导管的7×7杆束热工水力性能数值研究

摘要 本文对7×7棒束隔栅下游的热工水力性能进行了数值研究。通过比较两种棒束的流动和传热行为来揭示导管效应，一种没有导管，另一种有导管。发现横流对角线在 Z = 2 Dh 处完全发展，并且无法在间隔网格下游的 Z = 8 Dh 处维持。导管中断了横流对角线并且会降低二次流强度。下游温度分布受二次流和导管演变的影响。温度分布的不均匀性在 Z = 2 Dh 时具有最低值，导管会使温度分布更不均匀。此外，两个燃料棒束中的归一化努塞尔数在 Z = 2 Dh 处达到峰值，然后持续下降。但是，由于二次流仍然存在，传热至少可以提高 15%。带有导管的棒束中间隔网格下游的归一化努塞尔数小于没有导管的那些。总的来说，导管会抑制二次流并削弱隔栅下游的传热能力。