Natural circulation in an enclosed rod bundle of large aspect ratio
Natural circulation in an enclosed rod bundle of large aspect ratio
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大长径比封闭棒束自然循环
DOI：
10.1016/j.applthermaleng.2020.116534
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发表时间：
2021
影响因子：
6.4
通讯作者：
Chinembiri K
中科院分区：
文献类型：
--
作者：
Chinembiri K
用大涡模拟(LES)方法研究了封闭高杆管束内的强湍流自然环流。棒束由36根加热棒和一根被冷却的安全壳包围的绝缘中心管组成。这种几何形状与核燃料束和通用热交换器直接相关。对于核燃料捆绑，在事故情况下，自然循环是重要的。模拟了光束束的60°方位周期扇区。两种情况下基于高度的瑞利数分别为7.6×1012和1.23×1013。系统的流动、湍流和热特性在顶部、中部和底部(约0.2、0.6和0.2分裂)表现出强烈的明显特征，这些特征受到安全壳表面垂直发展的浮力驱动边界层的强烈影响。顶部区域流动基本停滞，热力层结较强，横流较弱。然而，在安全壳壁上形成了层流边界层，随后转变为湍流。这被证明是棒束中的主要流动特征。层流的相似解和无约束平板的Nusselt关联式分别很好地描述了这一顶部区域的速度分布和换热。在中等高度区域，流动可以自然地分为外部流动和中心流动区域。前者类似于简单的矩形、非对称加热/冷却空腔内的流动，而向安全壳的换热可以用湍流自然对流关联式来很好地表示。中心流区在很大程度上类似于加热向上的管道/通道流动中的混合对流，尽管来自外部区域的流体的卷吸意味着流动在轴向加速，直到中间高度。不考虑两个区域的差异，棒材和安全壳壁面上的流场和热场的近壁行为在不同高度以及两个区域之间具有很强的相似性。在简单的几何形状中，它们与浮力驱动的流动也是一致的。在底部区域，流动主要是来自安全壳壁面的撞击射流以及从外部区域到内部区域的横流。
Highly turbulent natural circulation in an enclosed tall rod bundle is investigated using Large Eddy Simulation (LES). The rod bundle consists of 36 heated rods and an insulated central tubeenclosed by a cooled containment wall. This geometry is directly relevant to nuclear fuel bundles and generic heat exchangers. For nuclear fuel bundles, natural circulation is of importance in accident scenarios. A 60° azimuthally periodic sector of the bundle is modelled. The Rayleigh number based on the height is 7.6× 10 12 and 1.23× 10 13 for the two cases studied. The flow, turbulence, and thermal characteristics of the system show strong distinct features in the top, middle, and bottom regions (about 0.2, 0.6, and 0.2 splits), which are strongly influenced by the vertically developing buoyancy-driven boundary layer on the containment surface. The flow in the top region is largely stagnant with strong thermal stratification and weak cross flow. A laminar boundary layer is however formed on the containment wall which later transitions to turbulence. This turns out to be the dominant flow feature in the rod bundle. The velocity profile and heat transfer in this top region are well represented, respectively, by a similarity solution for laminar flow and a well-established Nusselt correlation for an unconfined flat plate. In the middle-height region, the flow can be naturally split into an outer flow and a central flow zone. The former resembles the flow in a simple, rectangular, asymmetrically heated/cooled cavity, and the heat transfer to the containment is well represented by a turbulent natural convection correlation. The central flow zone largely resembles mixed convection in a heated upwards pipe/channel flow, though the entrainment of fluid from the outer zone means that the flow accelerates axially until the middle-height. Irrespective of the differences in the two zones, the near-wall behaviour of the flow and thermal fields on the rods and containment wall shows a strong similarity at different heights as well as between the two zones. They are also shown to be consistent with buoyancy-driven flows in simple geometries. In the bottom region, the flow is dominated by an impinging jet from the containment wall and a resultant cross flow from the outer zone to the inner one.
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影响因子：
4.6
作者：
E. Koschmieder
通讯作者：
E. Koschmieder
DOI：
10.1016/j.ijheatmasstransfer.2018.02.042
发表时间：
2018-08
影响因子：
5.2
作者：
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两个垂直平行板之间自然对流的湍流传热
DOI：
--
发表时间：
2002
期刊：
影响因子：
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作者：
T. Inagaki;S. Maruyama
通讯作者：
S. Maruyama
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DOI：
--
发表时间：
1986
期刊：
影响因子：
--
作者：
R. Cheesewright
通讯作者：
R. Cheesewright
DOI：
10.1016/s0142-727x(00)00033-3
发表时间：
2000-12-01
影响因子：
2.6
作者：
Betts, PL;Bokhari, IH
通讯作者：
Bokhari, IH