Research on coherent structure in 4-rod bundle lattice based on CFD

Abstract

Coherent structures exist only when the ratio of pitch to rod diameter (P/D) in the rod bundle lattice is less than 1.1. In order to produce coherent structures in large P/D lattices, roughness elements are arranged on the outer surface of the rod bundle. This method can enhance the heat transfer capability of the rod bundle lattice. The whole process of the generation and development of coherent structures are analyzed. The Reynolds stress model (RSM) is used for the numerical calculation of the flow and heat transfer of the working fluid in a 4-rod bundle lattice with a P/D of 1.25. The whole process of the generation and development of the coherent structures in the 4-rod bundle lattice is shown. The influence of different micro-rib size (e) on the coherent structures and the flow and heat transfer of the rod bundle lattice is analyzed. The interaction between the fluid channels in the 4-rod bundle lattice is also analyzed. The results show that with the arrangement of the micro-ribs in the large P/D rod bundle lattice, coherent structures are produced, which enhances the flow mixing between the channels of the 4-rod bundle lattice. The flow and heat transfer characteristics of the rod bundle lattice have been greatly changed, especially when P/(D + 2e) = 1.02, the heat transfer capacity of the rod bundle lattice increases by 44.1% while the flow resistance increases by 3.4 times. This research can provide theoretical support for the design and improvement of reactor fuel elements, heat exchangers and steam generators.