Phenomenological investigations on the turbulent flow structures in a rod bundle array with mixing devices

Detailed turbulent flow profiles have been measured on a square sub-channel geometry with typical mixing devices. For a fine examination of the lateral flow structure on a sub-channel geometry with 2D LDA, a 5 × 5 rod bundle array was fabricated as 2.6 times larger than the real bundle size. The mixing devices used were a typical split type and a swirl type. The experiments were performed at the condition of Re = 48,000 (axial bulk velocity 1.48 m/s) and the water loop was maintained at the conditions of 35 °C and 1.5 bar during an operation. As for the results, distinct intrinsic flow features were observed according to the type of mixing devices. In a typical split type, there was no remarkable swirling flow within a sub-channel and the lateral flow was vigorous in the gaps. In the swirl type, a single swirling flow was dominant within a sub-channel and there were relatively small lateral flows in the gaps.