Experimental study on the heat transfer enhancement in sub-channels of 6 × 6 rod bundle with large scale vortex flow mixing vanes

In this study, single-phase heat transfer characteristics for downstream flow in the support grid of 6 × 6 rod bundle were investigated. It is known that turbulence generated by a support grid with split mixing vanes enhances heat transfer in a rod bundle. However, the enhancement is observed in relatively short length. Further, a support grid with large scale vortex flow (LSVF) mixing vanes enhances heat transfer over a relatively longer distance. Based on the results of previous studies, heat transfer experiments were performed at Reynolds numbers of 30,000 and 50,000, and the effects of heat transfer enhancement with both i) the split mixing vanes and ii) LSVF mixing vanes were compared in this study. The results showed that the effects of heat transfer enhancement in the rod bundle region by the split mixing vanes were maintained up to a length of 15 Dh behind the spacer grid. At a Reynolds number of 50,000, it was observed that the effects of heat transfer enhancement by the LSVF mixing vanes were approximately 3% higher than those by the split mixing vanes for a distance ranging in 1-15 Dh behind the spacer grid.