Augmentation of single-phase forced convection heat transfer in tightly arrayed rod bundle with twist-vane spacer grid

The investigation on the augmentation of convection heat transfer of water rod bundle flow was performed experimentally. The 4 × 4 tightly arrayed rod bundle with narrow gap was tested and its P/D (Pitch-to-Diameter ratio) was ∼1.08. As the spacer grid, the twist-vane spacer grid was used. The axial mean bundle-flow velocity was U ∼ 1.0 m/s, and the corresponding Reynolds number was ∼10,400. Circumferential and axial distributions of rod-wall temperatures were measured. Upstream of twist-vane spacer grid, the rod-wall temperature at the subchannel center was measured to be lower than that at the rod-gap center. Downstream of twist-vane spacer grid, the rod-wall temperature toward the tip of twist-vane was lowest, which might be due to the deflected flow caused by twist-vane. The twist-vane spacer grid enhanced significantly the convection heat transfer in the tight-lattice rod bundle, and its maximum enhancement value was ∼77% near the downstream of spacer grid. Based on the present experimental data, the previous correlations of Nusselt number enhancement were compared and assessed. Then, the enhancement correlation of convection heat transfer for the twist-vane spacer grid in the tightly arrayed rod bundle was proposed.