Convective heat transfer experiment of rod bundle flow with twist-vane spacer grid

An experimental work was conducted to investigate the convective heat transfer enhancement in a rod bundle by adopting the twist-vane spacer grid. The twist-vane spacer grid invented by our research group was uniquely designed to improve the thermal-hydraulic performance of nuclear fuel bundle for pressurized water reactor. As the test fluid, water was used. Using the 4 × 4 rod bundle of pitch-to-diameter ratio∼1.35 with the twist-vane spacer grid, the circumferential and longitudinal distributions of rod-wall temperature were measured upstream and downstream of spacer grid. The bundle-flow velocity was ∼1.5 m/s and Reynolds number was ∼42,000. Upstream of the spacer grid, the rod-wall temperature in the rod-gap region appears to be higher than that in the central region. Downstream of the spacer grid, the rod-wall temperature toward the twist-vane tip showed the lowest value, which might be because the twist-vane deflects the water flow directed to certain angular position of rod. The Nusselt number was also estimated and compared with the previous experimental data and correlations. The longitudinal variation of Nusselt number showed the heat transfer enhancement of up to 30% near downstream of the twist-vane spacer grid. Our belief is that the experimental results presented in this paper can be utilized for the verification and validation of the computational fluid dynamics code.