Turbulent convective heat transfer behavior of supercritical water flowing upward in 2 × 2 rod bundle channels with various spacers

The turbulent flow and heat transfer characteristics of supercritical water, flowing in vertical 2 × 2 rod bundle channel, are numerically investigated to find useful methods to improve the cooling performance in the core of a supercritical water-cooled reactor. The heat transfer behavior as a function of mass flux and inlet temperature is analyzed and discussed. Standard grid and helical wire spacers are added to the channel, and overall heat transfer performance is evaluated and compared. The results indicate that the fuel rods can be cooled more effectively when the fluid temperature is near the pseudocritical point due to the high specific heat capacity at this temperature and pressure, and the local heat transfer coefficient can be improved greatly from the application of grid spacers; however, heat transfer enhancement only happens in limited regions downstream of the grid spacers. By contrast, strong swirl flow can be induced by a helical wire, thus the mixing of coolant is strengthened, and the convective heat transfer is enhanced. However, local hot spots also occur in the region near the wires. Both grid and helical wire spacers will lead to an increase in pressure loss, but the additional pressure drop induced by the helical wire is smaller, hence better comprehensive heat transfer performance is achieved for a wire-wrapped channel. Moreover, heat transfer performance can also be enhanced by reducing the pitch of the spacers. This suggests that applying spacers and optimizing their configurations and structures is helpful to achieving better cooling performance in rod bundle channels.