Numerical Analysis of Effects of Vane Deflection Angle on Flow-Thermal Characteristics in a Fuel Rod Assembly

The utilization of a grid spacer with vane is a significant component within reactor fuel channels. The presence of the vane has a notable impact on the mixing of flow and the enhancement of heat transfer within subchannels. The purpose of this work was to perform a numerical analysis of the effects of the vane deflection angle on the flow-thermal characteristics in a fuel rod assembly.

In the current analysis, a square array consisting of a 5 × 5 rod bundle was utilized. The pitch-to-rod diameter ratio was set to 1.33, while the blockage ratio of the grid spacer was determined to be 0.16. A relative study was made for flow-thermal characteristics with four different vane deflection angles, such as 21 deg, 25 deg, 29 deg, and 33 deg. Analyses were made for a fluid pressure of 15.5 MPa, an inlet temperature of 583 K, and a velocity of 4.74 m/s.

The present study investigated the Shear Stress Transport (SST) k-ω and Renormalization Group (RNG) k-ε turbulence models to analyze flow phenomena and thermal performance. The numerical results were validated through experimental data and also compared with correlations proposed by researchers. The analysis of the results was carried out using various methods, including the examination of data curves and streamlines, as well as vector and contour plots. The results indicate that a higher deflection angle leads to a greater reduction in temperature at the grid spacer. The swirl ratio was observed to be maximum close downstream to the grid spacer, and the persistence of the swirl ratio in the downstream can enhance the performance of departure of nucleate boiling. The vane on the grid spacer with a higher deflection angle enhances the coefficient of heat transfer remarkably close to the downstream grid spacer.