PIV measurements of the cross flow induced by a wrapped wire spacer

Abstract

Wrapped wire spacers have been incorporated as the spacing device in advanced nuclear reactors such as the sodium-cooled fast reactor and supercritical water-cooled reactor. The cross flow induced by the wrapped wire affects the subchannel mixing and fuel rod temperature, which is a concerned issue in the thermal-hydraulic design of the fuel assembly. In the present paper, an experiment has been conducted to study the cross flow of subcritical water in a square channel containing a single tube which was helically wrapped by a wire using particle image velocimetry. The global velocity distribution and local flow features were obtained. It was found that the cross-sectional small vortexes are generated by the fluid-wall interaction as well as the wrapped wire. Local measurements using higher spatial resolution could capture more detailed flow characteristics compared to the global measurements. The magnitude of the secondary flow weakened along the cross-flow direction due to the blockage of the wire. The cross flow became stronger with the decrease of wire pitch, but this effect was more visible when the wire pitch is shorter than a certain limit. In addition, it was also observed that the cross-sectional velocity magnitude and special turbulent kinetic energy increase gradually with increasing Reynolds number. The spatially high-resolution experimental data combined with the simple geometry and clear boundary conditions can be used for the validation of CFD codes and models in predicting the wire-induced cross flow.