Numerical study on transverse mixing characteristics of flow sweeping in helical cruciform rod bundle

•Flow sweeping is studied in the helical cruciform rod bundle.•The flow sweeping mixing parameters between different subchannels are calculated.•The conventional subchannel conservation equation is improved.•The helical cruciform rod can enhance transverse mixing. Fluoride salt serves as a coolant in the fluoride-salt-cooled high-temperature reactor and flows through the reactor core to remove heat produced by the nuclear fuel. To enhance the flow heat transfer performance of coolant in the fuel assembly, helical cruciform fuel rods are designed as a foundation fuel element. In the present study, the numerical method in helical cruciform rod bundle is used to analyze the transverse mixing characteristics of flow sweeping. A heat transfer fluid (Dowtherm A) flows and transfers heat by convection along the heated wall of helical cruciform rod. The fluid in the helical cruciform rod bundle exhibits a substantial flow sweeping crossflow phenomena as a result of the impact of the helical structure. The transverse mixing velocity and temperature profiles are analyzed. The subchannel conservation equation is optimized, and the correlation between flow sweeping mixing parameters and dimensionless local gap distance in various Reynolds number ranges is determined by fitting. Furthermore, the maximum of flow sweeping mixing parameter of the helical cruciform rod bundle is more than seventy times greater than the turbulent mixing parameter's maximum of the cylindrical rod bundle under an identical Reynolds number. It can be concluded that the helical cruciform rod bundle has considerable transverse mixing, which enhances the flow heat transfer performance of the reactor core. This study provides a guide for the numerical study of flow heat transfer in helical structures, and a foundation for the development of the subchannel mixing model.