Numerical simulation of flow and heat transfer characteristics of liquid lithium metal inside trapezoid shaped wire rod bundle channels

Abstract

The advancement of compact reactor technology, including the development of small and liquid metal reactors, has led to a surge of interest in the concept of wire-wound core arrangements for achieving enhanced compactness. The installation of trapezoid shaped wires permits the fuel rods to support themselves, facilitates the heat transfer through the channels, and allows for a compact configuration. However, the presence of wires introduces a degree of complexity to the flow and heat transfer process, prompting to investigate the thermo-hydraulic properties of fuel rod bundles with wires. This paper presents a numerical analysis model of a fuel rod bundle channel with trapezoid shaped wires in a hexagonal arrangement, with the objective of investigating the influence of trapezoid shaped wires on the flow and heat transfer characteristics. The results indicate the presence of transverse flow within the channel. The transverse velocity at the near-wall surface of the fuel rod is in alignment with the twisting direction of trapezoid shaped wires, whereas at the top of the wires, it is in opposition to this direction. The center rod and the corner rod exhibit low temperatures and high convective heat transfer coefficients at the trapezoidal winding wire. The transverse and axial velocities demonstrate periodic fluctuations with a period of approximately H/4, and a comparable pattern is evident in the fluctuations of the hot spot factor (F_HS) and Nusselt number (Nu). It is observed that frictional resistance coefficient (f) and convective heat transfer coefficient (h) of trapezoid shaped wire rod bundle channels are higher than those of classical round rod bundle channels. The pertinent research findings furnish a theoretical foundation for the utilization of this specific fuel rod in lithium-cooled fast reactors.