Investigation of buoyancy and spacer effects on heat transfer in low-flow-rate upward flow of Lead-bismuth alloy

Abstract

The influence of buoyancy on convective heat transfer in liquid lead‑bismuth (LBE) flow inside a smooth round tube and the spacer effects are studied numerically. The analysis indicates that the effect of buoyancy on convective heat transfer depends on the Bo number. The mixed convection heat transfer performance in a smooth circular tube is analogous to water, namely, mixed convection heat transfer deterioration and free convection heat transfer enhancement. However, this effect is much weaker compared to water. Detailed analysis of radial velocity and turbulent kinetic energy inside the smooth round tube reveals that the distortion of velocity curves induced by buoyancy leads to both deterioration and enhancement of mixed convection. Furthermore, the influence of the spacer, its radial structure and the blockage ratio on the flow and heat transfer is investigated. Unlike water, no heat transfer oscillations are found downstream of the spacer in LBE and orifice-type spacer creates a stagnation region where heat transfer deteriorates as Bo increases. In contrast, there is no stagnation region downstream of the disk-type spacer, with the downstream heat transfer enhancing initially and then deteriorating as Bo increases.