Study of the hydraulic roughness impact on turbulent heat transfer at supercritical pressure based on a fast direct numerical simulation method

Abstract

A numerical experiment on turbulent heat transfer of supercritical fluids (SCFs) in hydraulically rough heating tubes is performed using a fast direct numerical simulation method for characterizing hydraulic roughness. The objective is to assess the impact of hydraulic roughness on SCF turbulent flow and heat transfer and delve into the underlying mechanism. Four cases are simulated, including one case of smooth flow and three cases with varying roughness parameters. The simulations are conducted at a bulk inlet Reynolds number of Rein=2700 based on the tube radius and inlet parameters. The results demonstrate that hydraulic roughness effectively enhances heat transfer, leading to reduced wall temperatures and increased Nusselt numbers at the heated wall. As the roughness height increases, the heat transfer deterioration typically observed in SCF flows is significantly mitigated. This enhancement in heat transfer primarily arises from increased turbulent shear stress and turbulent heat flux induced by hydraulic roughness. Additionally, hydraulic roughness fosters more turbulent structures and intensifies vortex motion during transient flow, thereby further enhancing turbulent heat transfer. The insights gained from this research offer valuable guidance for addressing heat transfer deterioration in supercritical fluids.