Numerical study on the heat transfer deterioration and its mitigations for supercritical CO2 flowing in a horizontal miniature tube

A designed wall roughness approach to improve turbulent heat transfer to supercritical CO2 flowing in horizontal tubes

“…The sCO 2 heating experiments by Adebiyi and Hall in early 1970s [20] reported that buoyancy leads to the salient heterogeneity of heat transfer over the circumference where the temperatures along the top wall are much higher than those along the bottom wall, indicting serious heat transfer deterioration in the top region. Computational fluid dynamics (CFD) simulations, direct numerical simulations (DNS) and Reynolds-Averaged Navier-Stokes (RANS) modeling [21][22][23][24], demonstrated that this impairment is attributed to buoyancy-induced secondary flows taking the accumulated lighter and hotter sCO 2 fluids to the top wall. Wang et al [25] investigated the effect of tube diameter (4.6-22 mm) on turbulent heat transfer to sCO 2 flowing in horizontal tubes and concluded that the overall heat transfer performance was negatively influenced by the strong buoyancy induced by property variation even for pipes of small diameter.…”