Thermalhydraulic characterization and feasibility assessment of double-cooled annular channel under supercritical heat transfer

Abstract

Appearance of buoyancy-induced heat transfer deterioration is a common concern during supercritical heat transfer through vertical channels. A novel double-cooled annular configuration is proposed and numerically analyzed here in an attempt to eliminate such deterioration. Supercritical CO2 is allowed to flow in parallel through both inner circular duct and outer annular space, separated by an external volumetric heater. Axisymmetric conservation equations are solved, coupled with suitable turbulence model and property relations. Substantial improvement in heat transfer coefficient is observed for both the streams in comparison with an equivalent plain annular channel, along with considerable reduction in wall temperature. Axial gradient of bulk enthalpy and intensity of turbulence-inspired mixing are earmarked as the primary factors facilitating enhanced heat transfer. Increase is supply flow rate promotes turbulence, and results in significant gain in both peak and average heat transfer coefficient. Heat transfer performance degrades at higher power because of impaired mixing, leading to greater wall-to-bulk temperature differential, whereas exit pressure has only limited influence. Considerable difference can be observed in the mass flux, as well as in velocity and turbulence levels, across both the streams, which is augmented further during downward motion. No deterioration has been observed over the entire parametric ranges explored here. Proposed configuration successfully suppresses the impact of both buoyancy and acceleration on heat transfer, substantiating itself as a viable technical option.