Numerical Investigation of Heat Transfer Characteristics of CO2 in a Vertical Divergent Tapered Annular Channel

This numerical research uses the two equation SST \(k - \omega\) model to investigate supercritical carbon dioxide (sCO2) in a vertical divergent tapered annular channel at an axis-symmetric condition. Under the same operating conditions, this tapered annular channel enhances heat transfer over a simple cylindrical annular channel due to its geometrical configuration. This geometrical structure provides tapering to the heat generation rod because wall heat flux continuously changes along flow direction, and this effect appears in heat transfer. The computational domain is 3 m long, with 0.5 m at the beginning being regarded as an adiabatic section for fully developed turbulent flow and 2.5 m at the end for investigating the thermalhydraulic characteristics of sCO2. According to the report, the divergent tapered cylindrical annular channel’s wall temperature seemed lower with a more excellent heat transfer coefficient value at the same boundary conditions, including mass flux, power, pressure, and inlet temperature. Besides, the heat transfer has been observed to be impaired and enhanced relatively at low (400 to 500 kg/m2s) and high mass fluxes (600 to 700 kg/m2s) conditions. Heat transfer impairment at low mass conditions arises due to a substantial temperature disparity amid the core and wall fluids area, which induces strong buoyancy forces, unlike at high mass flux conditions.