Mitigation of Heat Transfer Deterioration of Supercritical CO₂ Vertical Tube Upward Flows by Introducing Truncated-Ribs in Helical-Like Distribution

To effectively alleviate the heat transfer deterioration (HTD) phenomenon of supercritical CO₂ flow in a vertical circular tube, this paper proposes multiple truncated ribs from a whole O-ring rib but distributed in helical-like distribution. The fluid hydraulics and thermal performance with a verified standard k–ω mode are numerically explored. The effects of the height, the distance, and the number of truncated ribs on flow characteristics, and heat transfer are observed and analyzed in detail. Results show that the heat transfer coefficient increases significantly with increasing rib height, and as the pitch decreases the fluid recirculation area behind each rib decreases, resulting in stronger mixing of swirling flow, which enhances turbulent kinetic energy in the downstream and weakens the buoyancy force, thus mitigating heat transfer deterioration. This study suggests that introducing multiple truncated ribs distributed along helices into circular vertical tubes can be a beneficial way to alleviate heat transfer deterioration and to enhance heat transfer of supercritical CO₂ flow.