Heat transfer enhancement of supercritical CO2 in heated vertical channels with internal protruded teardrop dimple at high heat flux

This study numerically investigated the suppression mechanism of heat transfer deterioration of supercritical carbon dioxide (CO2) in heated vertical channels with an internal protruded teardrop dimple (IPTD). The effects of IPTD structure parameters and management on flow field, vortex structure, buoyancy effect, thermal acceleration, heat transfer, pressure drop, and performance evaluation criterion (PEC) were analyzed. The results revealed that the complicated vortex reformation induced by IPTD could effectively suppress the heat transfer deterioration witnessed by peak wall temperature reduction and well-distributed as well as heat transfer coefficient improvement. It was indicative that the internal protrusion in teardrop dimple without additional heat surface could mitigate the formation of large primary-recirculation flow in the dimple cavity and generate the small secondary-recirculation flow surrounding the protrusion, shifting the flow separation and reattachment, weakening the flow impingement, while reducing the form drag and friction drag, which contributed to heat transfer enhancement and less pressure drop penalty, consequently PEC improvement. In addition, dimple depth increased, neighbor dimple space decreased, circumferential dimple number increased, and disordered arrangement could further boost the heat transfer performance by promoting vortical motion, flow pattern transition, and intensified flow mixing.