Mixed convection and radiative heat transfer analysis of a bladed cylindrical receiver

Bladed cylindrical external receivers can reduce thermal losses in concentrating solar power towers, yet the influence of blade geometry on radiative and mixed convective heat transfer remains insufficiently understood. This study examines an isothermal external receiver using three-dimensional steady RANS simulations with surface-to-surface radiation. The numerical model is verified against published drag data for circular cylinders and assessed using available mixed convection correlations for external receiver heat loss. The effects of blade number, blade length ratio, wind speed, and surface temperature are evaluated over ranges relevant to concentrated solar power (CSP) plant operation. Radiative heat loss decreases monotonically with increasing enclosure, because additional blades enhance inter-surface shielding and internal radiative exchange. The mixed convective response is more complex. A small number of blades can increase convection through boundary-layer disruption and improved cavity ventilation, whereas densely bladed configurations suppress convection by forming weakly ventilated recirculating cavities. Increasing the blade number reduces the mixed convective heat transfer coefficient by 34.2–37.2% relative to the simple receiver, while increasing the blade length produces a smaller reduction of 23.0–25.5%. Higher surface temperature further reduces the mixed convective heat transfer coefficient for the 12- and 24-blade configurations, while radiative exchange becomes increasingly dominant. Overall, the results clarify the roles of blade number and blade length in radiative shielding and convective ventilation, and provide guidance for the thermal design of bladed CSP external receivers.