Effects of geometric and operating parameters on thermal performance of conical cavity receivers using supercritical CO2 as heat transfer fluid

In this paper, a comprehensive optical-thermal numerical model of the conical cavity receiver using supercritical CO2 (S–CO2) as the heat transfer fluid (HTF) is established by combining ray tracing with computational fluid dynamics method, which is verified with published data in the literature. Based on the model, the effects of critical geometric parameters (tube inner diameter, aspect ratio and cone angle ratio) and operating parameters (solar direct normal irradiance (DNI), HTF inlet mass flow rate and inlet temperature) on the thermal performance of the receiver are discussed thoroughly. The results indicate that a decrease in the tube inner diameter is beneficial to improve the optical-thermal performance of the receiver. When the aspect ratio and cone angle ratio are 1.5 and 0.25, respectively, the optical-thermal conversion efficiencies reach their optima, which are 75.13% and 75.30%, respectively. Moreover, for the S–CO2 receiver with optimal geometric parameters, the HTF outlet temperature increases linearly with increasing DNI and inlet temperature. Increasing mass flow rate can improve the optical-thermal conversion efficiency, but once the flow rate exceeds 0.04 kg/s, it has little effect on the efficiency improvement. These results can provide a reference for the design and operation of the S–CO2 conical cavity receiver.