A comparison between lumped parameter method and computational fluid dynamics method for steady and transient optical-thermal characteristics of the molten salt receiver in solar power tower

Lumped parameter method (LPM), which neglects the change of the temperature within the cross-section of the molten salt, is widely used to predict solar receiver's steady and transient optical-thermal characteristics. To consider the influences of the temperature variation inside molten salts on the performance of solar receivers, the receiver's steady and transient thermal performance are comparatively studied by computational fluid dynamics method (CFD) and LPM. The results show that the rise time of the outlet temperature predicted by the CFD model under the start process, the change of mass flow rate, and the change of direct normal irradiance are more than two times those of the LPM model. Take the start process on spring equinox as an example, the rise time predicted by the CFD and LPM model are 52s and 22s, respectively. Therefore, the temperature distribution within the molten salt should be considered for predicting a more precise transient thermal performance of the receiver. The predicted outlet temperatures in the steady state by the two models are nearly the same, with an absolute difference less than 2.0 °C, which indicates that whether considering the temperature distribution within the molten salt does not influence receiver's steady thermal characteristics.