Transient numerical model for the thermal performance of the solar receiver

Highlights: • Evolutions of temperature distributions from initial values were investigated. • Transient and steady-state calculations were compared. • This model can adjust the flow rate to satisfy the outlet HTF temperature. • A high initial temperature may produce a soaring HTF temperature at risk. Transient thermal performance calculations are necessary to predict the thermal power output and to monitor the dynamic characteristics of solar receivers. So this study described the establishment of a transient numerical model for the thermal analysis on unsteady behaviors of the external solar receiver. The numerical integration method was used to solve this model including the rate of the temperature change with time and the temperature-dependent thermophysical properties of the receiver tube as well as the heat transfer fluid (HTF). This transient model can investigate on how the temperature distributions of the receiver and the HTF evolve from the initial values under different boundary conditions. The fundamental aim of this study is to demonstrate the transient performance of the receiver in order to benefit the operation strategies which are supposed to improve the receiver efficiency without risk to the receiver itself. Therefore, this study focuses on how the bulk temperature of the HTF responds to the initial and boundary conditions in consideration of the thermal capacity of the solar receiver. Especially, for the comparison between the transient and steady-state calculations, this study predicted the transient time, the convective heat loss, the radiative heat loss and the HTF heat gain in different operation modes or conditions. Thus, the results show that how essential impact factors such as the initial condition, the thickness of the receiver tube, the DNI level and the wind speed affect the transient thermal performance of the solar receiver. Additionally, the transient model has the function of the adjustment of the flow rate of HTF in order to satisfy the required HTF temperature at the receiver outlet under the various conditions including the concentrated solar flux and the wind speed.