Heat transfer enhancement of supercritical CO2 in solar tower receiver by the field synergy principle

Abstract

• The secondary flow generated in the horizontal tube can enhance the heat transfer. • The field synergy principle is used to determine the location of the enhancement structures. • The non-uniform enhanced heat transfer structures are proposed. • The triangular ribs tube is the best heat transfer enhancement structure. The supercritical CO 2 used as heat transfer fluid (HTF) in solar tower cavity receiver has higher pressure and operating temperature, and lower investment than traditional heat transfer fluid, such as water steam, molten salt, etc. Many researchers have analyzed the effects of mass flow rate, heat flux, tube diameter, operating pressure and inlet temperature near the critical point on the heat transfer performance of supercritical CO 2 . However, there are few studies on the convective heat transfer characteristics of supercritical CO 2 in tower solar receivers under the non-uniform heat flux boundary. In this contribution, in order to improve the convective heat transfer performance of supercritical CO 2 under non-uniform heat flux, we firstly analyze the effect of the arrangement of the receiver tube on the flow and heat transfer performance of supercritical CO 2 . Then, we apply the field synergy principle to guide the flow field enhancement, and design the non-uniform structure at the position with larger field synergy angle. Finally, we further analyze the effect of the non-uniform structure on the heat transfer performance of supercritical CO 2 . The results show that the triangular ribs tube is the best heat transfer enhancement structure, e.g., when the mass flow rate is 0.1 kg·s −1 , the Nusselt number is 956.11, which is 163% higher than that of the smooth tube. This contribution can provide a guidance for the structural enhancement of a practical supercritical CO 2 solar receiver to improve the heat transfer performance.