Thermomechanical behavior of mechanical attachments in solar power tower receivers under preheating conditions: A numerical study

Abstract

Thermal deflection of receiver tubes in solar power tower plants is typically reduced by means of mechanical attachments, each one consisting of a clip and a guide through which a rod connected to a reradiating wall can freely slide. As a side effect, these mechanical attachments act as heat sinks, promoting a local temperature reduction in the tube during the receiver preheating, thus increasing the risk of crystallization of the molten salt during the subsequent filling of the receiver. Additionally, the mechanical attachments and the tube are subjected to thermal stresses during the preheating of the system, remarking the importance of considering both thermal and mechanical effects during the design of these elements. This study uses three-dimensional thermomechanical simulations to characterize the behavior of both the mechanical attachment and the tube during the preheating of a solar power tower receiver. The results revealed that the areas of maximum stress occur in the tube, clip, and guide sequentially as the preheating process progresses. The maximum stresses are located in the connections of the clip with both the tube and the guide. An extensive parametric sweep on the dimensions of the mechanical attachment revealed a trade-off between the minimum temperature and the maximum stress of the tube. Based on this analysis, an optimal solution for the dimensions of the clip and guide in terms of their height is proposed. The systematic study here presented can serve as a basis for the design of improved mechanical attachments able to ensure an adequate minimum temperature of the tube during the preheating while keeping the stress of the system within acceptable limits.