Computational analysis of passive strategies to reduce thermal stresses in vertical tubular solar receivers for safety direct steam generation

Abstract

When exposed to high non-uniform heat fluxes on the receiving surface, significant temperature gradients develop in the tubes, producing thermal stress and deformations in the receivers. This paper reports a detailed investigation of the thermal and structural performance of a solar tower system that operates with direct steam generation tubes when the fins are added to the internal surface and thickness varies. Six tubes were evaluated, two without fins varying the wall thickness (5 mm and 3 mm) and four with fins under different configurations. The thermal system corresponds to a representative tube of an external tubular receiver of a central tower system. The thermal receiver operates with direct steam generation under a non-uniform concentrated solar flux with a maximum value of 0.93 MW/m2. The best configuration of the tube was with fins on the frontal surface of the tube, maintaining a receiving wall thickness of 3 mm and an adiabatic wall thickness of 5 mm. It could reduce maximum thermal gradients and temperature by 31% and 14%, respectively, maximum thermal stresses by 38%, and maintain vapor mass flow at the output (276 kg/h).