Coupled Thermo-Structural analysis of absorber tube for direct steam generation in parabolic trough solar collector

Abstract

The absorber tube is a key component of a parabolic trough solar collector, and the bending of the absorber has an important role in receiver failures. The detailed survey of existing commercial solar power plants reveals that 55 % of failures happened due to the rupture of glass envelope and 29 % due to the loss in annulus vacuum. In this study, coupled thermal–hydraulic and structural stability analyses have been performed to understand the thermo-structural performance of absorber tubes under realistic operating conditions of direct steam generation processes. The fluid flow and heat transfer equations have been solved using the FVM scheme, and structural equations have been solved using the FEM scheme. The impacts of absorber material selection have been studied using steel absorbers and copper-steel bimetallic absorbers. The study has been performed for operating pressure of 60 bar and 100 bar, mass flow rates of 0.4 kg/s and 0.6 kg/s, and DNI of 750 W/m2. The temperature gradient, deflection, strain, and stress in the absorber wall have been analyzed. It has been observed that the temperature gradient in the absorber could be reduced by 51 % and deflection by 40 % using a copper-steel bimetallic absorber instead of the steel absorber. The maximum thermal strain observed under the subjected boundary condition in the steel absorber is 6.27 mm/m, and in the bimetallic absorber is 6.06 mm/m. Further, the maximum equivalent stress of 31.1 MPa in the steel absorber and 39.8 MPa in the bimetallic absorber has been observed. The present work is useful for understanding the absorber's thermo-structural functionality in the preheating, evaporation, and superheating stages of direct steam generation in solar collectors.