Stress and Strain Analysis in the Absorber Tube of a Parabolic Trough Solar Collector for Direct Steam Generation

Direct steam generation in parabolic trough collectors presents challenges due to the non-uniform distribution of heat flux and the appearance of flow patterns. These conditions can induce stresses, deformations, and deflections that compromise the structural integrity of the absorber tube; therefore, this study developed a coupled numerical model (optical, thermohydraulic, thermal, and thermoelastic) capable of reproducing the absorber tube’s behavior under real operating conditions. The methodology includes the following: (i) an optical model using Monte Carlo ray tracing to obtain the non-uniform distribution of solar heat flux and the local concentration ratio; (ii) a two-fluid thermohydraulic model to describe the transition from subcooled liquid to superheated vapor; (iii) a thermal conduction model; and (iv) an analytical thermoelastic model to quantify stresses, deformations, and deflections. The results identify the region near 421.35 m as the most critical, where circumferential temperature differences reached 28.38 K, generating maximum deformations between 600 and 800 με and deflections up to 18 mm along a 25 m section, 1 mm about to touch the glass cover. These findings demonstrate that this model facilitates the identification of critical conditions and the assessment of structural risks, contributing to improved reliability and safety in parabolic trough solar thermal power plants.