Effect of optical errors on the thermal–hydraulic performance of direct-steam-generation parabolic trough collector

• The coupled optical-thermal-flow model of the DSG was built. • Thermo-hydraulic and heat transfer property of optical errors was analyzed. • Collector circumferential temperature distortion induced by slope and tracking error. • Slope and tracking errors (>8 mrad) significantly degrade DSG collector performance. • Y-axis absorber installed error raises temperature distribution uniformity and failure risk. Parabolic trough solar direct-steam-generation (PTC-DSG) technology is one of the favorable technologies to achieve low-carbon future by cleverly integrating clean energy with green carriers. There are various optical errors under actual operation, which cause heat flow distribution distortion and affect the performance of PTC-DSG, but there is a relative lack of research on the absorber tube’s two-phase flow and heat transfer performance under different optical errors. The coupled optical-thermal-flow model of the PTC-DSG collector is established in this paper based on Monte Carlo ray tracing method, Finite Volume method and Eulerian multiphase flow model. The absorber tube’s heat transfer performance and two-phase flow under slope error ( σ s ), tracking error ( σ t ) and absorber installation error ( σ x and σ y ) are comprehensively investigated. The results revealed that the circumferential temperature distribution distortion caused by optical errors has a significant impact on the absorber tube’s heat transfer performance and reliability. σ s made the temperature distribution more uniform, but significantly reduced the maximum circumferential temperature ( T a, max ), circumferential temperature difference (CTD), collector efficiency ( η c ), and vapor volume fraction (VVF) of the absorber tube, and reduced the threat to the DSG collector. High σ t (>8 mrad) significantly affects the absorber tube’s two-phase flow and heat transfer performance with rapid reduction of T a, max , CTD and VVF, and η c in evaporation and superheating stages are also reduced by about 33.3 % and 34.2 %, respectively. The effects of σ x and σ y on the absorber tube’s flow heat transfer performance are small, but significantly affect its circumferential temperature distribution and CTD. σ y (>0 mm) causes the most inhomogeneous circumferential temperature distribution, which threatens the DSG collector’s safety. Moreover, the absorber tube at low operating pressure has higher η c and VVF, but correspondingly higher CTD. Compared to the evaporation stage, the absorber tube in the superheating stage is subjected to greater thermal loads but also has higher η c , especially at low operating pressure.