Analysis of thermal-flow-stress performance of parabolic trough direct steam generation collectors under reflector installation deviations

The direct-steam-generation (DSG) technology as an important direction for parabolic trough solar systems and has significant advantages in terms of cleanliness and low carbon emissions. In actual operation, DSG collector tubes are subject to the dual effects of variable heat transfer coefficients inside the tubes and uneven thermal flux distribution without the tube, while the presence of reflector installation errors (σ) causes distortion in the uneven thermal flux distribution, significantly affecting the risk of its local overheating and structural failure, but the study of DSG collector tube performance under σ has not yet been reported. Therefore, the multi-physics coupling model covering DSG collector's optical-thermal-flow-stress phenomena is built according to the Euler two-fluid model, Monte-Carlo ray tracing, finite volume, and finite element method to explore the thermal-mechanical performance of the DSG absorber tube under σ. The results revealed that σ exhibits criticality in its influence on the flow thermal exchange property of collector (threshold of approximately 7 mrad), demonstrates differentiated responses to the thermoelasticity of the absorber tubes, and shows significantly higher equivalent stress and deformation at the superheating stage compared to the evaporation stage. When σ < 7 mrad, the whole system's thermal exchange property remains relatively stable, with collector efficiency at the evaporation stage approximately 62.4 % and fluctuations of only 1.8 % at the superheating stage. Case 2 and Case 1 (positive σ) are prone to local stress concentration and Y-axis significant deformation, remarkably increasing the risk of local overheating, stress concentration, and deformation failure in the collector tubes, especially the superheating stage. Case 3 has high stress peaks and concentration but low deformation values. Case 4 significantly increases X-axis deformation but has low overall equivalent stress. When σ > 7 mrad, the flow heat transfer performance and stress deformation of DSG collector tubes significantly decrease, especially with bilateral installation errors, where collector efficiency may even approach 0. Therefore, σ must be controlled within 7 mrad to ensure the efficient and safe operation of the DSG system, particularly avoiding Case 2 and Case 1 (positive σ).