Thermal design optimization of a parabolic trough collector receiver with a tube-bundle cavity

This work presents a numerical investigation of the thermo-hydraulic performance of a tube-bundle cavity (TB)receiver for parabolic trough collectors (PTCs). The proposed receiver replaces the conventional single absorbertube with multiple smaller tubes arranged in a circular bundle, forming a linear cavity that improves solar absorptionand reduces temperature non-uniformities on the absorber surface. A three-dimensional CFD model isdeveloped under real-scale operating conditions to assess several TB configurations through a two-stage optimizationprocedure. The designs are evaluated using thermal efficiency, pressure drop, and overall efficiencymetrics. The results indicate that, despite higher flow resistance, TB receivers significantly enhance thermalperformance compared to the conventional design. Hotspot temperature increases are reduced by up to 77%,while temperature uniformity increases by approximately 23%. Among the investigated configurations, the 12-tube design provides the best thermo-hydraulic compromise, achieving a maximum overall efficiency of 0.76 atan inlet temperature of 450 K, corresponding to a 7% improvement over the standard receiver. Additional analysesover inlet temperatures ranging from 400 to 550 K confirm the robustness of the optimized TB configurationin mitigating hotspot formation while maintaining superior overall performance.