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 absorber tube with multiple smaller tubes arranged in a circular bundle, forming a linear cavity that improves solar absorption and reduces temperature non-uniformities on the absorber surface. A three-dimensional CFD model is developed under real-scale operating conditions to assess several TB configurations through a two-stage optimization procedure. The designs are evaluated using thermal efficiency, pressure drop, and overall efficiency metrics. The results indicate that, despite higher flow resistance, TB receivers significantly enhance thermal performance 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 at an inlet temperature of 450 K, corresponding to a 7% improvement over the standard receiver. Additional analyses over inlet temperatures ranging from 400 to 550 K confirm the robustness of the optimized TB configuration in mitigating hotspot formation while maintaining superior overall performance.