A novel tri-pass receiver design for parabolic trough collectors: Experimental investigation and thermal analysis

One of the main challenges of solar parabolic trough collectors (PTCs) is their requirement for large land areas. To address this, a novel tri-pass receiver design has been experimentally developed, which is less sensitive to misalignments, easy to fabricate, maintain, and repair. First of all, the testbed thermal and optical efficiencies were evaluated. The PTC testbed comprises a polished stainless-steel reflector with a 44% optical efficiency integrated into a supervisory control and data acquisition system. No-load tests were initially performed, followed by an in-load test. These tests took place in North Africa, precisely in the northeast of Algeria. Initial experiments revealed a low PTC thermal efficiency of 20%. To address this issue, five different receiver configurations were manufactured, tested, and compared. the reference configuration is an uncoated copper tube. Therefore, a single black-coated copper tube receiver achieved a 27% increase in thermal efficiency. A bypass black-coated receiver showed a significant improvement, achieving 71% thermal efficiency. However, a three black-coated receiver with two centralized tubes experienced a 12% decrease in thermal efficiency. Yet, the three black-coated receiver with one central tube achieved the highest thermal efficiency of 85% due to the triangular pitch arrangement, which effectively focuses solar rays on the central tube while capturing deviated rays with the backside tubes. The no-load test determined the optimal fluid path for this configuration, ensuring smooth progression from preheating to heating as the fluid moved through increasingly hotter tubes. The in-load test confirmed the receiver's effectiveness.