Experimental assessment and thermo - hydraulic enhancement of a parabolic trough solar collector with optimized porous receiver inserts

This study examined the experimental performance and thermohydraulic improvements of a parabolic trough collector (PTC) with optimized porous receiver inserts for medium-temperature thermal applications. The complete PTC system, including the collector structure, solar-tracking unit, fluid-circulation loop, and thermal-storage tank, was designed, built, and tested under actual outdoor conditions. The numerical model forecasted a peak thermal output of 25.25 kW under optimal clear-sky conditions. In contrast, field experiments yielded approximately 10 kW. This observed reduction of 60.4% is ascribed to the combined influences of transient direct normal irradiance (DNI) fluctuations, optical losses, tracking inaccuracies, and unavoidable thermal losses encountered under actual operating conditions. These results underscore the importance of using long-term average DNI data for realistic collector sizing and performance forecasts. To enhance receiver efficiency, various porous disc inserts with different porosities, hole patterns, and orientations were analyzed numerically. Among the uniform hole designs, the D1 insert, with a porosity of 0.73, showed the best initial performance, achieving a thermal enhancement index (TEI) of 0.67 at 1.0 kg/s. Further optimization revealed that the half-disc non-uniform insert (D3) achieved the highest overall performance, with a maximum TEI of 1.132, nearly 69% higher than D1. Additionally, the D2 configuration produced 2.8–5.8% higher Nusselt numbers and 8.4–16% lower pressure drops than D1. Overall, this combined experimental and numerical study demonstrates that optimized porous inserts serve as an effective passive cooling method to enhance receiver heat transfer and improve the industrial potential of the PTC system.