Heat transfer enhancement on CSP tubular receivers using partially filled Raschig Ring porous inserts: A numerical study

• Several concepts of partial filled porous inserts are adopted in tubular CSP receivers, • Air flow features over the porous structures are simulated at pore-scale, • Partial filling outperforms simpler configurations in energy and exergy efficiency, • Comprehensive exergy analyses are provided, detailing the exergy loss and destruction. This study presents a computational investigation to evaluate and analyze the performance of partially filled porous inserts, composed of metallic Raschig Rings in gaseous concentrated solar power absorbers. Two filling configurations, Lateral Filling (placing inserts along the tube sides) and Central Filling (positioning them along the central axis), were analyzed with different designs. Comparison was conducted by varying filling indices to balance thermal enhancement and pressure drop reduction. The fluid dynamics, encompassing flow velocity, pressure, and temperature gradients were meticulously studied using validated 3D pore-scale computational fluid dynamics models. These models were successfully able to capture the transitional behavior of the fluid between porous and clear regions. The results reveal similar flow leakage trends in both configurations with notable variations along the porous medium. The two designs exhibited unique heat transfer mechanisms, resulting in different temperature profiles on the absorber wall. Partial Filling significantly reduced the pressure drop – a major limitation of fully filled designs –by up to 95%, while simultaneously enhancing the overall absorber performance. This study demonstrated that the partially filled design could achieve up to 40% higher energy efficiency and nearly 90% greater exergy efficiency compared to simple tube designs, offering an alternative for solar high-temperature systems.