Response Surface Analysis of Thermo-Hydraulic Performance of a Direct Absorption Solar Receiver Using Fe3O4 Nanofluid Under Concentrated Solar Irradiation

This study investigates the thermo-hydraulic performance of a spiral-channel direct absorption solar collector (DASC) using Response Surface Methodology (RSM). The objective of this study was to establish a design framework that balances thermal efficiency (ηth) and pressure drop (ΔP) by resolving inherent trade-offs. The results indicate that geometric parameters primarily influence hydraulic resistance, while optical factors govern thermal capture. To identify a robust operating region, a feasible design window was established under the constraints of ηth ≥ 0.90 and ∆P < 200 Pa. Analysis reveals that a minimum receiver height (Factor B) of 12.1 mm and a nanoparticle concentration (Factor A) of at least 0.052 wt% are required to satisfy the performance criteria. Within this identified space, an operating range of B = 18–24 mm and A = 0.06–0.08 wt% is recommended at fixed values of Factor C = 3 and Factor D = 0.59. This region-based approach provides a design foundation that respects thermodynamic limits while minimizing parasitic losses, offering practical guidelines for the optimization of spiral-channel DASC configurations.