Statistical optimization of radiative Al2O3-Fe3O4 hybrid nanofluid flow over an inclined thin needle for spacecraft radiator cooling: An RSM-CCD approach

In this context, effective thermal management of spacecraft radiators is critical to avoid overheating and to maintain system reliability for long-duration missions, especially with the ever-growing power densities in such systems. The flow and heat transfer of an Al 2 O 3 - Fe 3 O 4 hybrid nanofluid over an inclined thin needle embedded in a porous medium are numerically investigated in the presence of combined magnetohydrodynamic, thermal radiation, viscous dissipation, and internal heat generation effects, which represent the wick structure in a spacecraft heat-pipe radiator. The novelty of this work is the identification of the most effective ethylene glycol: water base fluid ratio (20:80, 40:60, and 50:50) and the statistically optimized optimization of the governing dimensionless parameters with the help of Response Surface Methodology and Central Composite Design, along with ANOVA, Pareto chart, and desirability-based analysis. The coupled nonlinear governing equations, based on the standard boundary-layer flow assumptions, are numerically solved using the bvp4c solver in MATLAB, and the numerical scheme is tested against previously published results. The two novel and important results include the finding that the maximum heat transfer coefficient and minimum skin friction of the three ratios analyzed occur at the 20:80 ratio of EG: water, and that with the thermal radiation parameter increasing, the Nusselt number increases significantly, while the skin friction decreases, indicating strong coupling for the radiative-convective transport in this flow regime. The linear regression models derived from RSM are found to possess high predictive accuracy for both responses, and the optimization technique yields operating parameter conditions (high radiation and needle-size parameters, and moderate Darcy-Forchheimer number and low heat-generation and Eckert numbers) that simultaneously maximize both responses and minimize flow resistance. The results in this work provide practical design recommendations for compact, energy-efficient, hybrid nanofluid-based radiator cooling systems for spacecraft thermal management.