A Sensitivity-Guided Selection Hyper-Heuristic for the Thermo-Hydraulic Design of a Solar Hybrid-Nanofluid Evacuated-Tube Collector

Hybrid nanofluids raise the thermal output of evacuated-tube solar collectors, but the heat-transfer gain comes at the cost of friction and pumping power, so the working fluid must be chosen in line with a constrained thermo-hydraulic criterion. Its design is posed here as a constrained single-objective optimisation over the hybrid pair, base fluid, weight fraction, component share and flow rate. A variance-based screening of a 54,432-run full-factorial dataset reduces the design space from eight variables to five, justified by the invariance of the optimal hybrid pair across thirty-six operating points. Gradient-boosted surrogates for the four state and constraint responses (efficiency, pumping power, Reynolds number and outlet temperature) reproduce the simulator to held-out coefficients of determination of 0.9998–1.0000; the performance-criterion surrogate has a lower global coefficient of determination (0.46) and is assessed by top-region ranking accuracy. The reduced problem is solved with a selection hyper-heuristic over twelve operators, pairing an upper-confidence-bound selector with late-acceptance hill-climbing. Under Friedman-, Nemenyi- and Holm-corrected Wilcoxon testing, it ranks within the leading statistically indistinguishable group, but is not separable from a random-selection ablation, locating its value in robustness rather than adaptivity; furthermore, it attains the grid-reference optimum within 0.40 percent. The criterion optimum is an Al2O3-Cu suspension in ethylene-glycol and water at three percent loading; the constrained-efficiency optimum reaches a surrogate thermal efficiency of 0.760, cross-checked against a grid-reference value of 0.762 and a reconstructed-model value of 0.760, conditional on the supplied reduced-order model and its single-tube dataset convention. The constrained-efficiency objective is treated as the primary design objective, while the performance criterion is reported as a secondary screening index that characterises the additive rather than selecting the operating fluid.