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Thermo-hydraulic performances of a new solar air heater with single V-notch patterns of hemispherical protrusions on the absorber plate are investigated experimentally for different relative protrusion heights (h p /D h = 0.027–0.069), relative pitch (p p /h p = 6–14), attack angle (α ap = 15°-75°), and Reynolds number (Re =3600–21,700). Three meta-heuristic algorithms, i.e., Ant colony optimization (ACO), Whale optimization algorithm (WOA), and Grass-hopper optimization algorithm (GOA), were used for single and multi-objective optimizations. Experimental results provide the maximum Nusselt number (Nu) as 127.07 at h p /D h = 0.050, p p /h p = 10, α ap = 600, and Re =21,700, whereas the minimum friction factor (f) becomes 0.0165 at h p /D h = 0.027, p p /h p = 10, α ap = 450, and Re =21,700. The highest normalized Nusselt number (Nu /Nu s) is found to be 2.56 for h p /D h = 0.050, p p /h p = 10, α ap = 600, and Re =7200, and the maximum normalized friction factor (f / f s) is observed as 4.30 at h p /D h = 0.050, p p /h p = 10, α ap = 450, and Re =7200. The highest thermo-hydraulic performance parameter (THPP) was to be 1.60 at p p /h p = 10, h p /D h = 0.050, α ap = 600, and Re =7200. Empirical correlations were developed. In single objective optimization for Nu, WOA provided the best results. For f , WOA gives a minimum value. The WOA metaheuristic algorithm outperformed the other algorithms. • Investigated V-notch pattern hemispherical protrusion on absorber plate experimentally. • Meta-heuristic optimization algorithms used for single and multi-objective cases. • In single objective optimization, the WOA provides the best result. • Maximum Nu = 144.56 at h p /D h = 0.07, p p /h p = 8.54, α ap = 750, and Re = 21,700. • In multi-objective, WOA delivers consistent non-dominated optimal solutions. [ABSTRACT FROM AUTHOR]