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Solar air heaters are extensively being used to heat air, but has low thermal efficiency because of poor heat transfer between the solar absorber plate and the air in transient through it, and also due to availability of solar radiation only during the day time and an increase in demand during the night. In the present study, the thermal performance of a solar air heater with pin fin absorber plate with pin immersed in paraffin wax as phase change material has been investigated experimentally. The proposed solar air heater has been designed, fabricated and tested under the weather conditions of Dhanbad, Jharkhand, India (latitude 23° 65'N and longitude 86° 47'E). The effects of varying the mass flow rate of air on the performance of the solar air heater have been further analysed. Experimental investigation shows that the average daily efficiency of the proposed solar air heater increases with an increase in the mass flow rate of air. Also, pin fin absorber plate with pin immersed in paraffin wax further enhances its performance with an increase in heat transfer rate from the absorber plate to Phase Change Material (PCM) bed during charging, and also from the PCM to the absorber plate during discharging, resulting an increase in the performance of the solar air heater. [ABSTRACT FROM AUTHOR]

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]