Performance analysis (4E) of a double-pass multi-V shaped hemispherical protrusions solar air heater absorber with paraffin wax nano-composite PCM thermal energy storage

Solar air heaters (SAHs) suffer from low thermal efficiency due to limited convective heat transfer and inadequate thermal storage, which restricts their applicability in continuous space heating and drying. To address this problem, the present study develops and evaluates an innovative double-pass solar air heater (DP-SAH) integrating nano-composite phase change materials (PCMs) for latent heat storage with multi-V-shaped hemispherical protrusions to enhance heat transfer. The system was experimentally tested under outdoor conditions in Tezpur, Assam, India, and its performance was assessed using energy, exergy, economic, and environmental (4E) indicators. A complementary numerical model in ANSYS Fluent examined initially the thermo-hydraulic influence of various protrusion geometries. It identified the 16 mm hemispherical protrusion as the most effective one. Experimental results showed that the protrusions increased outlet air temperature and heat transfer significantly, raising thermal efficiency from 38.46% to 81.86% as airflow increased from 0.005 to 0.02 kg/s. Thermal storage efficiency improved from 74.29% to 85.82%, while exergy efficiency decreased from 6.95% to 4.54%, indicating higher irreversibility at larger flow rates. Economic analysis showed an exergo-economic reduction from 1.43 to 0.41 kWh/$, and environmental assessment indicated an annual CO2 mitigation of 18.67 tonnes at 0.01 kg/s. Overall, the combined numerical and experimental findings demonstrate that integrating nano-composite PCMs with hemispherical protrusions substantially improves thermal performance and environmental benefit, making the proposed DP-SAH a promising solution for efficient solar air-heating applications.