Thermal performance augmentation of double pass solar air collector using coated absorber with activated carbon derived from waste tea dust

The extinction of fossil fuels to produce electrical energy and the demand for energy consumption is escalating every year. Several innovative approaches are developed to meet the present energy demand requirements, and one of the alternative and sustainable approaches is using renewable energy. In the present experimental investigation, a double pass SAC is fabricated, and the absorber plate is coated using activated carbon derived from the waste tea dust to augment the energy absorption rate. The thermal performance of the proposed system is compared by flowing the air through the rectangular cavity of the double pass SAC at different flow rates, namely 0.6, 1.2, and 1.8 kg/min. The output parameters, such as absorber temperature, heat transfer coefficient, air temperature leaving the duct, and thermal efficiency of the proposed double pass SAC, are compared with the conventional double pass SAC with black paint coating. The experimental studies revealed that the temperature of the absorber, air temperature leaving the duct, and thermal efficiencies are improved using activated carbon nanoparticles derived from the waste tea dust compared to the double pass SAC with black paint as a surface coating. Results demonstrated significant improvements: the activated carbon nanoparticle (ACNP)-coated absorber achieved an average thermal efficiency of 96.2% (vs. 77.8% for conventional) at 1.8 kg/min, with efficiency enhancements of 10.05–19.12% across flow rates. The exit air temperature and temperature difference between inlet/outlet increased by up to 10.71%, attributed to the ACNPs’ superior solar absorption and heat transfer properties. Exergy efficiency also improved markedly, reaching 6.2% (vs. 3% for conventional) at 1.8 kg/min. This study highlights the dual benefit of repurposing agricultural waste into high-performance solar thermal materials while advancing sustainable energy solutions.