Thermal–exergetic analysis of hemispherical solar still enhanced with activated carbon nanoparticles synthesized from spent tea dust

The growing problem of water scarcity worldwide necessitates the continuous development of various technologies to provide effective solutions. Among the various solutions for the desalination process, the solar still is the most prominent due to its cost-effectiveness and sustainable approach. The current experimental study proposes a new technique aimed at improving the functioning of hemispherical solar stills (HSS) by applying the carbonized nanoparticles (ACNPs) made from spent tea dust on the absorber plate. This method enhances the thermal conductivity and absorptivity of the surface. Incorporating ACNPs into the black paint results in increased thermal energy absorption, which raises the temperature of the absorber and water, thus increasing the yield of freshwater. To our knowledge, this is one of the first studies to incorporate waste-derived activated carbon nanoparticle coatings, examining their effects on the thermal and operational efficiency of HSS in realistic outdoor environments. This offers an inexpensive and easily adaptable upgrade to solar desalination systems. The research involved the fabrication of two identical solar stills: one featuring a conventional black surface coating, termed HSS, and the other incorporating activated carbon nanoparticles dispersed in black paint and applied on the absorber. The experimental results revealed that the thermal performance has significantly improved. The modified HSS recorded a peak absorber and water temperature of 74 and 72C, whereas the peak temperatures recorded from the conventional HSS were 71 and 69C, yielding average gains of 4.34% and 4.16% on absorber and water temperature, respectively. The improved heat transfer through evaporation leads to a higher temperature difference between the water and cover (20C (modified HSS) and 18 C (conventional HSS)), which results in an efficient condensation process. Moreover, there has been a substantial improvement in freshwater collection. The modified HSS produced a maximum hourly yield of 1.07 kg/ and a cumulative daily yield of 5.06 kg/, which is 33.67% higher than the conventional HSS yield of 3.72 kg/. This performance boost led to a substantial increase in efficiency. The daily thermal efficiency increased from 32.79% to 49.44%, and the daily exergy efficiency improved from 3.12% to 5.82%. An economic analysis demonstrated the viability of the modified system, with a payback period of 1.98 years and notable long-term savings. The use of spent tea dust for ACNP synthesis highlights the environmental and cost benefits of this approach. The findings highlight the potential of nano-enhanced coatings to enhance solar desalination technologies, offering an effective and sustainable solution for addressing global water challenges.