Performance improvement of tubular solar still using nano-coated hanging wick thin film, ultrasonic atomizers, and cover cooling

Three modifications were applied, in steps, on tubular solar still (TSS) to enhance its performance. First, three ultrasonic atomizers were placed under a hanging wick tent. Second, to enhance the thin-film evaporation from the wick layer, Cobalt Oxide nanoparticles (NP-Co₃O₄) were added to the hanging wick coating so that it could enhance the heat transfer and thermal properties. Finally, a cover cooling unit was integrated with the modified TSS (MTSS) to degrade the cover temperature and enhance vapor condensation. Besides, the cooling could increase the temperature difference between the wick and the cover to improve the free convection process. Comparison between the MTSS and conventional TSS (CTSS) was investigated in terms of some parameters, such as freshwater output, thermal energy efficiency, total heat transfer coefficient, and exergy efficiency. The results showed that the freshwater productivity was enhanced by 28, 59.2, and 82.5%, for the cases' order, respectively. The best case was TSS with the third modification (nanocoated hang wick, atomizers, and cover cooling), in which, the thermal efficiency, total heat transfer coefficient, and exergy efficiency were improved by 68.14, 40.5, and 119.1%. Moreover, a cost analysis was carried out on the three cases, which revealed that the maximum saving in freshwater price was 39.14%.