Enhancing the performance of double-slope solar still using nano-enhanced eutectic phase change materials and steel wool fibre as wick material

Energy storage in the form of sensible and latent heat is one of the most prominent method to enhance the performance of any solar thermal system. Solar desalination is a viable method to convert saline water into potable water, but due to its lower yield, it cannot be used as a regular source of water. The current investigation deals with the enhancement in water yield of double slope solar still by embedding eutectic phase change material (PCM) (Myristic acid + Stearic acid), nano-enhanced PCM, and wick material (steel wool fibre). Ag₂O₃ nanoparticles at concentrations of 1.5 wt% were mixed in eutectic PCM to increase the thermal conductivity of nano-enhanced PCM. The energy, exergy, and economic analyses of four various modified cases, namely CSS (still without PCM), DSS-1 (still with eutectic PCM), DSS-2 (still with eutectic PCM and Steel wool fibre), and DSS-3 (still with nano-enhanced eutectic PCM), was carried out in central India (23.24° N and 77.41° E). The findings reveal that the cumulative yields for CSS, DSS-1, DSS-2, and DSS-3 are around 1.82, 2.44, 3.40, and 4.22 kg/m². Additionally, DSS-3 cumulative freshwater production was around 132, 72.9, and 24.1% greater than that of CSS, DSS-1, and DSS-2, respectively. The maximum value of total heat transfer was achieved for DSS-3, which is higher by 45.9% than CSS, 32.8% than DSS-1, and 6.1% than DSS-2. The average energy efficiency of DSS-3 was 49%, which is greater than CSS (22.21%), DSS-1 (30.42%), and DSS-2 (41%). The findings also depict that the combined impact of PCM and nanoparticles displays an average exergy efficiency of 12.2%, which is greater than CSS, DSS-1, and DSS-2 by 3.18, 5.47, and 11%, respectively. Additionally, the economic analysis reveals that the cost per litre value of CSS, DSS-1, DSS-2, and DSS-3 was 1.06, 1.27, 1.22, and 1.07 (Rs/l). The integration of PCM-SWF in conventional still increases the cost of water by 13% with an increase in freshwater yield of 92%, whereas the integration of nano-enhanced PCM increases the cost of water by 1% with a tremendous increase in freshwater yield of 130%.