Experimental investigation of hybrid Ag–MWCNT nanofluid and PCM integrated solar still at varying water depths for enhanced thermal, exergy, economic, and environmental performance

This study experimentally examines the performance improvement of a stepped solar still integrated with phase-change material and a hybrid Ag-MWCNT nanofluid at three water levels (2 cm, 4 cm, and 6 cm). The maximum basin temperatures of the hybrid nanofluid structure (at 4cm and 6cm) were 54°C and 53°C, respectively, across all working conditions, indicating improved heat absorption and storage capability. The results show that a lower water level (2 cm) leads to faster heating, 4 cm achieves good thermal retention and an evaporation balance, and 6 cm shows a reduced effect due to greater thermal inertia. The Productivity of fresh water was significantly enhanced in the hybrid nanofluid, reaching 2925 ml at 4 cm and 2310 ml at 6 cm, both much higher than those of the baseline system. The boost in Productivity at 4 cm was observed to be in the range of 80-173%, and at 6 cm, in the range of 50-157%, confirming the synergistic effect of PCM and the hybrid nanofluid. Water quality investigation showed that the pH values of the feed (7.2) and distilled water (7.0) are within WHO standards (6.5-8.5), thereby providing safe, neutral water quality. The electrical conductivity decreased from 550 µS/cm to 120 µS/cm, indicating effective ion removal. The TDS was reduced from 330 mg/L to 72 mg/L, which was within the permissible limit (<500 mg/L). The hybrid Ag–MWCNT nanofluid with a PCM significantly improves thermal performance, freshwater yield, and water quality, making it a promising approach for efficient and sustainable solar desalination.