Performance improvement of an inclined stepped solar still via hybrid nano-enhanced phase change material

Inclined stepped solar stills are commonly employed for small-scale desalination and production of drinking water in arid areas. The stepped basin configuration of these stills increases the net evaporation area, improves water depth management, and optimizes solar radiation harvesting, thus increasing the productivity rate compared to traditional basin-type stills. In the current research work, an experimental study is performed to improve the performance of an inclined stepped solar still (ISS) by using a hybrid nano-enhanced phase change material (nano-PCM) incorporating graphene oxide and Al₂O₃ nanoparticles. Four different designs were taken into consideration: conventional ISS (Case 1), ISS with pure PCM (Case 2), ISS with 10 wt.% nano-PCM (Case 3), and ISS with 15 wt.% nano-PCM (Case 4). The impact of PCM and nanoparticle concentration on the rate of freshwater production, thermal efficiency, and heat transfer coefficient was examined. The findings revealed that ISS with 15 wt.% nano-PCM (Case 4) was more effective, with a production rate of 5025 mL/day, which is 57.7%, 17.8%, and 6.4% higher than Cases 1, 2, and 3, respectively. The daily energy and exergy efficiencies were 44.38% and 3.60%. The average evaporative heat transfer coefficient was 96.10 W/m²K, which is substantially higher than the other cases. Economic analysis indicated that the production cost is $0.025 per liter, thus establishing the techno-economic viability of the proposed modification.