Experimental investigation of magnetic ring fins with variable spacing in a hemispherical solar still: A 4E assessment

The shortage of freshwater and the high energy consumption of traditional desalination methods require the development of renewable energy-based desalination methods such as solar stills. Although solar stills are simple and low cost, their limited productivity remains a barrier to their widespread use. Therefore, the present study aims to enhance the performance of a hemispherical solar still using magnetic rings within the distillation basin. These rings work as fins and a source of a magnetic field that improves evaporation. The novelty of this study lies in the use of a variable-spacing array of magnetic rings by changing the number of rings and analyzing the effect on the performance using comprehensive 4E analysis. The experiments were performed in Al-Madinah Al-Munawarah, Saudi Arabia, during August 2025. The standard solar still (SHSS) was compared with four improved models containing 5, 10, 15, and 20 magnetic rings. The performance of different cases was assessed based on freshwater productivity, energy and exergy efficiencies, economic indicators, and environmental performance. The results indicated a significant enhancement in performance with an increase in the number of magnetic rings. Basin water temperature increased from 45°C in the SHSS to 50.5°C in the MHS-HFM-20. Daily productivity also increased from 4.37 L/m²·day to 7.50 L/m²·day, with an increase of 72%. Thermal and exergy efficiency also improved by 56% and 172%, respectively. Economically, the production cost reduced from $0.011/L to $0.007/L, a reduction of approximately 36% and payback period decreased from 0.27 to 0.176 year with a reduction of 35%. Environmentally, the quantity of mitigated carbon dioxide emissions increased from 2.52 tons to 4.55 tons, reflecting the positive impact of the proposed technology on carbon emission reduction.