Thermophysical behavior and transient thermal performance of a Fe3O4/paraffin nano-enhanced phase change material for solar desalination applications

The low thermal efficiency and limited nocturnal operation of conventional solar stills remain major challenges for sustainable solar desalination. This study experimentally investigates a paraffin-based phase change material enhanced with 1 wt.% Fe 3 O 4 nanoparticles as a thermal energy storage medium for improving the transient thermal behavior and overall performance of a single-slope solar still. The Fe 3 O 4 /paraffin nanocomposite was prepared using a surfactant-assisted dispersion method and characterized by SEM, DSC, FTIR, and thermal conductivity measurements. Outdoor experiments were conducted in Benguerir, Morocco, during four clear sky days in August 2024, representing typical summer operating conditions, using three configurations: a conventional solar still (CSS), a PCM-assisted solar still (PCMSS), and a nano-PCM solar still (NPCMSS). The thermal analysis further included the evaluation of internal convective, evaporative, and radiative heat-transfer coefficients, together with external thermal losses. Fe 3 O 4 incorporation increased paraffin thermal conductivity by approximately 47%, facilitating heat transfer within the storage medium and maintaining favorable basin-water temperatures and water to glass temperature differences during the cooling period. Although the NPCM exhibited an approximately 22% reduction in latent heat storage capacity, the NPCMSS achieved a 65.2% increase in freshwater productivity relative to the CSS, with a corresponding productivity uncertainty of 2.4%. The NPCMSS also attained daily energy and exergy efficiencies of 29.33% and 2.04%, with corresponding uncertainties of 2.3% and 2.6%, respectively. Economic and environmental assessments further indicated reduced freshwater production cost and improved CO 2 mitigation performance. Overall, Fe 3 O 4 /paraffin NPCM shows strong potential for improving passive solar desalination under the investigated conditions.