Enhancing the thermal efficiency of solar stills using magnesium oxide nanoparticles in a phase change material on a rotating hollow drum

Abstract

This study experimentally investigates the enhancement of thermal efficiency and freshwater productivity in a double-slope solar still through the integration of a rotating hollow metal cylinder combined with nano-enhanced phase change material (NPCM). Paraffin wax served as the latent heat storage medium, while magnesium oxide (MgO) nanoparticles at 1% volumetric
concentration were dispersed to improve thermal conductivity and heat distribution. The nanofluid was prepared via mechanical stirring and ultrasonic dispersion to ensure uniform stability. Field tests were conducted in Kirkuk, Iraq, from February to April 2025 under clear-sky conditions. The modified system achieved a maximum productivity of about 3,400 ml/m2·day at 0.25 rpm and 3 cm water depth, which is more than six times higher than the 520 ml/m2·day of the conventional still. Incorporating MgO nanoparticles raised the PCM tube temperature to 62°C compared to 46°C without additives, enhancing evaporation rates and extending production into nighttime hours. The improved design attained a peak thermal efficiency of 90%, outperforming PCM-only (66.5%) and smooth-cylinder (52.5%) systems. These gains are attributed to increased heat transfer surface area, superior thermal conductivity, and optimized rotational control. Compared with previous designs, the copper-tube cylinder with NPCM showed superior performance. Future studies should examine varying nanoparticle types, higher rotation-speed adaptability, and hybrid solar collector integration to further optimize cost-effectiveness and scalability in arid regions.