Performance analysis of single-slope solar stills with PCM-filled compartments: Numerical insights into glass angle and solar flux

This study focused on a computational modeling of a single-slope solar still integrated with circular compartments filled with a graphene-enhanced phase change material (PCM). The thermal behavior and humidity distribution inside the still over a 13-hour diurnal cycle are investigated via finite element method. The effects of varying the glass cover angle (10°–40°) and external convective heat transfer coefficient (5–300 W/m²·K) are analyzed. Key performance metrics include the temperature distribution of the system, the melting and solidification behavior of the PCM, and the internal relative humidity. Results show that a 10° glass angle promotes higher average moisture concentrations during the early and midday hours, while a 40° angle enhances moisture retention in the late afternoon. The maximum average relative humidity is recorded at a 40° angle with a 300 W/m²·K heat transfer coefficient, approximately 10.5 h into the simulation. The peak average temperature within the still is observed around 6.5 h after sunrise at a 10° glass inclination. The findings provide physical insight into the coupled thermal and moisture transport mechanisms and offer practical design guidance for enhancing the performance of passive solar stills integrated with phase change materials.