Performance analysis and optimization of solar-powered hybrid desalination systems using nitrogen-doped graphene composite phase change materials

The critical global challenge of potable water scarcity demands urgent attention, leaving no room to neglect the imperative of desalinating salt water. The hybrid FO-MD desalination system, when integrated with photovoltaic thermal solar energy and phase change material (PCM), demonstrates exceptional performance due to the PCM's high melting points. This study is novel as it examines the thermal enhancement of PCM composite materials, specifically nitrogen-doped graphene PCMs with outstanding thermal conductivity, on solar energy and the FO-MD hybrid water desalination systems. The investigation is conducted over a 24-h period under natural conditions, using four different PCM melting points (30, 40, 50, and 60 °C) to compare performance during the day and night. The exploration of water transfer rates in two desalination units- MD evaporation efficiency (EE) and specific thermal energy consumption (STEC)- reveals insights into the proposed system's performance across the four PCM melting points in the solar energy system. The highest volume of freshwater per day achieved using 60 °C, reached 200.79 L. If the comparisons were made during daylight hours only, using 60 °C achieved the highest MD EE and the lowest STEC, reaching 78.54 % and 916.69 kWh/m3, respectively. If the comparisons were made during nighttime hours only, then using 40 and 50 °C achieved the maximum freshwater, reaching 62.769 L and 67.96 L, respectively. While, using 30 and 60 °C achieved 26.2 L and 50.626 L, respectively. Notably, using 40 °C resulted in the most stabile production throughout the entire nighttime period. The highest MD EE and the lowest STEC, reached 38.43 % and 1846.98 kWh/m3, using a melting point of 40 °C. Furthermore, the investigation into the initial draw solution volume in tank highlights its significant influence on the system, particularly in managing divergence and convergence between water transfer rates in the two desalination units.