Solar-driven natural vacuum desalination system with inner condenser

Desalination under low pressure is an effective way of increasing freshwater productivity. A natural vacuum desalination system with inner condenser driven by solar energy was proposed in this study. Through gravity and local atmospheric pressure, a vacuum condition could be formed in distiller, which allows flowing seawater to absorb a small amount of solar heat to achieve phase change evaporation. In addition, the system can easily remove accumulated non condensable gas through the water-filling and air-exhausting process. Transient characteristics of the system under constant hot seawater temperature were presented. And performance of solar energy-powered distillation was tested under actual weather using flat-plate solar collectors with a total area of 18 m². The constant temperature experiment results show that freshwater yield and cycle time increase with the increase of hot seawater temperature. Hourly water yield can reach 12.45 kg/h when the hot seawater temperature is 60 °C and the seawater mass flow rate is 0.1 kg/s. Daily water yield is 154.14 kg, and the corresponding performance ratio is 1.36 under real weather with an average solar irradiance of 672 W/m². Finally, economic analysis results indicate that the pure water cost is $ 6.9 per ton.