Solar-driven natural vacuum desalination system with inner condenser

Abstract

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.