Thermodynamic study on an enhanced humidification-dehumidification solar desalination system with weakly compressed air and internal heat recovery

Abstract

Humidification-dehumidification (HDH) process has proved to be a promising technology for obtaining drinkable fresh water. Traditional HDH process exhibits limitations in steady working due to the dependence in the stability of heat and cold sources. A combination of heat pump and HDH has been proposed to solve effectively above challenge. However, the energy equalization between heat source and cold source must be guaranteed to maintain the continuing water production. A novel enhanced HDH method with weakly compressed air and internal heat recovery based on traditional mechanical vapor compression is therefore developed, in which moist air instead of vapor is used as the work fluid. Solar energy is required only for the system start-up, and cooling seawater and additional heat sources are no longer needed during steady operation stage. Meanwhile, the restrictions of evaporation and condensation temperature in the HDH process driven by heat pump can also be completely solved. It is found that the system performance can be significantly improved by increasing spraying seawater temperature. When the spraying seawater temperature is 70 °C, the maximum specific energy consumption and gained-out-ratio (GOR) are 18.35 kg/kWh and 12.24 respectively, and GOR is much larger than that of tradition HDH process (normally less than 6) driven by heat pump or solar energy. This new approach provides the possibility for high-efficient, steady and small-scale drinkable water production.