Sustainable humidification-dehumidification desalination system using low-grade heat source

Humidification-dehumidification desalination (HDH) cycle is one of the methods for producing freshwater from seawater or saline water for small-scale and low-cost applications. Major energy source of the desalination system is thermal energy that can be provided from any available low-grade heat sources such as industrial waste heat or solar thermal collectors. The working principle of HDH system is very similar to the rain cycle which air is humidified in by evaporation of seawater. Then the humidified air moved by wind streams to cooler places where it condenses to water droplets. In this project, at first mathematical thermodynamic based models for different types of the HDH cycle are developed, and the effect of operational parameters such as temperatures and flow rates on cycle performance parameters like gain output ratio (GOR) and recovery ratio (RR) are studied.  Also, the heat and mass transfer analysis of the cycle is conducted to examine the behavior of key performance parameters such as temperatures, flow rates, surface area, and air velocity on the heat and mass transfer rate. Further, a new concept of using a heat pump is investigated to simultaneously provide heating and cooling load requirements of the HDH system in an optimized way. A mathematical model is developed to investigate the optimum operating condition of the HDH system for fully coupled condition operation.  Experimental investigations of the cycle performance and potential of water production at different operating conditions, including the effect of temperatures, feed salinity, air to seawater flow rate ratios, and freshwater to seawater flow rate ratios studied. The experimental findings validated with the mathematical model. To reach an environmentally sustainable solution in HDH system, brine recirculation method is proposed, mathematically modelled, and experimentally investigated.  It is found that the brine recirculation method is practically feasible and can significantly reduce the rejected brine volume.