Experimental and Simulation Analysis for Optimization of Solar Desalination System Using Humidification-Dehumidification Method: Open and Close Air Cycle

Over the last decades, desalination of brackish water and seawater has been studied extensively for producing fresh water. Desalination technologies are divided into two major categories: Thermal and Membrane. Humidification-Dehumidification (HDH) which is the subject of the present research, is one of the thermal technologies. It is inspired by the rain cycle and is based on evaporation and consecutive condensation.

In a series of experiments, the processes of production of fresh water has been investigated under various operational parameters such as temperature and flowrate of cooling water, humidifier intake from water boiler, air flowrate and height of packed bed column. Subsequently, an appropriate mathematical model of the system has been developed and validated using the collected data. Furthermore, based on the developed model a series of simulations has been carried out in ASPEN Plus in order to obtain optimum physical parameters of various parts of the desalination system.

The experimental results showed that under constant heat flux and optimum air flowrate, three parameters increase the production of distilled water the most: increasing flowrate of cooling water, decreasing flowrate of water inlet and increasing temperature. Moreover, although increasing flowrate of cooling water leads to an augmentation in the distilled water flowrate, but this effect is mitigated at high rates.

Furthermore, based on the obtained overall heat transfer coefficients of the humidifier and condenser, the most reliable Height Equivalent to a Theoretical Plate (HETP) model of random packing is found to be Mangers & Ponter. The estimation error of the model in predicting the height of packed bed was less than 4%. Based on the results of this model, closed air system increases the efficiency of the production of distilled water by 15% in comparison to open air. This increase is the result of prevention of wasting of air humidity in the condenser outlet.

Finally, optimum parameters of operational units are obtained by applying a Differential Evolution (DE) strategy. The optimum values of flowrate and temperature of cooling water are 0.0298 m³/hr, 13 °C, respectively. The best value of flowrate of closed air is found to be 0.008075 m³/hr and of water intake to be 0.021497 m³/hr. These values produced fresh water with flowrate of 0.3777 m³/hr.