Energy and exergy analysis of a novel humidification-dehumidification desalination system with fogging technique

Abstract The availability of fresh water is essential for human being lives existence. But most of the time, it is not a naturally guaranteed and accessible option for nearly all the world's countries. As a mission to maintain the presence of freshwater, the aim of this paper is to provide and examine a new humidification-dehumidification (HDH) water desalination system. The provided HDH system is equipped with the fogging nozzles technique that is experimentally proofed, when compared to other HDH systems, to impacting the performance positively in terms of reducing the exergy destruction of the desalination process. A regular jet nozzle and two fogging nozzles with different droplet sizes (20 and 30 microns) were used to examine the effect of the droplet size on the amount of entropy generation. For all air flow rates, using the fogging nozzles reduces the total specific entropy generation greatly in comparison with the regular jet nozzle. The 20-micron nozzle shows a higher ability in reducing the specific entropy generation when compared to the 30-micron nozzle. The performance of the HDH system was judged using the gained-output ratio (GOR). The maximum GOR value of 3.4, and the minimum specific entropy generation value of 0.235 were achieved at a 0.78 mass flow rate ratio, which indicates that using the fogging nozzles technique increases the recovered energy from the humidifier's freshwater outlet. The entropy generation curve for the humidifier and the dehumidifier experienced no change under the variations of the mass flow rate ratio. Therefore, the fogging nozzles technique limits the entropy generation in the HDH system even at higher seawater inlet flow rates due to the larger contact area and the smaller water droplets that generate higher evaporation and condensation rates at the humidifier and dehumidifier units, respectively. Furthermore, it was found that increasing the inlet air temperature has positive effects on the HDH system by reducing slightly the total amount of entropy generation.