Study on the Heat and Mass Transfer Characteristics of Humidifiers in Humidification–Dehumidification Desalination Systems

The humidifier plays a key role in a humidification–dehumidification (HDH) desalination system; it directly affects both the freshwater production efficiency and energy consumption ratio of the system. In this study, for a humidifier in an HDH system, a heat–mass coupled differential equation model of spray water and air on the surface of the packing material was established, and the effects of parameters such as the spray water temperature ( t w ), mass flow rate of spray water ( m w ), air temperature ( t a ), and air mass flow rate ( m a) on the humidification performance of humidifiers composed of eight different types of packing materials were investigated. The results show the following: (1) Under the same inlet spray water and air conditions, the humidification performance of different packing materials from good to bad is as follows: cellulose paper, polypropylene, hackettes, saddles, snowflakes, wooden slats, polyvinyl chloride, gunny bag cloth. (2) Increasing the t w can significantly improve the humidification performance. To achieve higher humidification energy efficiency, it is recommended to increase the t w to above 80 °C. (3) With the increase in the m w , although the humidification efficiency ( ε hum ) decreases slightly, the humidification rate ( m hum ) increases, and the specific humidification energy ratio ( η hum ) decreases accordingly. To maintain a high m hum and a low η hum , it is advisable to control the m w at not less than 0.5 kg/s. (4) Increasing the humidifier inlet t a can improve the m hum , ε hum , and η hum , although not as effectively as increasing t w . (5) Increasing the m a can improve m hum and ε hum . However, it simultaneously increases the η hum . The results of this study can provide theoretical guidance for the selection of efficient packing materials and the optimization of humidifier operating conditions in HDH desalination systems.