Performance analysis of an air-heated humidification-dehumidification desalination plant powered by low grade waste heat

Humidification dehumidification desalination system has shown advantages to satisfy small scale freshwater demand. In this paper, an air-heated humidification dehumidification desalination system powered by low grade waste heat, coupled with plate heat exchangers, is constituted. Working mechanisms of the air-heated HDH desalination system are revealed, and performance for both the humidification dehumidification desalination unit and the plate heat exchangers is obtained and analyzed based on the established mathematical models. Entropy generation of both the components and the whole humidification dehumidification desalination system is calculated to judge the feasibility of the system cases and demonstrate the energy loss. Simulation results show that despite the top value of the gained-output-ratio, 3.51, at the balance condition of the dehumidifier with a negative specific entropy generation of the dehumidifier, the actual maximum value is 3.04 when the mass flow rate ratio between the seawater and the dry air is ṁsw/ṁda=1.28. Based on the elevation of the heat transfer rate and the descendant trend of the heat transfer coefficient, the heat transfer area of the plate heat exchangers rises from A = 5.25 m2 to A = 15.90 m2. Furthermore, it is summarized that the pressure drop of the plate heat exchangers will result in a very limited adverse influence on the energy utilization efficiency of the whole humidification dehumidification desalination system.