Study of a compact falling film evaporation/condensation alternate-arrayed desalination system

This work presents a highly integrated humidification-dehumidification desalination approach that is implemented by compact falling film evaporation/condensation. The featured structure is hot seawater, and cold freshwater is uniformly distributed by a compact membrane array with a hot–cold alternate method. Vapor generated from hot seawater films can directly transfer to cold freshwater films and condense. Thus, the mass transfer resistance is reduced considerably. A typical structure with a membrane size of 60 mm × 700 mm is designed, containing 6 cold membranes and 5 hot membranes. The heat and mass transfer characteristics are discussed theoretically and experimentally. The inlet seawater temperature is proven to be the most crucial factor affecting water productivity. In contrast, the mass flow ratio of freshwater and seawater has a weak influence on water productivity. The maximum water productivity is approximately 1344.8 g/h with a corresponding gained-output-ratio of 0.804 when the inlet temperatures of freshwater and seawater are 18.5 ℃ and 80 ℃, respectively, and the mass flow rate of seawater is 90 kg/h. Due to the compact structure, its unit volume water productivity is approximately 90.88 kg/(h·m³), which is much higher than that of other devices. This research may help improve the application of small-scale desalination systems.