Thermodynamic design and fouling of membrane distillation systems

Abstract

As water shortages intensify globally under the stresses of increasing demand, aquifer depletion, and climate change, the market for efficient desalination technologies has grown rapidly to fill the void. One such developing technology, membrane distillation (MD), has experienced keen academic interest and an increase in start-up businesses in the past decade. MD has expanded into a niche of small scale thermal desalination using solar and waste heat resources, due to its fouling resistance, scalability, and acceptable efficiency. Recent studies indicate that MD could attain the efficiencies of state-of-the-art mature thermal desalination technologies, although additional engineering and scientific challenges must first be overcome. The aim of this research is to better understand and provide solutions for two major challenge areas for MD: efficiency and membrane fouling. Studies on improving MD efficiency included examining the effects of tilt angle on MD performance using numerical simulations paired with experiments, devising a novel MD system design for with superhydrophobic surfaces to improved efficiencies, and an entropy-generation comparison of MD to other desalination technologies. For fouling studies in MD, a review of MD fouling was undertaken to synthesize conclusions from the literature and to explore gaps in the literature. This review lead to studies of the effect of filtration and bulk nucleation on MD fouling, a study on heterogeneous nucleation of inorganic salts with a fouling regime map to avoid nucleation, and fouling prevention via induced air-layers.