Analysis of the membrane effects on the energy efficiency of water desalination in a direct contact membrane distillation (DCMD) system with heat recovery

A theoretical analysis of the energy efficiency of a direct contact membrane distillation (DCMD) module with external heat recovery intended for desalination applications is carried out. A porous media model is proposed and validated against previously reported numerical and experimental results. A 2(n) planning scheme is employed to determine the most decisive membrane properties for maximizing the energy efficiency of the desalination system. The interaction between membrane parameters are found to be weak, allowing for the selection of manufacturing processes for emphasis in certain parameters. The porosity is shown to be a dominant factor, responsible for at least 40% of the variation of the energy efficiency metric, while the relative importance of other parameters is dependent on the heat recovery system effectiveness. An optimum membrane thickness is identified and observed to become smaller for better heat recovery systems, improving the energy efficiency of the process. The results obtained offer guidance to future membrane development efforts as to what should be emphasized to maximize the amount of distilled water produced for a given heat input. In particular, harnessing the interaction between the membranes parameters and the heat recovery system is essential to leverage the energy efficiency of the desalination system.