Computational Fluid Dynamics of Innovative Spacers for Flat-Sheet Membrane Distillation

Nowadays, one of the most important challenges for human life is the lack of drinking water resources. According to the United Nations, half of the world population will experience a degree of water scarcity by 2050. With such a scenario, the combination of the need for drinking water, the looming climate change and the possibility of exploiting renewable sources, gives rise to the creation of a device capable of water desalination in a sustainable way. These requests find an answer in the mission of the "MELoDIZER" project, which aims to implement high-performance membranes and modules in strategic and sustainable applications of membrane distillation, and whose collaboration has allowed the development of this work. The thesis investigates the use of direct contact membrane distillation technology through the use of computational fluid dynamics. For this purpose, the simulation software provided by enGits, the German company partner of the Melodizer project, is used. The aim is to design one of the main components of this process, the "spacer", suitable for promoting mixing and therefore reducing polarization phenomena that negatively affect the success of distillation. First of all, an excursus is provided on the numerical methods underlying the model, i.e. the Navier-Stokes equations that govern the process and the discretization methods in space and time used by the simulation software. The creation of the model is subsequently illustrated, whose purpose is to simulate the process taking into account both its hydrodynamics and thermodynamics. The model validation is achieved through comparison with experimental data provided by literature. Afterwards, an exploratory phase follows in which numerous geometries are specifically created through a modelling software, Blender, with the aim of testing their performances using the model. At the end of this phase only the best ones are selected. Whereupon the model is refined to take into account the presence of salt in the water and the evaporation phenomenon that occurs near the membrane. At this point, the best geometries are tested through this more complex version of the model. In conclusion, the obtained results finally decree the spacer's geometry that optimizes the overall performance.