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Membrane distillation (MD) is a thermally driven separation process in which separation is driven by phase change. A hydrophobic membrane presents a barrier for the liquid phase , allowing the vapour phase (e.g. water vapour) to pass through the membrane's pores. [ 1 ]
There are two main flow configurations of membrane processes: cross-flow (or tangential flow) and dead-end filtrations. In cross-flow filtration the feed flow is tangential to the surface of the membrane, retentate is removed from the same side further downstream, whereas the permeate flow is tracked on the other side. In dead-end filtration ...
Membrane distillation combines membrane separation and distillation, with hydrophobic membranes and differences in vapour pressure. The Vacuum Multi Effect Membrane Distillation (VMEMD) configuration used in Aquaver systems adds the advantages of low-temperature operation and multi-effects to the membrane distillation characteristics.
Distillation column in a cryogenic air separation plant The cryogenic separation process [ 4 ] [ 5 ] [ 6 ] requires a very tight integration of heat exchangers and separation columns to obtain a good efficiency and all the energy for refrigeration is provided by the compression of the air at the inlet of the unit.
The configuration of this stack can be either horizontal or vertical. The feed water passes in parallel through all the cells, providing a continuous flow of permeate and brine. Although this is a well-known process electrodialysis is not commercially suited for seawater desalination, because it can be used only for brackish water (TDS < 1000 ...
The membrane assembly consists of a pressure vessel with a membrane that allows feedwater to be pushed against it. The membrane must be strong enough to withstand the pressure. RO membranes are made in a variety of configurations. The two most common are spiral-wound and hollow-fiber. Only part of the water pumped onto the membrane passes through.
The morphology of a membrane is usually established by microscopy. Atomic force microscopy (AFM) is one method used to characterise the surface roughness of a membrane by passing a small sharp tip (<100 Ă) across the surface of a membrane and measuring the resulting Van der Waals force between the atoms in the end of the tip and the surface. [10]
Multi-stage flash distillation (MSF) is a water desalination process that distills sea water by flashing a portion of the water into steam in multiple stages of what are essentially countercurrent heat exchangers. Current MSF facilities may have as many as 30 stages.