Membrane Types

Membranes can be distinguished based on their (i) geometry, (ii) bulk structure, (iii) production method, (iv) separation regime, and (v) application, as shown in Figure 1. Most commonly, membranes are produced in fiat-sheet or tubular (hollow-fibre) geometry. Flat-sheet membranes are either packaged in plate-and-frame or spiral-wound modules, whereas tubular membranes are packaged in hollow-fibre modules. The choice of the optimum membrane and module type depends on a wide variety of process specific conditions. Although hollow-fibre modules offer the highest membrane area per module volume ratio, plate-and-frame and spiral-wound modules are also commonly used for large-scale separations because of their better control of fluid dynamics.

Membranes either have a symmetric (isotropic) or an asymmetric (anisotropic) structure. The structure of a symmetric membrane is uniform throughout its entire thickness, whereas asymmetric membranes have a gradient in structure. The flux of a fluid through a symmetric membrane is typically relatively low, as the entire membrane thickness contributes a resistance to mass transport. Asymmetric membranes consist of two structural elements, that is, a thin, selective layer and a microporous substructure. Typically, the bulk structure (99 + %) of an asymmetric membrane is highly porous and provides only mechanical strength. Separation of a fluid mixture in an asymmetric membrane is performed in a very thin surface layer, which is typically of the order of 0.1-0.5 |im thick. The most common symmetric and asymmetric membrane types are shown in Figure 2.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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