Depth straining

The unloading was conducted with the same rate as loading. In the given experiment the Berkovich indentor was used with the angle at the top of 65.3° and rounding radius of 200 nm. Indentations were carried out in the checked load regime with preload of 0.001 mN. For elasticity modulus calculation the obtained result in the experiment by nanoindentation course dependences of load on indentation depth (strain) in 10 points for each sample at loads of 0.01, 0.02, 0.03, 0.05, 0.10, 0.50, 1.0, and 2.0 mN were processed according to Oliver-Pharr method [18]. 

Figure 2.18 Schematic diagram of depth straining complete bloddng mechanism...

Although textile filter media are used in numerous types of filter, the mechanisms by which the particles are captured are commonly referred to as surface straining (alternatively screening), depth straining, depth filtration and cake filtration. These mechanisms are shown in Figs 7.8a-78d. 

Filtration mechanisms (a) surface straining (screening), (b) depth straining, (c) depth filtration and (d) cake filtration. 

Needlefelts are not as widely used in liquid filtration as they are in dust collection. Unless required for depth straining, as in the viscose industry, or unless the particles can be restricted to the surface as in some filter belt mining applications, the risk of premature blinding through pore blockage is always a threat. 

Most real media are, of course, not infinitely thin, but have a finite thickness in the direction of fluid flow, while most pores through such material vary in diameter along the fluid path. A second mechanism, termed depth straining, then applies when a particle moves through a pore until it meets a point where the pore is too small, and the particle is held entirely because of its size. The pore then is blocked, and remains so until the filter medium becomes too clogged in this way for it to have any further use. At this point it must be discarded, or, preferably, blown free of the trapped solids, by a reverse flow of fluid. 

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