Mechanical Operations
Height of liquid in agitation tank is normally maintained equal to the tank diameter. However, if the tank is too tall and a large liquid hold up is desired, then two or more impellers mounted on the same shaft may be used. The clearance between the tank bottom and the bottom most impeller should be about (where, D = impeller diameter)

2 D
1.5 D
0.5 D
D

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Mechanical Operations
Higher is the mesh number, smaller will be the aperture size of the screen. It means that the aperture size of a 200 mesh screen will be smaller than that of 20 mesh screen. This is valid for

American standard screens (ASTM and Tyler standard screens)
All of these
German standard screens (DIN 1171) etc
British standard screens

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