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A basic classification is into those that circulate the liquid axially and those that achieve primarily
radial circulation. Some of the many shapes that are being used will be described shortly.
popular turbine impeller, the ratio of diameters of impeller and vessel falls in the range, d/D t=0.3-0.6,
With commercially available motors and speed reducers, standard speeds are 37, 45, 56, 68, 84, 100,
125, 155, 190, and 320 rpm. Power requirements usually are not great enough to justify the use of
continuously adjustable steam turbine drives. Two-speed drives may be required when starting
torques are high, as with a settled slurry.
Expert opinions differ somewhat on this factor. As a first approximation, the
impeller can be placed at 1/6 the liquid level off the bottom. In some cases there
is provision for changing the position of the impeller on the shaft. For off-bottom
suspension of solids, an impeller location of 1/3 the impeller diameter off the
bottom may be satisfactory. Criteria developed by Dickey (1984) are based on
the viscosity of the liquid and the ratio of the liquid depth to the tank diameter,