What does the speed of a geared agitator depend on and how is it related to the agitator propeller size?
The rotational speed depends on the viscosity of the substrate. With viscous substrates, slower agitator propeller rotations are more efficient. The speed, in conjunction with the motor power, determines the propeller size. The lower the speed and the higher the power, the larger the propeller. For a perfect stirring result, the right choice of agitator is therefore crucial. See also "What effect does the propeller blade geometry have on the stirring process?"