When the agitator is mounted in the centre of a circular tank, the tank must be furnished with baffles to prevent the liquid from rotating. Higher viscosity may not require any baffles. ("Rule-of-thumb": Width of baffles should be 0.1 x tank diameter).
When the agitator is mounted excentric in a circular tank, no baffles are required. However, additional reaction forces from the tank walls usually make it necessary to design an excentric agitator for heavier duty. ("Rule-of-thumb": Agitator should be mounted 1/3 of tank diameter from the wall).
When the agitator is mounted in a square tank, no baffles are required.