A series of blades attached to a shaft used to provide radial current of a fluid when rotated. It is used in centrifugal pumps and for mixing purposes. Radial-flow impellers discharge the fluid in a horizontal (radial) direction to the vessel wall. If suitable baffles are provided, this device produces strong top-to-bottom currents. If the vessel is unbaffled, then swirling and vortexing may result. Axial-flow impellers create a flow parallel in the direction of the axis of the shaft. These devices produce more flow per unit power supplied than radial impellers, and are generally used in flow controlled operations. As with radials, swirling and vortexing may develop without the use of baffles. Compare propeller.