Editing Impeller (section)

== In agitated tanks ==
{{see also|Mixing (process engineering)}}
[[File:Mixing - flusso assiale e radiale.jpg|thumb|Axial flow impeller (left) and radial flow impeller (right)]]
Impellers in agitated tanks are used to mix fluids or slurry in the tank. This can be used to combine materials in the form of solids, liquids and gas. Mixing the fluids in a tank is very important if there are [[gradient]]s in conditions such as temperature or concentration.

There are two types of impellers, depending on the flow regime created (see figure):

* Axial flow impeller
* Radial flow impeller

Radial flow impellers impose essentially [[shear stress]] to the fluid, and are used, for example, to mix immiscible liquids or in general when there is a deformable [[Interface (chemistry)|interface]] to break. Another application of radial flow impellers is the mixing of very viscous fluids.

Axial flow impellers impose essentially bulk motion and are used on homogenization processes, in which increased fluid [[volumetric flow rate]] is important.

Impellers can be further classified principally into three sub-types:
*[[Propeller]]
*[[Paddle wheel|Paddles]]
*[[Rushton turbine|Turbines]]

=== Propellers ===
Propellers are axial thrust-giving elements. These elements give a very high degree of swirling in the vessel. The flow pattern generated in the fluid resembles a helix.