Stirred tanks or mixing tanks are process equipment commonly used in industry for mixing homogeneous and heterogeneous phases with and without chemical reaction, and when chemical reactions occur, it is usually called a chemical reactor.

They are generally cylindrical in shape and can be operated in batches, with recirculation or in continuous flow.

In an agitated tank the following unit operations can be carried out:.

Contenido

Los tanques agitadores contienen una hélice o impulsores en el extremo o a lo largo de una flecha") que se ubica en el centro del tanque, transversalmente o de forma excéntrica. Un tanque agitador puede contener una, dos o más flechas con una, dos o más hélices en cada flecha.

Drivers

Impellers used in agitated tanks can have purely axial flow (high efficiency impellers) or radial flow (Rushton turbine or 90° vertical vane impeller) or a combination of them (vane impellers with angles less than 90°). The impellers can be placed on the side of the tank centered or eccentric and secured with a flange "Flange (pipes)") or they can also be placed on the bottom of the tank. For small tanks, it is common to design them with multiple blades, while larger volume tanks have fewer blades and are also lined with rubber.

The speed reached by these equipment depends on what you want to mix; to mix two low-viscosity miscible liquids, a much lower shear force is required than that needed to disperse a high-viscosity liquid into another medium-viscosity liquid.

Some agitators operate from 100 RPM to several thousand RPM.

SO.

Laminar and turbulent regimes are important and must be taken into account for the design of mixing equipment, a number used by chemical engineers is the Reynolds number.

The (dimensionalless) agitator Reynolds number in a mechanically stirred tank is given by:

where:.

The presence or absence of turbulence in an agitated tank can be measured or estimated from the knowledge of the Reynolds number of the agitator and through parameters such as mass motion or Taylor diffusion, intensity and scale of turbulence. In the specialized literature it is generally accepted that for N_{Re} greater than 10,000 the flow can be considered as fully developed turbulent, while for N_{Re} less than 10 the flow can be considered as creeping laminar. In the interval between 10 and 10,000 the flow is considered transitional to turbulent.

Countercurrents also influence the development of flows that help the efficient mixing of materials.

The speed of the agitator and the characteristics of the impeller are basic for its proper functioning.