The nature of liquids to blend determines the equipment used. Mixing of liquids occurs frequently in process engineering. In this context, the act of mixing may be synonymous with stirring-, or kneading-processes. The type of operation and equipment used during mixing depends on the state of materials being mixed (liquid, semi-solid, or solid) and the miscibility of the materials being processed. A classical example of segregation is the brazil nut effect. A biofuel fermenter may require the mixing of microbes, gases and liquid medium for optimal yield organic nitration requires concentrated (liquid) nitric and sulfuric acids to be mixed with a hydrophobic organic phase production of pharmaceutical tablets requires blending of solid powders.

With the right equipment, it is possible to mix a solid, liquid or gas into another solid, liquid or gas. Some classes of chemical reactors are also mixers. Modern industrial processing almost always involves some form of mixing.

Mixing is performed to allow heat and/or mass transfer to occur between one or more streams, components or phases. Familiar examples include pumping of the water in a swimming pool to homogenize the water temperature, and the stirring of pancake batter to eliminate lumps (deagglomeration). In industrial process engineering, mixing is a unit operation that involves manipulation of a heterogeneous physical system with the intent to make it more homogeneous.

Anchor agitator design in powder