1. A device used to intimately combine materials. There are various types, the choice of which is dependent on the application. A commonly used mixer consists of a rotating shaft upon which blades are attached. These are either flat or pitched at an angle to provide radial or axial mixing, or a combination of both. Other designs include static mixers, which are ribbons of metal held within a pipe causing flowing liquids to alter their movement and mix.

2. A unit operation used in flowsheets to represent process input streams that combine together to provide a single output. It may be a simple vessel with a stirrer. A mixer does not allow a chemical reaction to occur, nor change of phase to take place.