Mixing (physics)

In physics, there are several distinct notions of mixing, all of which try to capture the common-sense notion of mixing, but using rather disparate formal methods, techniques and definitions.

A second approach considers the mixing of aggregates, such as rocks and sand, which are lumpy on the small scale; this is commonly seen in mixing in process engineering.

A third approach uses the mathematical formalisms of measure theory and measure-preserving dynamical systems, to define mixing abstractly for generic dynamical systems in arbitrary dimensions.

For example, by assigning a position and a velocity to each atom in a fluid, the mixing takes place in a

is the dimension of the phase space (position plus velocity) of a single atom.

The mixing of gases or liquids is a complex physical process, governed by a convective diffusion equation that may involve non-Fickian diffusion as in spinodal decomposition.

When fluid properties such as viscosity depend on composition, the governing equations may be coupled.

Small rigid objects (such as rocks) are sometimes mixed in a rotating drum or tumbler.

The 1969 Selective Service draft lottery was carried out by mixing plastic capsules which contained a slip of paper (marked with a day of the year).

A dynamical system is said to be mixing if the phase space of the system becomes strongly intertwined over time, according to at least one of several formal mathematical definitions.

A canonical example is the Cuba libre: suppose one is adding rum (the set

) will contain rum, and it will be in equal proportion as it is elsewhere in the glass.