Two-fluid model
Two-fluid model is a macroscopic traffic flow model to represent traffic in a town/city or metropolitan area, put forward in the 1970s by Ilya Prigogine and Robert Herman.
There is also a two-fluid model which helps explain the behavior of superfluid helium. This model states that there will be two components in liquid helium below its lambda point. These components are a normal fluid and a superfluid component. Each liquid has a different density and together their sum makes the total density, which remains constant. The ratio of superfluid density to the total density increases as the temperature approaches absolute zero.