Plug flow

In fluid mechanics, Plug Flow is a simple way of modelling flow of a fluid in a pipe or, more generally, a reactor. Essentially no back mixing is assumed with "plugs" of fluid passing through the reactor. This results in differential equations (DEs) that need to be integrated to find the reactor conversion and outlet temperatures.

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Other simplifications used are perfect axial mixing and a homogeneous bed structure.

The advantage of the plug flow model ensures that no part of the solution of the problem can be perpetuated "upstream". This allows one to calculate the exact solution to the DE knowing only the initial conditions, no further iteration is required to numerically converge, each "plug" can be solved independently provided the previous plug's state is known.