Consider a semi-continuous reactor fed with

and

(the inlet flow rates of species

and

). Initially, the content of the reactor and the feed are completely segregated;

, where

is the segregation intensity, which varies from zero (perfect mixing) to unity (no mixing).
If the inlet flows are constant and the reactor is initially empty, the volume of the reactant in the reactor,

, varies from zero to

(total reactor volume).
We have

and

, where

is the residence time of the reactor and

is the total flow to the reactor.
Before the reactor gets full (i.e., for

), the segregation intensity obeys the following ODE:

, where

is the mixing time.
When the reactor is full and overflowing (i.e., for

or

), the segregation intensity is the solution to the following ODE:

=

.
This Demonstration plots

versus time for values of the mixing time and residence time to be fixed by the user. The red portion of the curve corresponds to

for

while the blue section of the curve gives

for

.