1. Definition and main properties of residence time distributions

The concept of residence time distribution was introduced by Danckwerts in 1953, when he proposed a systemic approach to describe the hydrodynamic behavior of flows in real reactors.

Compared with the conventional approach, which uses local balances of matter, energy and momentum, the systems approach is distinguished by the fact that each entity present in the reactor is assigned a specific character. This systemic approach is better known as a population balance.

Thus, for the distribution of residence times, we can assign to each molecule :

• α its age, i.e. the time that has elapsed between its entry into the reactor and the moment of observation ;

• λ its life expectancy, i.e. the time remaining between the moment of observation and its exit from the reactor;...