What is residence time distribution and why is it important?

Residence Time Distribution (RTD) describes how long different fluid elements spend in a reactor. It is determined by tracer experiments - injecting a tracer pulse or step and measuring outlet concentration over time. E(t) is the exit age distribution. RTD diagnoses non-ideal flow: bypassing (short-circuiting), dead zones (stagnant regions), and channeling. Ideal PFR has narrow RTD (all elements same time); ideal CSTR has exponential RTD. RTD is used to predict conversion in non-ideal reactors.