Why drops the amount of back-mixing with mounting vessel numbers?

Formally you can write down the material balance for the cascade (either step by step or in a 'closed version' with the well known 'faculty operator formula') and omit the reaction term(s) in this formula(s), solve the differential equation and get the well known plots for the cascade RTD-spectrum with the number n of vessels as a parameter. But you can explain it also qualitatively in the following manner: The first vessel 'doesn't see', i.e. it doesn't get mixed back, the amount of tracer in the second vessel and so on. The larger the number of vessels the more can this effect be encountered. Remember that the total reactor volume doesn't change and that therefore the volume of a single vessel (that means also the residence time !!) drops down with a mounting number of vessels, the 'cells' get smaller and approach the disks in a cell model of a TFR, - ending in differential disks -> ideal TFR.

take your browser back for previous text or:

to main test page