Why PFR requires less volume than CSTR for same conversion and reaction rate?
The reason that PFR require less volume than a CSTR is the difference in residence time distribution between the reactors. Residence time is the amount of time molecules spend in the reactor which equal to v/vo (v=volume of the reactor and v0 is volumetric flow rate). Let us assume that we design a PFR and CSTR that have similar residence time i.e. ratio of volume v and v0 is the same and we are pumping about 100 molecule per minute to each reactor. In the case of PFR, all the 100 molecules will spend exactly the same time inside the reactor (v/v0). In the case of CSTR, things are little more complicated, once the 100 molecule hit the CSTR, they mixted instantaneously and thus some of these 100 molcule will leave from the reactor exit stream very early i.e. will spend much less time inside the reactor (less the v/v0) and of course some these 100 molecule will spend more time making the average residence time the same as the PFR. Therefore, with the chance that molecules will spend shor
