Definitions and concepts of residence time

As seen previously, the concentration varies with the reaction time or contact time in the batch reactor. 

In continuous reactors, the concentration varies with space time, which is a variable equivalent to time but measured as a function of reactor volume and inlet flow of the fluid (or inlet velocity of the fluid). The flow is measured experimentally by using a rotameter or mass flow meters (MFM) through conductor signals. They are concrete measurements. We can define the new variables as follows  

Space velocity ratio between the feed volumetric flow and reactor volume. It represents the feed rate per unit volume to achieve a given concentration or conversion of the reactant in the reactor outlet. One can interpret the space velocity as the velocity with which a fluid element or molecules pass through the reactor volume to achieve a certain conversion. If Bao (mol/h) is the molar flow, vq (m /h) is the volumetric flow at the reactor inlet, and V (m ) the reactor volume, then  

As an example, Ve = 5 h means a feed rate of 5 V h to process the reaction in order to achieve 80% conversion. On the other hand, r = 5 min represents the time required to process a feed rate in the volume V and achieve 80% conversion, or each 5 min one processes a load in the reactor volume to achieve 80% conversion. 

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