Non-ideal Flow and Residence Time Distribution

The deviation of a real reactor from ideal systems is deduced by a widely used method of inquiry, the stimulus-response experiment with a nonreactive tracer. The goal is not knowledge of all the hydrodynamic details of the real flow, but to know how long the molecules stay in the reactor or, more precisely, determination of the residence time distribution (RTD). Based on the RTD and a respective link to the mass balance and conversion equation, respectively, the conversion of a reactant in a real reactor can then be calculatecL We will learn this in Sections 4.10.5.2 and 4.10.6.2, limiting ourselves to the case of single-phase flow and steady-state operation. 

There are two simple ways to identify the RTD, the pulse and the step experiment. 

Different fluid elements may take different routes through the reactor and need a different time before thqr leave the vessel. The distribution of these times is the age distribution E (portion of the flow of tracer per unit of time, s ), and is found by dividing the actual tracer concentration at the exit by mtracet/V, that is, by the area under the curve of Cmcer versus time f  

Based on the dimensionless time 6 = t/r we acquire the exit age distribution in dimensionless form  

The dimensionless Ctracer curve of a step experiment is the cumulative F(f) function, and represents the fraction of elements in the exit stream with a residence time shorter than t  

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For a basic understanding of chemical reactor design, start with Sections 4.10.1 and 4.10.2, where different ideal and isothermal reactor types are introduced and the respective performance equations are derived. You should then study the behavior of real reactors (non-ideal flow and residence time distribution, Section 4.10.4) and the simplest model to account for deviations of real systems from ideal reactors, the tanks-in-series model (Section 4.10.5). 

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