Laminar Flow Tubular Reactor LFTR

The two previous examples involved reactors where deviations from ideality were caused by fiaws in design and/or construction. As a final example, let s consider a case where the deviation from ideal behavior is an inevitable consequence of the nature of flow through the reactor. 

In laminar flow, the velocity profile across the tube diameter is not flat. If the fluid is Newtonian, and there are no radial variations in temperature or concentration, the velocity profile will be parabolic. In laminar flow, there will be radial concentration gradients at any point along the axis of the tube, since the fluid velocity at the wall approaches zero, whereas the velocity at the center of the tube is at a maximum. The fluid at the wall of the tube spends a long time in the reactor. Therefore, the concentration of reactant is relatively low in this region. The fluid at the centerline of the tube has the highest velocity, so that the reactant concentration is relatively high at this position. 

The exact shape of these profiles will depend on a number of factors, e.g., the reaction rate, the enthalpy change on reaction, and the sensitivity of the fluid viscosity to temperature. However, the behavior of an LFTR is very different from that of an ideal, plug-flow reactor. 

Hopefully, the above discussion has established that every continuous reactor is not a CSTR or a PFR. The next thing we have to do is determine how to tell whether a given reactor is a PFR or a CSTR, or something in between, or something worse. 

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