Unit 27. Analysis of Transient PFRs

This website provides learning and teaching tools for a first course on kinetics and reaction engineering. Here, in Part III of the course, the focus is on the modeling of chemical reactors. In particular, it describes reaction engineering using the three ideal reactor types: perfectly mixed batch reactors, continuous flow stirred tank reactors and plug flow reactors. After considering each of the ideal reactor types in isolation, the focus shifts to ideal reactors that are combined with other reactors or equipment to better match the characteristics of the reactor to the reactions running within it.

Reaction engineering of the third of the three ideal reactor types, the plug flow reactor (PFR), is the subject of Section D of Part III. The discussion parallels that of the previous two sections: typical reaction engineering tasks are defined, qualitative performance is examined and full mathematical analysis is described and illustrated. Similar to CSTRs, plug flow reactors are typically designed to operate at steady state, but their start-up and shut-down involves transient operation, so both modes of operation are considered in this section.

Just as a CSTR occasionally must operate in a transient mode, so must a PFR. However, the corresponding modeling can be more challenging in the case of a PFR than it was for a CSTR. The reason for this is related to the kinds of equations needed to model the various reactors. For a CSTR, the steady state equations were algebraic, and to model transient CSTRs, ordinary differential equations were needed. With PFRs the steady state equations are ordinary differential equations, and the modeling of PFR transients requires one to solve partial differential equations. In light of the additional mathematical complexity and the introductory nature of this course, Unit 27 provides a thorough examination of setting up the equations needed to model a transient PFR, but it simply gives an overview of the solution of those equations. The unit also shows that certain kinds of PFR transients can be modeled precisely using only the steady state PFR design equations.

Learning Resources

• Archive (.zip) - Contains all learning resources listed below for this unit
• Documents to Read:
  • Unit 27 Informational Reading (.pdf)
  • Example 27.1 (.pdf)
  • Example 27.2 (.pdf)
• Videos to Watch (please right-click and save, then play back locally on your computer):
  • Unit 27 Informational Video (.mov)
  • Example 27.1 Video (.mov)
  • Example 27.2 Video (.mov)
• Reference Files:
  • Unit 27 Definitions, Nomenclature and Equations (.pdf)

Teaching Resources

• Archive (.zip) - Contains all teaching resources listed below for this unit
• Sample Class
  • Online Pre-class Quiz (.pdf file)
  • Redacted slides to make available to students before class
    • Keynote 09
    • PowerPoint
  • Class Lesson Plan (.pdf)
  • Complete slides to make available to students after class
    • Keynote 09
    • PowerPoint

Practice Problems