Chapter 5    Dynamic Behavior of Typical Process Systems
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Check Your Reading             Study Questions             Thought Questions

The questions will be categorized according to the the two keys concepts in the chapter.

Self-Regulation Structures of Simple Systems












Check Your Reading

Solidify the Concepts

What determines the
order of a dynamic model?




The number of constitutive equations in the model.


The number of fundamental balances in the model.


The number of first order differential equations in the model.

The number of material components in the system.










This second order process, which is
two first order systems in series, can never be underdamped.















Complete this statement:
Self-regulation is...


This is very important; Chapter 18 is dedicated to non-self-regulatory systems.




The tendency of a system to attain steady-state without external control being applied.

The tendency of an output variable to return to its initial value after a disturbance.
A term applied only to liquid in tanks.
A property of all systems with inherent positive feedback.











Processes are often connected in series. 
Non-interacting first order systems in series have the following property.

Structures of simple systems

Most (but not all) series processes are non-interacting.




The output of each system affects all other systems.


The output of each system affects only downstream systems.


The output of each system affects only one other system.

The output of each system affects no other system.











A quick way to estimate the overall dynamic model of a series of first order systems, is as a first order system with  the following equations.

Structures of simple systems




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Apparent dead time can result from...

Structures of simple systems

Dead time makes feedback difficult!




liquid flow through pipes.


solid transport by conveyer belt.


several first order systems in series.

a delay in measuring an output process variable.













Parallel systems can result in unique dynamic responses when...

Structures of simple systems

By unique, we mean that the output variable might not be reasonably approximated with a dead time-first order curve.  An example is an inverse response.




two gains have different signs.


both paths have dead times.

the dynamics of the two paths are very different.














A dynamic system with recycle...

Structures of simple systems



has the same gain as the series system without recycle.


is always much slower.

differs greatly from a series system when the recycle gain approaches +1.0.














In the distillation model, the equation for liquid flow rate leaving the tray is valid for all values of the liquid level.

Structures of simple systems

Engineers need to understand the range of conditions for "normal" plant operation.