Chapter 5 SQ

Apply Your Knowledge

5.10
Which responds faster, i.e. reaches steady state faster after a step input, (assume that V and F are the same)?

Structures of simple systems

We cannot estimate the dynamics from the "size" of the equipment.


	The concentration in a mixing tank to step in CAo.
	The temperature in a mixing tank to step in To.
	The concentration in an isothermal CSTR with a first order chemical reaction to step in CAo.

5.11
In Figure 5.3 which can be underdamped?

Structures of simple systems

We are learning principles that apply to all physical systems!

	CSTR; C_A0 -> C_B.
	Series of draining tanks; F -> L.
	Electrical circuit; E₀ -> E.
	Spring and shock absorber; h -> z.

5.12
Consider the physical process in the sketch with a sub-sonic flow of gas. Describe the system.

Structures of simple systems

Which flows are affected by the pressure in the middle vessel?


	Interacting series.
	Non-interacting series.
	Parallel.
	Recycle.

5.13
Consider the process in figure 1.8. Determine which variables are non-self-regulatory?

Self-Regulation

	These variables will be controlled using methods in Chapter 18.

5.14
Determine which of the following statements is true, and explain your response.

	A dynamic system with the same input and output variable behaviors must have the same intermediate variable behavior.
	If each individual process in a plant is stable, a recycle connection of these processes will be stable.
	Only input and output variables used for control are measured in a chemical plant.
	Dynamic systems that oscillate are always unstable.

	For a single continuous flow stirred tank system, the response of any input variable to any output variable is first order.
	When the steady-state gain (Kp) between a manipulated input variable and a controlled output variable is zero, feedback control is not possible.
	If the input and output measured variables of a process are behaving as desired, the process performance is desirable.

5.15 An extension of Textbook Example 5.1		Structures of simple systems

Consider two processes (1 & 2) in series. Both processes are second order. Sketch the output behavior for the series of these two systems for a unit step input using approximations.

system

t₁

t₂

1.6

0.95

3.3

1.33

2.6

5.2

1.5

0.75

5.16
An extension of Textbook Example 5.5

Structures of simple systems

Consider the case where the reaction is changed from exothermic to endothermic. The reactor gain would be less than 1.0; a typical result is given in the following equation.

wpe34C.gif (1530 bytes)

Compare the dynamic response of the modified reaction with that of the original system.