Process Dynamics Lecture 1

1
Process DynamicsLecture 1

• ChE 479
• Fall 2000
• Pr. Alexander Couzis

2
Process Dynamics

• Dynamics Implies that the process
  behavior/performance is not at steady state, i.e.
  the process variables change with time.
• The process still obeys the same laws (mass and
  energy conservation).
• The time derivative component , is not zero.

3
Example Well Mixed Tank

• Gather all relevant information
• The tank is well mixed
• Input flow rate is 0.085 m3/min
• Tank Volume is V2.1m3
• CAinit 0.925 mole/m3
• ?CA0 0.925 mole/m3
• The system is initially at steady state
• Assumptions
• Density of liquid constant

4
Example Well Mixed Tank

• Conservation Balance
• Accumulation Input- OutputGeneration
• Overal Material Balance
• Accumulation Input- Output
• Component Material Balance
• (Accumulation of Component i) (Input of i)-
  (Output of i)(Generation of Component i)
• Energy Balance
• Accumulation of EPEKE(EKEPE in)-(EKEPE
  out)Q-W

5
Example Well Mixed Tank

• Constitutive Equations
• Heat Transfer QhA?T
• Chemical Reaction Rate rAk0e-(E/RT)CA
• Fluid Flow FCv(?P/?)1/2
• Equation of State PVnRT
• Equilibrium yikixi
• Degrees of Freedom (DOF)
• DOF NV -NE
• DOF 0 exactly specified DOF lt 0 overspecified
  DOF gt 0 underspecified

6
Material Balance on Well Mixed Tank (Overal Mass
Balance)
Consitutive Equation
7
Material Balance on Well Mixed Tank (Overal Mass
Balance)
Variables are CA, and F1 gtDOF 2 - 2 0
? is the time constant of the system, in this
case it describes the residence time of the tank