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Process Dynamics Lecture 1

Process Dynamics Lecture 1. ChE 479 Fall 2000 Pr. Alexander Couzis. 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).

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Process Dynamics Lecture 1

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  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 V=2.1m3; • 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- Output+Generation • 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 E+PE+KE=(E+KE+PE in)-(E+KE+PE out)+Q-W

  5. Example: Well Mixed Tank • Constitutive Equations • Heat Transfer Q=hAT • Chemical Reaction Rate: rA=k0e-(E/RT)CA • Fluid Flow: F=Cv(P/)1/2 • Equation of State: PV=nRT • Equilibrium: yi=ki•xi • Degrees of Freedom (DOF) DOF = NV -NE DOF = 0 exactly specified; DOF < 0 overspecified DOF > 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 ===>DOF = 2 - 2 = 0  is the time constant of the system, in this case it describes the residence time of the tank

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