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Chapter 3

Chapter 3. Dynamic Modeling (Part 2). Unsteady-State Mass Balance. Unsteady-State Energy Balance. Constitutive Relationships. Usually in the form of algebraic equations. Used with the balance equations to model chemical engineering processes. Examples include: Reaction kinetic expressions

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Chapter 3

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  1. Chapter 3 Dynamic Modeling (Part 2)

  2. Unsteady-State Mass Balance Unsteady-State Energy Balance

  3. Constitutive Relationships • Usually in the form of algebraic equations. • Used with the balance equations to model chemical engineering processes. • Examples include: • Reaction kinetic expressions • Equations of state • Heat transfer correlation functions • Vapor/liquid equilibrium relationships

  4. Different Types of Modeling Terms • Dependent variables are calculated from the solution of the model equations. • Independent variables require specification by the user or by an optimization algorithm and represent extra degrees of freedom. • Parameters, such as densities or rate constants, are constants used in the model equations.

  5. Dynamic Model for CST Thermal Mixer • The model assumes perfect level control:

  6. Dynamic Model for CST Composition Mixer • The model assumes perfect level control:

  7. Dynamic Model for Tank Level • Accumulation of mass in the tank is equal to the mass flow rate in minus the mass flow rate out. • For a gravity drained tank,

  8. Dynamic Model for Tank Level • Actuator on flow out of the tank. • Process model • Level sensor since the level sensor is much faster than the process and the actuator

  9. Model for CSTR with a First Order Reaction

  10. Dynamic Model for CSTR • Actuator • Process model • Sensor

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