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# Chapter 3 PowerPoint PPT Presentation

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

Chapter 3

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## Chapter 3

Dynamic Modeling

(Part 2)

### 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

### 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.

### Dynamic Model for CST Thermal Mixer

• The model assumes perfect level control:

Dynamic Model for CST Composition Mixer

• The model assumes perfect level control:

### 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,

### 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

Model for CSTR with a First Order Reaction

Dynamic Model for CSTR

• Actuator

• Process

model

• Sensor