Chapter 2 Flashcards
development of dynamic models
- improve understanding of the process
- train plant operating personnel
- develop a control strategy for a new process
- optimize process operating conditions
Models can be classified based on how they are obtained:
theoretical models
empirical models
semi-empirical models
are developed using the principles of chemistry, physics, and biology
theoretical models
are obtained by fitting experimental data
empirical models
are a combination of theoretical and empirical models
semi-empirical models
theoretical models offer two very important advantages:
provide physical insight into process behavior
applicable over wide ranges of conditions
disadvantages of theoretical models
expensive and time-consuming to develop
one major disadvantage of empirical models
they do not extrapolate well
inherently involves a compromise between model accuracy and complexity on one hand, and the cost and effort required to develop the model
modeling
purpose of degrees of freedom
determines if the model is solvable
if degrees of freedom is 0
exactly specified
if degrees of freedom is more than 0
underspecified (infinite solutions)
if degrees of freedom is less than 0
overspecified if more equations than answers
formula for degrees of freedom
Nf = Nv - Ne
What is Ne
number of independent equations
What is Nv
Process variables
specify Nf input variables as either:
disturbance & manipulated variables
