MODEL.LA

1

• MODEL.LA
• Modeling Laboratory
• This guided introduction (produced from screen
  captures of the actual program) will provide an
  overview of the modeling capabilities of
  MODEL.LA.
• To advance through this tour, please press the
  right arrow key (?) on your keyboard, or click
  the left mouse button.
• To replay a portion of this tour, please press
  the left arrow key (?) on your keyboard until the
  desired location is reached.
• To quit the tour at any time, press the escape
  key (Esc) on your keyboard.
• Press the ? key to continue.

• The MODEL.LA Modeling Methodology
• MODEL.LA contains no predefined models. Rather
  it leads students through a structured sequence
  of modeling
• decisions--decisions the student makes based on
  the context of some engineering problem.
• From these decisions, MODEL.LA will automatically
  derive the necessary modeling equations and guide
  the student through their numerical solution.
• Thus, the educational focus shifts from textbook
  equation selection and solution, to the richer
  task of model formulation and analysis of process
  behavior.
• Press the ? key to continue.
• Press the ? key to review.

• Modeling Assistant
• A rich body of chemical engineering science
  exists and is currently taught to students in the
  context of abstract idealized examples. Modeling
  unifies these scientific principles in their
  application to real engineering problems.
• Unfortunately, students are never taught a
  modeling methodology. Rather they are forced to
  infer modeling techniques from exposure to
  example after example.
• The Modeling Assistant of MODEL.LA provides the
  starting point which guides the student in
  applying classic classroom concepts in a
  structured process of model development.
• Press the ? key to continue.
• Press the ? key to review.

Modeling Assistant (8) When the physico-chemical
phenomena-based description of the model is
complete, MODEL.LA automatically derives the
corresponding mathematical equations based on
chemical engineering first principles. Solution
of these equations allows the student to analyze
the resulting behavior of the process, appreciate
the relationship between phenomena and behavior,
and gain immediate feedback on the applicability
of the model. At any point the student is free
to revisit the assumptions made, make changes,
provide additional details, etc. Press the ?
key to continue. Press the ? key to review.

• Modeling Assistant (2)
• Models are much more than just equations. They
  are a concise representation of a real process.
  The most important step in model development is
  not the selection of equations from a textbook,
  but rather the identification and
  characterization of the relevant physical and
  chemical phenomena assumed to occur in the
  process.
• Model development begins with identification of
  control volumes of interest.
• Press the ? key to continue.
• Press the ? key to review.

Jacketed Continuous Stirred Tank Reactor (CSTR)
Example The following will illustrate the use of
MODEL.LA in the development of a model of a
Jacketed CSTR--a uniform continuous flow reactor
surrounded by a cooling jacket. The modeling
activity begins with declaration of a control
volume representing the Jacketed CSTR. The Add
New Process Units tab is selected. Press the ?
key to continue. Press the ? key to review.

• Modeling Assistant (3)
• It continues with perception of how these control
  volumes interact through transport of material,
  energy, and chemical species.
• Press the ? key to continue.
• Press the ? key to review.

Modeling Assistant (6) The mechanisms which
drive the transport of material, energy, and
chemical species are characterized. Press the ?
key to continue. Press the ? key to review.
Modeling Assistant (4) The relevant chemical
species and reactions must be identified. Press
the ? key to continue. Press the ? key to review.
Modeling Assistant (7) External control actions
may be applied. Press the ? key to
continue. Press the ? key to review.
Modeling Assistant (5) The control volumes are
further characterized and refined. Press the ?
key to continue. Press the ? key to review.
2
Naming of Jacketed_Cstr and the default name
Unit0 is changed to Jacketed_CSTR. Press the ?
key to continue. Press the ? key to review.
Hierarchical Tree
Flowsheet
Context-Sensitive Right-Click Menus A right
button mouse click on the modeled unit icon
activates a context- sensitive menu listing all
options available for that particular
modeled-unit. Press the ? key to continue. Press
the ? key to review.
Naming of Jacketed_Cstr The Rename option is
selected. Press the ? key to continue. Press the
? key to review.
Resize Icon The icon for the Jacketed_CSTR is
resized. Press the ? key to continue. Press the
? key to review.
Properties View
Declaration of CSTR Control Volume The Blackbox
Unit Icon is selected (meaning no internal detail
will initially be present in the unit). Press
the ? key to continue. Press the ? key to review.
Declaration of CSTR Control Volume The modeled
unit is added to the flowsheet. The Hierarchical
Tree pane lists all modeled units in the model.
The Properties View lists all assumptions made
regarding the currently selected modeled
unit Press the ? key to continue. Press the ?
key to review.
3
Load Icon and the option to load a new icon is
selected. Press the ? key to continue. Press the
? key to review.
Load Icon Graphical icons do not introduce any
new assumptions to the model, but allow the
modeler to provide visual clues to the purpose of
a model. Press the ? key to continue. Press the
? key to review.
4
Declaration of Interactions with
Surroundings and adding it to the
flowsheet. Press the ? key to continue. Press
the ? key to review.
Declaration of Interactions with Surroundings A
feed stream of reactants enters the Jacketed_Cstr
from the surroundings. This is declared by
selecting the Add New Fluxes tab of the Modeling
Assistant, selecting the Convective Flux Icon...
Press the ? key to continue. Press the ? key to
review.
Naming of Feed Stream The feed stream is renamed
reactants_input. This is accomplished by
selecting the Edit Fluxes tab of the Modeling
Assistant, selecting the Rename Flux
Icon... Press the ? key to continue. Press the ?
key to review.
Declaration of Interactions with
Surroundings The product stream,
products_output, transports material from the
reactor to its surroundings. It is added and
named is a similar manner. Press the ? key to
continue. Press the ? key to review.
Declaration of Interactions with
Surroundings Flows of coolant from
(coolant_inlet) and to (coolant_outlet) the
surroundings are also declared. Press the ? key
to continue. Press the ? key to review.
Naming of Feed Stream and entering the desired
name. Press the ? key to continue. Press the ?
key to review.
Press the ? key to continue. Press the ? key to
review.
5
Refinement of Jacketed_Cstr At the current level
of detail, the student realizes that there is no
way to state that the reaction mixture and
cooling jacket fluid are in separate vessels
within the Jacketed_Cstr. Therefore, the
structure of the Jacketed_Cstr must be refined by
selecting the Edit Process Units tab and
selecting the Specify Internal Subunits
option. Press the ? key to continue. Press the ?
key to review.
Review of Assumptions The Properties View is
automatically updated after each modeling
declaration. Press the ? key to continue. Press
the ? key to review.
6
Refinement of Jacketed_Cstr The Hierarchical
Tree reflects the refinement of the Jacketed_Cstr
into a Vessel and Jacket. Press the ? key to
continue. Press the ? key to review.
Load Icon A graphic icon representing the Vessel
is selected. Press the ? key to continue. Press
the ? key to review.
Naming of Vessel The subunit is renamed
Vessel. Press the ? key to continue. Press the ?
key to review.
Refinement of Jacketed_Cstr This activates the
refinement flowsheet for the Jacketed_Cstr.
The abstract boundary of the Jacketed_Cstr is
represented by the dashed line. Fluxes to/from
the unit initially appear terminating at this
boundary. New units added within this boundary
are subunits of the abstract unit. Press the ?
key to continue. Press the ? key to review.
Refinement of Jacketed_Cstr Refined subunits are
again added using the Add New Process Units of
the Modeling Assistant. In this case, the
first subunit is assumed to contain a single
liquid phase. Press the ? key to continue. Press
the ? key to review.
Refinement of Jacketed_Cstr The second subunit
is added to the Jacketed_Cstr... Press the ? key
to continue. Press the ? key to review.
Refinement of Jacketed_Cstr The subunit is added
to the Jacketed_Cstr. Press the ? key to
continue. Press the ? key to review.
Jacket the subunit is renamed Jacket, and a new
icon loaded. Press the ? key to continue. Press
the ? key to review.
7
Flux Mechanism A Surface Convection flux
mechanism is selected, where the heat exchanged
is proportional to the temperature difference
between the Vessel and the Jacket. Press the ?
key to continue. Press the ? key to review.
Declaration of Internal Interaction and dragging
on the refinement flowsheet from the Vessel to
the Jacket. Press the ? key to continue. Press
the ? key to review.
Flux Mechanism The amount of heat exchanged is
not known in advance. It is determined by a
temperature differential between the Vessel and
the Jacket. Flux mechanism are declared using
the Edit Flux Properties option on the Edit
Fluxes tab of the Modeling Assistant Press the
? key to continue. Press the ? key to review.
Naming of Flux The energy flux is renamed
q_exchange. Press the ? key to continue. Press
the ? key to review.
Declaration of Internal Interaction The two
subunits of the Jacketed_Cstr interact with the
transfer of energy from the Vessel to the
Jacket. This is declared by selecting the Energy
Flux icon on the Modeling Assistant... Press
the ? key to continue. Press the ? key to review.
8
Chemical Species In addition to the structural
description of the model, the chemical species
and reactions present must be declared. First
the chemical species are added using the Declare
Chemical Species option on the Specify Species
and Reactions tab. Press the ? key to
continue. Press the ? key to review.
Chemical Species Database The database contains
over 1400 chemical species with data on constant
and temperature- dependant physical and
thermodynamic properties. The species are
organized by chemical group, common name, IUPAC
name, chemical formula, and atomic
structure. Press the ? key to continue. Press
the ? key to review.
Chemical Species Database Four compounds have
been selected. Press the ? key to
continue. Press the ? key to review.
9
Chemical Reactions Once chemical species have
been declared, chemical reactions may be
specified. The reactions are added using the
Declare Chemical Reactions option on the Specify
Species and Reactions tab. Press the ? key to
continue. Press the ? key to review.
Chemical Reactions Reactions are characterized
by the stoichiometry of the reactant and product
species, any catalyst, and the reversibility of
the reaction. Press the ? key to continue. Press
the ? key to review.
Chemical Reactions The reversible reaction of
Acetic Acid and 1-Butanol to Water and n-Butyl
Acetate has been declared. Press the ? key to
continue. Press the ? key to review.
10
Chemical Reactions Any number of chemical
reactions may be specified. In this example,
only one reaction is considered. The rate law of
the reaction will now be characterized. Press
the ? key to continue. Press the ? key to review.
Chemical Reaction Rate Law Since the reaction is
reversible, rate laws for both the forward and
reverse reaction are specified. Press the ? key
to continue. Press the ? key to review.
Chemical Reaction Rate Law The forward reaction
rate is assumed to be second order with respect
to Acetic Acid and first order with respect to
1-Butanol. The reverse reaction rate is assumed
to be first order with respect to both water and
n-Butyl Acetate. More complex rate laws can be
specified, along with Arrhenius temperature
dependencies for all rate constants. Press the ?
key to continue. Press the ? key to review.
11
Reaction Assignment Since the Vessel has a
liquid phase, the reaction will be assigned to
that phase using the Material Content dialog. In
this dialog, the species present are also
selected, along with equation of state or
activity coefficient models for each
phase. Press the ? key to continue. Press the ?
key to review.
Reaction Assignment The reaction is assigned to
the liquid phase. The reactants and products of
the reaction are also automatically assigned to
the material content of the Vessel. Press the ?
key to continue. Press the ? key to review.
Reaction Assignment The reaction is now assumed
to only occur in the Vessel. The Vessel icon
is selected and the Assign Reactions and Species
option on the Edit Process Units tab is
activated. Press the ? key to continue. Press
the ? key to review.
12
Model Simulation When the student feels the
physico-chemical description of the model is
complete, the Model Simulation tab is selected,
and the Edit Simulation Options option is
activated. Press the ? key to continue. Press
the ? key to review.
Model Consistency Check A completeness and
consistency check of the model is activated using
the Check Model Consistency option. Press the ?
key to continue. Press the ? key to review.
Model Simulation The conditions under which the
equations will be generated are specified. Press
the ? key to continue. Press the ? key to review.
Model Consistency Check The model is analyzed
and determined to be inconsistent since the
boundary fluxes to the abstract Jacketed_Cstr
have not been allocated to the subunits. The
model cannot be simulated until this
inconsistency is remedied. Press the ? key to
continue. Press the ? key to review.
Flux Allocation The products_output flux
originates from the Vessel. Thus, the
products_output flux icon is selected and dragged
to the Vessel Icon. Press the ? key to
continue. Press the ? key to review.
13
Flux Allocation In a similar manner, the
reactants_input flux is allocated to the Vessel,
and coolant_inlet and coolant_outlet fluxes are
allocated to the Jacket. The model consistency
is then rechecked. Press the ? key to
continue. Press the ? key to review.
Consistency Check The model is still incomplete
because no species have been declared to be
present in the Jacket. Press the ? key to
continue. Press the ? key to review.
Species Assignment Water is assigned to the
Jacket. Press the ? key to continue. Press the ?
key to review.
Consistency Check The model is now
complete. Press the ? key to continue. Press the
? key to review.
14
Numerical Engine The numerical engine toolbar
guides the student through a consistent numerical
specification for solution of the model
equations. The first task is to select the
design (or known) variables and provide numerical
values. Press the ? key to continue. Press the ?
key to review.
Model Simulation Steady-state equations are now
automatically generated from the phenomena-based
model description provided by the student. Press
the ? key to continue. Press the ? key to review.
Model Equations The mathematical model consists
of 55 equations with 67 variables. The model
includes mass balances, energy balances, physical
and thermodynamic property correlations, reaction
rate expressions--all based fully on the modeling
assumptions of the student. Press the ? key to
continue. Press the ? key to review.
Design Variable Specification In this model, 12
variables must be selected and their values
specified. All variables appear grouped by their
corresponding modeled unit, flux, or chemical
reaction. Press the ? key to continue. Press the
? key to review.
Design Variable Specification The student uses
available data to decide which variables he/she
feels are appropriate. MODEL.LA ensures the
selection is structurally consistent, and
provides feedback if any subset of equations
would be overspecified by a variable
selection. Press the ? key to continue. Press
the ? key to review.
15
Model Simulation The model is now ready for
numerical simulation. Press the ? key to
continue. Press the ? key to review.
Model Simulation The student decides to observe
the effect of varying the volume of the Vessel on
the model behavior. Press the ? key to
continue. Press the ? key to review.
Model Results The model is solved numerically,
and the results plotted versus the varied volume
variable. Press the ? key to continue. Press the
? key to review.
16
Model Simulation The student decides to observe
the behavior of the model under dynamic
conditions. A new mathematical model is
generated, with 75 equations and 90
variables. Press the ? key to continue. Press
the ? key to review.
Initial Conditions Since the model is dynamic,
initial conditions must also be specified. Press
the ? key to continue. Press the ? key to review.
Model Simulation The dynamic model is now ready
for simulation. Press the ? key to
continue. Press the ? key to review.
Model Results The dynamic behavior of the model
is plotted versus time. The results may be
printed in graphical form, or exported to any
spreadsheet in tabular form. Press the ? key to
continue. Press the ? key to review.
Design Variables Without the steady-state
assumption, additional design variables must be
specified by the student. Press the ? key to
continue. Press the ? key to review.
Initial Conditions The initial condition
variables are specified by the student in a
manner analogous to that of the design variable
specification. Press the ? key to
continue. Press the ? key to review.
Model Simulation The student decides to simulate
for 5 minutes of simulation time. Press the ?
key to continue. Press the ? key to review.
17
External Control Action The student can enhance
the study of the Jacketed Cstr by imposing
external controllers on the process... Press the
? key to continue. Press the ? key to review.
External Control Action and observing the effect
of control on its dynamic behavior. Press the ?
key to continue. Press the ? key to review.
18
Jacketed CSTR Model Summary The Jacketed CSTR
example illustrates how MODEL.LA shifts the focus
of modeling from equation selection and
manipulation to the deeper task of articulating
the physical and chemical phenomena which
characterize the behavior of a process.
Examples such as these enforce the
understanding of abstract concepts taught in the
classroom. By making students active
participants in model development, they become
aware of the assumptions, limitations, and
applicability of such models. This is much
deeper than the superficial understanding they
gain as passive onlookers when a model is derived
on a blackboard or in a textbook. Press the ?
key to continue. Press the ? key to review.
Model Summary The student has complete
flexibility in revisiting any assumptions made,
making revisions, adding detail, etc. After any
changes, the consistency and completeness of the
modified model is verified, new equations are
generated, and the model is again solved
numerically. This provides immediate feedback to
the student on the applicability of the model,
and enforces the direct cause-effect relationship
of phenomena and process behavior. Press the ?
key to continue. Press the ? key to review.
Model Summary All assumptions behind the
completed model may be easily reviewed by the
student or the instructor using the Project Data
dialog. The Project Data organizes the
assumptions using a hierarchical tree of all
modeled units, materials, and phases in the
model. Selecting an item in the tree produces a
list of all associated assumptions, with
hypertext to navigate through the model. Press
the ? key to continue. Press the ? key to review.
Summary of Assumptions with Hypertext
Hierachical Tree
Model Summary chemical reactions and rate
laws... Press the ? key to continue. Press the ?
key to review.
Model Summary All assumptions regarding process
fluxes... Press the ? key to continue. Press the
? key to review.
Model Summary relevant chemical
species... Press the ? key to continue. Press
the ? key to review.
Model Summary process controllers... Press the
? key to continue. Press the ? key to review.
Model Summary and process transmission lines are
displayed. Press the ? key to continue. Press
the ? key to review.
19
Acetic Anhydride Plant Model Students become
confident with the chemical engineering concepts
and a methodology of modeling though examples
such as the Jacketed CSTR. Moreover, the
concepts they learn from these examples scale
tremendously as they are integrated into models
of complete chemical plants. The following
example illustrates the development of a model of
a plant for the production of Acetic Anhydride
from Acetone and Acetic Acid. Press the ? key
to continue. Press the ? key to review.
Acetic Anhydride Plant Model The plant model
starts as a simple blackbox, with two input
streams, two output streams, seven chemical
species, and three reactions. Press the ? key to
continue. Press the ? key to review.
20
Acetic Anhydride Plant Model Even at this
abstract level of detail, there is much to learn.
The student determines from simulation that the
yield of the intermediate product Ketene must be
at least 0.85 for the plant to make any
profit. Press the ? key to continue. Press the ?
key to review.
21
Acetic Anhydride Plant Refinement The student
uses a hierarchical approach to design and
refines the plant into a reaction section and a
separation section. At this level of detail, the
student learns from simulation that Acetic Acid
and Acetone must be recycled from the separation
section back to the reaction section for the
plant to be profitable. Press the ? key to
continue. Press the ? key to review.
22
Acetic Anhydride Reaction Section and selection
of a vapor phase equation of state and liquid
phase activity coefficient model in the 2 phase
reactor where the final product, Acetic
Anhydride, is formed. Press the ? key to
continue. Press the ? key to review.
Acetic Anhydride Reaction Section Synthesis of
the reaction section requires the student to make
decisions regarding the routing of feed, product,
recycle, and cooling streams among the
reactors... Press the ? key to continue. Press
the ? key to review.
23
Acetic Anhydride Separation Section Synthesis of
the separation section involves the use of
absorption for recovery of organics from a
gaseous waste stream, and distillation for
purification of the recycled raw materials and
final product. Press the ? key to
continue. Press the ? key to review.
24
Acetic Anhydride Plant Refinement The process of
refinement, simulation and refinement continues,
where simulation at each level of detail
determines decisions made at the subsequent
level. This continues until the plant is modeled
down to the level of vapor liquid equilibria on
each distillation column tray. Press the ? key
to continue. Press the ? key to review.
25
Acetic Anhydride Plant Summary The final
mathematical model, derived automatically from
the most detailed model description the student
provides, has 3894 equations and 4116 variables.
Without the high-level modeling assistance that
MODEL.LA provides, it would be infeasible for
students to derive and solve such real-world
engineering problems themselves. MODEL.LA
removes the tedium and frustration associated
with mathematical derivations and manipulations
and allows students to concentrate on the real
engineering decisions behind model
development--regarding physical and chemical
phenomena, topological and hierarchical
structure, cause-effect relationships, and
behavior characterization. Press the ? key to
continue. Press the ? key to review.
26
2-D Distributed Tubular Reactor The concepts
required for this model are the same as those for
models of lumped (non-distributed) systems. The
differential element approach is used. Here the
student assumes axial convective flux, axial and
radial energy flux, and axial and radial
diffusive flux of two chemical species. There is
also energy flux to a surrounding cooling jacket
at the outer radial boundary. Press the ? key
to continue. Press the ? key to review.
2-D Distributed Tubular Reactor The final
example illustrates the capability of MODEL.LA to
model spatially distributed systems. The model
portrays a tubular reactor with axial and radial
spatially distributed properties. Press the ?
key to continue. Press the ? key to review.
2-D Distributed Tubular Reactor The dynamic
mathematical model automatically derived from
this phenomena-based description consists of 91
partial differential, integral and algebraic
equations. Press the ? key to continue. Press
the ? key to review.
27
2-D Distributed Tubular Reactor Summary The
modeling of spatially distributed systems fills
most students with dread, and leaves even the
best students unsure about the formulation and
solution of the resulting partial differential
equations. As a result, many schools do not even
include the modeling of such systems in their
curriculum. Real engineering problem solving
requires such models. MODEL.LA not only makes it
possible for students to solve such problems, but
to do so with confidence, and with a deep
understanding of the chemical engineering
principles involved. Press the ? key to conclude
this tutorial. Press the ? key to review.
2-D Distributed Tubular Reactor The results for
the tubular reactor are plotted using animated
surface plots in Excel. The student observes
that a hot spot develops at the center of the
reactor near the reactor entrance. Press the ?
key to continue. Press the ? key to review.