ASCEND - A Modeling Environment from Carnegie Mellon University
Krishnan K. Chittur, Ph.D.
Professor, Chemical and Materials Engineering Department
University of Alabama in Huntsville
Huntsville, AL 35899
(256) 824 3596 (V), (256) 824 6839 (F)

ASCEND is a FREE, large equation based modeling system Currently called ASCEND IV from Carnegie Mellon University. ASCEND is an excellent environment for developing complex process models, debug it, get solutions and check the solutions. Go to the source to read more about ASCEND.

You can download the software and manuals for free from the official ASCEND website. In these pages, I have described how we can use ASCEND in undergraduate education, with detailed examples and code in the ASCEND language.

What does this program allow us to do? If we know how to model a specific system, know the equations that can be used to describe the system, the program provides an object oriented environment under which we can obtain solutions to the program. The program can solve sets of linear, non-linear equations. LSODE has been attached to ASCEND and hence the program will support the solution of initial value problems. The group from Carnegie Mellon University has also developed collocation models to allow one to do two point boundary value models. If you are interested, please visit the official site for ascend where you will find a lot of examples and some neat models.

Example Problems in ASCEND

This page will probably always remain under construction. It will improve as our understanding of the program improves - please let us know if you find any errors in our example problems or suggestions on how you can improve Model writing.

If you pick up the ASCEND distribution, you will find tons of examples in it. This program cannot be understood by reading the manual (even though it is well written!) - You understand only when you run the examples yourself - trust me, I know.


Please Note The example problems as you see them here are not written in a way that you can easily incorporate them into something you may want to use and reuse - they are written to solve a particular problem for a particular set of conditions. We will be rewriting these into models like Models in the ascend distribution.

Please watch this space for some helpful information about models and scripts. Do you ABSOLUTELY need a script? No. They why are they here? It helps you setup the model equations and obtain a solution. Can you do that from within ASCEND? Yes, ofcourse. I hope to place a summary here (or provide a link) to a philosophical discussion related to MODELS and how to solve them

Chemical Engineering Thermodynamics
Links to Model and Scripts Description
Model and Script Equations of State
Model and Script Problem 10.1, Smith, VanNess 7th Edition, page 370
Model and Script Example Problem 6.3, Smith, VanNess 7th Edition, pages 213-215
Model and Script Problem 10.1, Smith, VanNess 7th Edition, pages 352-356
Model and Script Example Problem 10.3, Smith, VanNess 7th Edition, pages 359-363
Use this script For Example 10.3 (Smith and VanNess), if you want to see how the azeotropic pressure varies with Temperature?
Model and Script for Problem 3.32, Smith, VanNess 7th Edition
PT Flash - Notes and here are Models and Script for the PT Flash Example (as described in book by Beigler/Grossmann/Westerberg)
Model using flash.a4l in ascend and Script For Flash Calculations using Built-In Models
Model and Script For Differential Distillation - How to use ASCEND with LSODE for a Differential Algebraic Problem - this was written at CMU
The NRTL Model and Script FOR the NRTL Model for Activity Coefficient Calculations
Model for P-xy diagram and Script For Smith, Van Ness and Abbott (5th Ed) page 444
Model and Script For Smith, Van Ness and Abbott (5th Ed) page 449
Models and Script and A brief tour by Pedro Vale Lima on Thermodynamic Models in ASCEND

Material and Energy Balances
Models, Equations, Notes and Here is a Script For Problem on Page 508 from Felder/Rousseau's Elementary Principles of Chemical Processes Book
Models, Equations, Notes and Here is a Script Problem on Page 510 from Felder/Rousseau's Elementary Principles of Chemical Processes Book
Models, Equations and Script - Integration and Plotting For Hines and Maddox - Mass Transfer (Fundamentals and Applications) - Problem on Page 61, Example 3.1
Models, Equations and Script - Integration and Plotting For Hines and Maddox - Mass Transfer (Fundamentals and Applications) - Problem on Page 62, Example 3.2

Numerics - Solution of Equations, Dimensionless Numbers etc
Model and Script For Problem from Janna, Example 3-3
Model and Script For Problem from Janna, Example 3-7
Model and Script For Calculating Reynolds Dimensionless Number (mix/match units)
Model and Script For Example 7.3, page 220 from Beigler/Grossmann/Westerberg
Model and Script for Example on Page 266 from Beigler/Grossmann/Westerberg
Model and Script for Example on Page 270 from Beigler/Grossmann/Westerberg
Model and Script For Himmelblau, 6th Ed, pg 121
I will appreciate help with cleaning up these examples (as far as I know, these models and scripts work - but there is significant room for improvement, make them much better. In a few examples, I have not used the units as defined in atoms.a4l - yet. For some examples, I have additional notes, explanations for first time users - I will be adding these ... in the near future. If you download any of these examples in the mean time and have improved on them, or if you find errors, Please let me know

- I will be happy to credit you with your example problem and solution (and for finding errors!) I do have a wish list - how I would like to see my programs improved! A barebones guide to how to model using a thermodynamics example, problem 3.32, VanNess/7th Edition, equations of state  Help me with my wish list? Why ASCEND?, IMHO
This document was translated from LATEX by HEVEA.