## Thermodynamics and AspenPlus

When doing process simulations, one of the key features you must get right is prediction of the thermodynamic properties of the system you are simulating. There are many choices of thermodynamic models, and I’m putting into the book more information about how to choose the one that is right for you. Some of the information comes from statistical thermodynamics – how thermodynamic functions are changed due to interactions between molecules based on their dipole moments, charge, etc. While I’m not giving the details of statistical thermodynamics in the book, I am trying to show undergraduates how what they are learning in their thermo courses can be usefully applied. Since simulators have all those options in them already, the emphasis is on the choice – a reasonable, correct choice – rather than the calculations. But you have to learn how to use the simulator and compare with experimental data.

I’ve found the new book Statistical Thermodynamics (Wiley, 2010) by Stan Sandler very good for educating me. It is a graduate textbook but clearly shows how the thermodynamic models must become more complicated as additional molecular interactions are introduced. I’ve also found his undergraduate text, Chemical, Biochemical, and Engineering Thermodynamics (Wiley, 2006) useful. (Disclosure: Stan and I shared an office our first year in graduate school at the University of Minnesota.) The book: Engineering and Chemical Thermodynamics by Milo Koretsky (2003) is very good, too.

I’ve now rewritten Chapters 2-4 with more discussion of thermodynamic models for the systems treated there, but have planned a chapter going in depth. Some of the problems are easy enough to do in Excel or MATLAB, but some need a full-fledged process simulator. I’m using AspenPlus and Aspen Properties. Part of the delay in writing this blog was to get the newest version (7.2) working on a Macintosh computer using Parallels and Windows 7. I now have that running correctly. I won’t tell the students that I did all the Aspen problems in those chapters in a couple of days.

I have several major projects ahead: model some energy processes (and this will give more simple thermodynamic problems for Ch. 2-4), develop microfluidic design problems for Chapters 10 and 11 (based on projects over 100 undergraduate researchers have done with me over the past few years), and add material on numerical analysis.  This last item goes contrary to my philosophy of using the simulators but checking the chemical engineering output carefully. But, I’ve found that some professors really like to teach numerical methods, so I’ll include some.  I like to teach them, too, but few practicing engineers program anymore. When I describe my philosophy to industrial engineers they have all agreed with me. But, I have to sell books, too!

Bruce A. Finlayson