A book in revision and an old book resurfaces!

January 15, 2014

I have revised the material in Introduction to Chemical Engineering Computing to be consistent with AspenPlus 8. The interface looks different when you start, but the ultimate windows where you define the problem are the same. It took me a bit to get used to, but I like the new version. One of the main things is that there are three tabs, and the ribbons (across the top) are different for each tab. Thus, if you want to define the chemicals or the thermodynamic model, you have to have selected the Properties tab or you won’t find the appropriate windows. Then when you define the process you must have chosen the Simulation tab in order to prepare the flowsheet. The thermodynamics are not there in the Simulation tab, so you may have to go back and forth. The third tab is Energy Analysis. The advantage of this format is that the things seen in the ribbon are all pertinent to the tab you have chosen, which makes for fewer options, but the right ones. This format is called a ribbon format and was introduced by Microsoft for Excel some time ago. Then Aspen changed to it, and Comsol just changed to it. Matlab also changed to it, but in my book most of the time I’m describing actual programs, not the icons. The revised book will be available in April, 2014, with a stamp on the front identifying that it uses Aspen Plus 8.

The next thing I have to report is the republication of my 1972 book, Method of Weighted Residuals and Variational Principles by the Society of Applied Mathematics (SIAM) as a SIAM Classic 73. (I’m 73th in the list of classic applied mathematics books chosen by them in their history. In 1972, computers were just beginning to make an impact on the solution of differential equations. The first part of it treats differential equations governing transport problems, of flow, heat, and mass, using approximate methods and a series of functions, but using only a few terms. The Galerkin, collocation, least squares, and integral methods were all subsumed under the phrase Method of Weighted Residuals. The second part describes variational principles (or not) for those problems and shows how to find them and use them to construct error bounds and create stationary principles. Finally, the variational principles are used to derive error bounds that can be calculated for some problems. This was important because the series used in the approximate methods for nonlinear problems could not be extended to a large number of terms without the use of a computer. Since then computers have advanced considerably and much more sophisticated numerical techniques are available, but the mathematical principles described in the book are still valid, and still useful.

Chapter 11 in particular gives error bounds for many problems. Examples are given in the book, but there is a need to expand the coverage to include higher approximations and numerical methods that are now possible. Thus, problems are being formulated and posted at www.ChemEComp.com/MWR that use the error bounds, but also use methods like the finite difference method and finite element method. Some of the problems are given with solutions, some with partial solutions, and some have no solutions on the website, but they are available to instructors via SIAM. Right now there are only two problems – a boundary value problem and an eigenvalue problem, but each problem has about four sub-problems. The areas covered are boundary value problems (1D), eigenvalue problems, elliptic partial differential equations, parabolic partial differential equations in 1D and 2D. In each type there will be one problem with complete solutions using a variety of methods so that everyone can get a good head start.  Additional problems will be added as time permits, but they do give good examples of the value of error bounds and make use of modern computational tools like MATLAB® and Comsol Multiphysics®, the finite difference and finite element methods (when applicable – sometimes the error bounds are derived with pretty stringent mathematical conditions). So check it out, and keep checking it out as I add problems.

Bruce Finlayson

About chemecomp

Bruce A. Finlayson, retired Rehnberg Professor of Chemical Engineering, University of Washington
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