DWSIM Development Blog

Just minor fixes and a gift: The Lee-Kesler-Plöcker Property Package. Changelog:

- [NEW] Lee-Kesler-Plöcker Property Package
- [FIX] Fixed K-value calculation call in the Sum Rates method for solving Absorption Columns
- [FIX] Fixed IO Flash calculation in single phase region
- [FIX] Fixed Critical Point calculation with PR and SRK Equations of State
- [FIX] Fixed portions of GUI language that were not being set on the first run

Click here to go to the downloads page.

Regarding the new PP, I would like to count on your help to test it against other simulators.

I just tried a different approach to solve the single phase temperature problem with the IO flash and it seems to be faster and equally reliable as the nested loops one. I did some benchmarking and here are the results (numbers represent execution time in seconds):

That's definitely an improvement, except when the IO flash is used to calculate bubble and dew points without proper initialization, which is the case when we solve columns with no initial temperature estimates.

I also finally found the error in the triple sum routine for critical point calculation. It was, in fact, an error in the equation on the paper (by Michelsen and Heidemann, "Calculation of Critical Points from Cubic Two-Constant Equations of State"). They wrote an "alpha" were it should be an "a". I found another paper with the correct expression, and now the calculated critical points seem to be consistent:

Pretty nice, eh?

The original IO algorithm is intended to work only in the VLE region, that is, it was not meant to use in single-phase scenarios. That's why you'll see DWSIM slowing down when calculating PH/PS flashes in the single-phase region with the IO algorithm.

I'm still trying to find a way to tune the parameters and make the algorithm at least as fast as the nested loop one but, for now, be advised. If you would like to test it, try to run the Cavett simulation with the IO method and check the compressor calculation time - it is very slow because it is only gas, and there is a PS flash and a PH one right after.

Also, the critical point calculation is not behaving as expected. The problem is in the "triple sum" calculation, because the stability curve is being calculated correctly. I'll try to find another paper with the formulation for the PR EOS and check against the one I used to make the code. This only affects the phase envelope and critical point utilities, but it is important for you to know that this is a known bug.

Build 3840 introduces the Gibbs Reactor and comes with important changes in the thermodynamics framework. Changelog:

- [NEW] Gibbs Reactor model (vapor phase only) with two solving methods: reaction extents and direct minimization
- [NEW] New global settings for Property Packages: Flash Algorithm and Calculate Bubble/Dew points
- [NEW] New approach for equilibrium calculation: Inside-Out by Boston and Britt
- [NEW] Added an option to adjust Rackett Parameters and Acentric Factors to match SG and NBP in Petroleum Characterization Utilities
- [NEW] New Quick Settings toolbar: Unit system and number formatting
- [NEW] New menu gives quick access to DWSIM Tools
- [NEW] Added the option to select stream component amounts as properties to show on PFD tables
- [CHG] Completely rewritten Equilibrium Reactor model
- [CHG] Updated ChemSep database loading code to support ChemSep 6.62
- [FIX] Fixed an exception when working with pump curves to calculate pump power
- [FIX] Fixed a bug in temperature calculation with the Steam Tables Property Package

Click here to go to the downloads section.

In the next days I'll add some content to the Wiki:

- A tutorial on how to use the Gibbs Reactor
- A source code guide telling where to find what
- Explanation of the new flash algorithm
- Explanation of the gibbs and equilibrium reactor modeling

That's all for now. Thanks for your support!

/Daniel

Component amounts in property tables: component amounts (mass/molar fraction/flow) will be available as selectable properties for display in flowsheet table and as selectable properties for adjusts, specifications and optimization.

Phase diagram with IO flash: fixed, now it is giving the same results as the default algorithm, but faster.

Bubble and Dew point calculations on streams: The user will be able to calculate bubble and dew points at stream conditions, and display the results in the property grid (if the stream is at liquid-vapor equiibrium).