DWSIM Development Blog

The Inside-Out approach shows some difficulty in converging non-bubble points. From what I've found during my tests, this originates from the higher temperature variation on each iteration towards convergence, leading the equation of state to generate trivial solution K-values (all close to 1).

On the other hand, my new and improved algorithm is showing very good results:

DWSIM 1.7 is coming in a few days... just wait a little more time.

In DWSIM 1.7 you will have the option to choose between two flash algorithms or schemes - DWSIM Default (traditional Rachford-Rice for PT flash and nested loops for PH/PS flashes) and Inside-Out (from Boston and Britt). There will be a global setting which controls calculations done by all Property Packages OR you can define this setting in a per-Property Package basis. The default for each added property package is the global setting.

Source code changes are much more deeper. I removed all repeated code from property packages and now all equilibrium calculations are handled by the base class (PropertyPackageBaseClass) and flash methods in separate classes, grouped by scheme. The property packages will provide only the necessary K-value, Fugacity, Enthalpy and Entropy values for the equilibrium routines.

I just finished coding the IO Flash algorithm by Boston and Britt in DWSIM. And it is working! Convergence of my test problem was actually a bit slower than the current method but I guess that it is something related to my initial estimates...

Anyway, DWSIM 1.7 will contain this new flash code and also a new, more conservative Michelsen two-phase flash algorithm which is guaranteed to converge even on difficult cases like those near the critical point.

I can't wait to see the Phase Envelope utility without bubble points going towards infinity....

The Gibbs Reactor is done and the Equilibrium Reactor was completely rewritten. The first can be solved using equilibrium reaction information or not, just like in UNISIM/HYSYS. With the same mixture and reactions, these three methods should always give the same results, although through completely different calculation methods. The results were validated against UNISIM and book examples.

Also, there are some changes in the Petroleum utilities. In the Distillation Curve charac. utility you can now provide a single density or molar weight value which will be taken into account when calculating pseudocomponents.

On both utilities, you'll have the option to tune Acentric Factors and Rackett parameters to match NBPs and specific gravities, using the default Property Package (first on the list) or the Peng-Robinson EOS, if there isn't any. In the case of NBP fitting, you'll get a better phase behavior
agreement with experimental data.

The result is the calculated density matching the value provided while characterizing the sample, for the ZRa adjustment. If that still doesn't work, you can force an ideal mixing rule for the calculation of liquid density in the property package configuration window (because Rackett's method uses averaged properties - Tc, Pc, ZRa, Vc, etc. for the whole mixture by default). And THEN it should work.

I included a new "Tools" menu item which contains the component and reaction tools available only in the simulation configuration window until now.

Also updated is the ChemSep database loading code to reflect some changes they did in the PCDManager's output XML. DWSIM 1.7 will contain these and other minor changes/fixes and will be released as soon as I finish updating the documentation and some tutorials.

/Daniel