July 29, 2019

PASS/HYDRO SYSTEM and Thermodynamic Libraries

By Alex Matveev
Thermodynamics is the basis of any fluid flow and process simulation software and for PASS/Hydrosystem as well. The more complex thermal and hydraulic calculation we need, the more data on fluid properties and phase equilibrium is necessary.

For simple pressure drop calculation of isothermal incompressible liquid flow, we need just to know the fluid density and roughly estimate fluid viscosity (except for laminar flow when you need to know the exact value of viscosity). In addition, it is useful to know vapor pressure for possible cavitation prediction.

For heat loss calculation, we also need to follow up on how the above fluid properties depend on the temperature (and they can depend significantly!), plus we need to know enthalpy, heat capacity and conductivity of the fluid and how they depend on the temperature.

For compressible fluid flow, we need to follow up on how all these properties depend on the pressure value, and we should know isentropic exponents, entropy, and sound velocity.

For gas-liquid flashing/condensing flow we need also to know surface tension (as it can influence flow pattern and interaction between gas and liquid phases), and to be able to make phase equilibrium calculations. The later includes finding an envelope and vapor fraction and composition of phases depending on different pairs of thermodynamic parameters – p, T or p, x or p, h or p, s.

Therefore, the more complex is the fluid flow analysis case, the more powerful thermodynamic libraries we need! But are such libraries available for every process or piping engineer for affordable prices?

answer is yes, and PSRE Co makes its best to help you to get access to them!

To start with, if the process engineer has access to some process simulation software (HYSYS, PetroSim, UniSim, Aspen Plus, PRO/II, VMGSim, etc. ), then this software always includes powerful thermodynamic libraries. Some of process simulation software vendors also deliver such libraries as separate products. It’s worth to mention such powerful and known libraries as VMGThermo and MultiFlash in this context. However, these libraries usually are quite expensive…

Nevertheless, there is good news for fans of inexpensive (but powerful) software. Open-source (or free or almost free) powerful libraries of this type DO exist!

First, I should mention a very interesting and actively progressing and supported DWSim software (by Daniel Medeiros), which is in fact not only a thermodynamic library but a process simulator.


There is also a very powerful similar Russian product NERSim (it’s developer Stanislav Demchenko works now as Chief Process Engineer in our group of companies).



Another very famous, useful and inexpensive tool is NIST REPRO – which is considered to be one of the most accurate software products for commonly used pure substance properties.


There are also many special libraries for water and steam, as well as for air and mixture of atmospheric gases. I would recommend WaterStemPro software for this purpose as the most advanced and convenient of them.


So what PASS/Hydro system provides for thermodynamics? You can see this in the video “How to enter the fluid properties in Hydrosystem”.

PASS/Hydrosystem makes all necessary thermodynamic calculations “on the fly” (in background mode), we have a whole spectrum of features. The user can enter a table of known properties (for a specific value of the temperature), and the program interpolates on the base of the table. Or the user can set fluid composition and tell the software to use specific thermodynamic libraries for fluid properties and phase equilibrium calculations. The following libraries are embedded and delivered with PASS/Hydrosystem (or can be purchased as add-on products):

  • small (but fast) embedded ‘Properties” library for physical properties calculation of ~150 most common pure substances and their mixtures;
  • embedded WaterSeamPro library;
  • embedded GERG-2008 library – the most advanced modern library for natural gas calculation (including liquidized natural gas);
  • add-on PVTSim module (PVTSim Hydrate Open Structure) to predict gas hydrates formation;
  • and our own embedded STARS library with a database of ~1500 pure substances, which can calculate physical properties and phase equilibrium of complex mixtures of pure substances and oil fraction on the basis of very advanced Hirschfelder Equation of State and a number of phase equilibrium models.

Our experience shows that the STARS library works on the same level of accuracy as thermodynamic libraries in such systems as Aspen HYSYS for the fluids in the refining and petrochemical industry.

However, there are fluids and conditions, which are outside the scope of application of the STARS library. For example:

  • Complex mixtures in supercritical conditions;
  • Mixtures containing a significant percentage of polar components;
  • Aqueous and other solutions;
  • Liquid-liquid or liquid-liquid-gas phase equilibrium (oil-water-natural gas mixture for example);
  • Liquidized cryogenic gases and their mixtures;
  • And some others.

Usually, these are fluid in chemical, biochemical and other industries.

But we have an affordable solution for these cases too. For them, we propose (and use ourselves) Simulis Thermodynamics from ProSim.

Simulis Thermodynamics

Simulis-Thermodynamics is an extremely advanced thermodynamic library with the database of more than 2000 pure substances, binary interaction constants, group contribution databases (UNIFAQ, etc) and really fantastic spectrum of supported modern methods for fluid properties and phase equilibrium calculation (and ProSim continues to improve and extend it further and further!). It is very open – you can add your components and methods, and use the CAPE-OPEN Thermo interface. It is a COM component and seamlessly integrates with MS Excel and our software – you can use it inside our software or without it! In addition, it is priced at the same level as our software and can be supplied with it. Kudos to ProSim for their wonderful work!

And there are some other very interesting and promising new software tools in this field, which we and our partners are following up: Cranium and Synapse properties prediction software from Molecular Knowledge Systems; Online tools and Mol-Instincts database for quantum mechanics based property prediction from ChemEssen; COSMO-RS technology; and many more.

So we have and use a lot of tools to correctly define and simulate your fluid behavior in our software. As members of Co-Lan society, we try to do it in the most accurate, flexible, but affordable way.

Please tell us about your thermodynamics problems – and join us
in our journey for dark and secret places and hidden treasures
of piping hydraulics!

About Author Leonid Korelstein (PSRE Co): Leonid Korelstein (LinkedIn) – VP on R&D of PSRE Co (LinkedIn), and one of the leaders of PASS Suite (LinkedIn, Facebook) team. He is also the Product Manager of PASS/HYDRO SYSTEM (LinkedIn group), PASS/RELIEF and PASS/INSULATION software. Leonid has Ph.D. in Mechanics and Mathematics and is Associate Professor (for Chemical Plant design and simulation software) in Mendeleev Chemical University, member of AIChE, active participant of DIERS, EDUG, and TUFFP research communities, co-author of AIChE CCPS GPREH book and Russian GOST 12.2.085-2017 standard for pressure relieve systems sizing. He is also an active member of the ASSESS Initiative.