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With more than 1.000 download of the free version per year, FluidProp is probably one of the most popular software packages for thermodynamic calculations.

FluidProp is the ultimate thermodynamic property library:

- Six different thermodynamic (+transport) property models.
- Large set of fluids and mixtures (more can be added upon request).
- Accurate and fast thermodynamic properties for all situations and applications.
- Easy to couple to your specific application: with just a few clicks you can start doing thermodynamic property calculations from your preferred computing environment.

FluidProp is more than just a fluid property library: it is a common interface to various state-of-the-art thermodynamic and transport property models: independently of the model implementation, the user needs to know one single logical syntax to call the function for the desired property or set of properties. By changing just a single function argument, you can switch from, e.g., the ideal gas model to a cubic equation of state model and appreciate if there is difference in the results (real-gas behavior).

This FluidProp interface also provides an extremely rich set of partial derivatives of thermodynamic properties, or so-called secondary thermodynamic properties. These are available for any of fluid models . These are typically needed in complex simulations such as CFD and dynamic energy system modeling.

Originating from the energy engineering sector, FluidProp provides fluid models that are accurate over a wide range of temperatures and pressures, thus for many oil&gas and chemical processes. It usually outperforms any other fluid-property code when it comes to speed of execution thanks to its advanced algorithms.

FluidProp is easy to use. It is accessible as a plug-in from Excel and OpenOffice Calc. It is available under both Linux and Windows (both 32 bits and 64 bits) and through its COM and .NET interface, it is easily accessed from common tools such as Matlab/Simulink, Maple, Modelica and most common programming languages (Fortran, C, C++). In addition, a CAPE-OPEN interface is available for ease of use in the process industry.

The six thermodynamic sub-libraries that are currently available in FluidProp are GasMix, IF97, RefProp, StanMix, TPSI and vThermo

**GasMix** implements the ideal gas model for fluids and mixtures. It is very fast, but obviously has all the limitations of the ideal gas model: it cannot compute liquid properties and cannot deal with vapor-liquid equilibrium. It can be used to model any mixture, but obviously with limited accuracy as the interaction between the consituents are not taken into account.

**IF97** (Industrial Formulation) calculates the thermodynamic and transport properties of water and steam according to International Association for the Properties of Water and Steam (IAPWS). It is the reference calculation for industrial applications of water and steam.

**RefProp** is the thermodynamic property library from the National Institute of Standards and Technologies in the USA.

It implements *reference equations of state* as well as *technical equations of state* for pure fluids and mixtures. Reference equations of state are able to describe all experimental thermodynamic property data available for a certain fluid within their experimental uncertainty. Technical equations of state are less accurate but quite sufficient for most technical applications.

Mixture properties can also be calculated using a generalized model described in the RefProp documentation. Mixtures can be composed from the list of available pure fluids. RefProp contains an advanced mixture model for natural gas components, namely the GERG-2008 model.

You can use your copy of RefProp if you already bought it from NIST and more easily couple it to your program through the FluidProp interface. Alternatively, you can buy RefProp at the same price from Asimptote as part of the FluidProp package

**FreeStanMix** implements the PRSV cubic equation of state, which is one of the most accurate cubic equations of state to predict the properties of non-ideal fluids. In particular provides accurate estimations of saturation properties up to the vicinity of the critical point. It is particularly useful in case fluid data for RefProp are not available, as it requires only few parameters to model a fluid. These can also be estimated by Asimptote upon request, if they are not available in the database. In addition, being a simpler model than the ones implemented in RefProp, it is faster, thus the model of choice when computational time is more important than extreme accuracy. An advanced version of FreeStanMix, which is more accurate and reliable, is available in the StanMix add-on (see below).

**StanMix **implements the iPRSV equation of state, a recent improvement of the PRSV equation of state that solves the artificial discontinuity in the calculation of properties in the standard PSRV equation of state. Accuracy has also been slightly improved. This feature is relevant to some scientific and industrial applications. Further advantages of StanMix over FreeStanMix include:

- The critical point of mixtures can be computed directly and very fast, and is much more accurate than in FreeStanMix.
- Advanced and efficient algorithms for phase equilibria (bubble and dew point, PT-flash calculations) that avoid e.g. convergence problems close to the critical point and for mixtures with polar fluids. These algorithms also reduce computational time.

For mixtures, StanMix uses the Wong and Sandler mixing rules which are suitable for the modeling of highly non-ideal mixtures, and are thermodynamically consistent.

One of the nice features of the StanMix model is that we can easily add extra fluids to those that are already supplied. So, even if your particular fluid is not yet avialble, it will not cost you much to get it into the library.

**PCP-SAFT **implements the Perturbed Chain Polar SAFT equation of state (an improved version of the PC-SAFT equation of state), which is based on molecular models and is known for its ability to predict vapor/gas-liquid equilibria of complex fluids (e.g., macromolecules, copolymer systems, etc.) and fluid mixtures for a broad range of conditions (including, e.g., strongly polar systems and ionic-liquid + CO_{2} systems). Due to its theoretical nature, it is robust, consistent, predictive when applied to mixtures and reliable for extrapolations over the regions where the parameters were fitted.

**TPSI** implements accurate thermodynamic models for a number of fluids as described in:

Reynolds, W.C., Thermodynamic properties in S.I., Department of Mechanical Engineering - Stanford University, Stanford, CA, 1979.

FluidProp was developed by a team of researchers of the Propulsion and Power group at Delft University of Technology and at other universities.

The researchers behind FluidProp continually improve the software to meet the challenges of the research that is being done in their institutes. This means that by using FluidProp, you get access to the most up-to-date insights in thermodynamic modeling.

Even though it is largely developed in research institutes, FluidProp does not have the relatively poor quality that is so often the hallmark of academic software. The researchers readily acknowledge that industry can only work with their software if it is reliable and stable. Therefore, the company Asimptote was formed to intermediate between the researchers and the industry. Asimptote guards the stability of the code and offers support for its industrial users.