Managed Reference Properties is a wrapper for the NIST Reference Fluid Thermodynamic and Transport Properties that was created by Eric Lemmon to grab the properties of the thermodynamic fluids in either pure and mixed configuration.
The library is written in C++/CX to propagate the functionality of the NIST Fortran library into the .NET world.
It provides a true object oriented approach for calling the properties calculation in an extreme optimized way which lets the developer focus on the engineering problem itself without thinking about the hassle of determining how to obtain specific information about certain fluid.
The library source code can be conducted at Managed Refprop at Codeplex
A sample of the library can be found in the following software that calculates the rankine cycle
Download Rankine Actual Cycle