Version 9.0 of the REFPROP software has been released. This new update adds many new standards that either have been recently adopted, or are in the process of becoming standards. Most notably are the AGA-8 and GERG-2004 equations for natural gas. AGA-8 has been the current standard for natural gas properties since 1992 but was not available in previous versions of REFPROP since it was only valid in the gas phase. This standard did not have the ability to calculate phase equilibrium properties, including dew points and bubble points. Although properties at the dew point were within the limits of the AGA-8 equation, the unknown equilibrium point became a real hindrance for natural gas processors. The GERG-2004 equation set out to overcome this deficiency and to add properties in the liquid phase and critical region. It was designed to be more accurate than the AGA-8 equation in the gas phase, so that it could become a new standard for the gas industry. This equation is currently being adopted by ISO, and other organizations will accept the ISO approval once it is available. The new equation dramatically improves the representation of not only natural gas properties, but properties of mixtures for other components as well that are cryogenic or contain carbon dioxide. The model is set up simply so that additional compounds can be included in the mixture by adding interaction parameters for systems with limited data. For those systems with extensive data, the excess Helmholtz energy portions of the mixture model can be incorporated as well with one additional parameter that determines the extent of the excess portion that is added.
Many other changes have been incorporated into the new version of REFPROP. New equations of state have been added for 33 fluids and new transport equations have been added for 15 fluids. All of these equations represent either fluid representations with lower uncertainties or new equations for important fluids that were not available previously. Some of these fluids include acetone, carbon monoxide, ethane, hydrogen, hydrogen sulfide, krypton, nitrous oxide, propane, sulfur dioxide, toluene, and xenon. Fluids with new transport equations include methane, octane, nonane, decane, R125, hydrogen sulfide, methanol, and ethanol. Work is in progress to add surrogate mixture models for aviation fuels and rocket propellants, models for biofuels, and updated transport surfaces for hydrogen to future versions of the REFPROP program.