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REFPROP Documentation Release 10.0 EWL, IHB, MH, MML May 21, 2018

CONTENTS 1 REFPROP Graphical User Interface . . . 1.1 General Information . . 1.2 Menu Commands . 1.3 DLLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 REFPROP DLL documentation . . 2.1 High-Level API 2.2 . Legacy API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 6 26 27 27 55 i

REFPROP Documentation, Release 10.0 REFPROP is an acronym for REFerence ﬂuid PROPerties. This program, developed by the National Institute of Standards and Technology (NIST), calculates the thermodynamic and transport properties of industrially important ﬂuids and their mixtures. These properties can be displayed in Tables and Plots through the graphical user interface; they are also accessible through spreadsheets or user-written applications accessing the REFPROP dll. REFPROP is based on the most accurate pure ﬂuid and mixture models currently available. It implements three models for the thermodynamic properties of pure ﬂuids: equations of state explicit in Helmholtz energy, the modiﬁed Benedict-Webb-Rubin equation of state, and an extended corresponding states (ECS) model. Mixture calculations employ a model that applies mixing rules to the Helmholtz energy of the mixture components; it uses a departure function to account for the departure from ideal mixing. Viscosity and thermal conductivity are modeled with either ﬂuid-speciﬁc correlations, an ECS method, or in some cases the friction theory method. CONTENTS 1

REFPROP Documentation, Release 10.0 2 CONTENTS

CHAPTER ONE REFPROP GRAPHICAL USER INTERFACE 1.1 General Information 1.1.1 About REFPROP REFPROP is an acronym for REFerence ﬂuid PROPerties. This program, developed by the National Institute of Standards and Technology (NIST), calculates the thermodynamic and transport properties of industrially important ﬂuids and their mixtures. These properties can be displayed in Tables and Plots through the graphical user interface; they are also accessible through spreadsheets or user-written applications accessing the REFPROP dll. REFPROP is based on the most accurate pure ﬂuid and mixture models currently available. It implements three models for the thermodynamic properties of pure ﬂuids: equations of state explicit in Helmholtz energy, the modiﬁed Benedict-Webb-Rubin equation of state, and an extended corresponding states (ECS) model. Mixture calculations employ a model that applies mixing rules to the Helmholtz energy of the mixture components; it uses a departure function to account for the departure from ideal mixing. Viscosity and thermal conductivity are modeled with either ﬂuid-speciﬁc correlations, an ECS method, or in some cases the friction theory method. The property formulations and ﬂuid data ﬁles were programmed by: Eric W. Lemmon, Ian H. Bell, Marcia L. Huber, and Mark O. McLinden Applied Chemicals and Materials Division National Institute of Standards and Technology Boulder, CO 80305 eric.lemmon@nist.gov ian.bell@nist.gov marcia.huber@nist.gov The user interface was written by Eric W. Lemmon. IMPORTANT: Please visit the REFPROP FAQ web site as your ﬁrst resource when you encounter difﬁculties or have questions. Most email enquiries are answered by pointing to the FAQ. Using the FAQ will save valuable NIST resources that can be used to further develop REFPROP. *Certain trade names and other commercial designations are used in this work for the purpose of clarity. In no case does such identiﬁcation imply endorsement by the National Institute of Standards and Technology, nor does it imply that the products or services so identiﬁed are necessarily the best available for the purpose. 3

REFPROP Documentation, Release 10.0 1.1.2 Cautions Users of the REFPROP program should be aware of several potential pitfalls: If you experience large differences in your expected values of enthalpy or entropy as compared to those calculated by the program, see information on Reference State. Changing the units in the Options/Units menu does not change the units on the tables already created, but only for new tables and plots. The equation parameters for mixtures composed of natural gas ﬂuids come from the 2008 GERG model (see Pref- erences for the reference). The default pure ﬂuid equations of state in REFPROP are not the same as those used in the GERG model, rather they are more complex with lower uncertainties. The GERG equations for the pure ﬂuids are shorter, less complex, and faster, but slightly less accurate. To use the GERG model, as published, choose the corresponding option under Options/Preferences. The preference screen also has an option to use the AGA8 model for natural gas calculations. The NIST REFPROP program is designed to provide the most accurate thermophysical properties currently available for pure ﬂuids and their mixtures. The present version is limited to vapor-liquid equilibrium (VLE) only and does not address liquid-liquid equilibrium (LLE), vapor-liquid-liquid equilibrium (VLLE) or other complex forms of phase equilibrium. The program does not know the location of the freezing line for mixtures. Certain mixtures can potentially enter into these areas without giving warnings to the user. Some mixtures have components with a wide range of volatilities (i.e., large differences in boiling points), as indicated by a critical temperature ratio greater than 2. Certain calculations, especially saturation calculations, may fail without generating warnings. Plotting the calculation results may reveal such cases–looking for discontinuities in density is a good check. Such mixtures, including many with hydrogen, helium, or water, may not have Type I critical behavior, that is they do not have a continuous critical line from one pure component to the other. The estimated critical parameters speciﬁed in the Substance/Fluid Information screen for these types of mixtures will not be displayed. There are cases where an input state point can result in two separate valid states. The most common is temperature- enthalpy inputs. Viewing a T-H diagram will help show how there can be two valid state points for a given input. For example, nitrogen at 140 K and 1000 J/mol can exist at 6.85 MPa and at 60.87 MPa. When this situation occurs, REFPROP returns the state with the higher density. See the Speciﬁed State Points section for information on calculating the upper and lower roots. There are certain properties pertaining only to the saturation line, such as dp/dT. For most cases, displayed properties at saturation states are those for the single phase on the saturation boundary. Thus, derivative properties at saturation as well as saturation properties that are given along constant property paths, such as Cv, Cp, or Csat, pertain to their state in the single phase. Those properties label with a ‘[sat]’ indicate a path along the saturation line. For pure ﬂuids, when the ‘Show 2-phase’ option in the plot menu is selected, the generated lines for pressure and temperature represent metastable ﬂuid states and the calculated lines between them. These are calculations from the equation of state disregarding any saturation states and generally have no physical signiﬁcance. Two equations of state are available for hydrogen to account for the different quantum spin states of the molecule. Normal hydrogen should be used in applications where it was created and stored at 250 K or above, or when it was cooled to below 250 K and stored without a catalyst for less than a day. The parahydrogen equation should be used where hydrogen was catalyzed or stored for several days at the normal boiling point (NBP) and used at any temperature within 1 day of storage at the NBP. Since the rate of conversion between quantum states is dependent on temperature, pressure, and the storage container, these values are only estimates. For more information, see the Leachman et al. literature reference in the Fluid Information window for hydrogen. 1.1.3 Copyright and Disclaimer REFPROP is a product of the National Institute of Standards and Technology (NIST). Developed and maintained by: 4 Chapter 1. REFPROP Graphical User Interface

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