name	nist-refprop
description	Query high-accuracy thermodynamic properties from NIST REFPROP database (commercial)
category	databases
domain	fluids
complexity	intermediate
dependencies	["ctREFPROP"]

NIST REFPROP Database Skill

Query high-accuracy thermodynamic and transport properties using the NIST REFPROP (Reference Fluid Thermodynamic and Transport Properties) database - the gold standard for thermophysical property calculations.

Overview

NIST REFPROP is a commercial-grade thermophysical property database developed by the National Institute of Standards and Technology (NIST). It provides:

Pure Fluids: 147+ pure fluids with the highest available accuracy
Mixtures: Predefined and custom mixtures with advanced mixing rules
Refrigerant Blends: All common refrigerant blends with temperature glide
Transport Properties: Viscosity, thermal conductivity, surface tension
Thermodynamic Properties: Enthalpy, entropy, density, specific heat
Phase Equilibrium: VLE, LLE, VLLE calculations for mixtures
Highest Accuracy: Reference-quality data validated against experimental measurements

REFPROP is the industry and research standard for:

Critical engineering design requiring highest accuracy
Validation of other property libraries (CoolProp is validated against REFPROP)
Mixture calculations with complex phase behavior
Refrigerant blend applications with temperature glide
Research and publication-quality data

Licensing

COMMERCIAL LICENSE REQUIRED

NIST REFPROP is NOT free or open-source software. You must purchase a license from NIST:

Standard License: ~$300 USD (one-time purchase)
Academic Pricing: Available for educational institutions
Purchase: https://www.nist.gov/srd/refprop

License includes:

REFPROP software (Windows GUI)
Fluid database files
Excel add-in
FORTRAN/DLL libraries
Python wrapper compatibility

Important Notes:

License is per-user, perpetual (one-time fee)
Updates and new fluid files provided for ~5 years
Required for commercial applications
Cannot be redistributed

Installation

Step 1: Purchase and Install REFPROP

Purchase REFPROP license from NIST: https://www.nist.gov/srd/refprop
Download and install REFPROP (typically to C:\Program Files (x86)\REFPROP\)
Note the installation directory path

Step 2: Install Python Wrapper

pip install ctREFPROP

The ctREFPROP package provides a Python interface to REFPROP using ctypes.

Step 3: Set RPPREFIX Environment Variable

The Python wrapper needs to know where REFPROP is installed:

Windows:

# PowerShell
$env:RPPREFIX = "C:\Program Files (x86)\REFPROP\"

# Or set permanently via System Properties > Environment Variables

Linux/Mac:

export RPPREFIX="/path/to/REFPROP/"

Python (alternative):

import os
os.environ['RPPREFIX'] = r'C:\Program Files (x86)\REFPROP'

Step 4: Verify Installation

from ctREFPROP.ctREFPROP import REFPROPFunctionLibrary

# Initialize REFPROP
RP = REFPROPFunctionLibrary(os.environ['RPPREFIX'])
RP.SETPATHdll(os.environ['RPPREFIX'])

# Test query
print(RP.RPVersion())

Available Fluids

REFPROP includes 147+ pure fluids organized by class:

Common Industrial Fluids

Water (H₂O) - IAPWS-95 formulation
Air - Dry air mixture
Carbon Dioxide (CO₂)
Nitrogen (N₂)
Oxygen (O₂)
Argon (Ar)
Helium (He)
Hydrogen (H₂)

Hydrocarbons (40+ fluids)

Alkanes: Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane, Decane (and isomers)
Alkenes: Ethylene, Propylene, Butene
Aromatics: Benzene, Toluene, Xylenes
Cyclic: Cyclohexane, Cyclopentane

Refrigerants (60+ fluids)

CFCs: R11, R12, R13, R113, R114, R115
HCFCs: R22, R123, R124, R141b, R142b
HFCs: R23, R32, R125, R134a, R143a, R152a, R227ea, R236fa, R245fa, R365mfc
HFOs: R1234yf, R1234ze(E), R1233zd(E), R1336mzz(Z)
Natural: R717 (Ammonia), R744 (CO₂), R290 (Propane), R600a (Isobutane)
Blends: R404A, R407C, R410A, R507A, R407F, R448A, R449A, R450A, R513A

Cryogenic Fluids

Helium, Neon, Argon, Krypton, Xenon
Hydrogen, Deuterium, Parahydrogen
Nitrogen, Oxygen, Fluorine
Methane, Ethane (LNG components)

Specialty Fluids

Siloxanes: D4, D5, D6, MD2M, MD3M, MD4M, MDM, MM (ORC applications)
Alcohols: Methanol, Ethanol, Propanol, Butanol
Other Organics: Acetone, Benzene, Toluene
Inorganics: Ammonia, Sulfur dioxide, Hydrogen sulfide

See reference.md for complete fluid list.

Property Queries

Core Functions

REFPROP uses different function calls than CoolProp:

from ctREFPROP.ctREFPROP import REFPROPFunctionLibrary
import os

# Initialize
RP = REFPROPFunctionLibrary(os.environ['RPPREFIX'])
RP.SETPATHdll(os.environ['RPPREFIX'])

# Define fluid
MOLAR_BASE_SI = RP.GETENUMdll(0, "MOLAR BASE SI").iEnum
fluid = "WATER"

# Single component
r = RP.REFPROPdll(fluid, "TP", "D;H;S;CP;CV;W;VIS;TCX", MOLAR_BASE_SI, 0, 0, 298.15, 101.325, [1.0])

# Access results
density = r.Output[0]      # kg/m³
enthalpy = r.Output[1]     # J/kg
entropy = r.Output[2]      # J/kg/K
cp = r.Output[3]           # J/kg/K
cv = r.Output[4]           # J/kg/K
sound_speed = r.Output[5]  # m/s
viscosity = r.Output[6]    # Pa·s
conductivity = r.Output[7] # W/m/K

Input Specifications

Code	Property	Unit
`TP`	Temperature, Pressure	K, kPa
`TH`	Temperature, Enthalpy	K, J/kg
`TS`	Temperature, Entropy	K, J/kg/K
`TD`	Temperature, Density	K, kg/m³
`PH`	Pressure, Enthalpy	kPa, J/kg
`PS`	Pressure, Entropy	kPa, J/kg/K
`PD`	Pressure, Density	kPa, kg/m³
`TQ`	Temperature, Quality	K, -
`PQ`	Pressure, Quality	kPa, -

Output Properties

Code	Property	Unit
`D`	Density	kg/m³
`H`	Enthalpy	J/kg
`S`	Entropy	J/kg/K
`U`	Internal energy	J/kg
`CP`	Heat capacity (const P)	J/kg/K
`CV`	Heat capacity (const V)	J/kg/K
`W`	Speed of sound	m/s
`VIS`	Viscosity	Pa·s
`TCX`	Thermal conductivity	W/m/K
`KV`	Kinematic viscosity	m²/s
`PRANDTL`	Prandtl number	-
`STN`	Surface tension	N/m
`P`	Pressure	kPa
`T`	Temperature	K
`Q`	Quality (vapor fraction)	-

Multiple properties can be requested in one call, separated by semicolons: "D;H;S;CP;VIS;TCX"

Mixture Calculations

One of REFPROP's key advantages is sophisticated mixture handling:

# Define mixture by components and mole fractions
fluid = "METHANE;ETHANE;PROPANE"
z = [0.9, 0.07, 0.03]  # Mole fractions (must sum to 1.0)

# Query mixture properties
r = RP.REFPROPdll(fluid, "TP", "D;H;S", MOLAR_BASE_SI, 0, 0, 250.0, 5000.0, z)

Mixture Features:

Up to 20 components in a mixture
Advanced mixing rules (GERG-2008, Kunz-Wagner, etc.)
Temperature glide calculations for zeotropic blends
Vapor-liquid equilibrium (VLE) calculations
Liquid-liquid equilibrium (LLE) for certain systems

Advantages Over CoolProp

While CoolProp is excellent and free, REFPROP offers:

1. Higher Accuracy

REFPROP is the reference standard that other libraries validate against
More precise equations of state, especially near critical point
Better transport property correlations
Typical accuracy: 0.01% for density vs 0.1% for CoolProp

2. More Fluids

147+ pure fluids vs ~120 in CoolProp
All latest refrigerants (HFOs: R1234yf, R1234ze, R1233zd, etc.)
More industrial and specialty chemicals
Frequently updated with new fluids

3. Better Mixture Handling

Superior mixing rules (GERG-2008, advanced models)
Handles complex non-ideal mixtures
Temperature glide for zeotropic refrigerant blends
VLE/LLE calculations
Up to 20 components vs limited mixture support in CoolProp

4. Extended Property Range

Valid over wider temperature and pressure ranges
Better extrapolation behavior
More reliable in extreme conditions

5. Additional Capabilities

Humidity calculations (psychrometrics)
Flash calculations (PT, PH, PS, etc.)
Saturation properties with Jacobian
Ancillary equations
Pseudo-pure fluid approximations

6. Official Support

Maintained by NIST (National Institute of Standards and Technology)
Technical support available
Regular updates with latest research
Publication-quality results

When to Use REFPROP vs CoolProp

Use REFPROP when:

Highest accuracy is required (±0.01%)
Working with complex mixtures
Need latest refrigerant data (HFOs)
Publication or critical design work
Budget allows commercial license
Working with zeotropic blends (temperature glide)

Use CoolProp when:

Budget constraints (free/open-source)
Basic property needs (±0.1% accuracy acceptable)
Pure fluids only
Open-source license required
Quick prototyping

Validation Note: CoolProp is validated against REFPROP, confirming REFPROP as the reference standard.

Common Workflow Example

from ctREFPROP.ctREFPROP import REFPROPFunctionLibrary
import os

# Setup
os.environ['RPPREFIX'] = r'C:\Program Files (x86)\REFPROP'
RP = REFPROPFunctionLibrary(os.environ['RPPREFIX'])
RP.SETPATHdll(os.environ['RPPREFIX'])

MOLAR_BASE_SI = RP.GETENUMdll(0, "MOLAR BASE SI").iEnum

# Query water at 25°C, 1 bar
fluid = "WATER"
T = 298.15  # K
P = 100.0   # kPa

r = RP.REFPROPdll(fluid, "TP", "D;H;S;CP;VIS;TCX", MOLAR_BASE_SI, 0, 0, T, P, [1.0])

print(f"Water at {T} K, {P} kPa:")
print(f"  Density: {r.Output[0]:.4f} kg/m³")
print(f"  Enthalpy: {r.Output[1]:.2f} J/kg")
print(f"  Entropy: {r.Output[2]:.2f} J/kg/K")
print(f"  Cp: {r.Output[3]:.2f} J/kg/K")
print(f"  Viscosity: {r.Output[4]*1000:.4f} mPa·s")
print(f"  Conductivity: {r.Output[5]:.4f} W/m/K")

Error Handling

REFPROP returns error codes and messages:

r = RP.REFPROPdll(fluid, "TP", "D", MOLAR_BASE_SI, 0, 0, T, P, z)

if r.ierr > 0:
    print(f"Error {r.ierr}: {r.herr}")
elif r.ierr < 0:
    print(f"Warning {r.ierr}: {r.herr}")
else:
    print(f"Success: {r.Output[0]}")

Units

REFPROP uses different unit conventions than CoolProp:

Default Units (with MOLAR BASE SI):

Temperature: K (Kelvin)
Pressure: kPa (kilopascals) - Note: CoolProp uses Pa
Density: kg/m³
Enthalpy: J/kg
Entropy: J/kg/K
Viscosity: Pa·s
Thermal conductivity: W/m/K

Unit Systems Available:

SI with molar units
SI with mass units (default shown above)
English units
Custom units

Best Practices

Always set RPPREFIX before importing ctREFPROP
Check ierr for errors after each call
Use exact fluid names (case-sensitive, from FLUIDS directory)
Pre-calculate compositions for mixtures (must sum to 1.0)
Cache RP instance - don't reinitialize repeatedly
Use appropriate input pairs for each phase region
Validate results against known values initially
Read error messages - REFPROP provides detailed diagnostics

References

Official Resources

NIST REFPROP Website
- URL: https://www.nist.gov/srd/refprop
- Purchase and download
REFPROP Documentation
- Included with installation
- REFPROP.pdf in installation directory
ctREFPROP Documentation
- URL: https://github.com/usnistgov/REFPROP-wrappers/tree/master/wrappers/python
- GitHub: https://github.com/usnistgov/REFPROP-wrappers

Key Publications

Lemmon, E.W., Bell, I.H., Huber, M.L., McLinden, M.O. (2018). "NIST Standard Reference Database 23: Reference Fluid Thermodynamic and Transport Properties-REFPROP, Version 10.0", National Institute of Standards and Technology.

Support

NIST Support: refprop@nist.gov
Issue Tracker: https://github.com/usnistgov/REFPROP-issues
Forum: https://groups.google.com/g/refprop

Quick Reference

# Initialize
from ctREFPROP.ctREFPROP import REFPROPFunctionLibrary
RP = REFPROPFunctionLibrary(os.environ['RPPREFIX'])
RP.SETPATHdll(os.environ['RPPREFIX'])
MOLAR_BASE_SI = RP.GETENUMdll(0, "MOLAR BASE SI").iEnum

# Pure fluid
r = RP.REFPROPdll("WATER", "TP", "D;H;S", MOLAR_BASE_SI, 0, 0, 300.0, 101.325, [1.0])

# Mixture
r = RP.REFPROPdll("METHANE;ETHANE", "TP", "D;H;S", MOLAR_BASE_SI, 0, 0, 200.0, 5000.0, [0.9, 0.1])

# Check for errors
if r.ierr != 0:
    print(f"Error/Warning: {r.herr}")

NIST REFPROP is the gold standard for thermophysical properties. While it requires a commercial license, the investment is justified for applications requiring the highest accuracy, mixture calculations, or publication-quality results. For open-source alternatives, see the coolprop-db skill.