RefProp-Connector for CHEMCAD Help

This page explains how to use RefProp property calculations in CHEMCAD and how to add RefProp components to the CHEMCAD database. The properties that can be transferred from RefProp calculations into CHEMCAD are

  • vapor pressure
  • enthalpy (this includes the constant pressure heat capacity)
  • liquid density and
  • liquid viscosity.

The Reference Fluid Thermodynamic and Transport Properties (RefProp) database is a software package provided by the National Institute of Standards and Technology (NIST). For more details on purchase conditions and update information see https://www.nist.gov/srd/refprop.

RefProp is a database of parameters for High Precision Equations of State (HPEoS) for several fluids. Flash algorithms for solving the HPEoS are also part of the package and the density can be obtained from such calculations. Viscosity calculations in RefProp might use special routines instead of the HPEoS, depending on the substance selected.

Why use the RefProp-Connector?

The CHEMCAD models for the calculation of thermodynamic properties are very generic and can be applied to almost any kind of components and mixtures. However, this flexibility is on cost of accuracy. Whenever highly accurate property calculations for pure components are required, the usage of HPEoS and RefProp is a good choice. Typical applications are safety relief, the simulation of Carbon Capture and Storage (CCS) processes, especially for the compression part, and all kind of Rankine Cycles, Refrigeration Cycles, Heat Pump Systems, etc. Furthermore, novel functional substances for HVAC applications commonly are available first in RefProp before they are added to the DIPPR data base.


Which Fluids are supported by RefProp?

The Version 10.0 of RefProp includes parameters for 147 pure fluids and 5 predefined mixtures. Please refer to https://www.nist.gov/srd/refprop for a detailed list or check the “…\fluids” folder of your RefProp installation.

How to use the RefProp Property Calculations

To use the RefProp vapor pressure calculations select ADDK as K-value model from the Thermodynamic Settings menu. This automatically selects ADDH as enthalpy model in CHEMCAD versions higher than 7.0.3, which means that RefProp is calculating the enthalpy.

To use the RefProp liquid density calculation select “usradd:ccapi_refprop_density” as liquid density mixing rule. To use the RefProp liquid viscosity calculation select “usradd:ccapi_refprop_viscosity” as liquid viscosity mixing rule.

Warning: Only pure component properties are calculated by RefProp. Selecting a “Mixing Rule” is used for the connection to RefProp, no mixing rule is applied to RefProp calculated density and viscosity!

We recommend the usage of the RefProp liquid density and liquid viscosity calculations together with the RefProp calculation for the vapor pressure (ADDK) and the enthalpy (ADDH) since this leads to consistent results. However, it is possible to use e.g. the RefProp liquid density calculation for the pressure drop in a PIPE unit operation together with NRTL, Latent Heat and DIPPR viscosity.

Special care must be taken for calculations within the supercritical region (P > PC). In the supercritical region, CHEMCAD switches between a liquid density model (e.g. DIPPR) and a vapor density model (e.g. SRK) depending on a stream’s temperature. Problems that may occur in this region can be avoided by selecting ADDK and ADDH in these cases.

How to add Components which are in RefProp but not in CHEMCAD?

Some components, especially novel refrigerants, are not in the CHEMCAD database but are available in RefProp. To use these fluids in CHEMCAD simulations they are added as user components. Therefore, go to the Thermophysical -> Component Database -> Create New Component menu. The Component name must match the name of the related .FLD file in the \fluids folder of the RefProp installation. (e.g. R1233ZD.FLD should be added in CHEMCAD as R1233ZD)

The Normal boiling point can be taken from the RefProp fluid information screen (RefProp menu: Substance -> Fluid Information). Use the default correlation Pseudo component to create the new component. Vapor pressure and enthalpy of the new component are now calculated with RefProp when ADDK and ADDH are selected. However, to avoid inconsistent calculations of entropy or the isochoric heat capacity cv respectively (see section Limitations) the estimated critical properties and polynomial ideal gas heat capacity must be replaced. Take the critical properties from the RefProp fluid information screen. For implementing the ideal gas heat capacity, we recommend using the CHEMCAD property regression tool. Create a Cp-T Diagram at P = 0 MPa in RefProp and use Edit -> Save Plot Data Points to generate a table that can be copy-pasted into CHEMCAD. Make sure to select the same Engineering Units in both tools.

Limitations

  • RefProp calculations are only used for streams with pure components. In case of mixtures the Soave-Redlich-Kwong Equation of State (SRK) is the fallback method for vapor pressure (K-value) and enthalpy calculations
  • In case of mixtures the highlighted liquid density method and liquid viscosity methods are the fallback methods while mole% weighting for density mixing rule and log average by mole fraction for viscosity mixing rule are used.

 

  • Entropy is calculated with the SRK. This affects isentropic unit operations like compressors, expanders and the isentropic flash mode. Therefore, we recommend regressing the ideal gas heat capacities from RefProp and run compressors and expanders in “Polytropic with ideal cp/cv” mode. Check the results carefully!
  • Vapor densities are calculated with CHEMCAD routines (e.g. SRK).
  • Vapor viscosities are calculated with CHEMCAD routines (e.g. DIPPR).

Requirements

The following requirements must be met:

  • CHEMCAD 7.0.3 or above is installed on your machine.
  • RefProp must be installed in the folder “C:\Program Files (x86)\RefProp”.
  • You have downloaded and installed our free CC-API Add-on manager.
  • You have purchased “RefProp-Connector for CHEMCAD”

Examples for the REFPROP flash calculation

Example 1: Refrigeration Cycle

Use novel coolants for evaluation in refrigeration cycles. The simulation Example 1 Refrigeration Cycle.cc7 shows a typical application of R1234 ze(E) for air conditioning. In this case the flowrate, the superheating of stream 4 and the pressures are fixed. Feel free to optimize this case for your application!

Download R1234-ze-E.cc7

Example 2: Throttling of Methanol Vapor

Throttling commonly occurs during safety relief cases. But it is also used for low temperature applications (e.g. Linde process) and it is an effect of pressure drop in pipelines and valves. The simulation Example 2 Throttling of Methanol Vapor.cc7 shows how much a precise calculation of vapor enthalpies effects the Joule-Thomson coefficient and the temperature behind the throttle or relief valve. Compare these results with the results calculated with SRK or Latent Heat!

Download RP Example MeOH.cc7

Example 3: CO2 Pipeline

In the supercritical region the calculation of properties is difficult, as either DIPPR equations regressed to liquid properties must be extrapolated or Equations of State must be used, which commonly are not very accurate in estimating densities and viscosities. By using High Precision Equations of State these difficulties are avoided. Therefore, reliable results can be obtained for the calculation of the pressure drop in a CO2 pipeline, operated in the supercritical region by using the RefProp Property Calculation (Example 3 CO2 Pipeline.cc7).

Example 4: Density of Water

The representation of liquid densities in a flowsheet simulator commonly is not very accurate. Equations of State often show a large deviation from measured data, as (in most of them) there is no parameter to be adjusted to fit real densities. Even the new VTPR equation fails when the density of water is calculated at 1.013 bar and 4°C, although it has a volume parameter to be adjusted. Therefore, it is recommended to use density functions from DIPPR. These have been regressed to measured data in the subcritical region.

Table 1: Density of water at P = 1.013 bar and T = 4°C calculated with different models

Model SRK VTPR DIPPR REFPROP
Density 768 kg/m³ 1088 kg/m³ 1000 kg/m³ 1000 kg/m³

 

However, only a temperature dependency is considered by DIPPR, the effect of pressure is ignored. And even though DIPPR uses up to seven parameters, it seems to be impossible to show the well-known density peak of water at 4°C AND to fit the density along the whole subcritical region with an acceptable accuracy. These problems are overcome by using the RefProp Properties Calculation package:


Requirements

All the following requirements must be met:

  1. CHEMCAD 7.0.3 or above is installed on your machine.
  2. REFPROP is installed in the folder “C:\Program Files (x86)\REFPROP”. See the REFPROP website what licenses are available.
  3. You have downloaded and installed our free CC-API Add-on manager.
  4. You have purchased “RefProp-Connector for CHEMCAD“.

Limitations

  • REFPROP calculations are only used for streams with pure components. In case of mixtures the Soave-Redlich-Kwong (SRK) Equation of State and the selected Liquid Density method and Liquid Viscosity methods are the fallback method.
  • Entropy is calculated with the Soave-Redlich-Kwong (SRK) Equation of State. This affects isentropic unit operations like compressors, expanders and the isentropic flash mode. Therefore, we recommend regressing the ideal gas heat capacities from REFPROP and run compressors and expanders in “Polytropic with ideal cp/cv” mode. Check the results carefully!
  • Vapor densities are calculated with Soave-Redlich-Kwong (SRK) Equation of State.

Changelog

Version 1.0: Published 31 August 2019

We are enhancing the functionality from time to time.

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Frequently Asked Questions

Unfortunately, the authors make confusing statements, so they clarify themselves that REFPROP is a program, not a database containing measurements.
The REFPROP product page has all technical and commercial information about the latest version of the REFPROP program.
You must have the REFPROP program installed and a valid REFPROP license. You do not need to start the graphical user interface (GUI). Refprop-Connector for CHEMCAD is an application for CHEMCAD, published by us, and accessing the REFPROP DLL file. Download Refprop-Connector for CHEMCAD here!

References

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