REFPROP Flash Calculation Help

posted in: Help, REFPROP Flash | 0

This page explains how to use REFPROP flash calculations in CHEMCAD and how to add REFPROP components to the CHEMCAD database.

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.

Why use the REFPROP Flash Calculation?

The CHEMCAD models for equilibrium calculations (K-value Models) and enthalpy calculations (Enthalpy Models) 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 Flash Calculation

To use the REFPROP Flash 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.

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 must be installed in the folder “C:\Program Files (x86)\REFPROP”.
  • 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.
  • 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 SRK.
  • Liquid densities and other transport properties are calculated with the DIPPR equations or the related estimation formulas. More accurate results for liquid densities and liquid viscosities can be obtained by using the REFPROP Property Calculation Add-On.

 

Example 1: Refrigeration Cycle

Use novel coolants for evaluation in refrigeration cycles. The simulation RP Example R1234 ze(E).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 RP Example MeOH.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

 

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