AFT Product Tips
Get More Flexible With Your Fluids
Here at AFT we are always looking for more ways to bring more convenience and accuracy to our model files. One of the ways we are doing this is with NIST REFPROP, the new fluids database that we have incorporated into AFT Fathom 10 and is coming soon in AFT Arrow 7 and AFT Impulse 7. Unlike Chempak, REFPROP is included at no additional cost to users. In this blog I will highlight a few reasons why you may want to take advantage of this database.
New variety of Fluids
There are over 150 fluids included in the REFPROP database for AFT Fathom 10, including the addition of a wide variety of new refrigerants, hydrocarbons, and other constituents. If you don't find the mixture you are looking for in the list, you also have the ability to create your own mixture from the fluids in the database using either a mole or mass basis, as shown in Figure 1. To quickly search the list, you can either use the Search button, or simply click in the list of fluids and begin typing the name of the fluid you are searching for.
Defining Mixtures in Multiple Files
Like the Chempak Database, NIST REFPROP offers the ability to export mixture data to import to a new mixture. This makes it quick and easy to save complex mixtures to use in multiple model files and to pass between users.
To do this, first define the fluid in the System Properties window. You can then click "Export Mixture to File…", which will save the mixture as a .cpt file, as is shown in Figure 2 below.
In the model you want to Import the Mixture to, simply open the System Properties window, choose NIST REFPROP and go to the mixtures button. You can then choose "Import Mixture from File…" to upload the information and quickly define the fluid.
Analysis with REFPROP
With the AFT Standard Database, curve fits are used to represent the fluid properties. This allows for quick calculations, but also decreases the accuracy. NIST REFPROP increases the accuracy of its calculations by using more complex correlations and equations to calculate its results. Depending on the model this can significantly increase the run time, but these extra calculations provide several benefits.
With NIST REFPROP, unlike the standard database, the additional information contained in this database gives you the option to define the phase of the fluid being used, as well as a temperature and a pressure for the default fluid properties. This means that REFPROP can provide the user with a caution when the fluid is evaporating or condensing. Since AFT Fathom and Impulse assume single phase flow, this is especially important to be aware of. In our upcoming release of Arrow 7, NIST REFPROP will also give users the ability to analyze dynamic mixing in the model. This can be done easily by assigning the desired fluids at different inputs in the model and allowing Arrow to calculate the final mixture for the system outlets.
Overall the NIST REFPROP database is a great new addition built into our new releases which will make it easier to get more accuracy in your results and will provide more variety in calculation options.
Thanks for your question! Yes, you can model non-newtonian fluids such as sludge in AFT Impulse using one of the non-newtonian viscosity models included in AFT Impulse, or using our settling slurry add-on module, SSL. Alternate viscosity models can be defined in the System Properties window.