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Name That Fluid - Databases 201 (AFT) - 2016-03-23

Name That Fluid - Database 201

AFT Software offers lots of different fluid modeling options of common fluids with the AFT Standard Fluids that are available in AFT FathomAFT Arrow, and AFT Impulse.  The AFT Standard Fluids can be accessed in the System Properties window and they provide fairly accurate thermophysical properties.

But what happens when there is a fluid that you need to model and it does not exist as an AFT Standard Fluid in the software?  Well, there is no need to fret in this situation!  You can very easily create your own custom fluid and add it to the fluid database!

The Fluid Database is just one of the many databases that you can access from the Database menu within the software.  The Fluid Database will display all the AFT Standard fluids as well as any custom fluids that you create.  If you only want to display the custom fluids you have created, then simply uncheck the box for "Show Fluids Provided by AFT ".

 Creating a new custom fluid is very easy.  In the Fluid Database, simply click on "Add New Fluid".  Then just give the fluid a name and maximum and minimum allowable temperatures.  Then specify the density and viscosity as functions of temperature.  For optional heat transfer calculations, specify the heat capacity and thermal conductivity of the fluid as functions of temperature as well as an enthalpy reference.  Finally, to know if your fluid is cavitating or to perform NPSHA calculations, enter the vapor pressure as functions of temperature.

The custom fluid "Heavy Water" (i.e., Deuterium Oxide) is shown in Figure 1 for AFT Fathom.  After the data is entered, the data needs to be fit with a curve and then the software will use the curve fit for thermophysical property calculations.  The better the curve fits the data, the more accurate the thermophysical property calculations will be.

Figure 1 - Heavy Water Custom Fluid in AFT Fathom

Creating a custom fluid for AFT Arrow is just as easy, but there is slightly more information that needs to be entered for gases in AFT Arrow than for liquids in AFT Fathom.  In AFT Arrow, required input is a fluid name, maximum/minimum allowable temperatures, viscosity, and heat capacity as functions of temperature.  Molecular weight and an enthalpy reference is also required.  Figure 2 shows the thermophysical property data entered for Laughing Gas (i.e., Nitrous Oxide).

Figure 2 - Laughing Gas Properties for AFT Arrow

For AFT Arrow, there is some additional data that can be specified which is on the Other Data tab.  This information includes the molecular weight, compressibility factor, critical pressure/temperature, acentric factor, enthalpy data, and pressure points for density and enthalpy curve fits.  Figure 3 shows the additional data for Laughing Gas.

Figure 3 - Additional thermophysical property information entered on Other Data tab for AFT Arrow

For AFT Arrow, density and enthalpy data points are only optional.  However, the data can still be entered for density or enthalpy as functions of temperature.  And each set of data for enthalpy and density are for a constant pressure.  This is why the pressure points for density and enthalpy can be entered on the Other Data tab.

Overall, there are many fluid modeling options available to you through AFT Standard fluids, ASME steam tables, and Chempak.  However, if the fluid you need to work with does not exist in any of those sets of data, or if you have your own data that you trust more, then easily create your own fluid data set and you can play "Name That Fluid" as much as you want!

source: www.aft.com

 


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