Fluid Panel

The Fluid panel controls the properties of the fluid in the model. A default fluid is not selected - one must be defined to run any simulation unless one was previous defined on the Startup Window.

The first selection that must be made is what Fluid Library to use. The default selection of User Specified requires the manual definition of Density, Dynamic Viscosity, and Vapor Pressure (optional if cavitation detection is not required). The available Fluid Libraries are:

• AFT Standard - Common fluids from various industry standard sources have been curve fit to optimize calculation speed. This fluid library offers the best balance between accuracy and computation time. Many of these fluids have thermal property information that allows for the calculation of heat transfer.

• ASME Steam/Water - Properties are calculated via the Equations of State which were used to generate the classic steam/water tables in the IAPWS Industrial Formulation (1997).

• NIST REFPROP - The Reference Fluid Thermodynamic and Transport Properties (REFPROP) Database is licensed from the National Institute of Standards and Technology (NIST) where properties for approximately 150 fluids are calculated via Equations of State. REFPROP supports user-specified fluid mixtures. For more info see the following sources: Program Summary, REFPROP FAQ, NIST Chemistry WebBook, NIST Chemical Name Search.

• Chempak Fluid - Optional add-on for purchase which contains data for approximately 700 fluids and supports user-specified fluid mixtures. Chempak is licensed from Madison Technical Software.

• User Library Fluid - If the desired working fluid is not available via the other sources, custom fluid properties can be entered and saved to the User Library for repeated use in the future. Fluids can be created using the Fluid Libraries menu.

Select a library by clicking the radio button next to the name of the library. After selecting a library, the Fluids Available in Library list is populated. One of the fluids can be selected and used with the Add To Model button.

Note: All fluids in Fathom are treated as incompressible as stated in the Engineering Assumptions. This includes fluids in the gas phase and fluids above the critical point.

AFT Standard Fluid Library

Common fluids from various industry standard sources have been curve fit to optimize calculation speed. This fluid library offers the best balance between accuracy and computation time. Many of these fluids have thermal property information that allows for the calculation of heat transfer.

Generally, fluids in the AFT Standard library are assumed to have properties that only vary with temperature which follows the incompressible engineering assumption of Fathom.

To add a fluid into your model, select it from the Fluids Available in Library list and click the Add to Model button. The fluid will appear in the Fluids in Current Model area. Once the fluid is added, specify the temperature in the Fluid Properties area on the right to calculate values of density, dynamic viscosity, and vapor pressure, as shown in Figure 1.

Vapor pressure is listed as optional since it is only needed to check if cavitation exists in the pipes/junctions.

ASME Steam/Water Library

Properties are calculated via the Equations of State which were used to generate the classic steam/water tables in the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam (ISPWS-IF97ASME Press, ASME International Steam Tables for Industrial Use (CRTD-Vol. 58), published by the American Society of Mechanical Engineers, Three Park Avenue, New York, NY 10016.), see ASME Press in References.

After selecting ASME Steam/Water, "ASME '97 Water" is automatically added to in the Fluids in Current Model area. Select the Fluid Phase and enter a Pressure and Temperature to calculate the properties as shown in Figure 2.

Detailed fluid property information from SteamCalc can be calculated using the AFT SteamCalc Viewer, which can be accessed from Tools > Fluid Property Viewers > SteamCalc. The SteamCalc Viewer will be launched as a separate application, which can then be used to calculate fluid properties at various conditions.

For more information on AFT SteamCalc Viewer see the SteamCalc Help File.

Figure 2: Fluid panel in Analysis Setup with the ASME Steam/Water fluid library selected

NIST REFPROP Library

The Reference Fluid Thermodynamic and Transport Properties (REFPROP) Database is licensed from the National Institute of Standards and Technology (NIST) where properties for approximately 150 fluids are calculated via Equations of State. The data comes from Version 10 of the library. For more info see the following sources: Program Summary, REFPROP FAQ, NIST Chemistry WebBook, NIST Chemical Name Search.

Add a fluid from the Fluids Available in Library list by selecting it and clicking Add to Model. Select the Fluid Phase and enter both a Pressure and Temperature in the Fluid Properties area on the right, as shown in Figure 3.

Fluids from the NIST REFPROP library support fluid mixtures, but no chemical reactions are modeled as listed in the Engineering Assumptions.

Chempak Fluid Library

Optional add-on for purchase which contains data for approximately 700 fluids. Chempak is licensed from Madison Technical Software.

Fluids from the Chempak library support fluid mixtures, but no chemical reactions are modeled as listed in the Engineering Assumptions.

Add a fluid from the Fluids Available in Library list by selecting it and clicking Add to Model. Select the Fluid Phase and enter both a Pressure and Temperature in the Fluid Properties area on the right, as shown in Figure 4.

Information on the theory and calculation methods used in Chempak is given in the Chempak Technical Information topic.

Detailed fluid property information from Chempak can be calculated using the AFT Chempak Viewer, which can be accessed from Tools > Fluid Property Viewers > Chempak. The Chempak Viewer will be launched as a separate application, which can then be used to calculate fluid properties at various conditions. A Chempak Database license is required to use the Chempak Viewer.

For more information on AFT Chempak Viewer see the Chempak Viewer Help File.

State Property Accuracy Options

The State Property Accuracy options are applicable only to Chempak fluids and are located on the Fluid panel below the Fluids in Current Model area.

The State Property Accuracy influences the number of elements used in curve fits for calculating property data. There are two accuracy options: Standard and High. You will usually want to start with standard accuracy, which is selected by default, and use high accuracy for final runs, depending on the importance and run time for the model. The high accuracy option will increase run time by about a factor of two.

When performing interpolations for properties, a 4 point or 16 point interpolation scheme can be used. The 4 point scheme implemented in AFT Fathom is the Standard Accuracy option. The 16 point scheme is the high accuracy option. Use of the High accuracy option will roughly double the run times for models.