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This is what you should currently see under Models.

 
Now let's set the "material properties" i.e. properties of air that appear in the governing equationsour boundary value problem.

Materials > Fluid air >  Create/Edit...

Since variations in absolute pressure are small in our pipe, we'll use a constant absolute pressure in the ideal gas law as discussed in the powerpoint presentation. This is called the "Incompressible ideal gas" model in FLUENT (it's non-standard nomenclature).  Change the Density (kg/m3) from constant to incompressible-ideal-gas. The constant absolute pressure to be used in the ideal gas equation is specified later as Operating Pressure.

The other properties are also functions of temperature. However, we'll use constant values equal to the average values over temperature range obtained in the experiment. Enter the following constant values:We will use the properties of heated air. Enter for following properties for air.
Cp (Specific Heat) (j/kg-k): 1005
Thermal Conductivity (w/m-k): 0.0266
Viscosity (kg/m-s): 1.787e-5
Molecular Weight (kg/kgmol): 28.97
 

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