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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 presentationPre-Analysis step. 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.

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https://confluence.cornell.edu/download/attachments/111221574/heated%20wall.png

 
As discussed in the powerpoint presentationPre-Analysis step, we need to set:

• velocity and temperature (plus k and epsilon for the turbulence model equations) at the inlet
• pressure at the outlet

For incompressible subsonic flow, the flow adjusts to the pressure at the outlet (consider this as a signal you are sending the flow about what it needs to do inside the pipe).

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