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Here are the steps for generating a plot of Nu vs Pr for Re = 40,000.

1. For Pr=1 (Air Cp of 1440.9 j/Kg-k), go to the csv file exported from CFD Post and read off the Nusselt number value for Re = 40,000 (shown in the Nusselt Number Variation video above). This is the Nusselt number for Pr=1 at that Reynolds number.  

2. Change Air Cp in

   Fluent 

   Fluent under Setup>Materials>Fluid>Air (To get a Pr=2, you need to double the Cp value for air)Image Added

3. Run more iterations until the you get convergence (when the residuals are below 1e-6). Note you don't need to reinitialize the guess values since the velocity and pressure fields remain the same

   since

   . Cp affects only the energy equation. 

4. Export Nux vs. Rex to a csv file. Read off the Nux value for Rex = 40,000. This is Nux for the new Prandtl number. 

5. Create a list of values in Excel from these runs with the following three columns

        Cp      Pr     Nux

6. Plot Nux vs Pr and add the trend line to get a fit and the exponent m

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