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Part 2: Flat Plate Convection

 

Pre-Analysis

 

 

 

Model Setup and Solution

 

 

 

Post Processing

 

 

 

Nusselt Number Variation

 

Note: When you create graphs of the Nusselt number in Excel, you need to transfer the data points from the exported CSV file from ANSYS over to an Excel workbook file (.xlsx). A CSV file is just a flat text file that uses a delimiter to separate the fields (in this case, a comma). It CANNOT save any formulas or plots. A xlsx file is the typical file format for Excel, just as docx is for Word. In a xlsx file, you can save the formulas, graphs, pivots, etc in the file. It was mentioned in the video, but we wanted to emphasize.

 

 

Plotting Nux vs Pr

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

  1. For Pr=1, go to the csv file exported from CFD Post and read off the Nusselt number value for Re = 40,000 (this process is 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 under Setup>Materials>Fluid>Air (to get a Pr=2, you need to double the Cp value for air, note that the values below may be wrong, the picture is just for locating where to to change Cp)

  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. 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 the Nux value for the new Pr. 

  5. Create a list of values in Excel from these runs with the following three columns (you are only changing the Pr number through the Cp of air enough times to notice a trend, 3 data points are not enough to notice a trend but 20 data points might not be the most efficient use of time)

         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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