Nusselt CFX Post
 

Hi guys,
I'm trying to calculate Nusselt on the heat wall. I wrote Expression and use it to show the Nusselt, but it haven't the distribution around cylinder, whereas I use Fluent, I have Nu distribution around cylinder. I don't understand why. My boundary condition is heat flux on wall, velocity+temperature inlet, gauge pressure outlet.
My expression:
Tdifferent=massFlowAve(Temperature)@outlet-massFlowAve(Temperature)@inlet
Tbulk=massFlowAve(Temperature)@inlet +(x*0.4846[m])/0.872[m]*Tdifferent
h=5000[W m^-2]/(Temperature-Tbulk)
Nu=h*0.0235[m]/0.0254[W m^-1 K^-1]
Nuave=ave(Nu)@heatwall ( I use )
Please someone help to understand and fix this error.

You have to simplify your debugging process into your critical pieces.

I suggest to:
1 - Make a contour of Tbulk, is the distribution linear as you expected?
2 - are the minimum/maximum values as you expect
3 - Make a contour of (Temperature - Tbulk), is the distribution as you expected? Recall that for uniform heat flux boundary condition the difference between wall temperature and bulk temperature becomes constant once the flow is thermally developed; otherwise, the contour should be closer together from the inlet and spreading further along along the flow direction
4 - Now you get the idea; therefore, "rinse and repeat" using h, then Nu

Hope the above helps,