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-   -   How to find Mean Nusselt Number? (https://www.cfd-online.com/Forums/fluent/110798-how-find-mean-nusselt-number.html)

 abhishek4890 December 21, 2012 04:00

How to find Mean Nusselt Number?

I am doing an computational analysis on natural convection heat transfer through rectangular fins attached to a wall. After the simulation, Surface Nusselt number for hot wall which I am getting in higher than (twice) the experimental results. The way I am following for finding the mean nusselt number is : Report--> Surface Integrals-->Facet Average-->Wall Fluxes-->Surface Nusselt number.
Please provide me the solution. Also let me know whether I am using the right way of finding the nusselt number or not. If not then please provide me an alternate way of finding the Average Nusselt Number.

 LuckyTran December 22, 2012 03:24

Two things:

1) Heat transfer coefficient needs a reference temperature
2) Nusselt number needs a reference length scale.

Both of these reference quantities are specified on the reference values task pane. Did you remember to specify them?

I have always used area-weighted average and not facet average, but I believe they yield similar results. You should be able to get the average Nusselt number the way you are doing.

 djamila77 December 12, 2016 08:21

hi

Quote:
 Originally Posted by LuckyTran (Post 398640) Two things: 1) Heat transfer coefficient needs a reference temperature 2) Nusselt number needs a reference length scale. Both of these reference quantities are specified on the reference values task pane. Did you remember to specify them? I have always used area-weighted average and not facet average, but I believe they yield similar results. You should be able to get the average Nusselt number the way you are doing.
What you mean by length scale, when I use length in a rectangular cavity do you mean depth ( hydrolics diameter )

 azizi0407 December 12, 2016 10:50

Hi, u need to precribed the bulk temperature and characteristic length in the reference value in order to calculate the Nusselt number.

 djamila77 December 12, 2016 15:15

i already did

Quote:
 Originally Posted by azizi0407 (Post 629285) Hi, u need to precribed the bulk temperature and characteristic length in the reference value in order to calculate the Nusselt number.
i already did
but my Question is what means length in CFD when you use 3dpp.
My problem is in three dimensional
length is it the hydraulics Diameter

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