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How to find Mean Nusselt Number?

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Old   December 21, 2012, 04:00
Default How to find Mean Nusselt Number?
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Abhishek
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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.
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Old   December 22, 2012, 03:24
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Lucky Tran
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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.
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Old   December 12, 2016, 08:21
Question hi
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Quote:
Originally Posted by LuckyTran View Post
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 )
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Old   December 12, 2016, 10:50
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Hi, u need to precribed the bulk temperature and characteristic length in the reference value in order to calculate the Nusselt number.
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Old   December 12, 2016, 15:15
Default i already did
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Quote:
Originally Posted by azizi0407 View Post
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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