# How to evaluate Nu-average

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March 26, 2016, 16:04
How to evaluate Nu-average
#1
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Hello I am wondering how I can estimate average Nusselt number from Fluent for flow through a duct like the equation appear at the image attached?

Thanks
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March 28, 2016, 10:07
#2
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Quote:
 Originally Posted by mariam.sara Hello I am wondering how I can estimate average Nusselt number from Fluent for flow through a duct like the equation appear at the image attached? Thanks

 March 28, 2016, 10:44 #3 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 1,873 Rep Power: 26 You can go under reports, do a surface integral of Nusselt number. You can't do exactly what you have written (by integrating the average Nu at a given section) because that is for 1D flow, and Fluent is 3D. There is no convenient average Nusselt number at a cross-section because a cross-section is not conveniently generalizable to 3D. mariam.sara likes this.

March 28, 2016, 10:49
#4
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Thank you for the reply. I do not mean exactly what I mention at the relation actually I am running 3D channel and want to know how I can predict Nusselt average on it? You mean I need to find integral for Nusselt over the overall domain? is that will represent Nu average?

Quote:
 Originally Posted by LuckyTran You can go under reports, do a surface integral of Nusselt number. You can't do exactly what you have written (by integrating the average Nu at a given section) because that is for 1D flow, and Fluent is 3D. There is no convenient average Nusselt number at a cross-section because a cross-section is not conveniently generalizable to 3D.

March 28, 2016, 23:10
#5
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Quote:
 Originally Posted by mariam.sara Thank you for the reply. I do not mean exactly what I mention at the relation actually I am running 3D channel and want to know how I can predict Nusselt average on it? You mean I need to find integral for Nusselt over the overall domain? is that will represent Nu average?
A type of weighted-integral, yes. Isn't that what an average is?

For example, an area-weighted average integral as you have written.

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