# Nusselt number calculation help

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 March 24, 2012, 03:00 Nusselt number calculation help #1 Member   Join Date: Aug 2011 Posts: 53 Rep Power: 8 Hi everyone, I have a symmetric geometry model of a 25mm*25mm*1600mm geometry. The near wall node spacing is 0.05mm corresponding to Y+ = 1 I have forced 5m/s at inlet, outlet is a opening BC with zero pr. gradient across it. All the walls are specified with a heat flux of 625W/mm^2 I get a htc of around 16 (for a side) which gives me Nu = hD/K = 14.5 But the Nu from Dittus-Boelter equation gives me a Nu = 25. All the sides have almost same htc of 16, should the results be multiplied with some constant to take in to account of number of sides with specified heat flux or is the Nu computation from htc is correct? Can someone help ma asap? Thanks in advance

 March 26, 2012, 09:53 #2 Member   Join Date: Nov 2009 Posts: 49 Rep Power: 9 Hi, To get a Nu number coherent with the empirical one try to set the bulk temperature in the expert parameter window to the average temperature of the domain.

 March 26, 2012, 10:42 #3 Member   Join Date: Aug 2011 Posts: 53 Rep Power: 8 Hi Abou ali, u mean the volume averaged temperature of fluid domain?

 March 26, 2012, 11:01 #4 Member   Join Date: Nov 2009 Posts: 49 Rep Power: 9 yes, it's right.

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