Surface Nusselt with Volume-weighted average?
 

Hi guys,

Quick question: I'm looking to obtain results for the Nusselt number in a heat exchanger (fin and tube type). But I'm wondering what's the best way to go about this: volume weighted average or area weighted(over the tube and fin walls where heat transfer are taking place).

As far as I understand, volume-weighted average is the surface Nusselt over the volume of the domain. Is this understanding correct?

Just to give some numbers,
Nu for area-weighted is 2000+. Volume-weighted is between 9-11 (which is the right one with regards to data validation).

Some clarification (and subsequent suggestions) on the 2 different methods will be greatly appreciated!

Brian