Nusselt number evaluation

robro92 · July 12, 2015, 07:48

hello everyone; i have to evaluate the Nu number for a triangular duct in turbulent flow with liquid water. We imposed the Twall , thus we calculate the heat flux q [W/m2] on all the pipe length. Our doubt is about the bulk mean temperature, h=q/(Twall-Tbulk). Which Bulk mean temperature should I use?? We use the bulk temperature at the outlet of the pipe.

JulianP · July 13, 2015, 02:43

This is not a problam, actually. You just have to choose one (e.g. the inlet temperature) and stick to it.

If you want to be safe, you can always talk about the "Nusselt number calculated using the inlet temperature".

robro92 · July 13, 2015, 03:28

Thanks a lot ! However we solved the doubt..we used the bulk mean temperature close to the outlet, because we have fully developed conditions only there ( at the beginning we have the entry region). So we isolate a small volume there in cfd post

July 12, 2015, 07:48	Nusselt number evaluation	#1
robro92 New Member roberto Join Date: Jul 2015 Posts: 4 Rep Power: 10	hello everyone; i have to evaluate the Nu number for a triangular duct in turbulent flow with liquid water. We imposed the Twall , thus we calculate the heat flux q [W/m2] on all the pipe length. Our doubt is about the bulk mean temperature, h=q/(Twall-Tbulk). Which Bulk mean temperature should I use?? We use the bulk temperature at the outlet of the pipe.

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July 13, 2015, 02:43		#2
JulianP New Member Join Date: Sep 2012 Posts: 11 Rep Power: 13	This is not a problam, actually. You just have to choose one (e.g. the inlet temperature) and stick to it. If you want to be safe, you can always talk about the "Nusselt number calculated using the inlet temperature".

July 13, 2015, 03:28		#3
robro92 New Member roberto Join Date: Jul 2015 Posts: 4 Rep Power: 10	Thanks a lot ! However we solved the doubt..we used the bulk mean temperature close to the outlet, because we have fully developed conditions only there ( at the beginning we have the entry region). So we isolate a small volume there in cfd post