variable Thermal conductivity in Nusselt

ngonbadipoor@yahoo.com · August 8, 2017, 14:36

Hi
I have laminar nanofluid in a pipe under constant heat flux. I need h.d/k to find the local nusselt number. the thermal conductivity is variable along the pipe. is there any method in ansys fluent / post CFD to calculate the Nusselt along the pipe versus location? (like a xy result)
Thanks
Navid

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LuckyTran · August 9, 2017, 02:57

First you need to figure out how to calculate kref(x,y) and Tref(x,y), and in my opinion these are much more difficult problems.

Assuming you have kref and Tref locally, you can define new field functions inside Fluent or inside CFD post and apply the correction factors. You could also do this externally in excel or your favorite programming language after you have exported the necessary values.

However, there's not a simple automatic way to do it. I.e. you can't just tell Fluent to use a reference temperature field and reference conductivity field. Your options in the reference values are limited.

August 8, 2017, 14:36	variable Thermal conductivity in Nusselt	#1
ngonbadipoor@yahoo.com Member NGP Join Date: Mar 2016 Posts: 33 Rep Power: 10	Hi I have laminar nanofluid in a pipe under constant heat flux. I need h.d/k to find the local nusselt number. the thermal conductivity is variable along the pipe. is there any method in ansys fluent / post CFD to calculate the Nusselt along the pipe versus location? (like a xy result) Thanks Navid Sent from my iPad using CFD Online Forum mobile app

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August 9, 2017, 02:57		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	First you need to figure out how to calculate kref(x,y) and Tref(x,y), and in my opinion these are much more difficult problems. Assuming you have kref and Tref locally, you can define new field functions inside Fluent or inside CFD post and apply the correction factors. You could also do this externally in excel or your favorite programming language after you have exported the necessary values. However, there's not a simple automatic way to do it. I.e. you can't just tell Fluent to use a reference temperature field and reference conductivity field. Your options in the reference values are limited.