[argenisbnl]

Hello everyone, I'm simulating a double pipe counterflow heat exchanger (2D axisymetrical), my thermal boundaries conditions are inlet temperatures, and I want to get heat flux along the pipe to then calculate Nusselt number along the pipe.
I'm not trying to find the total heat flux, I want to get heat flux at every x location (along the pipe), and then calculate Nusselt number at every x location (along the pipe). Is there anyway I can get this?
Again, I'm not trying to get what you find in heat transfer literature, where Nu sub x is Nusselt number untill that x location, I want to get Nusselt number AT that x location in this way:
q=h*ΔT ;
Nu= hD/k;
Nu= q*D/(ΔT*k)

So, if I can get heat flux (q) at any x location I would be able to find Nusselt number at any x location along the pipe. That's what I have in mind, and I would like to know if this is possible. (No matter if I have to use a UDF).

[evcelica]

Check out the FAQs:
https://www.cfd-online.com/Wiki/Ansy...ficient_in_CFX

[argenisbnl]

Can I do that in fluent? I don't know much cfx

[ztdep]

Originally Posted by argenisbnl

Hello everyone, I'm simulating a double pipe counterflow heat exchanger (2D axisymetrical), my thermal boundaries conditions are inlet temperatures, and I want to get heat flux along the pipe to then calculate Nusselt number along the pipe.
I'm not trying to find the total heat flux, I want to get heat flux at every x location (along the pipe), and then calculate Nusselt number at every x location (along the pipe). Is there anyway I can get this?
Again, I'm not trying to get what you find in heat transfer literature, where Nu sub x is Nusselt number untill that x location, I want to get Nusselt number AT that x location in this way:
q=h*ΔT ;
Nu= hD/k;
Nu= q*D/(ΔT*k)

So, if I can get heat flux (q) at any x location I would be able to find Nusselt number at any x location along the pipe. That's what I have in mind, and I would like to know if this is possible. (No matter if I have to use a UDF).

of couse, you can do that. creat a line in fluent along the boundary, then report the heat flux , and write to a file.

[LuckyTran]

The surface heat flux is readily available is it not?


But since Nusselt number isn't a field variable, you do have do something special to convert the heat flux into Nusselt number. I.e. export it out of Fluent and then calculate it, or you must use a udf to calculate it within Fluent.

[argenisbnl]

Originally Posted by LuckyTran

The surface heat flux is readily available is it not?


But since Nusselt number isn't a field variable, you do have do something special to convert the heat flux into Nusselt number. I.e. export it out of Fluent and then calculate it, or you must use a udf to calculate it within Fluent.

Yes, I'm going to get heat flux this way: q= k*dT/dY, and then Nusselt Number (out of fluent). I have only one doubt, dT/dY is calculated as dT/dR when the axisymmetric condition is enabled?

[ztdep]

Originally Posted by argenisbnl

Yes, I'm going to get heat flux this way: q= k*dT/dY, and then Nusselt Number (out of fluent). I have only one doubt, dT/dY is calculated as dT/dR when the axisymmetric condition is enabled?

The heat flux is available, is is a default quantity in FLUENT.