How to write a udf of htc function in fluent

ymya · July 21, 2021, 06:11

Hi everyone...
I have a function of heat transfer coefficient

htc=(0.0487)+(0.581)V-(0.00646) V^2

where V is the velocity of air, and its value should extract from the solver of fluent first, and then substituted it in the function above to compute the value of htc at different velocities. How could I write this function in UDF to compile it in fluent?

pakk · July 21, 2021, 15:30

Do you use a no-slip BC at the wall? Hick makes your velocity zero? In that case, HTC is also zero...

Be clear about which V you are exactly talking!

ymya · July 21, 2021, 23:44

Thank you very much for replay...
Yes, I use a no-slip BC at the wall. But the HTC that I want is overall my domain (that is, in every cell in the domain).

pakk · July 22, 2021, 01:17

Sure, you can calculate a HTC everywhere, but isn't the only place where it is used for anything at a solid-fluid interface?

In my view, you are just requesting a complicated way to get adiabatic conditions...

ymya · July 22, 2021, 01:57

I have a file including a porous medium with heat transfer. And in a second file I test the HTC that must be in the porous medium with different velocities by making a real wall and fluid (without porous medium in second file). Finally, I get the function which I wrote above…

In the first file, the values of velocities is unknown (it depending on the operating fluid). What did you think should I do? I’m really appreciate your reply... thank you very much.

pakk · July 22, 2021, 02:41

Quote:

Originally Posted by ymya

And in a second file I test the HTC that must be in the porous medium with different velocities by making a real wall and fluid (without porous medium in second file).

Different velocities where? At the wall? Far away? At the inlet?

Be clear about which V you are exactly talking!

ymya · July 22, 2021, 04:08

At inlet, in the second file the domain is very simple, just a vertical rectangular, the outlet and inlet at top and bottom respectively, and thermal wall at one side. And then I want to apply the above function at the wall of the first domain. Can I do that

pakk · July 22, 2021, 10:00

Heat transfer is best described by local properties. Not by velocities at a distance... So I don't understand why you decided to link the heat transfer at the wall to the velocity at the inlet. It's like coupling the HTC to the free disk space on your hard drive. Sure, you could do it, but why? A local property, such as wall shear stress or velocity gradient at the wall, makes much more sense...

Edit: but possibly I completely misunderstand the porous zone. Probably.

ymya · July 22, 2021, 12:50

thank you pakk... thank you very much for your reply.

July 21, 2021, 06:11	How to write a udf of htc function in fluent	#1
ymya New Member Younus M. Younus Join Date: Aug 2020 Location: Iraq Posts: 7 Rep Power: 6	Hi everyone... I have a function of heat transfer coefficient htc=(0.0487)+(0.581)V-(0.00646) V^2 where V is the velocity of air, and its value should extract from the solver of fluent first, and then substituted it in the function above to compute the value of htc at different velocities. How could I write this function in UDF to compile it in fluent?

July 21, 2021, 15:30		#2
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	Do you use a no-slip BC at the wall? Hick makes your velocity zero? In that case, HTC is also zero... Be clear about which V you are exactly talking! ymya likes this. __________________ "The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform" is NOT the error after compiling. It is the error after loading. To see compiler errors, look at your screen after you click "build".

July 21, 2021, 23:44	How to write a udf of htc function in fluent	#3
ymya New Member Younus M. Younus Join Date: Aug 2020 Location: Iraq Posts: 7 Rep Power: 6	Thank you very much for replay... Yes, I use a no-slip BC at the wall. But the HTC that I want is overall my domain (that is, in every cell in the domain).

July 22, 2021, 01:17		#4
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	Sure, you can calculate a HTC everywhere, but isn't the only place where it is used for anything at a solid-fluid interface? In my view, you are just requesting a complicated way to get adiabatic conditions... ymya likes this. __________________ "The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform" is NOT the error after compiling. It is the error after loading. To see compiler errors, look at your screen after you click "build".

July 22, 2021, 01:57	How to write a udf of htc function in fluent	#5
ymya New Member Younus M. Younus Join Date: Aug 2020 Location: Iraq Posts: 7 Rep Power: 6	I have a file including a porous medium with heat transfer. And in a second file I test the HTC that must be in the porous medium with different velocities by making a real wall and fluid (without porous medium in second file). Finally, I get the function which I wrote above… In the first file, the values of velocities is unknown (it depending on the operating fluid). What did you think should I do? I’m really appreciate your reply... thank you very much.

July 22, 2021, 04:08		#7
ymya New Member Younus M. Younus Join Date: Aug 2020 Location: Iraq Posts: 7 Rep Power: 6	At inlet, in the second file the domain is very simple, just a vertical rectangular, the outlet and inlet at top and bottom respectively, and thermal wall at one side. And then I want to apply the above function at the wall of the first domain. Can I do that

July 22, 2021, 10:00		#8
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	Heat transfer is best described by local properties. Not by velocities at a distance... So I don't understand why you decided to link the heat transfer at the wall to the velocity at the inlet. It's like coupling the HTC to the free disk space on your hard drive. Sure, you could do it, but why? A local property, such as wall shear stress or velocity gradient at the wall, makes much more sense... Edit: but possibly I completely misunderstand the porous zone. Probably. __________________ "The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform" is NOT the error after compiling. It is the error after loading. To see compiler errors, look at your screen after you click "build".

July 22, 2021, 12:50		#9
ymya New Member Younus M. Younus Join Date: Aug 2020 Location: Iraq Posts: 7 Rep Power: 6	thank you pakk... thank you very much for your reply.

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