Modeling Internal Fan

elthamer · March 9, 2021, 15:41

I have a simple non-ventilated enclosure where inside this closed box (the fluid domain) there is fan which is used to circulate the air to cool an object generating heat. But since the fan is pulling the air from inside this box it doesn’t make sense that I define the temperature of the inlet & opening of the fan in the boundary condition since that temperature is dependent on the solution (air temperature inside the enclosure).
I was wondering if there is a tutorial available that covers solution dependent expressions for fan cooling simulation. Or a way of coupling the inlet temperature to the air temperature from the solution.
Here’s a brief description of my model:

The volume where the fan is occupied is cut out. Here, there are: walls, one face for fan intake and one face for fan opening.
For the “opening” side (back of the fan) I am using: 0 Pa pressure with a guess value of what the air temperature going in is (this needs to be corrected since this should be solution dependent)
For the "inlet" side (flow into the fluid domain), I am using: mass flow rate (toward the fluid domain) with a guess value of what the air temperature going out is (this also needs to be corrected since this should be solution dependent)
For the remaining faces (wall sides), I assigned a constant heat flux to represent the heat dissipation of the fan.

I am using CFX. Any help or tips on how to correctly simulate this would be greatly appreciated.

Thanks,
Thamer

ghorrocks · March 9, 2021, 17:04

You are not modelling this a good way. The best way to model the fan is to use a momentum source term. That way the heat is automatically taken care of, and all you do is use the source term to apply the amount of momentum to the fluid to represent the fan.

elthamer · March 9, 2021, 17:16

Ah, I see. I will try what you suggested. Thanks for replying ghorrocks.

elthamer · March 9, 2021, 18:02

For anyone who is interested in learning how to model a fan using momentum source term and fan curve I found this video very helpful.

https://www.youtube.com/watch?v=Q-mMbt_3CCc

aero_head · March 9, 2021, 22:33

Quote:

Originally Posted by elthamer

For anyone who is interested in learning how to model a fan using momentum source term and fan curve I found this video very helpful.

https://www.youtube.com/watch?v=Q-mMbt_3CCc

Hello Thamer,

Thanks for this addition!

March 9, 2021, 15:41	Modeling Internal Fan	#1
elthamer New Member Thamer Hussein Join Date: Mar 2015 Posts: 3 Rep Power: 11	I have a simple non-ventilated enclosure where inside this closed box (the fluid domain) there is fan which is used to circulate the air to cool an object generating heat. But since the fan is pulling the air from inside this box it doesn’t make sense that I define the temperature of the inlet & opening of the fan in the boundary condition since that temperature is dependent on the solution (air temperature inside the enclosure). I was wondering if there is a tutorial available that covers solution dependent expressions for fan cooling simulation. Or a way of coupling the inlet temperature to the air temperature from the solution. Here’s a brief description of my model: The volume where the fan is occupied is cut out. Here, there are: walls, one face for fan intake and one face for fan opening. For the “opening” side (back of the fan) I am using: 0 Pa pressure with a guess value of what the air temperature going in is (this needs to be corrected since this should be solution dependent) For the "inlet" side (flow into the fluid domain), I am using: mass flow rate (toward the fluid domain) with a guess value of what the air temperature going out is (this also needs to be corrected since this should be solution dependent) For the remaining faces (wall sides), I assigned a constant heat flux to represent the heat dissipation of the fan. I am using CFX. Any help or tips on how to correctly simulate this would be greatly appreciated. Thanks, Thamer

March 9, 2021, 17:04		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You are not modelling this a good way. The best way to model the fan is to use a momentum source term. That way the heat is automatically taken care of, and all you do is use the source term to apply the amount of momentum to the fluid to represent the fan. aero_head likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 9, 2021, 18:02		#4
elthamer New Member Thamer Hussein Join Date: Mar 2015 Posts: 3 Rep Power: 11	For anyone who is interested in learning how to model a fan using momentum source term and fan curve I found this video very helpful. https://www.youtube.com/watch?v=Q-mMbt_3CCc evcelica and aero_head like this.

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March 9, 2021, 17:16		#3
elthamer New Member Thamer Hussein Join Date: Mar 2015 Posts: 3 Rep Power: 11	Ah, I see. I will try what you suggested. Thanks for replying ghorrocks.