How to insert a heat source only in the fluid part of a fluid-air domain?

milabvieira · August 20, 2015, 07:19

Dear all,

I am dealing with a problem in which I have to insert a source only in the fluid domain of a fluid-air system. So far I have created an expression which is written below:

304 [W/m^3]*Fluid 1.Volume Fraction

After few interactions I checked in my output file if the power in each domain where I've inserted the source corresponded to the correct power. Indeed, the power was correct for the Fluid part of each domain, but in the air part, which should not contain any power, it also contained a power (19% of the power in the Fluid part).

Therefore, I would like to know if anyone here could help me to understand why does this power, in the air part of the domain, appear and how to prevent this to happen, since I am interested in put a heat source term in the fluid part only.

Thank you very much in advance.

Camila

Opaque · August 20, 2015, 10:05

Not sure about your multiphase setup details, i.e. homogeneous or not. However, is the fluid dependent sources tab available ? if so, you only add the source to the fluid of interest.

milabvieira · August 20, 2015, 10:33

Thank you for your comment.

Actually I have a porous domain, in which the free surface is an interface to air. The source which should only be in the fluid, located in the porous region, is an uniform volumetric heat source. Therefore, I have created a subdomain (inside my domain which contains the porous region and air on top of it) with Energy Source corresponding to the following expression:

304 [W/m^3]*Fluid 1. VolumeFraction (1)

The idea of multiplying the volumetric source by the Fluid 1. VolumeFraction is an attempt to guarantee that the source would only be applied in the volume where there is fluid. For the part of the domain without fluid, only air, the source should be 0, since Fluid 1.VolumeFraction is zero.

However, I have not observed that in my output file, once I have also seen in my results that I have power been generated in the air.

Could you please explain why does this power appear in the air region? Would my approach (Eqn. 1) be defined in a wrong way? What would be a better way to define my uniform volumetric heat source only in the porous domain with the fluid and avoid any power to be in the air part of my domain?

Thank you very much for your help!

Camila

ghorrocks · August 20, 2015, 18:26

The approach you describe should work as far as I know.

But keep in mind at the interface (or any mixed region) the VF will be an intermediate value, so the air in this region will get heated. This air will convect away and heat the bulk air.

To get around this you could replace Fluid 1.volumefraction with something like (Fluid 1.volumefraction)^10. This would only heat the regions which are just about pure water and any significant amount of air would stop the heating.

milabvieira · August 21, 2015, 07:09

Thank you very, very much!!

August 20, 2015, 07:19	How to insert a heat source only in the fluid part of a fluid-air domain?	#1
milabvieira New Member Camila Braga Vieira Join Date: Apr 2012 Posts: 9 Rep Power: 14	Dear all, I am dealing with a problem in which I have to insert a source only in the fluid domain of a fluid-air system. So far I have created an expression which is written below: 304 [W/m^3]*Fluid 1.Volume Fraction After few interactions I checked in my output file if the power in each domain where I've inserted the source corresponded to the correct power. Indeed, the power was correct for the Fluid part of each domain, but in the air part, which should not contain any power, it also contained a power (19% of the power in the Fluid part). Therefore, I would like to know if anyone here could help me to understand why does this power, in the air part of the domain, appear and how to prevent this to happen, since I am interested in put a heat source term in the fluid part only. Thank you very much in advance. Camila

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August 20, 2015, 10:05		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	Not sure about your multiphase setup details, i.e. homogeneous or not. However, is the fluid dependent sources tab available ? if so, you only add the source to the fluid of interest.

August 20, 2015, 10:33		#3
milabvieira New Member Camila Braga Vieira Join Date: Apr 2012 Posts: 9 Rep Power: 14	Thank you for your comment. Actually I have a porous domain, in which the free surface is an interface to air. The source which should only be in the fluid, located in the porous region, is an uniform volumetric heat source. Therefore, I have created a subdomain (inside my domain which contains the porous region and air on top of it) with Energy Source corresponding to the following expression: 304 [W/m^3]*Fluid 1. VolumeFraction (1) The idea of multiplying the volumetric source by the Fluid 1. VolumeFraction is an attempt to guarantee that the source would only be applied in the volume where there is fluid. For the part of the domain without fluid, only air, the source should be 0, since Fluid 1.VolumeFraction is zero. However, I have not observed that in my output file, once I have also seen in my results that I have power been generated in the air. Could you please explain why does this power appear in the air region? Would my approach (Eqn. 1) be defined in a wrong way? What would be a better way to define my uniform volumetric heat source only in the porous domain with the fluid and avoid any power to be in the air part of my domain? Thank you very much for your help! Camila

August 20, 2015, 18:26		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The approach you describe should work as far as I know. But keep in mind at the interface (or any mixed region) the VF will be an intermediate value, so the air in this region will get heated. This air will convect away and heat the bulk air. To get around this you could replace Fluid 1.volumefraction with something like (Fluid 1.volumefraction)^10. This would only heat the regions which are just about pure water and any significant amount of air would stop the heating.

August 21, 2015, 07:09		#5
milabvieira New Member Camila Braga Vieira Join Date: Apr 2012 Posts: 9 Rep Power: 14	Thank you very, very much!!