Why is my heat transfer so bad?

federernadal · April 1, 2016, 18:00

Trying to model a coil. Coil is a rectangular plate that I modeled as a porous domain. Did an isothermal heat transfer on the coil with -20F.

Then did an enclosure for the air. Fluid domain. Had air coming in at 70F.

Why am I getting such poor heat transfer?

ghorrocks · April 2, 2016, 06:36

You will need to provide more information for us to help.

What do you mean by "Did an isothermal heat transfer on the coil with -20F"? Why did you do this and what did it tell you?

Regarding "Why am I getting such poor heat transfer?" - heat transfer between what? Poor relative to what? What results are you comparing to?

federernadal · April 2, 2016, 12:28

So I create a rectangular plate to model an evaporator (cooling) coil. Then I enclose it with air.

Basically air comes in at 70 degree fahrenehit, and the idea is that it should go through the coil (right side of the coil plate) and become cold (on the left side of the coil plate).

I made the coil (rectangular plate), a porous domain that was isothermal and -20degree Fahrenheit.

The BCs are pretty straightforward from the images - air flows in with specified mass flow rate (at 70 deg F), and leaves at P=0 static pressure.

Why is my air not cooling when it goes through the coil (porous domain)?

ghorrocks · April 3, 2016, 06:28

What version of CFX are you using? I don't think heat transfer between porous solids and the fluid is supported in some older versions.

federernadal · April 3, 2016, 13:11

R15.0 Professional.

federernadal · April 4, 2016, 09:21

Ok, I seem to be getting heat transfer by modeling the faces of the coil (porous plate) as Walls with a specified (cold) temperature.

Is that the right approach?

ghorrocks · April 4, 2016, 18:09

That depends on what you are trying to achieve. It does not appear you are getting any heat transfer from the porous domain to the fluid, but if this approach is OK then feel free to use it.

federernadal · April 6, 2016, 18:09

In this paper, on the top of page 435, when he says "creating cavity domain", is he creating an enclosure or an Add frozen? Any boolean subtracts?

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April 2, 2016, 06:36		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You will need to provide more information for us to help. What do you mean by "Did an isothermal heat transfer on the coil with -20F"? Why did you do this and what did it tell you? Regarding "Why am I getting such poor heat transfer?" - heat transfer between what? Poor relative to what? What results are you comparing to?

April 2, 2016, 12:28		#3
federernadal Member Join Date: Oct 2015 Posts: 56 Rep Power: 10	So I create a rectangular plate to model an evaporator (cooling) coil. Then I enclose it with air. Basically air comes in at 70 degree fahrenehit, and the idea is that it should go through the coil (right side of the coil plate) and become cold (on the left side of the coil plate). I made the coil (rectangular plate), a porous domain that was isothermal and -20degree Fahrenheit. The BCs are pretty straightforward from the images - air flows in with specified mass flow rate (at 70 deg F), and leaves at P=0 static pressure. Why is my air not cooling when it goes through the coil (porous domain)?

April 3, 2016, 06:28		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	What version of CFX are you using? I don't think heat transfer between porous solids and the fluid is supported in some older versions.

April 3, 2016, 13:11		#5
federernadal Member Join Date: Oct 2015 Posts: 56 Rep Power: 10	R15.0 Professional.

April 4, 2016, 09:21		#6
federernadal Member Join Date: Oct 2015 Posts: 56 Rep Power: 10	Ok, I seem to be getting heat transfer by modeling the faces of the coil (porous plate) as Walls with a specified (cold) temperature. Is that the right approach?

April 4, 2016, 18:09		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	That depends on what you are trying to achieve. It does not appear you are getting any heat transfer from the porous domain to the fluid, but if this approach is OK then feel free to use it.

April 6, 2016, 18:09		#8
federernadal Member Join Date: Oct 2015 Posts: 56 Rep Power: 10	In this paper, on the top of page 435, when he says "creating cavity domain", is he creating an enclosure or an Add frozen? Any boolean subtracts?