Volume or Bulk condensation

somas123 · April 10, 2018, 04:07

I am trying to simulate volume or bulk condensation in a cuboid type of enclosure. The image of the geometry is attached below. Initially, the enclosure contains air at 1bar and 120 deg. cel. The lower face is the inlet and all other faces are adiabatic walls. I plan to inject steam with a constant mass flow rate (for 120 s) so that it's partial pressure equals its saturation pressure at 120 deg. cel. Now I don't have a clear idea on how to model this problem so that volume condensation takes place. Is there any tutorial available or has any one done a similar simulation before? I'm planning to use the droplet condensation model in CFX.

ghorrocks · April 10, 2018, 06:46

I don't recall seeing a volume condensation case in the CFX examples. Have a look at the tutorial examples in the ANSYS Customer webpage but I suspect you won't find one. Then contact ANSYS Support as they may well have an example of this available.

By the way, the water won't start condensing at the saturation pressure. You are going to have to super-saturate it to get it to form condensation. How much you have to super-saturate it depends on the nucleation sites in your gas volume. Welcome to the world of non-equilibrium thermodynamics

Gert-Jan · April 10, 2018, 07:07

I think you could get started with a 2-fluid apporach with air and steam-water combination. Look in the help for paragraph 1.2.2.3.4 IAPWS Equation of state
I think you need to use Steam4vl for the vapour-liquid combination. But I am not sure.

Remember that it is an equilibrium model, meaning that CFX assumes equilibrium between vapour and liquid in each numerical element, with might be a fair first assumption. And you have to check whether if air interferes here.

If not, you have to include the mass and heat transfer rates yourself, which can be a significant amount of work.

April 10, 2018, 06:46		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,816 Rep Power: 144	I don't recall seeing a volume condensation case in the CFX examples. Have a look at the tutorial examples in the ANSYS Customer webpage but I suspect you won't find one. Then contact ANSYS Support as they may well have an example of this available. By the way, the water won't start condensing at the saturation pressure. You are going to have to super-saturate it to get it to form condensation. How much you have to super-saturate it depends on the nucleation sites in your gas volume. Welcome to the world of non-equilibrium thermodynamics __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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April 10, 2018, 07:07		#3
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,885 Rep Power: 27	I think you could get started with a 2-fluid apporach with air and steam-water combination. Look in the help for paragraph 1.2.2.3.4 IAPWS Equation of state I think you need to use Steam4vl for the vapour-liquid combination. But I am not sure. Remember that it is an equilibrium model, meaning that CFX assumes equilibrium between vapour and liquid in each numerical element, with might be a fair first assumption. And you have to check whether if air interferes here. If not, you have to include the mass and heat transfer rates yourself, which can be a significant amount of work.