[turbo]

Please help me completing the pre-processing step for this simple case.

• Inlet (a) : 100% water liquid (with pressure, temperature and flow rate known)
• Inlet (b) : 100% water vapor (with pressure, temperature and flow rate known)
• Outlet : Both are mixed, and all the water vapor from the inlet (b) is expected to be condensed to water liquid before going to the exit.

What I tried is as follows :

• Domain General Option
  • Fluid selection = Water + Water Ideal Gas
• Fluid Models
  • Multiphase Options > Homogeneous Model Checked
  • Heat Transfer > Homogeneous Model Unchecked > Option = Fluid Dependent
  • Turbulence > k-Epsilon with scalable
• Fluid Details
  • Water = Continuous Fluid (with Heat Transfer = None)
  • Water Ideal Gas
    • Morphology = Droplets with Phase Change (*)
    • Heat Transfer = Total Energy
• Fluid Pairs
  • Interface Transfer = Particle Model
  • Mass Transfer = Thermal Phase Change (with Saturation Temperature as input)
• Inlet (a) Boundary
  • Total pressure is given
  • Volume Fraction for Water = 1 and Water Ideal Gas = 0
• Inlet (b) Boundary
  • Total pressure is given
  • Volume Fraction for Water = 0 and Water Ideal Gas = 1
  • Heat Transfer = Static Temperatrue given as input (**)
  • Droplet Number = Specified Diameter given as input (***)
• Outlet Boundary
  • Bulk Mass Flow Rate is given as input

(*) Phase change is only allowed with droplets, even though my case has 100% continuous fluid of water vapor at inlet (b).
(**) No total temperature input is available.
(***) No idea what size of droplets I have to put, because it is continuous fluid in reality.

With those combinations the solution collapses. Could you allow me to get any hints to overcome troubles? I do not think CFX-v11 cannot handle such a simple two-phase calculation.

Many thanks in advance.

[ckleanth]

0) what do you want to do?
1) read the manual especialy on boundary conditions choices and code stability
2) switch the input BC for massflow and output BC for static pressure to get you started

[ghorrocks]

"Simple two-phase calculation"???!!! I don't think so! You are actually doing quite a difficult simulation and it does not surprise me you are having convergence problems. Condensation is a tricky process to model at the best of times.

You might want to consider using a Homogeneous Binary Mixture. Providing the phase change stuff can be treated as equilibrium this does a pretty good job of handling simple phase change. Is this approach valid for you? If your condensation is non-equilibrium then you can't use it.

Whatever approach you use I guarantee it is going to be tricky to get working. Start simply with single phase flows and add the physical models one at a time making sure everything works before adding the next bit.

Glenn Horrocks

[turbo]

ghorrocks :

I appreciate your comments to let me realize my case is challenging. I will follow your suggestion, and if it doesn't work I will have to ask FLUENT people if FLUENT can solve the case.

ckleanth :

You seem to think I am trying to get gold without any effort. If you carefully look into details of CFX manuals for multi-phase parts, you will come to know how poor they are with providing insufficient knowledge.

[ckleanth]

Originally Posted by turbo

You seem to think I am trying to get gold without any effort. If you carefully look into details of CFX manuals for multi-phase parts, you will come to know how poor they are with providing insufficient knowledge.

not at all, its just as if you set the pressure on the outlet you have more chances to converge at that pressure. as for he manuals ; however I do quite like cfx and in many ways i think its better and more versatile than fluent.

[kasuyima]

I encountered the same problem,
I do not kown how to define the meterial of steam and water ?
using constant propertity or using IAPWS Equation of State?
and using Thermal Phase Change,how to define Saturation Temperature?


thanks in advance!!!

[zjh335]

turbo：
have you workd out this difficult simulation？

[foolstop]

Originally Posted by turbo

ghorrocks :

I appreciate your comments to let me realize my case is challenging. I will follow your suggestion, and if it doesn't work I will have to ask FLUENT people if FLUENT can solve the case.

ckleanth :

You seem to think I am trying to get gold without any effort. If you carefully look into details of CFX manuals for multi-phase parts, you will come to know how poor they are with providing insufficient knowledge.

have you succed in the process of condensation?

[wwjshirley]

Originally Posted by ghorrocks

"Simple two-phase calculation"???!!! I don't think so! You are actually doing quite a difficult simulation and it does not surprise me you are having convergence problems. Condensation is a tricky process to model at the best of times.

You might want to consider using a Homogeneous Binary Mixture. Providing the phase change stuff can be treated as equilibrium this does a pretty good job of handling simple phase change. Is this approach valid for you? If your condensation is non-equilibrium then you can't use it.

Whatever approach you use I guarantee it is going to be tricky to get working. Start simply with single phase flows and add the physical models one at a time making sure everything works before adding the next bit.

Glenn Horrocks

how will it do if changing the pure vapor inlet into mixing vapor and saturated water inlet but still another pure water inlet?

Many thanks in advance!

[ghorrocks]

I do not understand your question. Can you say it again more clearly?

[wwjshirley]

Originally Posted by ghorrocks

I do not understand your question. Can you say it again more clearly?

I mean wet steam mix with subcool-water or saturated water

[ghorrocks]

CFX has the IAPWS water properties model built in so it has all the water material properties (including subcooled/superheated regions). It will be a multiphase model with phase change so a challenge at the best of times but it should be possible. But the devil is in the detail - exactly how are you mixing it and what results are you looking for?

[wwjshirley]

Originally Posted by ghorrocks

CFX has the IAPWS water properties model built in so it has all the water material properties (including subcooled/superheated regions). It will be a multiphase model with phase change so a challenge at the best of times but it should be possible. But the devil is in the detail - exactly how are you mixing it and what results are you looking for?

I'm sorry to reply late. I want to know how will the volum of vapor change when they are mixing.