[raskolnikov]

Hi everyone,

i have an issue with my basic condensation model on star ccm+. My problem is following:

the heat exchanger to condensate the water-vapor consists of an inlet and two outlets for the vapor phase. I have already defined air and water-vapor as multi-component gases at the inlet (air is here for definition of an inert gas). There I have to also define their specific mass fractions for initial conditions (air: 0.001, vapor: 0.999 related to Evaporation/Condensation Model).

So the phase change will occur by an amount of heat transfer to the cold fluid. For that i have naturally an another liquid region, which is surrounded by solid pipes. Actually it is a simple heat exchanger model. So the mass fraction of the liquid must be also entered at the fluid physics. (water: 0.001, otherweise i get the error: sum of mass fraction is zero)

The gas flow enters the heat exhanger at over 100 degrees (it doesnt matter now) with a defined velocity.

The problem is not to understand how to define the phase conditions (mass fractions) and volume fractions at the inlet boundary condition for the gas flow.

At the boundary conditions i have defined the same values as at initial conditions. So i can start my simulation with given boundary conditions but the solution is not realistic because i cant observe a phase change. Also the mass and volume fractions stay constant how i defined them at the initial or boundary conditions. No phase change!

I would be glad if you help me at this point. Thanks all of you!

[me3840]

If there is no phase change occurring then you either do not have sufficient cooling or the multiphase models are not set up for condensation correctly. What multiphase model are you using here?

[raskolnikov]

Hey me3840, thanks for your post. I want to give some details about my settings. Maybe you are right that I have chosen the wrong physics models. As you see at the pictures, I have defined a VOF-VOF Phase Interaction.

At the inital conditions of eulerian phases are the species mass fractions:

Air: 0.001
H20-Vapor: 0.999
Water: 0.001 (i cant not assume 0, -- Error: sum of mass fractions is Zero)

The same values for mass fractions i have also defined at the gas inlet boundary condition.

I am sure that in my case the temperature of vapor decreases under 100 degree to occur the phase change, so I think my mistake ist at the model definition (wrong mass fractions, physics or initial conditions?).

Also i couldnt unterstand why i have to define the volume fractions at inlet if i have already given the mass fractions values on physics or boundary conditions?!

[linxi]

The Multi-Component Liquid just H2O(F),it is ok to run?

[CFD2DXY]

Originally Posted by raskolnikov

Hey me3840, thanks for your post. I want to give some details about my settings. Maybe you are right that I have chosen the wrong physics models. As you see at the pictures, I have defined a VOF-VOF Phase Interaction.

At the inital conditions of eulerian phases are the species mass fractions:

Air: 0.001
H20-Vapor: 0.999
Water: 0.001 (i cant not assume 0, -- Error: sum of mass fractions is Zero)

The same values for mass fractions i have also defined at the gas inlet boundary condition.

I am sure that in my case the temperature of vapor decreases under 100 degree to occur the phase change, so I think my mistake ist at the model definition (wrong mass fractions, physics or initial conditions?).

Also i couldnt unterstand why i have to define the volume fractions at inlet if i have already given the mass fractions values on physics or boundary conditions?!

I have the same Problem.. Do you fix it?
Maybe one another have an idea ;-)

CFD2DXY

[AutoCFD]

Any resolution to this? I also have a similar problem.