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[rohitroxkp7]

Hello all,

I have performed a multiphase simulation where there are three phases...water, R134a gas, and R134a liquid. The Liquid is a primary phase, the other two being secondary phases.

In the images, it can be seen that it's a counter-flow type heat exchanger. In the water domain, however, towards the exit when the gas volume fraction result is turned on in the CFD postprocessor, the region near the outlet of the water domain shows traces of R134a gas. How is this possible in a domain where only water liquid flows?

Also, since there is a gas volume fraction present, the refrigerant liquid volume fraction also shows similar trends in the same spots in the water liquid domain. The simulation is axisymmetric type.

Boundary conditions: [Ref means Refrigerant]

Ref inlet: velocity type. The volume fraction of gas is 1, water is zero.

Water inlet: velocity type. Vol fraction of water is 1, gas is zero.

Both outlets are pressure types.

Side walls are adiabatic, the topmost wall has convection BC and inner walls are coupled. Problem is multiphase type with volume fraction and conjugate heat transfer.

I would appreciate any answer to this.

Thanks.

[Karthik Remella]

Hello Are you experiencing any reversed flow in your simulation? What is the backflow volume fraction you have specified at your pressure outlet bc?
Karthik

[DrAmine]

You need to define a mixture of water liquid and R134a liquid. That mixture will be your liquid-phase In the water domain you fix the mass fraction of R134a liquid to zero.

[rohitroxkp7]

I understood the issue, the initial few time steps had some refrigerant volume fraction initialized at t=0s in the solver. Hence those values.

[rohitroxkp7]

The water domain needed to be patched with purely water

[DrAmine]

Yes, there you set the mass fraction of pure water to 1 or the refrigerant mass fraction to 0.