You have to go to surface monitor and define the integral of gaz phase at outlet

Thank you so much about your answer it is very helpful.

There is no problem. Any code (PHOENICS, FLUENT ,etc ) will predict the VOLUME FRACTION of phases everywhere and at the outlet( if I understood you correctly, that is!)

Thanks for all of you, actually I have tried many different times to get distribution of the liquid volume fraction along a horizontal tube , but unfortunately I just got an ''Error: Divergence detected in AMG solver: k'' .I played with the UR as much as possible but there is no change with that the issue still same. any advise to solve this issue. I will much appreciate that .

I am very surprised because your problem is easy for FLUENT or PHOENICS.Test again your input data at inlet

you have to specify the fraction at outlet, you have to go BC and at outlet to choice gaz / multiphase and write the backflow volume fraction

Have you tried under-relaxation?

Yes, I have tried all of them.

Because flow is parabolic do not use BC's at outlet and see what happens.

okay,but in this case do you mean leave the outlet without any setting.

usually, I am using pressure outlet at the outlet Bc.

Try without and let me know please. I presume that at inlet you specify velocity,mass flow rate and volume fractions .Do you?

You have to specify the volume fraction at outlet

In a pipe flow you do not.The program solves "marching" (parabolic,effects downstream do not affect upstream).The volume fraction at outlet will be computed correctly

If you specify the volume fraction at inlet, you have to do it at outlet it will be the same, if you have not phase change in the pipe.

I assume this is a 2D problem not a 1D one.Then the integral will be the same but the distribution may be different and you should not force it..

I have used 3D symmetry plane along pipe and the B.C at inlet is velocity inlet and at the outlet is pressure out let. I set just the pressure at the outlet, solution was converged, but when I set the volume of fraction at the outlet the solution was fluctuated and I could not get the convergence.

I will try to predict how much liquid and gas at outlet to calculate the vapour quality .

I will try to simulate same case with 2D. Looking for same result if it is possible to save time.

I have this problem too,but I don't know how can I define two phases flow, quality in the inlet is x=0.2 and in the outlet is x=1 and which section I have to go for define this quality in Fluent?

 You can extract the vapour quality by the following formula: x=(vapor mass flow rate) / (vapor mass flow rate + liquid mass flow rate).

I extract this from the Fluent Theory guide