Two phase pressure drop in plain tube

This is a very tricky problem, especially if you have condensation/ evaporation happening inside your control volume.

It sounds like too many variables and unknowns. Even CFD FEA will not have any fidelity if you don't give it correct input.

If one phase seems predominant, you might try a rough estimate by neglecting the other. Add a generous uncertainty margin. If you can experiment, then you can validate whatever calculation results...

You might also try 'Waermeatlas' (German handbook, also translated into english). I don't remeber right now, but it might have some simple approximate calculation for your case.

Hope this helps.

Thans for your interest and recommendations I use VDI Atlas it is not comprehensive about this subjet.

I find some 7 correlations about this subject and I try them.

have nice day