Two phase momentum
 

Can anybody please clarify what is [vi] (velocity transported across interface) in the momentum conservation equation [see picture below]?

I have two phase stratified flow with almost stagnant water (v=0.03 m/s) and steam enters at 10 m/s. Steam is condensing at the interface. Ag and Al are constant along the channel.

What should I enter as [vi] for gas phase and what for liquid phase?


http://wins.engr.wisc.edu/teaching/mpfBook/img83.gif