modelling liquid-vapour multiphase in an eveporator
 

Hi everyone
I am trying to model liquid-vapour multiphase in an evaporator. the evaporation process takes place under vacuum. the evaporator has two outlets one on the top to collect the vapour and another down to pass the liquid to another chamber. I have tried Mixture and Eulerian models and both gave me a reverse flow at the vapour outlet. Both outlets at (-50000 pascal) gauge pressure and the operating pressure is 53000 pa. I need your help to find out how to avoid the reverse flow .
Many thanks