Pipe Flow Expert does not calculate the pressure drop for two-phase flow. 


When two different fluids (or two different fluid states) exist together, it is possible that two-phase flow may occur at some point in a system. Flows transitioning from pure liquid to vapor as a result of external heating can lead to two-phase flow. Two-phase flow can produce an extremely high pressure drop that is many times greater than the pressure drop from either individual fluid phase. The user should make due allowance for any two-phase flow pressure drop, possibly by using a component to add an appropriate additional pressure loss.