What are the challenges of designing for two-phase flow?

Two-phase flow challenges: Flow regime identification - stratified, slug, annular, mist flow have different characteristics; use Baker chart or similar. Pressure drop - higher than single-phase; methods include Lockhart-Martinelli, Beggs and Brill for pipes; must consider elevation effects. Slug flow - cyclic surging, structural vibration, control upsets; avoid or mitigate with slug catchers. Line sizing - consider maximum velocity (erosional), minimum velocity (liquid accumulation). Slug catcher sizing - accumulate liquid from slug while maintaining continuous flow to downstream. Control - level control on separators challenged by slugging. Safety - relief sizing for two-phase more complex (HEM, omega method). Special considerations: risers (liquid holdup), downcomers (flooding), heat exchangers (maldistribution). Use specialized software (OLGA, PIPEPHASE) for complex systems.