What special considerations apply when designing heat exchangers for two-phase flow?

Two-phase challenges: flow regime transitions (stratified, slug, annular affect heat transfer and pressure drop), maldistribution between parallel tubes/channels, phase separation at headers, and varying heat transfer coefficient along flow path. For evaporators: avoid dryout (critical heat flux limitation), maintain adequate velocity for annular flow in tubes. For condensers: proper drainage, avoid flooding (vapor-liquid counterflow). Design requires mechanistic models (not single-phase correlations), careful header design, and often pilot testing for critical applications.