It is significant to accurately predict the flow boiling and dryout for the design

safe and reliable operation of once-through steam generators. The once-through steam generator of B&W company is simplified reasonably

the two-fluid three-flow-field mathematical model and wall heat flux partition model are introduced to simulate the flow boiling in actual steam generator based on constant heat flux and coupled method respectively. The results show that:Heat transfer performance declines sharply when dryout occurs

soaring maximum of the wall temperature at constant heat flux is considerable (about 300 K·m-1)

while a soaring maximum of 25 K·m-1 at coupled method

which is consistent with the actual operating process. The subcooled boiling occurs in preheating region at both thermal boundaries and the heat transfer methods near the wall consist of liquid convective

evaporation and quenching heat transfer. The main heat transfer method in nucleate boiling region is evaporation

accompanied with liquid convective and quenching heat transfer. The liquid convective and quenching heat transfer all drop to 0 when dryout occurs and the heat transfer method is vapor phase convective heat transfer in post-dryout heat transfer region.