Abstract:

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.

Key words: heat transfer, multiphase flow, coupled method, dryout, heat flux partition, phase change

摘要：

准确预测直流蒸汽发生器流动沸腾及蒸干对其设计、安全可靠运行极其重要。通过对B&W公司直流蒸汽发生器进行合理简化，引入两流体三流场数学模型及壁面热通量分区模型，分别进行基于常热通量和耦合传热的蒸汽发生器流动沸腾数值模拟。结果表明：蒸干发生时传热性能急剧下降，常热通量边界下壁温升高的幅度相当大（约300 K·m^-1），而耦合传热边界下壁温飞升幅度约为25 K·m^-1，与实际情形相一致；两种热边界中预热区会发生过冷沸腾，壁面处传热由液相对流换热、淬火换热和蒸发换热3部分构成，核态沸腾区蒸发换热为主要换热方式，同时伴随着液相对流换热和淬火换热，蒸干发生时淬火换热和蒸发换热全部降到0，在蒸干后传热区域换热方式为气相对流换热。

关键词: 传热, 多相流, 耦合方式, 蒸干, 热流分区, 相变