核动力直管式直流蒸汽发生器蒸干传热机理研究

Dryout is a limited phenomenon which has a direct effect on the safe reliability of once- through steam generator (OTSG). Therefore it is important for safety analysis of the OTSG to predict accurately the heat transfer mechanism of dryout and post-dryout. This project aims at studying the impact of operation parameters in the primary and secondary loop on the dryout heat transfer characters of OTSG, and then offers a theoretical guarantee to prevent steam generator tube raptures..It is considered as the pointcut to reveal the mechanism of dryout heat transfer in the OTSG. The straight tube OTSG experimental device is established to carry out experiments to study the dryout heat transfer by the dielectric heating. The impact of key parameters in the primary and secondary loop on the dryout heat transfer in the OTSG is to be revealed by the method of high-dimensional experimental data processing adopting statistical techniques and curve characteristic techniques. The two-fluid three-filed mathematical model of dryout heat transfer is planed to built after determining the correlating equations about the source term of mass and heat transfer applied to coupling heat transfer based on the proper boundary condition reflecting interaction and coupling of the primary and secondary loop. The characteristics of dryout heat transfer and the influence of dryout on the heat transfer performance of the OTSG are to be revealed through the full-range numerical simulation of the actual OTSG based on the approximation modeling method. Ultimately the model and method of predicting the dryout heat transfer on the basis of the coupling of the primary and secondary loop in the OTSG ought to be proposed.

蒸干是直接影响直流蒸汽发生器安全可靠性的一个重要限制现象，因此准确预测蒸干和蒸干后传热特性对直流蒸汽发生器的安全分析至关重要。本项目研究一、二回路运行参数对直流蒸汽发生器蒸干传热特性的影响规律，进而为防止蒸汽发生器传热管破损提供理论保障。.本课题以揭示直流蒸汽发生器蒸干传热机理为切入点，建设直管直流蒸汽发生器蒸干传热实验台，进行介质加热条件下直流蒸汽发生器蒸干传热实验研究，利用统计学技术与曲线特征化技术进行高维实验数据处理的方法，揭示一、二回路关键参数对直流蒸汽发生器蒸干传热的影响规律；引入反映一、二回路互扰与耦合的适当的边界条件，确立适用于一、二回路耦合传热的质量与能量传递源项的准则关联式，得到表征蒸干传热的两流体三流场数学模型；基于近似模化法进行实际直流蒸汽发生器全范围数值模拟，揭示其蒸干传热特征及蒸干对传热性能的影响。最终提出基于一、二回路耦合的直流蒸汽发生器蒸干传热预测模型与方法。

随着压水堆核动力系统对蒸汽发生器效率和体积的要求越来越高，直管式直流蒸汽发生器以高效率、结构紧凑和模块化建造等优点受到国际上的广泛关注。直管式直流蒸汽发生器二次侧流体经历从过冷水被加热到过热蒸汽的复杂汽液两相流动与换热过程，不可避免地发生蒸干传热恶化现象。蒸干的发生导致二次侧流体与管壁间的表面传热系数急剧下降，壁温急剧上升，使传热管束更易遭受应力腐蚀和老化失效等问题。目前研究以定热流加热方式下直管内蒸干为主，尚缺乏针对实际直流蒸汽发生器内蒸干的预测。因此开展直流蒸汽发生器蒸干及蒸干后传热特性研究对其安全稳定运行具有重要意义。.本文以Babcock & Wilcox公司设计的直管式直流蒸汽发生器为原型，基于近似模化法建立其简化的三维单元管物理模型。在此基础上，建立能够准确描述直流蒸汽发生器单相对流换热与传热管导热的数学模型和二次侧汽液两相流动与换热数学模型，并补充流场间质量、动量、能量传递以及流场与壁面间相互作用的封闭关联式，进行了如下研究：.针对实际直管式直流蒸汽发生器蒸干及蒸干后传热特性，分别进行了基于拟合热流和一、二次侧耦合换热的研究。耦合换热边界下二次侧壁温飞升幅度较小（约26 K），壁温轴向变化率仅为几十K/m。与此相比，定热流边界下不仅蒸干位置较耦合换热边界提前，而且蒸干发生处壁温轴向变化率高达几百K/m。这意味着对于涉及到蒸干的直流蒸汽发生器或换热设备，要重点关注蒸干传热恶化引起的较高的壁温轴向变化率以及可能由此引发的应力腐蚀、甚至烧毁问题。.针对直管式直流蒸汽发生器不同工况和支撑板结构下的蒸干特性，研究了运行参数和支撑板对蒸干及蒸干后传热的影响。研究发现质量流速对蒸干后壁温的影响规律与偏离核态沸腾相反，这是由于发生两类传热恶化的机理不同所致。压力影响蒸干位置及蒸干处的壁温飞升幅度，随压力的增大蒸干位置逐渐向下游移动，相应的壁温飞升幅度减小。有支撑板且考虑缝隙时的滑速比低于其他两种结构，并且蒸干位置位于不考虑支撑板时的上游。支撑板下游漩涡产生的强化换热效应能够在一定程度上降低蒸干引起的壁温飞升，定热流边界条件下壁温飞升幅度由不考虑支撑板时的300 K降低到约200 K，并且壁温轴向变化率减小。这说明流道间布置的支撑结构在一定程度上有利于降低壁面温度。