非能动余热排出热交换器流动和传热数值模拟

Numerical simulation of flow and heat transfer characteristic in passive residual heat removal heat exchanger

非能动余热排除系统(Passive Residual Heat Removal system,PRHR)是非能动核电厂的重要安全设施,在全厂断电事故下,大部分的堆芯衰变热是通过PRHR热交换器传递至内置换料水箱(In-containment Refueling Water Storage Tank,IRWST)。但PRHR热交换器属于大型非稳态换热器,其传热机理十分复杂。基于PRHR系统的重要性和复杂性,有必要研究PRHR系统的流动和传热特性。利用计算流体动力学(Computational Fluid Dynamics,CFD)软件针对非能动堆芯冷却系统试验装置中的PRHR系统进行建模计算,分析了PRHR热交换器及IRWST的流动和传热特性,发现IRWST内部沿垂直高度上呈现明显的温度分层现象,温度沿水平方向的分布趋于均匀;IRWST内部的流动主要是沿着C型传热管竖直段向上流动,流速逐渐增大,但在两相阶段,水箱上部区域流动明显增强;C型传热管上部水平段和竖直段上部区域的换热系数要明显高于其它区域,且在上部水平段与竖直段连接弯管处换热系数最大,在两相阶段,上部区域的换热系数明显增大。

Background： The passive residual heat removal system （PRHR） is an important safety facility for passive nuclear power plants. In the station blackout accident, most of the core decay heat is transferred to the in-containment refueling water storage tank through PRHR heat exchanger to ensure the safety of nuclear reactors. The transfer process of PRHR heat exchanger is not steady, and the transfer mechanism is very complex. Purpose： This study aims at the flow and heat transfer characteristics of the PRHR system by computational analysis. Methods： The computational fluid dynamics （CFD） software was employed to establish the geometric model for PRHR in the passive reactor cooling system test facility, and the physical model （turbulence, thermal phase change） and boundary conditions were defined for numerical calculation. Results： The temperature field, velocity field and heat transfer coefficient of the heat transfer tubes in in-containment refueling water storage tank （IRWST） were obtained, and their regularities were analyzed. Conclusions： Obvious temperature stratification phenomenon was found along the vertical height, and the temperature distribution in the horizontal direction tends to be uniform. The flow in IRWST is mainly along the vertical section of the C-type heat transfer tubes, and the velocity increases gradually. In the two-phase stage, the flow of the upper tank is obviously enhanced. The heat transfer coefficient of the upperhorizontal segment and the upper vertical segment of the C-type heat transfer tube is obviously higher than that of the other area, and the heat transfer coefficient of the joint of upper horizontal segment and the vertical segment is the largest. The heat transfer coefficient of the upper region in tank increases obviously in the two-phase stage.