热负荷阶跃变化条件下热回流式换热系统缺陷机理及优化方法研究

The Defect Mechanism of Heat Exchanger with Inverse Flow during Heat Load Step Change and its Optimization

针对国内某北方核电厂的设备冷却水系统热回流式换热器,分析了不同热负荷下热回流式换热系统的稳态特性及负荷阶跃变化下热回流式换热系统缺陷机理,提出了热回流式换热器系统优化方法。研究表明:在不同热负荷下热回流式换热器系统切换的关键是与不同热负荷对应的具有特定温度的伴流的形成;热负荷阶跃变化下状态转换瞬态过程中存在系统缺陷,其根本原因在于单纯采取调节热回流率的方法,具有较大的时间滞后性;调节换热器冷介质侧的流体流量,改变换热器传热系数,强化了对状态改变的快速响应;采取热回流叠加换热器旁流方法,可以解决原有系统状态转换瞬态过程中存在的缺陷。

For the system of hot inverse flow in the cooling water system of a nuclear power plant in the north of China,the steady-state characteristics of this heat exchanger system under different heat loads were analyzed.The defect mechanism of heat exchanger with hot inverse flow under load step change was studied.The optimization method of this heat exchanger system was put forward.The results show that the key to the state transition in the heat load step change is the formation of hot inverse flow with specific temperature corresponding to different heat loads;the system defect in the transient process of state transition under the step change of heat load is mainly caused by the simple method of adjusting the heat return flow rate,which has a large time-delay;by adjusting flow rate of the cold medium,the heat transfer coefficient of the heat exchanger is changed,and the fast response to the state change is strengthened;the optimization scheme,which adopts the method of hot inverse flow superimposing the bypass flow,could solve the defects existing in the transient process of the original system state transition.