【作者】 冯鹏；

【导师】 周小为； 陈德奇；

【作者基本信息】 重庆大学 ， 工程（动力工程）（专业学位）， 2022， 硕士

【摘要】 当反应堆发生冷却剂丧失事故后,应急堆芯冷却系统触发,冷却剂开始注入堆芯。短时间内燃料元件表面从高过热温度骤冷至饱和温度,此过程称为再淹没冷却。高过热燃料元件表面的沸腾传热直接影响到燃料元件乃至整个堆芯的完整性。过渡沸腾是再淹没过程中沸腾形式由膜态沸腾向核态沸腾转变中的一个典型区域。在此区域,不稳定的膜态沸腾和核态沸腾随机交替出现,这导致了过渡沸腾区域换热系数出现非线性变化,对淹没过程传热预测造成重要影响。过渡沸腾反映了淹没过程中过热燃料元件温度迅速变化,直接关系事故工况下燃料元件是否得到充分冷却。本文采用典型窄矩形流道来模拟窄矩形流道在冷却剂丧失事故下的再淹没冷却过程。通过开展不同入口过冷度(30～50 K)、不同淹没速度(3～9 cm/s)、不同系统压力(0.1～0.5 MPa)、不同初始壁面温度(300～500℃)及不同加热热流密度(57.5～77.5 k W/m~2)下的窄矩形流道再淹没冷却可视化实验,得到了充分的壁面温度瞬态变化数据及可视化数据。详细分析了不同热工参数对再淹没过程及过渡沸腾的影响。结果表明:骤冷完成时间与入口过冷度和淹没速度成正相关,与初始壁面温度和加热热流密度成负相关。通过可视化数据发现过渡沸腾存在汽液两相频繁周期性的交替润湿壁面;过渡沸腾区域的换热系数波动幅度随入口过冷度上升和热流密度下降而减小;随初始壁面温度下降与压力上升而更符合线性化变化趋势;随着淹没速度增加,换热系数依次呈现上升、下降、再上升。同时,本文基于瞬态数据分析及可视化数据图像观察到汽液交替润湿壁面现象,提出润湿因子,从而开发适用窄矩形流道的过渡沸腾预测模型。该模型与实验值最大误差范围在±25%以内,预测结果与实验结果吻合好。此外,基于预测模型的关键参数,开发了适用窄矩形流道的最大热流密度预测关系式,预测结果与实验最大误差在±25%以内。更多还原

【Abstract】 After the reactor coolant loss accident,the emergency core cooling system triggers the coolant to inject into the core from the bottom.In a short time,the surface of the fuel element is cooled from high superheat to saturation temperature,which is called reflooding process.The boiling heat transfer on the surface of high superheated fuel element directly affects the integrity of fuel element and even the whole core.Transition boiling is a typical region in the transition of boiling from film boiling to nuclear boiling during reflooding In this region,the unstable film boiling and nuclear boiling appear randomly alternately,which leads to the nonlinear change of heat transfer coefficient in the transition boiling region,and has an important influence on the heat transfer prediction of the reflooding process.In this paper,a typical narrow rectangular channel is used to simulate the reflooding cooling process of plate fuel element under the accident of coolant loss.The visualization experiments of reflooding cooling in narrow rectangular channel under different inlet subcooling(30 ~ 50 K),different reflooding velocity(3 ~ 9 cm/s),different pressure(0.1 ~ 0.5 MPa),different initial wall temperature(300 ~ 500°C)and different heating power(57.5 ~ 77.5 k W /m2)were carried out,and sufficient wall temperature transient data and visualization data were obtained.The effects of different thermal parameters on reflooding process and transition boiling were analyzed in detail.The results show that the completion time of quenching is positively correlated with inlet subcooling degree and reflooding velocity,and negatively correlated with initial wall temperature and heating heat flux.Through visualization,it is found that there is frequent periodic alternate wetting wall between vapor and liquid in transition boiling,and the change of heat transfer coefficient in transition boiling region is more stable with the increase of inlet subcooling degree and the decrease of heating heat flux.It has a more linear trend with the decrease of initial wall temperature and the increase of pressure;With the increase of reflooding speed,the average heat transfer coefficient will rise first,then decline,and then rise again.Based on the analysis of transient data and frequent periodic alternate wetting wall between vapor and liquid in transition boiling,a transition boiling prediction model suitable for narrow rectangular channel is developed.The error range between the model and the experimental value is within±25%,and the predicted results are in good agreement with the experimental results.In addition,based on the key parameters of the prediction model,the relational formula of maximum heat flux and the difference between wall temperature and fluid temperature suitable for narrow rectangular channel are developed.The error between the prediction results and the experiment is within ±25%.更多还原