Choking Flow in Supercritical Fluids

在超临界水反应堆（SCWRs）中，一个特别的安全问题是在假设的冷却剂丢失事故（LOCA）期间对可能发生窒息流的冷却条件的估计。这种情况既决定了反应堆冷却剂库存的演变，也决定了反应堆压力速率的变化。大多数堵塞流预测都是基于亚临界数据建立的模型。为了确定这些模型是否适用于超临界流体，我们提出了一个旨在收集超临界条件下用水堵塞流动数据的程序的延续。因此，一个超临界回路正在École Polytechnique建设中；它由高压高温分支与中压蒸汽-水回路相连组成。高压系统用于控制试验段入口的超临界水流状况。中压回路是实现连续稳态排放流量实验所需的压控储层，下游压力可任意控制。不同的试验段，配有压力传感器和温度测量装置，具有不同的排放几何形状和直径，将被用来研究它们对超临界堵塞流动的影响。对于不同的超临界进水条件，通过改变和控制下游（排放）压力来收集压力分布数据。然后，实验信息将用于模型验证。如果需要，这些数据将用于开发一个新的模型来估计超临界条件下的堵塞流量。

A particular safety concern in Supercritical Water Reactors (SCWRs) is the estimation of cooling conditions during a postulated Loss-of-Coolant Accident (LOCA) under which choking flow may occur. Such a situation determines both the evolution of the reactor coolant inventory and reactor pressure rate changes. Most of choking flow predictions are based on models developed from subcritical data. To determine whether these models are appropriate or not for supercritical fluids, we present the continuation of a program intended to collect choking flow data using water at supercritical conditions. Thus, a supercritical loop is under construction at École Polytechnique; it consists of a high-pressure, high-temperature branch interconnected to a medium pressure steam-water loop. The high-pressure system is used to control supercritical water flow conditions at the inlet of a test section. The medium pressure loop serves as a pressure controlled reservoir required to achieve continuous steady-state discharge flow experiments with the downstream pressure controlled at will. Different test sections, instrumented with pressure transducers and temperature measurement devices, having different discharge geometries and diameters will be used to study their effects on supercritical choking flows. For different supercritical water inlet conditions, pressure distribution data will be collected by changing and controlling the downstream (discharge) pressure. The experimental information will then be used in model validations. If needed, these data will be used to develop a new model to estimate the choking flow rate at supercritical conditions.