超临界流体并联管流动不稳定性及传热特性研究

超临界流体在拟临界区域奇异的物性变化给超临界水冷堆的热工水力设计带来各种挑战，其一是堆芯并联燃料组件内超临界流体的流动不稳定性及其引起的传热变化认识和预测是关键的问题之一。目前针对超临界流体不稳定性研究极少，仅限于单管的理论研究和自然循环单管实验研究。本项目以加热并联管内超临界流体流动不稳定现象为研究对象，建立描述超临界流体流动不稳定性的无量纲准则数和数学模型，获得无量纲准则不稳定边界,以超临界氟利昂实验数据为主、超临界水实验数据为辅验证无量纲边界对不同物性的普遍适用。基于氟利昂实验数据和流动数学模型认识并联管内超临界流体不稳定流动时域特性，进一步建立传热数学模型，揭示流动不稳定下以传热恶化为代表的异常超临界流体传热的发展规律。本项目研究旨在为超临界水冷堆堆芯的流动传热不稳定性分析提供理论基础和数学模型。

The strong variation of the thermal-physical properties of supercritical fluids in the vicinity of the pseudo-critical line results in challenging tasks in thermal-hydraulic design of Supercritical water cooled reactor (SCWR). One of the main challenging tasks is to understand and to predict the flow instability and heat transfer oscillation among the parallel assemblies in SCWR,which is rarely reported. The present study will focus on the supercritical fuild flow instability and heat transfer performance in parallel heating tubes which share the similar geometry features with the parallel assemblies.Based on the mass, momentum and energy conservation equations, nondimensional parameters and novel numerical models will be developed for predicting the onset of flow instability of supercritical fluids in the parallel heated tubes.Meanwhile, experimental study will be carried out on the parallel two tubes and three tubes.We will mainly use the supercitical freon R134a which has a lower supercritical pressure and temperature than the supercirical water, and use the supercritical water as a supplement.The transient feature of flow instability will be analyzed with the suport of detailed experimental results of supercritical freon and numerical simulation results. The effect of flow instability on the heat transfer performance will be further stuided. Numerical model to predict the heat transfer to supercritical fluids will be established, as well as the critireon for the onset of the heat transfer deterioration. Through the above mentioned work,we will get to know the basic laws and provide numerical models for the flow instability and heat tranfer ossilation in the SCWR.