A point-hydraulics model for flow stability analysis

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 a supercritical water-cooled reactor (SCWR). One of the challenging tasks is to understand and to predict the dynamic behavior and flow stability of supercritical water-cooled systems. The present study introduces a new method, the so-called point-hydraulics model (PHM), to establish a criterion for predicting the onset of a self-sustaining flow oscillation in a closed cooling system. Four dimensionless numbers are clarified which affect the onset of flow instability. Based on this model, stability maps are derived which can be applied to any kind of fluids and operating conditions. The PHM model is applied to a simplified system cooled by supercritical water. Parameters affecting the flow stability are discussed. A good agreement is achieved between the PHM model and the numerical results obtained using the SASC code which was developed specifically for analyzing the dynamic behavior of systems cooled by supercritical fluids.