开式自然循环系统不稳定性实验研究

Experimental Study on the Instability of the Open Natural Circulation System

核电站非能动安全系统依靠自然循环将热量导出,然而系统中的驱动压头、流动阻力、流量等相互影响,容易引发流动不稳定性,导致流动沸腾临界热流密度大幅降低,带来安全问题。因此,流动稳定性是自然循环热力系统的重要研究对象。本文以开式竖直加热圆管为实验本体,通过实验和物理建模的方法,研究了自然循环条件下管内间歇沸腾现象和流动不稳定特性。研究结果表明:随着热流密度的升高,系统将经历初始状态、低频脉动、高频脉动和稳定的自然循环四个阶段。基于实验数据,建立了不稳定边界的预测模型,预测值和实验值符合良好,误差在±10%内。

The passive safety system of nuclear power plant relays on natural circulation for heat dissipation. However, the hydraulic pressure, flow resistance, and flow rate in the system will affect each other, which can easily cause flow instability and greatly reduce the corresponding CHF value. Therefore, the instability is one of the important research topics in the natural circulation thermal system. In this paper, a vertical round heating tube with an open outlet is tested under various heat fluxes and inlet subcooled temperatures. Through experimental results and theoretical analysis, the characteristics of geysering boiling and flow instability under natural convection conditions in the tube are studied. The results show that with the increase of heat flux, the system has four stages: initial state, low-frequency pulsation,high-frequency pulsation and stable natural circulation. Based on th e experimental data, a prediction model of the unstable boundary is established. The predicted value and the experimental value are in good agreement, and the error is within ±10%.