| Popis: |
Two-phase flow instability plays an very important role in operation safety and reliability of heat exchange equipment. The mechanism of two-phase flow instability was very complicated. Two-phase flow instability may occur when the fluid volume in the circulation loop changes greatly due to heating or cooling. In this paper, the onset of flow instability (OFI) was investigated under the condition of: P = 2.2MPa, G = 2000∼4000kg/(m2·s), ΔTsat = 100∼15 °C, q = 1000∼1500kW/m2 in upward tube (2400 × 8.2 mm) with deionized water. When the fully developed subcooling nucleate boiling (FDB) happens in the test section, the fluctuating flow appears between the circulation loop and the pressurizer, also the test section. The inlet and outlet water temperature, the pressure drop of the test section and the exit valve, the liquid level of the pressurizer and the other system related thermal parameters become unstable after the FDB condition, which is caused by the generation and departure of large amount of bubbles in the test section. The point of FDB can be considered to the onset of flow instability in the circulation loop. An empirical correlation was developed by comparing the heat flux leading to OFI with that leading to saturation: qOFI = 2.11qsat0.73, and the deviation is within ±15% for all the conditions. |
