The influence of non-uniform heating on two-phase flow instability in subchannel

• Published in: Nuclear engineering and design Vol. 345; pp. 7 - 14
• Main Authors: Wang, Sipeng, Yang, Bao-Wen, Mao, Hu, Lin, Yu-chen, Wang, Guanyi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.04.2019; Elsevier BV
• Subjects: Binary systems; Boilers; Crack propagation; Fatigue failure; Flow instability; Flow stability; Heat transfer; Heating; Heating systems; High temperature effects; Multiphase flow; Non-uniform heating; Nuclear engineering; Nuclear reactors; Nuclear safety; Phase change number; Phase transitions; Power factor; Reactor safety; Reactors; Shape effects; Shape factor; Subchannel; Subcooling number; Thermal fatigue; Two phase flow; Vibrations; Phase change number; Subcooling number; Flow instability; Non-uniform heating; Subchannel
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2019.01.024

•An open channel model is introduced and validated by experimental results.•The system stabilities under uniform, axial and radial non-uniform heating conditions are analyzed.•Effects of peak value, power peak location and power curve shape are analyzed under axial non-uniform heating condition. Two-phase flow instability is a very common phenomenon in two-phase systems, such as steam generator, BWR, boiler, condenser and so on. Normally, flow instability is not allowed to appear in the systems because it might result in potential issues such as thermal fatigue damage, mechanical vibrations, problems with system control as well as changing of heat transfer characteristics which may cause a boiling crisis. A lot of studies were presented on this subject based on uniform heating. However, non-uniform heating is the biggest characteristic in nuclear reactors which is different from most of the uniform heating systems. It is necessary to conduct research concerning non-uniform heating effect on two-phase flow instability for the reactor safety. This paper studies the flow instability in subchannels. The validation of subchannel model is performed using data from a GE 3 × 3 rod bundle test. The effects of peak value of power factor, peak location, and power curve shape along axial direction are examined. The stability comparisons based on stability boundaries are plotted with the phase change numbers versus subcooling numbers. The increase of peak value makes the system more stable when peak is at the downstream half of the test section and makes the system more unstable when peak is at the upstream side of the test section closer to the inlet. With power peak moves from inlet to outlet, the stability increases first and then levels off. With the increase of power shape factor F, which is the standard deviation of power curve data used to reflect power shape effect, stability increases when power peak is close to the exit and decreases when power peak is near the inlet of the test section. The radial non-uniform heating effect is not obvious in subchannel. According to the results of this stability study, recommendation is made on how to avoid conditions where two-phase flow instability easily occurs.