Characteristics of Parallel and Countercurrent Flooding Instability of Annular Flow in Rod Bundle Channel
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摘要:
开展堆芯流动单元内两相逆流行为的实验研究,能为不同形态反应堆系统的顺利运行和应急处理提供足够的理论支撑。本研究对3×3棒束通道环状流中并流-逆流不稳定性的携带行为、流动参数特性和形成机理进行了分析。结果表明,一个携带周期由携带上行起始区域、完全上升环流区域和整体下行区域组成。实验工况根据Wallis判别式判断处于携带状态,根据Zapke和Alekseev判别式的预测结果则处于携带和不能携带的转换线上。当压差达到局部最大值时,高速摄影捕捉到上行起始点;当压差达到局部最小值时,高速摄影拍摄到下行起始点。当液相流速低于0.1 m/s时,整体周期长度并无明显变化;当液相折算速度在0.1~0.3 m/s范围内,整体周期随气相折算速度的增加而减小,上行与下行的时间比值变化较小,液相折算速度高于0.3 m/s时该比值则随气相折算速度的增大而增加。当液相流速低于0.2 m/s时,携带起始混流上升速度高于气相折算速度;当液相流速逐渐增加,携带起始混流上升速度高于气相折算速度的量逐渐减小;当液相折算速度高于0.2 m/s,在高气相折算速度条件下携带起始混流上升速度低于气相折算速度。发生并流-逆流不稳定性的原因是在不同区域内气芯变化的携带力和液相重力的周期性起主导作用。
Abstract:Carrying out the experimental researches on the two-phase countercurrent behaviors in the flow unit of reactor core can provide sufficient theoretical supports for the smooth operation and emergency treatment of different forms of the reactor systems. In this research, the flooding phenomenon, the characteristics of flow parameters and formation mechanisms of parallel and countercurrent flooding instability of annular flow in rod bundle channel were analyzed, and the result indicates that one flooding cycle could be divided into the onset flooding region, the full flooding region and the whole liquid phase downstream region. The experimental conditions where the flow instability appeared in the rod bundle structure are in the flooding state according to the criterion from Wallis, but on the conversion line of flooding and not flooding state according to the criterion from Zapke and Alekseev. The experimental pressure drop changing with time was compared to the instability behaviors of annular flow, and the result shows that when the pressure drop reaches a local maximum, the high-speed photography captures the starting point of onset flooding region, and when the pressure difference reaches a local minimum, the starting point of whole liquid phase downstream region is seen in the field of view. According to the high-speed photographic image data processing, the parallel flow time, the countercurrent flow time and the overall cycle time were acquired and analyzed. When the liquid phase flow rate is lower than 0.1 m/s, the overall cycle time does not change significantly, and the parallel flow time is lower than the countercurrent flow time. When the liquid superficial velocity is within the range of 0.1-0.3 m/s, the overall cycle time decreases with the increasing gas superficial velocity, and the time ratio of the parallel and countercurrent flow time changes little. When the liquid superficial velocity is higher than 0.3 m/s, the time ratio increases with the increasing gas superficial velocity. The study on the micelle velocity for onset-flooding shows that when the liquid superficial velocity is lower than 0.2 m/s, the micelle velocity for onset-flooding is higher than the gas velocity. The value with which the micelle velocity for onset-flooding is higher than gas superficial velocity decreases gradually with the increasing liquid velocity. At some conditions with high gas velocity, the micelle velocity for onset-flooding is lower than the gas superficial velocity when the liquid superficial velocity is higher than 0.2 m/s. The formation mechanisms of parallel and countercurrent flooding instability depend upon the changing force of gas core and the effect of liquid gravity in different flooding regions.
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Keywords:
- rod bundle channel ,
- annular flow ,
- flow instability ,
- countercurrent flow
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