自然循环条件下窄通道内气泡速度特性

Bubble velocity characteristics in narrow channel under natural circulation

气泡运动速度是气泡行为重要参数,对建立完善的气泡换热机理模型具有意义。以水为工质开展自然循环流动条件下窄通道内气泡速度特性实验研究。分析了单气泡和气泡群速度变化规律、影响因素以及引入摇摆运动后的速度特性。气泡速度主要取决于气泡尺寸和主流速度两个因素,摇摆条件下气泡速度会发生周期性波动,竖直稳态或摇摆动态条件下气泡形心液相速度与气泡速度近似相等。

Techniques of two-phase flow under natural circulation have been used in reactor safety equipment. Bubble velocity is a necessary parameter to describe bubble behaviors and to establish profound bubble heat exchanger models. However, there are rare investigations of bubble velocity in subcooled flow boiling under natural circulation. Subcooled flow boiling under natural circulation was studied for bubble velocity characteristics in a narrow channel with water as working media, which a high speed camera was used to record bubble images in a visualization section of cross area 40 mm×2 mm. The analysis of change in velocity profile of single bubble and bubble cluster, their influencing factors, and velocity characteristics at rolling motion showed that bubble velocity was closely related to bubble size and mass flow rate. The velocity probability density of bubble cluster fitted well to normal distribution. Under rolling motion, bubble velocity exhibited periodic wavelike increase and decrease. The local liquid velocity at bubble center was comparable to bubble velocity at vertical steady state or rolling dynamic state.