定位格架搅混翼附近气泡运动特性可视化实验研究

Phenomenological Investigation of Gas Bubble Behavior in the Vicinity of Mixing Vane of Spacer Grid

针对3×3棒束采用可视化实验技术研究棒束通道内气-液两相流动过程,获得了定位格架搅混翼附近的气泡行为特性。通过实验发现在搅混翼背流面存在气泡滞留的现象。在稳定工况下,滞留气泡的高度基本不变,滞留气泡相界面在流动、来流气泡合并过程中存在波动,并在液相的夹带下从滞留气泡末端分裂成多个小气泡。滞留气泡末端被液相夹带分裂是棒束通道中气泡尺寸变化的主要原因之一,并且分裂后的气泡尺寸小于来流气泡尺寸。在相同空泡份额条件下,随着液相流量的增加,滞留气泡高度增加,从滞留气泡上分裂的气泡尺寸相比来流气泡减小、数量增加;在相同液相流量条件下,随着空泡份额的增加,滞留气泡大小基本不变。来流气泡尺寸影响滞留气泡相界面的波动幅度,同时搅混翼背面存在滞留气泡时,气泡从搅混翼迎流面和背流面经过搅混翼时,在下游具有不同的运动特性,导致格架下游子通道间相态分布的差异性。

Visualization technique was adopted to study the gas bubble behaviors in the vicinity of mixing vane of spacer grid in a 3x3 rod bundle under ambient temperature and atmospheric pressure. It was found that the bubble stagnation, which is dependent on liquid flow rate and volume fraction, occurs at the leeward of the mixing vane. The stagnation bubble interface oscillated with flow and inflow bubble coalescence. Smaller bubbles were generated by liquid entrainment at the end of the stagnation bubble, which is one of the main mechanisms of bubble size redistribution. The stagnation bubble size increased and break-up bubble size decreased with the increasing of the liquid flow rate under identical void fraction. The stagnation bubble size was independent upon void fraction under identical liquid flow rate, while the oscillation of stagnation bubble interface was strongly influenced by the void fraction, especially the inflow bubble size. The bubbles, passed through the mixing vane from windward and leeward mixing vane, led to different bubble flow directions and phase distribution at the downstream of the spacer grid.