Abstract: In order to clarify the cause of tube failures in high pressure waste heat boilers with vertical U-shaped tubes, a series of tests was made to study flow pattern transitions over wide velocity ranges of ambient air-water mixtures in a 21.5mm 1. D. vertical U-shaped tubes with 180°-bends of radii 694,500 and 320 mm respectively. The flow patterns observed in these bends were similar to those in horizontal two-phase flow. The data obtained showed that the differences from the horizontal flow were the expansion of stratified flow and restriction of wavy and intermittent flow. Both annular and dispersed transitions were quite close to those in horizontal tubes. The transition data obtained in the present tests were compared with the transition correlations of Mandhane et al. and Weisman et al. forhorizontal tubes. An overall flow pattern diagram based on the present tests was established in terms of superficial gas and liquid velocities, VsG and VSL. Correlations for determining flow pattern transitions were suggested. The effects of the bend radii on flow pattern transitions are small within the test range.

摘要： 对垂直U型管弯管段空气-水同向流动时气液两相流在不同速度范围内流型间转变进行了试验,试验用内径21.5mm有机玻璃管,弯管半径分别为694、500和320mm.流型采用直接观察法及电导探针法确定.所得数据与Mandbane等人及Weiman等人的水平管转变关系式作了比较.根据试验结果,给出了以折算气体和液体速度V_(SG)及V_(SL)为座标的总流型图,提出了计算流型转变的关联式.