T he bubble coalescence in narrow rectangular channel during subcooled boil-ing was studied by experiment .The channel size was 2 mm × 40 mm × 700 mm and the experiment parameters were as following :The inlet absolute pressure pin =0.55 MPa , the inlet subcooling Δtin = 31 ℃ ,the mass flux G=516 kg/(m2 · s ) and the average velocity v=0.52 m/s .The high speed camera was used to photograph the bubbles and the speed was set as 5 000 frame per second .The bubble coalescence process was divid-ed into four stages :T he approaching stage ,the coalescence stage ,the adjustment stage and the steady stage .After coalescence ,the bubble velocity would increase and then decrease ,and finally approach steady .The ellipsoid and sphere bubble shapes would alternate to appear .Along with the shape changing ,the angle and the axis length would change also . Finally , a new small bubble may be induced during the coalescence process .%采用实验方法对窄矩形通道内过冷沸腾时的汽泡聚合行为进行了可视化研究。矩形通道的尺寸为2 mm ×40 mm ×700 mm。实验参数为：实验段入口处绝对压力 pin ＝0.55 M Pa ，入口过冷度Δtin ＝31℃，质量流速G＝516 kg/（m2· s ），平均速度v＝0.52 m/s。采用高速摄影仪对实验流道进行拍摄，拍摄速度为5000帧/s。将汽泡聚合过程分为4个阶段：靠近、融合、调整和稳定阶段。发现聚合后的汽泡运动速度会先增大再减小，最后趋于稳定。调整阶段汽泡形态不断变化，椭球形、圆形交替出现；伴随着形变，聚合汽泡的角度、长短轴长也会有相应的变化。最后发现在汽泡聚合过程中会诱导出一个新的小汽泡。
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