正方形截面直通道内二次流现象的实验研究

Experimental Investigation on Secondary Flow of Air-Water Two-Phase Flow in Straight Channel with Square Cross-Section

以空气-水为介质,通过可视化实验的方法,对边长为10 mm的正方形截面通道内空气-水垂直上升流动的两相流流型进行了实验研究,表观气速为0.04-100 m/s,表观水速为0.001-6 m/s.观察到了正方形截面通道内两相流动的典型流型,通过管外可视化及内视镜伸入管道内拍摄到清晰的环状流和爬动流流型,证实了正方形截面直通道内存在“二次流”现象,且对气-液两相流动的相分布有较大影响.将正方形截面爬动流与圆通道内的溪状流进行了比较,由于其中的作用力不同,它们在发生条件、流动形态及液膜形状上有很多异同点,圆通道内溪状流的液膜是随机出现和分布的,数条液带、液丝的位置不确定,尺寸相差悬殊.利用单能γ射线传感器测量了正方形通道内爬动流及环状流的液膜厚度,得到壁面上液膜厚度的分布图,证明了正方形通道内随着表观气速的增大,二次流作用逐渐增强,使得壁面上液膜分布的不均匀,壁面中心处液膜最厚.

An experimental investigation was conducted on the vertically upward flow of Mr-water twophase in a channel with a square cross-section. The hydraulic diameter of the channel was 10mm; the superficial air velocity was 0. 04-100m/s; the superficial water velocity was 0. 001- 6 m/s. The typical flow patterns, creep flow and rivulet flow, were observed by flow visualization with a DV camera and an endoscope, and the flow pattern map and flow pattern transition boundaries were obtained. The thickness of liquid film of the creep flow and the annular flow in the square channel was measured by a γ-ray instrument. The results show that the mechanism to form the creep flow in the square channel is different from that to form the rivulet flow in a circular tube and a secondary flow exits in the square channel. The phase distribution on the inner wall of the noncircular channel indicates that the influence of the channel geometry results in the steeper radial distribution of the phases and velocities, and eventually turbulent secondary flow. With the increase in the gas velocity, the film thickness at center of the wall is greater than that at corner, indicating the significant effect of the secondary flow on the phase distribution in the noncircular channel.