真空环境液体闪蒸射流实验研究

Experimental Study on Flashing Liquid Jets in Vacuum Environment

本文实验研究了蒸馏水经内径0.226 mm、长度16.5 mm薄壁不锈钢直管向真空环境排放时形成的液体闪蒸射流现象.实验观察到3种射流形态。在液体初始温度低于背压所对应的饱和温度时,液体不会发生闪蒸,液体射流喷出后保持完整;反之,液体表面蒸发会导致液体射流核周围出现不规则蒸发波,射流破碎散落;进一步降低背压,会使得射流一出喷口即快速破碎形成扩张角大于90°的雾状射流。射流流量在背压低于某个临界数值时出现壅塞现象,即流量不再随背压降低而增加,表现出强烈的可压缩流动特征。

Flashing liquid jets of distilled water through a long,straight stainless steel capillary with an inner diameter of 0.226 mm and a length of 16.5 mm into a vacuum environment are studied experimentally.Three kinds of jet patterns are observed.For the case of low initial temperature which is lower than the saturated temperature corresponding with the backpressure inside the vacuum chamber,no evaporation occurs,and then the flow of the liquid jet from the nozzle exit remains intact and follows a straight path.On the other hand,if the initial temperature is higher than the saturated temperature corresponding with the backpressure,evaporation will take place,which results in a visible irregular evaporation waves around the liquid core and then a shattering jet.On further decreasing the backpressure,the liquid jet shatters giving rise to a cloud of droplets with a spray angle usually bigger than 90 degree,indicating a large number of nucleation sites and rapid bubble growth.It is also shown that there is flow choking behavior as the flow rate becomes constant and insensitive to pressure reduction below some backpressure threshold,and thus,the flow exhibits a strong compressible characteristic.