ECT研究浅层鼓泡塔中的气含率行为

Gas Holdup in a Shallow Bubble Column Measured by Electrical Capacitance Tomography(ECT)

在内径0.14 m的浅层鼓泡塔内采用电容层析成像技术（ECT）研究了孔口气速和孔径大小对鼓泡塔气含率行为的影响。实验选用空气-去离子水体系,在轴向高度4.75、17.75 cm处同时测定气含率曲线,孔口气速范围为4~186 m/s。以单管为气体分布器,开孔率和孔径范围分别为0.14%~1.31%和5.3~16.0 mm。实验结果表明：气含率随气速的增大而增大;当孔径d0=10.5 mm,孔口气速大于19 m/s时,气含率曲线斜率发生变化,一定程度上表明此时的流型由鼓泡流开始向射流转变;在相同孔口气速下,气含率随孔径的增大而增大,且能谱图主频大小和谱宽也随孔径的增大而增大;得到了鼓泡过程中流型转变孔口气速uN,trans,发现uN,trans随孔径增大而减小,并对比文献认为对于空气-水体系,d0=10 mm可能是区分大小孔径的合理标准。

The influence of orifice gas velocity and orifice diameter on time-averaged gas holdup distributions were investigated in a 0.14 m inside diameter shallow bubble column using ECT.In all the experiments,deionised water was liquid phase and air was gas phase.The gas holdup profiles were measured at two axial locations at 4.75 and 17.75 cm above the distributor level.Orifice gas velocity was varied from 4 to 186 m/s.Single nozzle sparger was used as gas distributor.The free area of sparger plates and orifice diameter were varied in the range of 0.14% to 1.31% and 5.3 to 16.0 mm,respectively.It is found that the gas holdup increases with the increase of orifice gas velocity.As the gas velocity increases beyond u_N=19 m/s,a change of slope profile marks the regime transition from bubbling regime to jetting regime.Gas holdup increases with the increase of orifice diameter at the same orifice gas velocity.A higher dominant frequency and a broad band are observed with the increases of orifice diameter.In addition,the transition gas velocity （u_（N,trans）） is obtained and decreases with the increase of orifice diameter.Finally,the value of orifice diameter（d_0） that distinguished the small and larger orifice is estimated in air-water systems compared with the results of other researchers.