Study On Effects Of Bubbles In The Liquid On The Atomization

Liquid atomization is very common in chemical industry,transportation and aerospace industry,atomization performance has a significant influence on the chemical reaction and mass transport.The high-speed camera and Malvern laser particle size analyzer was used to investigate the atomization process of liquid with inner bubbles.The strengthening effect of inner bubbles on the atomization performance is analyzed.The model of the breakup and air-blast coaxial atomization of the jet with inner bubbles is derived.The main contents and results are summarized as follows:1.The air,CO2,H2 and water were used as the working fluid to study the breakup of the jet with inner bubbles.The breakup length of the jet with inner bubbles decreased with the increase of the bubble diameter and increased with the jet velocity when the jet was in the Rayleigh regime.It was found that the gas with a smaller density could realize a more significant decrease in the breakup length.The classical linear stability theory and equivalence of surface disturbance and velocity disturbance were adopted to explain the strengthening effect of inner bubbles on the jet breakup,variation rule of the breakup length of jet with different gas was presented.The model predicting the breakup length of the jet with inner bubbles was derived.2.The jet breakup process of various glycerol-water solutions was investigated.Results show that the bubble in the jet could shorten the breakup length of viscous jet significantly.The breakup length of a viscous liquid jet decreases with increasing bubble size.Increasing liquid viscosity increases the breakup length.A model combining the instability theory and the inhibition of liquid viscosity on the jet velocity fluctuation induced by bubbles was deduced to predict the breakup length of the viscous jet with inner bubbles.3.The jet breakup process of surfactant-laden jet was investigated using the high-speed camera.The experimental results show increasing concentration of surfactant solution leads to the increase of jet breakup length when the jet is in the Rayleigh regime.The surfactant in the jet has two effects on the jet breakup.On the one hand,surfactants in the jet decreases the dynamic surface tension and the growth rate of the unstable wave;on the other hand,the inhomogeneous distribution of surfactants on the jet surface induces Marangoni effect.These effects both lead to the larger jet breakup length.Basing on the instability theory and Marangoni effect,the breakup of surfactant-laden jet was modeled and analyzed.It was also found that inner bubbles decreased the breakup length of surfactant-laden jet significantly.Increasing the bubble size decreases the breakup length.It is attributed to the combined effect of jet velocity fluctuations due to the bubble and the absorption of surfactants on the bubble.4.The secondary atomization of the droplet with inner bubble was studied,the time character and space character of the bag breakup of the droplet with inner bubble was analyzed.It was found that the initial time increases with the bubble size.The bubble in the droplets has less influence on the bag lifetime and droplet breakup time.On the basement of conservation of energy,the dependence of initial time on the bubble size was obtained.The droplet maximum cross stream diameter increases with the bubble size.A correlation between the droplet maximum cross stream diameter and bubble size was built through the force analysis of the droplet.The critical Weber number of secondary atomization and transition Weber number between the bag breakup and bag-stamen breakup were obtained.5.The air-blast coaxial atomization with bubbles in the liquid jet was investigated using the high-speed camera and Malvern laser particle size analyzer.It was found that the reduction of droplet size is about 6%when the ratio of the volumetric flow rate of the aerating gas to the co-flowing air stream is about 0.03%.The bubbles in viscous liquid jet have various influences on the air-blast coaxial atomization.First,bubbles in viscous liquid jet decrease the relative velocity between the air stream and liquid jet,which leads to larger droplet.Second,bubbles in viscous liquid jet shorten the Rayleigh-Taylor wavelength,which results in smaller droplet.Third,bubbles in viscous liquid jet increase the gas-liquid mixture viscosity,which increases the droplet size.The droplet size depends on the competition of these factors.Basing on the instability theory,the model describing the air-blast coaxial atomization with bubbles in the liquid jet was derived.A contour map describing the dependence of the droplet size on the several dimensionless factors was obtained.The nonmonotonic trend of the droplet size was analyzed and a promising atomization method with less gas consumption was proposed.