Effect of velocity and radius distribution on jet breakup

The focus of this paper is on the effect of velocity and radius distribution on jet breakup. A theoretical model is established to analyze and predict the velocity distribution along the jet, which is physically and mathematically continuous. The simplified forms of the breakup time, the disturbance growth rate, and the disturbance level considering the velocity and radius distribution are presented. A series of prediction methods for predicting the jet breakup length and droplet size are developed. A Newtonian laminar jet falling vertically was experimentally observed to validate the theoretical model and prediction methods. It is shown that the relaxation of the velocity profile leads to the rapid contraction of the jet radius near the outlet, which leads to the increase in the growth rate of the instability disturbance. The surface tension prevents the growth rate of disturbance from increasing by restraining the contraction of jet radius. The final amplification of jet velocity and contraction due to gravity acceleration depend on the Froude number and breakup length. When the influence of jet radius distribution on the growth rate of disturbance is considered, the breakup time is indirectly affected by the breakup length. The experimental and predicted results show that the accelerated falling of jet lengthens the breakup length traveled by the jet in a shortened breakup time due to the contraction of jet radius. The droplet volume is proportional to the predicted jet cross-sectional area at the breakup position and the Rayleigh wavelength determined by the nozzle radius.