Breakup of annular viscous liquid jets in two gas streams

Abstract

Linear stability theory is applied to study the breakup process of an annular viscous liquid jet exposed to both inner and outer gas streams of unequal velocities; The absolute liquid and gas velocities are considered in this temporal instability analysis. It is found that not only the velocity difference across each interface, but also the absolute velocity of each fluid is important for the jet instability, although the effect of absolute velocity is secondary compared with that of relative velocity. A high-velocity coflowing gas stream is found to significantly improve atomization performance. A high-velocity gas inside of the annular liquid jet promotes the jet breakup process more than the gas of equivalent velocity outside of the jet. For equal liquid and gas velocities, surface tension, liquid, and gas density exhibit effects on wave growth rates different from those when a velocity discontinuity is present across interfaces. However, the viscous damping effect on jet instability always exists for the cases with and without velocity differences at high Weber numbers. The liquid inertia, density ratio, and high gas velocity all contribute to better atomization performance, whereas surface tension and liquid viscosity increase the resulting droplet size.