A study on dual role of viscosity on the stability of a viscous planar liquid sheet surrounded by inviscid gas streams of equal velocities, and prediction of resulting droplet distribution using maximum entropy formulation

Abstract

Low sensitivity to rheological properties of fluid and ability to produce fine sprays at low liquid pressure make airblast atomizers a preferred choice to process viscous liquids. Airblast atomizers essentially employ kinetic energy of coflowing gases to disintegrate a liquid sheet into fine spray. The present study employs the perturbation technique to carry out nonlinear investigation of the sinuous mode of instability in a thin planar viscous liquid sheet sandwiched between two inviscid gas streams moving at equal velocities. This paper analyzes temporal instability as well as droplet characteristics for a range of Reynolds numbers, Weber numbers, gas to liquid density ratios, and velocity ratios and reports the dual behavior of liquid viscosity at different operating conditions. For higher gas to liquid velocity ratios, this study identifies three regimes at all Weber numbers and gas to liquid density ratios: the first regime represents the stabilizing effect of viscosity at low Reynolds numbers, the second regime indicates the destabilizing effect of viscosity at intermediate Reynolds numbers, and the third regime further depicts the stabilizing effect of viscosity at high Reynolds numbers. However, for low gas to liquid velocity ratios, the third zone disappears at lower Weber numbers and gas to liquid density ratios, and the effect of viscosity is characterized by two regimes representing the weak stabilizing and destabilizing effect at low and relatively higher Reynolds numbers, respectively. Investigation of spray characteristics reveals that an increase in liquid viscosity produces relatively larger droplets at all flow conditions.