화학공학소재연구정보센터
Atomization and Sprays, Vol.29, No.2, 105-121, 2019
THE VISCOUS EFFECT ON THE TRANSIENT DROPLET DEFORMATION PROCESS UNDER THE ACTION OF SHOCK WAVE
The transient droplet deformation behaviors induced by shockwaves were experimentally recorded by high-speed shadowgraphic technique. Three Ohnesorge number (Oh) conditions (0.07, 0.32, and 0.66) and Weber number (We) ranges between 45 and 4000 were tested. Results show that the effects of viscosity on deformation are correlated with the extent of interaction inertia. At small We conditions, the time-dependent deformation (d(c)/d(0)) shows three stages before breakup. Initially, d(c)/d(0) stays constant for all Oh conditions. d(c)/d(0) increases as a function of time, and increased viscosity leads to a slower d(c)/d(0) rate due to a higher rate of dissipation. A less viscous droplet shows a flat d(c)/d(0) period, while for more viscous droplets, d(c)/d(0) oscillates before breakup. For higher We cases, only the constant d(c)/d(0) stage followed by a steady increase is observed, and higher viscous droplets still result in a lower d(c)/d(0) increase rate in the second stage. (d(c)/d(0))(max) decreases with the increase of viscosity at low We because the viscous dissipation consumes more inertia. However, at higher We, (d(c)/d(0))(max) increases because at this We, the increase of viscosity actually postpones the breakup, resulting in a larger (d(c)/d(0))(max). The initiation time (T-ini, the time scale of droplet deformation), decreases with the increase of We due to accelerated breakup through enhanced disruptive inertia. Increased Oh lengthens this time scale because a more viscous droplet consumes the inertia faster, counteracting the effect of We. This time scale variation also explains the (d(c)/d(0))(max) dependence on Oh and We.