ID 281

Secondary atomization- vindication of new breakup regimes and detailed drop sizing

 

Abstract:

Secondary breakup of water and single-component surrogate fuels such as n-dodecane and n-hexadecane is experimentally investigated. Mono-disperse droplets (200±4 µm - droplet sizes found in practical sprays) of the test liquid are introduced into an air jet issued from a contoured nozzle. The aerodynamic Weber number (We) is varied by changing the air-jet velocity. In the present study, apart from the commonly reported regimes namely - bag breakup, bag and stamen breakup, shear breakup and catastrophic breakup - two more regimes, namely dual-bag breakup and multi-bag breakup regimes, are also observed. While dual bag regime occurs in the range of We = 30 – 46, it is followed by multi-bag regime in the range of We = 46 - 80. The Sauter Mean Diameter (SMD) of resultant droplets reduces for from We 12 to 18 and increases for We 18 to 24 and monotonically reduces for We above 24. However, at a given We, variation in liquid properties has minimal effect on the SMD. A tri-modal drop size distribution is observed for bag breakup mode, which transforms to a bi-modal distribution as the We is increased. The droplet size distribution resulting from the breakup of water is different than those of the other two liquids in the larger droplet size range, and is attributed to its higher surface tension. The experimental data presented here is useful to validate computational models for secondary breakup phenomenon for simulation of water sprays or sprays of diesel fuel surrogates such as n-dodecane and n-hexadecane.