The breakup of viscous jets with large velocity modulations

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Abstract
The surface-tension-driven breakup of viscous jets is observed for a range of Weber and Ohnesorge numbers. The breakup is enhanced with a sinusoidal modulation or pulsation of the jet's exit velocity; the velocity modulation amplitudes and wavenumbers are larger than previous values reported in the literature. The combinations of modulation amplitude and wavenumber that produce uniform droplets are identified for each pair of Weber and Ohnesorge numbers. Satellite droplets are eliminated at values of the Ohnesorge number greater than 1.6. Droplet pairing and merging occurs at high wavenumbers; droplet merging has not been reported in the jet breakup literature. The timescale for breakup is predicted within the data scatter by the thin filament equation of Bousfield et al. (1986) with no fitted parameters. An upper bound on satellite droplet size is predicted by the thin-filament equation and the average satellite droplet volume is qualitatively predicted. An algebraic expression is derived to predict the breakup time of viscous jets with large velocity modulation amplitudes.

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