Timing jitter of monodisperse droplets generated by capillary jet breakup

Abstract

Uniform droplets generated by Rayleigh breakup of liquid jet are widely applied in science and engineering. The droplets are produced by imposing a periodic velocity perturbation on a micro-sized liquid jet. In practical situations, the frequency of droplet generation is not perfectly steady like the preset perturbation frequency. This unwanted timing jitter poses kinds of problems. We studied the fluid mechanism of the jitter at short working distance and its dependence on various parameters. We found that at short distance, the jitter is mainly affected by the reduction rather than the dispersion in the droplet velocity. The magnitude of the jitter is related to the velocity reduction and the unsteadiness of the perturbation. The velocity difference between the droplet and the jet is analytically obtained based on one-dimensional linear analysis of drop formation in liquid jet, and numerical simulations validate the results. The influence of the unsteady perturbation is explained by the evolution of control volumes with different initial amplitudes. The degree of jitter is finally deduced, and its relationships with each variable are compared with experiments. Optimization methods are given to mitigate jitter by adjusting the perturbation parameters and jet properties.

Modulation of coaxial cone-jet instability in active co-flow focusing

“…These shortcomings highlight the necessity for on-demand control of jet breakup and droplet production. Currently, the controlled breakup of a single jet falling into a stationary air environment has been widely studied, and the jet breakup has been successfully modulated by laser illumination (Liu et al 2021;Zhao et al 2021), a thermal field (Basaran, Gao & Bhat 2013;Kamis, Eral & Breugem 2021), electrical field (Yang et al 2014;Xu et al 2022a) and mechanical vibration (Moallemi, Li & Mehravaran 2016;She et al 2022;Luo et al 2023). As for the flow focusing system with an immiscible liquid phase, previous works by our group have considered the response of a liquid jet to an external periodic perturbation added to the flow rate, either through experiments (Yang et al 2019) or numerical simulations (Mu et al 2018b).…”

“…2022 a ) and mechanical vibration (Moallemi, Li & Mehravaran 2016; She et al. 2022; Luo et al. 2023).…”