Liquid jet breakup and subsequent droplet dynamics under normal gravity and in microgravity conditions

Abstract

We present an experimental study on the characteristics of liquid jets in different configurations. We consider jets injected perpendicular to gravity, jets injected parallel to gravity, and jets injected in a microgravity environment. We study the role played by gravity in the jet breakup length and in the dynamics of the droplets generated after breakup. We analyze droplets obtained in the dripping and jetting regimes, focusing the study on their size, trajectory, oscillation and rotation. The particularities of the considered injection configurations are analyzed. In normal gravity conditions, in the dripping and jetting regimes, the breakup length increases with the Weber number.The transition between these regimes occurs at We cr ≈ 3.2. Droplets are notably larger in the dripping regime than in the jetting one. In the latter case, droplet mean size decreases as the liquid flow rate is increased. In microgravity conditions, droplet trajectories form a conical shape due to droplet bouncing after collision. When a collision takes place, coalescence tends to occur at low modified Weber numbers (We m < 2), while bouncing is observed at higher values (We m > 2). The surface of a droplet oscillates after bouncing or coalescence events, following a damped oscillator behavior. The observed oscillation frequency agrees with theoretical predictions.

Oscillatory motion and merging responses of primary and satellite droplets from Newtonian liquid jets

“…Although we have presented some unique features that augment the understanding of the intricate characteristics of droplet merging using VOF technique, however, our results do not show features wherein (i) a satellite never merges with a primary droplet but reaches the target without encountering any collision and (ii) cases where bouncing behaviour of droplets are featured from liquid jets (Suñol and Cinca, 2015).…”

“…Conversely, for the case of a free or during a random breakup of droplets from Rayleigh jetting regime, the coalescence of drops was shown to widely be promoted by the oscillation of droplets after the breakup. Also, it was reported that even if the distance between droplets is kept constant, the amplitude of the oscillation was found to be sufficiently large to allow droplets to collide and, consequently, bounce or coalesce (Suñol and Cinca, 2015).…”

Breakup and coalescence of drops during transition from dripping to jetting in a Newtonian fluid

“…Despite well predicting the overall behavior and salient features within the dripping to jetting transitions, one may note that the coalescence of two axis-symmetric primary drops arising from a laminar jet or during modes of dripping may not strictly lead to the formation of an axis-symmetric droplet in which case, the model will exhibit its pitfalls in revealing such formations. Also, recent experiments (Suñol and Cinca, 2015) have demonstrated that in addition to drops coalescing, they also exhibit the characteristics of bouncing when they come into contact one another in certain scenarios; such realizations are beyond the realm of the current set of equations used in the present study. In the future, we aim to extend the current study to describe the onset of coalescence of primary drops and satellites from free laminar jets and present a scaling relationship with dimensionless numbers to quantify their merging length, pattern and timescales.…”

“…al., 1991). Broadly, such oscillations in droplets are generated due to mechanisms such as breakup from mainstream, through coalescence or due to bouncing (Suñol and Cinca, 2015). Within this focus, our current numerical simulations predict plethora of interesting dynamics that identify four possible modes of satellite drop formation and coalescence as described in Fig.11.…”

Convective and absolute instability of viscoelastic liquid jets in the presence of gravity

“…These two types of instabilities are referred to as dripping and jetting, respectively. 8 Rayleigh 9 was the first to use linear stability analysis to investigate liquid jet instability. He derived the dispersion relation between the growth rate and the wavenumber for an inviscid liquid jet.…”