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

Abstract

We present numerical simulations of dripping to jetting transitions that occur during the flow of a Newtonian liquid. An axis-symmetric, Volume of Fluid (VOF) model along with Continuum Surface Force (CSF) representation is developed to capture various regimes of drop formation. By numerically studying different nozzle diameters subjected to various flow rates, we examine the critical conditions under which the dripping to jetting transition takes place. At every stage of dripping and jetting, we assess the accuracy of the present simulations through a number of comparisons with previously published experimental data and empirical correlation and find reasonable agreements. Our numerical simulations show different responses that characterize the dripping and the dripping faucet regimes leading to chaotic dripping patterns. Within the chaotic regime, we identify four unique modes of satellite formation and their merging patterns which have not been reported earlier. Finally, we observe that as soon as the flow rate approaches a threshold the jetting regime begins where, subsequent disintegration of drops and coalescence patterns are observed downstream. Detailed flow patterns, pressure distributions and drop shapes are provided for various dimensionless numbers alongside the spatial-temporal resolutions of both jetting and coalescence of primary drops. Of the many complex dynamics that influence the primary droplet coalescence, we find that the oscillatory motion of drops during their travel downstream, which is dampened normally due to viscous effects, can be influential and can aid both coalescence and breakup of droplets.

Microfluidic Device for High-Throughput Production of Monodisperse Droplets

“…The increase of the breakup length with the flow rate can be clearly seen. The threshold value selected for the squeezing regime transition is L D / D = 1. − Droplets with a low breakup length ( L D / D < 1) were considered to be generated in the squeezing regime. This cut off is equivalent to a flow rate of 4.5 mL h –1 nozzle –1 .…”

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

“…The selected grid size corresponds to ~110 orders of magnitude higher in resolution than compared to the capillary length scale ( ) to jet diameter (D) ratio. The resulting total grid corresponds to ~2.2 million elements and satisfies the sizing requirements of the grid independency study that was ascertained from previously published work (Viswanathan, 2019). To reduce the computational resource requirements, only half of the jets were simulated by applying conditions of symmetry along with other boundary conditions for numerical closure, as shown in Fig.…”

Prediction of Newtonian Droplet Breaking Time from a Capillary at Low Weber Numbers

“…In the past decades, computational fluid dynamics simulation has developed vigorously, which has gradually become a powerful tool for analyzing complex interphase coupling problem. 11 The process of liquid outflows through the capillary, which is governed by the Navier–Stokes equation, and forms a droplet that can be considered as an axisymmetric flow; thus, a cylindrical coordinate is usually adopted, and the three-dimensional model can be simplified to a two-dimensional model in most cases. From this fundamental assumption, many improvements of the simulation method have been published.…”

“…Even though many experimental studies on droplet formation have been carried out, the complete mechanism under the process is still not well understood due to the insufficiency of the experimental data. In the past decades, computational fluid dynamics simulation has developed vigorously, which has gradually become a powerful tool for analyzing complex interphase coupling problem . The process of liquid outflows through the capillary, which is governed by the Navier–Stokes equation, and forms a droplet that can be considered as an axisymmetric flow; thus, a cylindrical coordinate is usually adopted, and the three-dimensional model can be simplified to a two-dimensional model in most cases.…”