Flow regime mapping of high inertial gas–liquid droplet microflows in flow-focusing geometries

Drop formation in microfluidic cross-junction: jetting to dripping to jetting transition

“…It should appear only in flowfocusing devices with geometrical focusing, when the forming neck elongates beyond the focusing part. This conclusion is in line with the literature data: transition from the dripping to tubing regime for an increase of Ca d in the range of low Ca c was observed in devices with hydrodynamic focusing (Cubaud and Mason 2008;Fu et al 2012;Wu et al 2017), whereas transition to drop formation in jetting regime was found using a combination of hydrodynamic and geometrical focusing (Shahriari et al 2016). If the flow rate of the continuous phase increases, the drag force increases.…”

“…The transition to the tubing regime in Cubaud and Mason (2008), Fu et al (2012) instead of jetting observed in the present study can result from much higher viscosity ratio and the difference in geometry, as only hydrodynamic focusing in the cross-junction was used in Cubaud and Mason (2008), Fu et al (2012). It can be assumed, however, that the difference in geometry is the most important parameter because in Shahriari et al (2016) the ascending branch with transition to jetting was reported for the case of high viscosity ratio in a flowfocusing device of more sophisticated geometry including geometrical flow-focusing, whereas transition to tubing/ threading along the ascending branch was observed in Wu et al (2017) for a viscosity ratio of 0.6. Transition from dripping to jetting was found in Wu et al (2017) at Ca c > 2 × 10 −3 demonstrating a plateau and partially descending branch in good agreement with our study.…”

“…Conversely, in the jetting regime, where drops are formed due to convective instability, a broader size distribution is observed (Cordero et al 2011;Chen et al 2013). Therefore, finding the parameter space where drops are formed in the squeezing/dripping regime (thereafter referred to as dripping regime) is of critical importance and many microfluidic studies have been carried out to produce such flow maps (Anna and Mayer 2006;Cubaud and Mason 2008;Fu et al 2012;Shahriari et al 2016;Mastiani et al 2017;Wu et al 2017;Kovalchuk et al 2018b).…”

“…In a number of studies (Cubaud and Mason 2008;Fu et al 2012;Shahriari et al 2016;Mastiani et al 2017;Kovalchuk et al 2018b), the transition from dripping to jetting in various microfluidic flow-focusing devices was observed by an increase in the flow rate of the dispersed phase but in Wu et al (2017), this transition was reported to happen by an increase in the flow rate of both continuous and dispersed phases, whereas in Anna and Mayer (2006) it was observed only by an increase of the flow rate of the continuous phase. Besides in most studies (Fu et al 2012;Shahriari et al 2016;Mastiani et al 2017;Wu et al 2017;Kovalchuk et al 2018b), the critical flow rate of the transition-defining phase was dependent on the flow rate of the second phase, whereas in Anna and Mayer (2006), Cubaud and Mason (2008) it was practically constant.…”

Optimised multi-stream microfluidic designs for controlled extensional deformation

“…This is arguably the most common set-up used in the literature for an FF configuration (Arratia et al 2008;Cubaud and Mason 2009), where the widths of all channels (inlets and outlets) are set to be the same. Alternative designs have also been considered in other studies, where configurations have varying values of width ratios (Steinhaus and Sureshkumar 2007;Ballesta and Alves 2017) and different angles between the entrance channels (Gossett et al 2012a;Shahriari et al 2016). The length of the desired constant strain-rate region is as previously correlated to w 1 , where for the bulk of the simulations we set n 1 = 3 .…”