Breakup of Droplets in Micro and Nanofluidic T-Junctions

We employ numerical simulations to investigate the breakup of droplets in micro- and nanoscale T junctions, which are used to produce small droplets from a large droplet. For this purpose a Volume f Fluid (VOF) based method is used and for verifying the reliability of the numerical outcomes, the results are compared with the available experimental and analytical results. Our results reveal that breakup time and breakup length of the droplets play important roles in handling these systems optimally. Our results also indicate that for nanoscale Tjunctions by increasing the capillary number the performance increases while for the micro-scale systems there is a specific capillary number for which the system is in its optimum condition

A Novel Method (T-Junction with a Tilted Slat) for Controlling Breakup Volume Ratio of Droplets in Micro and Nanofluidic T-Junctions

We propose a novel method for producing unequal sized droplets using a titled slat in the center of a T-junctions. In the available methods for generating unequal-sized droplets such as T-junction with valve and T-junction with a heater, the minimum breakup volume ratio that is accessible is approximately 0.3 while the system of this paper can generate droplets with the volume ratio 0.05. Therefore, the manufacturing cost of the system decreases considerably because it does not need to the consecutive breakup systems for generation of small droplets. The employed method was investigated through a numerical simulation using the volume of fluid (VOF) algorithm. The simulation results are reported for micro and nano-scaled T-junctions in various tilted slat sizes, capillary numbers (a dimensionless group describes the ratio of the inertial forces to the surface tension forces) and slat angles. Our method decreases (increases) considerably the breakup time (speed of the breakup process). For example in the case Ca=0.1 and volume ratio 0.4, dimensionless breakup time of our method and the method of T-junction with valve are 0.25 and 3.6, respectively. The results revealed that the breakup length of the nanoscale T-junction is smaller than microscale and increases by increasing the slat angle in both scales. The results demonstrated the breakup volume ratio decreases by increasing the tilted slat length. Also the breakup volume ratio minimizes in a specific slat angle. The results showed the breakup time is reduced by decreasing the slat angle. We also found that the pressure drop of the system is almost independent of the system geometry

Breakup of confined drops against a micro-obstacle: an analytical model for the drop size distribution

International audienceA confined drop flowing against a rectangular obstacle placed off-center in a microfluidic conduct may break into two daughter droplets of different volumes when the capillary number at play C, the ratio between viscous and capillary effects, exceeds a threshold C b. We study the influence of the viscosity ratio p between dispersed and continuous phases on that process by discussing the experimental variations of the volume fraction of the daughter droplets with C and p. A single free-parameter model that yields an analytical formula for the volume of the daughter droplets as a function of the variables at play is introduced. Using this model that well describes our experiments, we accurately determine C b for different p. Our findings underline the key role of confinement on drop breakup showing that C b is three orders of magnitude smaller than the value found in bulk experiments under shear flow and that C b decreases with p in our study