11,391 research outputs found
Role of inertia in two-dimensional deformation and breakup of a droplet
We investigate by Lattice Boltzmann methods the effect of inertia on the
deformation and break-up of a two-dimensional fluid droplet surrounded by fluid
of equal viscosity (in a confined geometry) whose shear rate is increased very
slowly. We give evidence that in two dimensions inertia is {\em necessary} for
break-up, so that at zero Reynolds number the droplet deforms indefinitely
without breaking. We identify two different routes to breakup via two-lobed and
three-lobed structures respectively, and give evidence for a sharp transition
between these routes as parameters are varied.Comment: 4 pages, 4 figure
Edge states control droplet break-up in sub-critical extensional flows
A fluid droplet suspended in an extensional flow of moderate intensity may
break into pieces, depending on the amplitude of the initial droplet
deformation. In subcritical uniaxial extensional flow the non-breaking base
state is linearly stable, implying that only a finite amplitude perturbation
can trigger break-up. Consequently, the stable base solution is surrounded by
its finite basin of attraction. The basin boundary, which separates initial
droplet shapes returning to the non-breaking base state from those becoming
unstable and breaking up, is characterized using edge tracking techniques. We
numerically construct the edge state, a dynamically unstable equilibrium whose
stable manifold forms the basin boundary. The edge state equilibrium controls
if the droplet breaks and selects a unique path towards break-up. This path
physically corresponds to the well-known end-pinching mechanism. Our results
thereby rationalize the dynamics observed experimentally [Stone & Leal, J.
Fluid Mech. 206, 223 (1989)
Modeling of droplet breakup in a microfluidic T--shaped junction with a phase--field model
A phase--field method is applied to the modeling of flow and breakup of
droplets in a T--shaped junction in the hydrodynamic regime where capillary and
viscous stresses dominate over inertial forces, which is characteristic of
microfluidic devices. The transport equations are solved numerically in the
three--dimensional geometry, and the dependence of the droplet breakup on the
flow rates, surface tension and viscosities of the two components is
investigated in detail. The model reproduces quite accurately the phase diagram
observed in experiments performed with immiscible fluids. The critical
capillary number for droplet breakup depends on the viscosity contrast, with a
trend which is analogous to that observed for free isolated droplets in
hyperbolic flow
Viscoelastic Multicomponent Fluids in confined Flow-Focusing Devices
The effects of elasticity on the break-up of liquid threads in microfluidic
cross-junctions is investigated using numerical simulations based on the
"lattice Boltzmann models" (LBM). Working at small Capillary numbers, we
investigate the effects of non-Newtonian phases in the transition from droplet
formation at the cross-junction (DCJ) and droplet formation downstream of the
cross-junction (DC) (Liu & Zhang, , 082101
(2011)). Viscoelasticity is found to influence the break-up point of the
threads, which moves closer to the cross-junction and stabilizes. This is
attributed to an increase of the polymer feedback stress forming in the corner
flows, where the side channels of the device meet the main channel.Comment: 4 pages, 2 figures, AIP Conference Proceedings, 201
Evaporating pure, binary and ternary droplets: thermal effects and axial symmetry breaking
The Greek aperitif Ouzo is not only famous for its specific anise-flavored
taste, but also for its ability to turn from a transparent miscible liquid to a
milky-white colored emulsion when water is added. Recently, it has been shown
that this so-called Ouzo effect, i.e. the spontaneous emulsification of oil
microdroplets, can also be triggered by the preferential evaporation of ethanol
in an evaporating sessile Ouzo drop, leading to an amazingly rich drying
process with multiple phase transitions [H. Tan et al., Proc. Natl. Acad. Sci.
USA 113(31) (2016) 8642]. Due to the enhanced evaporation near the contact
line, the nucleation of oil droplets starts at the rim which results in an oil
ring encircling the drop. Furthermore, the oil droplets are advected through
the Ouzo drop by a fast solutal Marangoni flow. In this article, we investigate
the evaporation of mixture droplets in more detail, by successively increasing
the mixture complexity from pure water over a binary water-ethanol mixture to
the ternary Ouzo mixture (water, ethanol and anise oil). In particular,
axisymmetric and full three-dimensional finite element method simulations have
been performed on these droplets to discuss thermal effects and the complicated
flow in the droplet driven by an interplay of preferential evaporation,
evaporative cooling and solutal and thermal Marangoni flow. By using image
analysis techniques and micro-PIV measurements, we are able to compare the
numerically predicted volume evolutions and velocity fields with experimental
data. The Ouzo droplet is furthermore investigated by confocal microscopy. It
is shown that the oil ring predominantly emerges due to coalescence
Efficient homogenisation of photographic dispersions
The formation of fine droplets in a photographic emulsion which is forced through an orifice disperser consisting of a tube with one or more abrupt constrictions is considered. Some design ideas for reducing the droplet size are presented
- …