Download Chris Kleijn (TUD) Dynamics of droplet breakup in a T

Chris Kleijn (TUD)
Dynamics of droplet breakup in a T- junction
The application of bubbles and droplets in microfluidics requires precise control and manipulation of
droplet sizes. One of the basic techniques to manipulate droplet sizes is the passive breakup of
droplets at a T-junction: a single droplet is split into two daughter droplets by extensional flow [1]. In
this paper, we present a computational fluid dynamics (CFD) study on the dynamical behaviour of
the breakup of droplets in a three-dimensional T-junction microchannel. A finite volume based opensource CFD package, OpenFOAM [2], was used to perform the numerical simulations.
The fluid interface was modeled using the Volume of Fluid (VOF) method with interface sharpening
techniques.
We quantitatively describe the breakup process and the mechanism of droplet pinch-off. Similar to
the formation of droplets at T-junctions [3], the interface of the droplet first moves at a nearly
constant speed, after which it rapidly collapses prior to breakup. As we will show, droplet dynamics
in two- and three-dimensional simulations is similar at the first stage but significantly different prior
to breakup. Two-dimensional simulations do not capture the rapid collapse such that the breakup
time is significantly overestimated. By contrast, the rapid collapse is accurately captured in threedimensional simulation and its onset agrees well with our theoretical model. The results presented in
this paper are useful for the design of droplet-based laboratories-on-a-chip and stress the need to
perform simulations in three dimensions to capture the interfacial dynamics of droplet in microfluidic
devices.
References:
[1] D. R. Link, S. L. Anna, D. A. Weitz & H. A. Stone (2004). Geometrically mediated breakup of drops
in microfluidic devices. Phys. Rev. Let. 92, 054503.&
[2] H. G. Weller, G. Tabor, H. Jasak and C. Fureby (1998). A tensorial approach to computational
continuum mechanics using object-oriented techniques. Com. in Phys. 12, 6, 620-631.&
[3] V. van Steijn, C. R. Kleijn & M. T. Kreutzer (2009). Flows around confined bubbles and their
importance in triggering pinch-off. Phys. Rev. Let. 103, 214501.