(383a) Breakup Dynamics of Bubbles/Droplets In a Microfluidic T-Junction
AIChE Annual Meeting
2011
2011 Annual Meeting
Engineering Sciences and Fundamentals
Interfacial-Dominated Flows I
Tuesday, October 18, 2011 - 3:15pm to 3:30pm
The physical mechanism for the breakup of bubbles/droplets in a microfluidic T-junction has been a topic of debate in literature for a number of years now. Link and coworkers [1] ascribed breakup to a Rayleigh-Plateau instability. For 2-dimensional situations, in which Rayleigh-Plateau instabilities are not operative, Leshansky and Pismen [2] proposed a mechanism based on an increased upstream pressure due to lubrication flow in a thin film between the drop and the channel wall, and they claimed this to likely be the dominant mechanism for breakup in 3 dimensions as well. Both theories are supported by (experimental and numerical, respectively) data.
In the present paper, we resolve this debate by presenting a detailed description of the dynamic breakup behavior, both from 3-dimensional transient numerical two-phase flow simulations, and from experimental high speed imaging observations. Presented 3-dimensional images of droplet shapes, pressure distributions and fluid velocities in both phases, as obtained from the numerical simulations, clarify the basic mechanisms taking place. The numerically simulated evolution of the droplet interface during breakup is in good agreement with experimental observations.
The breakup of bubbles/droplets follows two stages: initially, the droplet interface is squeezed due to the increased upstream pressure; Once the neck of the thread has reached a critical radius, it becomes unstable and collapses at an accelerated rate. At this moment of the rapid collapse, we observed an increment of pressure at the neck of the bubbles/droplets, and consequently a flow from the neck to the tip of the bubble/droplet. In our numerical simulations, this rapid collapse progressed even when the flow of the continuous fluid was stopped and external pressures were consequently eliminated. Thus, our observations conclusively show that the rapid collapse is initiated by a Rayleigh-Plateau instability, rather than pressure effects.
References:
[1] Link, D. R., Anna, S. L., Weitz, D. A. & Stone, H. A. (2004). Geometrically mediated breakup of drops in microfluidic devices. Phys. Rev. Let. 92, 054503.
[2] Leshansky, A. M. & Pismen, L. M. (2009). Breakup of drops in a microfluidic T junction. Phys. of Fluids. 21, 0233303.