Effects of viscoelasticity on droplet dynamics and break-up in microfluidic T-Junctions: a lattice Boltzmann study

Abstract

The effects of viscoelasticity on the dynamics and break-up of fluid threads in microfluidic T-junctions are investigated using numerical simulations of dilute polymer solutions at changing the Capillary number ($\mbox {Ca}$), i.e. at changing the balance between the viscous forces and the surface tension at the interface, up to $\mbox{Ca} \approx 3 \times 10^{-2}$. A Navier-Stokes (NS) description of the solvent based on the lattice Boltzmann models (LBM) is here coupled to constitutive equations for finite extensible non-linear elastic dumbbells with the closure proposed by Peterlin (FENE-P model). We present the results of three-dimensional simulations in a range of $\mbox{Ca}$ which is broad enough to characterize all the three characteristic mechanisms of breakup in the confined T-junction, i.e. $squeezing$, $dripping$ and $jetting$ regimes. The various model parameters of the FENE-P constitutive equations, including the polymer relaxation time ${\tau }_P$ and the finite extensibility parameter $L^2$, are changed to provide quantitative details on how the dynamics and break-up properties are affected by viscoelasticity. We will analyze cases with $DropletViscoelasticity$ (DV), where viscoelastic properties are confined in the dispersed (d) phase, as well as cases with $MatrixViscoelasticity$ (MV), where viscoelastic properties are confined in the continuous (c) phase. Moderate flow-rate ratios $Q\approx \mathcal{O}(1)$ of the two phases are considered in the present study. Overall, we find that the effects are more pronounced in the case with MV, as the flow driving the break-up process upstream of the emerging thread can be sensibly perturbed by the polymer stresses.

16 pages, 14 figures; This Work applies the Numerical Methodology described in arXiv:1406.2686 to the Problem of Droplet Generation in Microfluidic T-Junctions. arXiv admin note: substantial text overlap with arXiv:1508.00559

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• Statistical Mechanics of the Fluctuating Lattice Boltzmann Equation
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Cited by in corpus (3)

• Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media
• Droplet breakup driven by shear thinning solutions in a microfluidic T-Junction
• Lattice Boltzmann Simulations of Droplet formation in confined Channels with Thermocapillary flows