Effects of viscoelasticity on droplet dynamics and breakup in microfluidic TJunctions: a lattice Boltzmann study
Abstract
The effects of viscoelasticity on the dynamics and breakup of fluid threads in microfluidic Tjunctions 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 NavierStokes (NS) description of the solvent based on the lattice Boltzmann models (LBM) is here coupled to constitutive equations for finite extensible nonlinear elastic dumbbells with the closure proposed by Peterlin (FENEP model). We present the results of threedimensional simulations in a range of $\mbox{Ca}$ which is broad enough to characterize all the three characteristic mechanisms of breakup in the confined Tjunction, i.e. ${\it squeezing}$, ${\it dripping}$ and ${\it jetting}$ regimes. The various model parameters of the FENEP 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 breakup properties are affected by viscoelasticity. We will analyze cases with ${\it Droplet ~Viscoelasticity}$ (DV), where viscoelastic properties are confined in the dispersed (d) phase, as well as cases with ${\it Matrix ~Viscoelasticity}$ (MV), where viscoelastic properties are confined in the continuous (c) phase. Moderate flowrate ratios $Q \approx {\cal O}(1)$ 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 breakup process upstream of the emerging thread can be sensibly perturbed by the polymer stresses.
 Publication:

arXiv eprints
 Pub Date:
 August 2015
 arXiv:
 arXiv:1508.00141
 Bibcode:
 2015arXiv150800141G
 Keywords:

 Physics  Fluid Dynamics;
 Condensed Matter  Soft Condensed Matter
 EPrint:
 16 pages, 14 figures