Experimental investigation on the breakup dynamics for bubble formation in viscous liquids in a flow-focusing device

Self‐similar breakup of viscoelastic thread for droplet formation in flow‐focusing devices

“…In the “flow‐driven” stage (Figures a−4, b1–4, c1–4), the breakup of the viscoelastic dispersed thread is similar to that of the Newtonian reference fluid (Figures a′1–4, b′1–4, c′1–4) under the same operating conditions. A concave neck forms gradually in the dispersed thread, and the profiles of the liquid‐liquid interface are symmetrical parabola along the axial direction at r = 0 as shown in Figure a, which have been observed for the rupture of the thread at both macroscale and microscale . In the “elastocapillary” stage (Figures a−7, b5–7, c5–7), compared to the quick stretching and rupturing for the dispersed thread of Newtonian fluid, as clearly shown in Figures a′5–7, b′5–7, and c′5–7, the viscoelasticity of the viscoelastic fluid significantly inhibits the finite‐time singularity that happens at breakup for the Newtonian fluid and leads to the formation of a long‐lived dispersed thread.…”

“…The asymmetric profiles of gas‐liquid interface along the radial direction due to the effect of buoyancy have also been observed at macroscale . Those asymmetric profiles demonstrate that the interfaces would extend in the axial direction when some forces perpendicular to radial direction exert on the dispersed thread, both at macroscales and microscales . As illustrated in the inset of Figure a, the axial curvature κ at the minimum width w m of the dispersed thread increases with the decrease of w m .…”

“…However, in comparison to macroscale, both the thinning rate in the radial direction and the stretching rate in the axial direction of the dispersed thread are influenced by the external fluid flow and the confinement of microchannel at microscale, resulting in the acceleration of the evolution of the dispersed thread in both directions to achieve an equivalent variation rate. Nevertheless, the evolution velocity in the axial direction is larger than that in the radial one for the thinning of the gas‐liquid interface for bubble formation at macroscale and microscale, and the self‐similar profiles of the gas‐liquid interface can be achieved using two adjustable parameters, which may attribute to the divergence in the surface tension of both directions during bubble breakup …”

“…Will the viscoelasticity and the initial conditions affect the dynamics of the singularity? To the best of our knowledge, only Lu et al have demonstrated that the evolution of gas‐liquid interface for the bubble formation in viscous Newtonian liquids in a flow‐focusing device is self‐similar . In this work, the scaling law for the thinning of the neck of the dispersed phase, the evolution of liquid‐liquid interface and the cone angles in the final rupture of the viscoelastic dispersed thread were studied experimentally by varying the flow rate of the continuous phase and the dimension of the channel for the flow‐focusing microdevice, aiming at exploring the influence of initial and boundary conditions on the rupture of the viscoelastic dispersed thread and further highlighting whether the rupture process is self‐similar or not at microscale.…”

CFD Analysis of Taylor Bubble in a Co-Flow Microchannel with Newtonian and Non-Newtonian Liquid

“…However, liquid film thickness was not captured due to poor grid resolution, and different bubble shapes were reported by varying wall adhesion property. Flow-focusing junction is another popular configuration used for bubble generation in microchannels . Yu et al carried out experiments and Lattice Boltzmann simulations of air–oil two-phase flow in cross and converging shaped microchannels.…”