Characterizing droplet breakup rates of shear-thinning dispersed phase in microreactors

Abstract

A two-phase flow predictive model with the integration of conservative level-set method (LSM) and Carreau-Yasuda constitutive equation was developed herein. The LSM was chosen as a potential interface capturing scheme for elucidating the interfacial phenomena including insight into the mechanism of shear-thinning droplets. In present paper, the dynamics of shear-dependent droplet emergence, growth, detachment and translocation in a Newtonian microsystem were examined via computational fluid dynamics (CFD) analysis. Dilute sodium carboxymethylcellulose (Na-CMC) solution was treated as dispersed phase (70 mPa.s < <10.2644 Pa.s) whereas the olive oil (68 mPa.s) was designated as continuous phase. Visualisation experiments were carried out and these laboratory data were used to validate the simulation results. Detailed 2D simulations were presented to examine systematically the impact of fluid properties on the droplet breakup rate at predefined flow rate ratio, Q of 0.05. The results yielded an inflection point in the dependence of droplet breakup rate on Na-CMC concentration was found in between the dilute and semi-dilute concentration regimes. This inflection point displays a non-monotonic profile which is mainly caused by the considerable viscosity effect of Na-CMC polymer when its concentration increases above a critical value (C > C*~0.40 wt%). This striking

Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

“…Rostami et al [25] experimentally showed that using non-Newtonian fluids for a dispersed phase affect the system behaviour and identified flow rates for squeezing, dripping and jetting regimes for such a system. Wong et al [26,27] experimentally and numerically investigated a Carreau-Yasuda polymeric dispersed phase in a T-junction using the level set method in a range of polymer concentrations and concluded that droplet pinch-off time and the frequency are highly dependent on fluids' physical properties [26,27]. Research in this field is still lacking and more analysis for different geometries and fluids using different numerical approaches are needed.…”

Effects of capillary number and flow rates on the hydrodynamics of droplet generation in T-junction microfluidic systems

“…The interfacial force ( ) between the two fluids is governed by the following relation. is calculated from the surface area of the dispersed phase (Liu and Zhang, 2011;Jamalabadi et al, Hydrodynamics of droplet generation in microfluidic systems 2017; Wong et al, 2017Wong et al, , 2019 as follows.…”

“…However, it is found that there is no single correlation is known to predict whether there is a droplet formation or not for a specific value of c and r . Numerous computational fluid dynamics (CFD) approaches such as the volume of fluid (VOF) method, lattice Boltzmann method (LBM), phase field method (PFM), and level set method (LSM) are used in the literature to explore the hydrodynamics of droplets in emulsion/multiphase flows (Olsson and Kreiss, 2005;van der Graaf et al, 2006;De menech et al, 2008;Bashir et al, 2011;Li et al, 2012;Akhlaghi Amiri and Hamouda, 2013;Shi et al, 2014;Nekouei and Vanapalli, 2017;Yu et al, 2019;Wong et al, 2019). All the CFD approaches have primarily focused on tracking of the topological changes of the interface in motion.…”

“…and numerical(van der Graaf et al, 2006;Wong et al, 2019) works in Figure2. The present values are closely consistent with the results of van der Graaf et al (2006),Wong et al (2019) andGarstecki et al (2006) for 2 × 10 −3 ≤ ≤ 4 × 10 −2 , = 10 −1 and ≤ 10 −2 , respectively.…”

Modeling the motion of a Taylor bubble in a microchannel through a shear-thinning fluid

“…Thus, we solve the Carreau constitutive model [32], which includes an additional term for the viscosity at zero shear rate, and, therefore, it overcomes the limitations of the power-law viscosity model [33]. The solution of the Carreau model introduces further novelty in our works because the application of this constitutive equation in microfluidics is scarce: the current studies on the bubble hydrodynamics in Carreau fluids [34,35,36,37,38,39] limit their results to a single fluid (carboxymethylcellulose) and are valid below the tested operating conditions.⇥…”