Comparison of the jet breakup and droplet formation between non-Newtonian and Newtonian fluids

Jet breakup and droplet formation are used in various applications including the production of pharmaceutical microcapsules, biomedical sensors, lab-on-chips, and more. Many of these fluids have shear-thinning behavior. The main aims of the present numerical study are to investigate the effect of non-Newtonian rheology of shearthinning fluids on jet breakup and droplet production in different regimes. Therefore, three Newtonian and three shear-thinning non-Newtonian fluids are injected into the air through a nozzle, and the jet breakups are investigated and compared with each other. The volume of fluid model (VOF) and a finite volume solver are implemented to conduct numerical simulations and the Carreau model is used to model the viscosity of shearthinning fluids. Results are first validated against previous published experimental data, and then the breakup length, droplet production frequency, and droplet volume in all fluids have been studied for various Weber numbers (We = 2 to 6) and Ohnesorge numbers (Oh = 0.013 to 0.219). Three different regimes are covered, including periodic dripping (PD), dripping faucet (DF), and jetting (J). Results indicate that in PD and DF regimes, viscosity and non-Newtonian rheology of shear-thinning fluids do not affect the properties of the jet breakup such as droplet volume, jet breakup length, and production frequency. In the J regime, increasing the viscosity increases the jet breakup length considerably; for instance, in We=6, the breakup length of Newtonian fluid 2 (& mu;=56 mPa.s) is twice that of Newtonian fluid 1 (& mu;=3.5 mPa.s). Also, in fluids with higher viscosity, regime transition occurs at lower We numbers. Furthermore, results show that the difference in neck geometry between Newtonian and shear-thinning fluids is significant. It seems because of the difference in neck geometry, the production of satellite droplets of shear-thinning fluids is lower than that of Newtonian fluids.

Automated summary

Jet breakup and droplet formation in different regimes are studied using three Newtonian and three shear-thinning non-Newtonian fluids. Results show that in periodic dripping and dripping faucet regimes, viscosity and non-Newtonian rheology of shear-thinning fluids do not affect jet breakup properties. However, in the jetting regime, increasing viscosity significantly increases jet breakup length and leads to a lower regime transition at lower Weber numbers.